Thermoelectric switching element, use of a thermoelectric switching element and method for producing a thermoelectric switching element

Abstract

The invention relates to a thermoelectric switching element (2), comprising a first layer (4) at least partially consisting of a ferromagnetic material, and a second layer (6) at least partially consisting of a metallic material, wherein the ferromagnetic material of the first layer (4) and the metallic material of the second layer (6) have different thermal expansion coefficients, wherein the thermal expansion coefficient of the ferromagnetic material of the first layer (4) and the thermal expansion coefficient of the metallic material of the second layer (6) are selected and the first layer (4) and the second layer (6) are connected to one another and arranged relative to one another in such a way that, upon reaching a predetermined temperature, a predetermined deformation of the composite of the first layer (4) and the second layer (6) is achieved, and wherein the first layer (4) and the second layer (6) are connected by an adhesive bond (10) with atomic diffusion (12),optionally via an intermediate layer (22). The invention also relates to the use of a thermoelectric switching element (2) and a method for producing a thermoelectric switching element (2).

Description

The invention relates to a thermoelectric switching element having at least two layers and to the use of a thermoelectric switching element and to a method for producing a thermoelectric switching element.Thermoelectric switching elements of the type of interest here can be used for various purposes and are used in particular as switching elements, for example as a switch or part of a switch, in devices or installations, in particular in electronic devices or installations. Furthermore, the aforementioned thermoelectric switches are used in the fields of electrical engineering, electronics, smart devices, cookware such as cookware or cookware such as pots, pans, sheets, pizza bricks or other devices with or in which foods can be heated or cooked, white goods such as large household appliances such as electrical ovens, refrigerators, deep-cooling structures, washing machines, dryers or dishwashers, energy stores, fuel cells, electrolysers, batteries and battery management systems and energy converters. In addition, the aforementioned thermoelectric switches are used in the field of water extraction, in particular by seawater desalting, and in the field of geothermal energy.In particular, a process can be triggered by means of the thermoelectric switching elements on the basis of thermal and / or electrical, for example thermoelectric, effects. For example, an electrical circuit can be closed or opened. In particular, it is possible by means of the thermoelectric switching element to use an electrical voltage for generating a temperature difference or to use a temperature difference for generating an electrical voltage. Applications as an element of a circuit breaker or as an U-hot protection are conceivable, for example. Use of the thermoelectric switching elements mentioned as electromechanical components or components is also conceivable, for example a mechanical process can be effected by applying an electrical voltage or an electrical voltage can be induced by effecting a mechanical process. Thermoelectric switching elements can thus be used, for example, in devices with which heating of various substances takes place or a heating process can be controlled in the widest sense, and in applications with switching mechanisms, in particular in connection with heating processes.In the aforementioned ranges, fundamentally different requirements are placed on the material properties of a thermoelectric switching element. In particular, the required properties are dependent on the prevailing or targeted temperatures in the respective application. When using the thermoelectric switching element in connection with heating processes, the required material properties are in particular dependent on the specific heating process or the substances to be heated or on the respective switching mechanism. Furthermore, thermoelectric switching elements are often constructed from different materials, for example from different layers of different materials.In general, by a combination of two or more layers, in particular layers comprising different metallic materials, the material-specific properties of the layers can advantageously be combined with one another. However, it must be noted that the composite can influence the properties of the component obtained by the composite. In the case of components which have a plurality of, i.e. two or more, in particular different, layers and which are assigned an electromagnetic and / or electromechanical function, for example when used as a thermoelectric switching element, the quality of the composite of the two or more layers is decisive. It is important here that the composite does not significantly adversely affect the electromagnetic and / or electromechanical properties of the component. For example, there should be no substantial negative influence in that energy is lost due to inhomogeneities at the transition between different materials and / or layers, and / or that the electromagnetic or electromechanical properties deviate greatly from the desired properties.For example, thermoelectric switching elements are known from the prior art, which have, in particular, different metallic layers and in which an effect or switching mechanism is based on the, in particular different, electromagnetic and / or electromechanical properties of the metallic materials of the layers. Examples of such effects include the Seebeck effect, the Peltier effect or the Thomson effect. For the use of these effects, for example for cooling sensitive electronic components, it is important that the materials used do not deviate from their predicted behavior, or deviate only insignificantly from their predicted behavior.The composite of two metallic materials having different coefficients of thermal expansion is known as a bimetallic element or a thermobimetal. As a rule, the composite is present in the form of two layers lying one above the other in a metal strip. When a predetermined temperature is reached, in particular when the temperature rises, one of the two layers of the metal strip expands more strongly than the other layer because of the different coefficients of thermal expansion, as a result of which the strip bends in the direction of the layer having the lower coefficient of thermal expansion. Materials used are, for example, iron (Fe), nickel (Ni) or steel and alloys with these materials or combinations of these materials. This effect can be used as a switching mechanism, for example for temperature regulation. For example, an application is possible in which an electrical circuit is closed by a predetermined deformation of the layers at a predetermined temperature and an electrical switching signal is thus generated. This can be used, for example, for switching a heating process on or off or for indicating that a predefined temperature has been reached.Furthermore, the prior art discloses the composite of layers, in particular layers arranged side by side. At least one layer consists of a high-resistance material (resistance material) and at least one further layer, as a rule two further layers, consists of a material that is more conductive electrically in comparison to the resistance material (conductive material). This composite is known as a shunt resistor (also known as a "shunt"). The layers of the conductive material generally serve for contacting and are preferably arranged on the outside of the shunt resistor. For this purpose, the conductivity material surrounds the resistance material on at least two sides. A shunt resistor is typically connected in parallel with a portion of a circuit to derive an electrical current from that portion. A shunt resistor can also be connected in parallel with a current measuring device in order to extend the measurement range of the current measuring device. The current intensity that can be measured directly by the current measuring device can thus be extended. The measured current can furthermore be used as an electronic switching signal.A shunt can also be used as a current measuring resistor, generally as a low-impedance electrical measuring resistor. This generally small precision resistor is integrated into a current path, for example. By measuring the voltage drop in the measuring resistor, which is proportional to the current flowing through the measuring resistor, the current can be calculated knowing the value of the measuring resistor. This application is particularly relevant for the exact current measurement in power supplies, battery management systems and drives. It is advantageous here that shunts can generally be produced cost-effectively and at the same time enable an exact current measurement and thus, among other things, also an exact circuit based on a current measurement by means of the targeted selection of resistors. The precisely defined resistance value of the shunt should not be influenced in an unpredictable manner by the composite of the materials, in particular by possibly resulting inhomogeneities in the composite.In addition, in thermoelectric switching elements known from the prior art having at least two layers connected to one another, the lifetime of the thermoelectric switches can be limited by the composite. This is because the thermoelectric switch represents a possible loss of material due to, for example, inhomogeneities present or additionally introduced (adhesive) layers.Furthermore, the use of ferromagnetic materials is known from the prior art. In general, for ferromagnetic materials, when the material-specific Curie temperature T c is reached, the ferromagnetic properties of the materials disappear completely, so that the materials are only paramagnetic above this temperature. Below this temperature, which thus marks the reversible phase transition of ferromagnetic materials into their paramagnetic high-temperature form, the materials recover their ferromagnetic properties. This effect is used, for example, for temperature control in thermostats or for data storage by means of magneto-optical media and can thus likewise be used as a switching mechanism.Against this background, the present invention is based on the technical problem of specifying a thermoelectric switching element and a method for producing a thermoelectric switching element which improve the disadvantages described for the prior art and in particular have a high quality with a long service life.The technical problem mentioned above is solved according to a first teaching according to the invention in a thermoelectric switching element, having a first layer at least partially consisting of a ferromagnetic material and having a second layer at least partially consisting of a metallic material, wherein the ferromagnetic material of the first layer and the metallic material of the second layer have different coefficients of thermal expansion, and wherein the coefficient of thermal expansion of the ferromagnetic material of the first layer and the coefficient of thermal expansion of the metallic material of the second layer are selected and the first layer and the second layer are connected to one another and arranged with respect to one another in such a way that when a predetermined temperature is reached a predetermined deformation of the composite of the first layer and the second layer is achieved, in that the first layer and the second layer are connected to one another by an adhesion bond with atomic diffusion, optionally via an intermediate layer.The coefficient of thermal expansion of the ferromagnetic material of the first layer and the coefficient of thermal expansion of the metallic material of the second layer are selected and the first layer and the second layer are connected to one another and arranged with respect to one another in such a way that a predefined deformation of the composite of the first layer and the second layer is achieved when a predefined temperature is reached. This is understood in particular to mean that the first layer and the second layer are connected to one another, wherein the coefficient of thermal expansion of the ferromagnetic material of the first layer and the coefficient of thermal expansion of the metallic material of the second layer are of different sizes, wherein the composite of the first layer and the second layer has a predefined deformation when a predefined temperature is reached. In particular, it is sufficient for the presence of different coefficients of thermal expansion if the coefficients of thermal expansion only have a minimum difference, for example differ only by approximately 0.1*10 -6 K -1. In particular, different thermal expansion coefficients can be achieved by the targeted selection of the materials of the first and the second layer.According to a second teaching according to the invention, the aforementioned technical problem is furthermore solved in the case of a thermoelectric switching element, having a first layer at least partially consisting of a ferromagnetic material, and having a further layer which has at least: a resistance region at least partially consisting of a metallic material, and two conductive regions which at least partially consist of a metallic material different from the metallic material of the resistance region, wherein the conductive regions are each arranged adjacent to different sides of the resistance region and are connected to the resistance region, in that the first layer and the further layer are connected to one another by an adhesion bond with atomic diffusion, optionally via an intermediate layer.In particular, a high-resistance resistor alloy can be provided as the metallic material of the resistor region, for example an alloy based on nickel-chromium, on copper-nickel or on iron-nickel. As the material of the conductive regions, in particular a material at least partially consisting of copper or of aluminum can be provided. The further layer can have a thickness of 10 mm or less, preferably of 8 mm or less.Within the scope of the invention, it has been recognized that a bonding of two metallic layers of a thermoelectric switching element can be achieved in a reliable manner by an adhesion bond with diffusion. In this way, a thermoelectric switching element with improved material properties, in particular with improved electromagnetic and / or electromechanical properties, can be provided. By means of such a combination, it is possible, for example, to reduce internal voltages at the transition of the binding partners involved and thus in the interior of the thermoelectric switching element. Inhomogeneities in the composite can also be reduced or even avoided by the gradual diffusive transition of the materials of the connected layers.Furthermore, the thermoelectric switching element according to the invention can achieve a long service life with a permanently high quality, since the bond can be achieved without the addition of adhesive layers or filling layers. In this case, the first and the second layer or the further layer can be directly connected to one another by the adhesion bond with atomic diffusion or optionally connected to one another via an intermediate layer. The intermediate layer can be designed to be electrically insulating, for example the intermediate layer can consist at least partially, preferably essentially, of non-metals, metal oxides, ceramics or plastic. Alternatively, the intermediate layer can also be designed to be electrically conductive, so that electrical properties of the thermoelectric switch can still be specifically influenced by means of the intermediate layer. By means of the thermoelectric switching element, the service life of the components and components for which or in which the thermoelectric switching element is used can thus also be increased. In addition, the thermoelectric switching element can be recycled well, in particular since it preferably comprises only purely metallic materials.Furthermore, by providing the first layer at least partially consisting of a ferromagnetic material, a switching mechanism based on the property of a ferromagnetic material having a reversible phase transition at the Curie temperature T c can be linked to further switching mechanisms or thermoelectric properties of the thermoelectric switching element by the second or the further layer in an advantageous manner. For example, it is possible to expand the switching mechanism by the ferromagnetic material of the first layer based on the different thermal expansion coefficients of the first and second layers (thermobimetal effect) in order to expand a switching mechanism functioning as an over-hot protection. Preferably, the coefficients of thermal expansion of the ferromagnetic material of the first layer and of the metallic material of the second layer are selected such that a predefined temperature greater than or equal to 37° C. leads to a predefined deformation of the composite of the first layer and the second layer. In particular, the thermoelectric switching element is further configured such that a predefined deformation leads to triggering of a switching mechanism, for example by opening or closing a circuit, in particular by producing a conductive contact by the deformation or by omission of a conductive contact by the deformation.In particular, the ferromagnetic material of the first layer can have a Curie temperature T c below which heating is to take place and above which heating is to be switched off. The electrothermal switching element can be correspondingly configured such that when the Curie temperature T c of the ferromagnetic material of the first layer is reached, a switching mechanism is caused which interrupts or switches off a heating process.For example, the reversible phase transition of the ferromagnetic material at T c can be detected by measuring the specific material properties of the first layer at least partially consisting of the ferromagnetic material, for example the specific resistance, and switching can thus be effected. In particular, a sensor or a measuring element can be provided on the switching element or connected to the latter for this purpose. The effect of the change of the ferromagnetic material to a paramagnetic material can be used directly as a switching mechanism, for example by opening a previously closed magnetic circuit by the loss of magnetism of the previously ferromagnetic material when T c is reached.In addition, further advantageous material properties can be introduced into the electrothermal switching element by the material of the second or further layer and used as a switching effect. If the material of the second or of the further layer is likewise ferromagnetic, it can be provided that the material of the second or of the further layer has a Curie temperature Tc which is above the Curie temperature T c of the material of the first layer.In particular, by means of the thermoelectric switch according to the invention, a switching mechanism based on the reversible phase transition at the Curie temperature T c can be combined with a switching mechanism based on different thermal expansion coefficients (thermobimetal) and / or with the current measurement by means of a shunt resistor (shunt).In addition to the layers mentioned, the first layer, the second layer or the further layer and the optional intermediate layer, at least one additional layer made of a ferromagnetic and / or metallic material or another material, such as plastic or graphene, for example, can also be provided. This allows further advantageous properties to be introduced into the composite. The at least one additional layer can have a coefficient of thermal expansion that differs from the already present layers. Preferably, the at least one additional layer is also introduced into the composite by an adhesion bond with atomic diffusion. Alternatively, the at least one additional layer can be present as a layer which is not introduced into the composite by means of adhesive bonding with atomic diffusion, for example as an adhesive layer which adheres by means of an adhesive.In the present case, a compound by an adhesion bond with atomic diffusion is understood to mean a bond between two binding partners in which, by atomic diffusion of the materials of the binding partners, a transition layer forms as a binding zone via which a continuous adaptation of the material properties takes place. The adhesion bond with atomic diffusion is thus formed by the formation of the transition layer between the layers.In the transition layer, the atoms of the binding partners are gradually mixed, and the formation of a bond takes place by space change processes (diffusion) in the transition layer, also called the binding zone. This transition layer causes the reduction of internal stresses. The extent of the transition zone is dependent here on the binding partners used in each case, in particular the diffusion properties of the materials involved.To characterize the adhesion bond with atomic diffusion in the bond zone and its properties, analyses can be used by various methods. These methods include optical light microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), secondary ion mass spectrometry (SIMS) and analyses of microhardness curves.Such a composite can be referred to as a cladding composite, for example. Preferably, the two binding partners are metallic materials and the plating composite represents a metallic compound of the two or more binding partners or plating partners. In particular, the binding partners of the composite are arranged in layers so as to be planarly adjoining one another. The binding partners in the plating composite can be joined by plating. For this purpose, plating may be performed by cold rolling plating or hot plating.The connection of the binding partners can alternatively also be produced by welding metal strips, in particular diffusion welding or electrowelding, or by packetizing and partial welding. Furthermore, production by sintering or by hot isostatic pressing (HIP) and by 3D printing is possible.The aim and in this respect preferred is to form the layers in each case as continuous layers in order to achieve the respectively sought property of a layer in the best possible manner. The layers can also be designed as a discontinuous layer, however, since the continuity of the layers cannot be completely guaranteed, if necessary, during production. On the other hand, depending on the materials used, the production of a layer formed as a discontinuous layer can also be sought, so that the material of one layer can penetrate the material of another layer. In this way, further properties of the composite such as conductivity or resistance can be improved. The material of a layer can also have further constituents and inclusions. The materials of the first layer and of the second or of the further layer can consist essentially of a metal or be a metallic alloy. The term "substantially consisting of" is understood here to mean that the material can have unavoidable impurities, such as, for example, small amounts of oxygen (O) or carbon (C), in addition to the material specified. In particular, it is preferred that the indicated material, in particular the metallic material, has a high degree of purity, for example a purity of at least 99.9%, preferably of at least 99.95% and particularly preferably of 99.99%.In particular, the thermoelectric switching element is designed as a flat composite part, i.e. the at least two layers are arranged so as to adjoin one another in a planar manner, optionally by means of an intermediate layer, for example the two layers, and optionally the intermediate layer, are present in the form of a stack lying one above the other. The bonding zone as a transition layer is preferably formed at the interface between the at least two layers, optionally in each case at the interface between a layer and the intermediate layer.In general, the transition layer in which the adhesion bond with atomic diffusion has formed can have a plurality of contiguous or non-contiguous regions. The transition layer can also be formed homogeneously, for example of constant thickness, or inhomogeneously, for example with a thickness that is higher in sections. Thus, a thermoelectric switching element with sectionally different properties can be achieved by the transition layer.The thermoelectric switching element may have a rectangular shape. The production of this comparatively simple form is uncomplicated and therefore cost-effective. However, other forms of the thermoelectric switching element are also possible. For example, the thermoelectric switching element may take the form of a distance compensation element, which is also called a gap filler. A distance compensation element serves for the secure arrangement of components with varying dimensions in component groups and is arranged between these components. For example, the thermoelectric switching element, in particular for use as a distance compensation element, can be designed as a metal foil with integrally formed spring elements. The spring elements project from the plane of the metal foil and are in contact with at least one of the two components between which the distance compensation element is arranged.Furthermore, the thermoelectric switching element can be designed in the form of a worm or spiral, i.e. for example as a metal foil which is present in a form rolled up as a worm. This shape is advantageous, for example, when using the thermoelectric switching element in a thermometer, in particular for temperature indication by means of the deformation of the thermoelectric switching element due to the different thermal expansion coefficients of the materials of the first layer and of the second layer of the thermoelectric switching element. Furthermore, the thermoelectric switching element can also be designed in the form of a snap disc (SnapDisc), for example as a flat metal foil with a ball cap-shaped curved region. In particular, it is possible to provide and arrange the layers of the thermoelectric switching element in such a way that the curvature of the ball cap-shaped curved region changes under the influence of temperature, in particular forms in the opposite direction. This change in the curvature can be used advantageously as a switching mechanism. The snap-action disc can also be used as a switch by a mechanical action, for example in the form of a mechanical actuation by exerting pressure on the curvature.According to another teaching, the technical problem presented above is also solved according to the invention by using a thermoelectric switching element as an overhitz protection, in particular in the case of a cookware or an electronic circuit, wherein the thermoelectric switching element is designed according to one of the examples and variants explained above. In particular, a use as overhitz protection of the thermoelectric switching element is understood to mean that the latter is configured such that, when a predefined temperature is reached, a switching mechanism is triggered which brings about the switching off of a heating mechanism or of a current flow and thus prevents overheating. The switching mechanism can be triggered, for example, when the Curie temperature T c is reached as a result of changed electrical or magnetic properties of a material of a layer and / or as a result of thermal expansion of a material of a layer and / or as a result of temperature-dependent electrical properties, for example the specific resistance, of a material of a layer.In general, the use of the specified thermoelectric switching element or an embodiment thereof is preferably in the fields of electrical engineering, electronics, smart devices, cookware such as cookware or cookware such as pots, pans, sheets, pizza bricks or other devices with or in which foods can be heated or cooked, whiteware such as large household appliances such as electrical stoves, refrigerators, frozen barries, washing machines, dryers or dishwashers, energy stores, fuel cells, electrolysers, batteries and battery management systems and energy converters.A cookware can also be an oven or oven or a part thereof. The cookware can also be a device by means of which substances are heated or heated or processed outside the domestic kitchen.Furthermore, the thermoelectric switching element or an embodiment can also be used in a device for evaporating, for example for evaporating liquid. For example, it can be a device for drinking water production, by means of which seawater can be evaporated and thus desalted. Further condensation applications of other liquids are also conceivable. Furthermore, uses in the field of geothermal heat are also conceivable, wherein the natural thermal energy from the interior of the earth can be used in particular for heating substances and liquids such as (sea) water.The technical problem listed above is also solved according to the invention by a method for producing a thermoelectric switching element, in particular the thermoelectric switching element described above or an embodiment thereof, in which a first layer is provided at least partially consisting of a ferromagnetic material, in which a second layer is provided at least partially consisting of a metallic material, in which an intermediate layer is optionally provided, in which the first layer and the second layer are arranged adjacent to one another, optionally by means of the intermediate layer arranged between the first layer and the second layer, and in which an adhesion bond with atomic diffusion is produced between the first layer and the second layer, optionally in each case by means of the production of an adhesion bond with atomic diffusion between the first layer and the intermediate layer and between the second layer and the intermediate layer.The method enables an individual composite construction of layers of different materials and a variation of the layer thicknesses of the individual layers with high adhesive strength of the layers to one another. In particular, the layers are joined together to form a composite material. Overall, this allows a targeted adaptation of the properties of a thermoelectric switching element to various applications. Furthermore, the thermoelectric properties of the thermoelectric switching element can thus be influenced in particular by targeted material selection of the layers and adapted in a targeted manner to different applications and in particular to different temperatures at which a switching process is to be triggered. Furthermore, by selecting materials with different coefficients of thermal expansion, a so-called working of the layers among one another, and the loads resulting therefrom, can be positively influenced. A variation of the layer thicknesses of the individual layers is also possible by means of the above-mentioned method, so that the desired properties of the thermoelectric switching element can be influenced further in a targeted manner.The first layer which is provided consists at least partially, preferably completely, of a ferromagnetic material. Further preferably, the second layer consists at least partially, preferably completely, of a metallic material, in particular of a metallic material different from the ferromagnetic material of the first layer. Optionally, an intermediate layer is provided and optionally the first layer and the second layer are arranged adjacent to each other by means of the intermediate layer arranged between the first layer and the second layer. In this case, the adhesion bond between the first layer and the second layer is formed by forming an adhesion bond with atomic diffusion between the first layer and the intermediate layer and between the second layer and the intermediate layer. This means that a transition layer with atomic diffusion is produced both between the first layer and the intermediate layer and between the second layer and the intermediate layer in the case of an existing intermediate layer. Preferably, the first layer and the second layer are each arranged on opposite sides of the intermediate layer. If no intermediate layer is provided, the adhesion bond is produced with atomic diffusion, in particular directly, between the first layer and the second layer, so that a diffusion of atoms of the material of the first layer into the second layer and of atoms of the material of the second layer into the first layer takes place.Furthermore, provision can be made and accordingly the transition layer can be formed in such a way that the (atomic) diffusion between the first layer and the second layer extends over the intermediate layer. Accordingly, the transition layer can be formed in such a way that atoms of the first layer diffuse via the intermediate layer into the second layer and atoms of the second layer diffuse via the intermediate layer into the first layer. In this way, the properties caused by the transition layer are enhanced; for example, the bond of the plies can thus be further enhanced.The optional intermediate layer can be designed to be electrically insulating, for example as a plastic layer, or electrically conductive, for example at least partially consisting of a metal, such as copper (Cu), for example.In particular, the method can provide that the ferromagnetic material of the first layer and the metallic material of the second layer have different coefficients of thermal expansion, wherein the coefficients of thermal expansion of the ferromagnetic material of the first layer and of the metallic material of the second layer are selected and the first layer and the second layer are arranged with respect to one another in such a way that when a predefined temperature is reached, a predefined deformation of the composite of the first layer and the second layer, which optionally also includes the intermediate layer, is achieved.In the above-mentioned method, the respective binding partners, in the present case the first and the second layer and optionally the intermediate layer, are arranged adjacent to one another and brought into intimate contact, in particular approximated to atomic distances. The arrangement of the layers one above the other can be preceded by a cleaning process in which the contacting surfaces are freed, for example, from absorbed gases, oxide layers or impurities such as oil residues.The cleaning process and in particular the removal of the oxide layers increases the binding capacity of the surfaces of the binding partners. The oxide layers and generally the surface layers of the binding partners can also be broken up or roughened by further processes, for example forming processes, in order to increase the surface reactivity. Further processes such as rolling or stretching are also used to solidify near-surface regions of the binding partners and to generate highly active surfaces.According to a further teaching according to the invention, the abovementioned technical problem is also solved by the use of a thermoelectric switching element in a cookware item, wherein the thermoelectric switching element comprises: a first layer at least partially consisting of a ferromagnetic material, and a second layer at least partially consisting of a metallic material, wherein the first layer and the second layer are connected to one another by an adhesion bond with atomic diffusion, optionally via an intermediate layer. In particular, the metallic material of the second layer differs from the ferromagnetic material of the first layer. For example, the metallic material of the second layer and the ferromagnetic material of the first layer may have different coefficients of thermal expansion. In particular, the ferromagnetic material of the first layer comprises nickel (Ni) or a nickel alloy.In this way, the last-mentioned thermoelectric switching element can ensure during a cooking process that a specific temperature, in particular a temperature above the Curie temperature T c, is not exceeded, so that food prepared by means of the cookware or other substances to be heated are not heated too hot. A cookware item can be, for example, cookware item or further cookware items such as pots, pans, sheets, pizza bricks or other devices with or in which foods or other substances such as drinking water can be heated or cooked. A cookware can also be an oven or oven or a part thereof. The cookware can also be a device by means of which substances are heated or heated or processed outside the domestic kitchen. Furthermore, the latter thermoelectric switching element can also be used in a device for evaporating, for example for evaporating liquid. This can be, for example, a device for drinking water production, by means of which seawater can be evaporated and thus desalted. Further condensation applications of other liquids are also conceivable.Preferably, the use of the last-mentioned thermoelectric switching element in the case of a cookware, for example a cookware with a built-in thermoelectric switching element, achieves the effect that, for example in the context of inductive heating, the maximum temperature that can be achieved by the cookware can be regulated. If the Curie temperature T c of the ferromagnetic material of the thermoelectric switching element is reached, it loses its ferromagnetic properties and the inductive heating stops. A maximum heating temperature can thus be selected by the characteristic Curie temperature T c of the thermoelectric switching element, wherein, when this temperature is exceeded, the inductive heating can be stopped by the reversible phase transition of the ferromagnetic material. In this way, the thermoelectric switch can be used for heating temperature sensitive materials when used in a cookware. For example, the maximum temperature can be limited by the cookware, in particular when nickel (Ni) or a nickel alloy is used as the ferromagnetic material of the first layer, to temperatures of 360° C. or below, such that the preparation of foods can be optimized by means of the cookware with thermoelectric switching element. In particular, burning of foods can thus be prevented. The cooked product is used in particular in cooking or frying.Furthermore, when using the thermoelectric switching element, in particular in the case of a cookware, the advantageous properties of the first layer at least partially consisting of nickel (Ni), in particular its ferromagnetic properties, can be used. At the same time, the second layer can ensure that the thermoelectric switching element can also be used in applications in which nickel or nickel-containing materials are disadvantageous, for example since their use would lead to contamination of substances, for example foods or drinking water. In particular, in such applications, the second layer can be in contact with the substances and preferably serve as a barrier between these and the first layer, so that contact between the substances with nickel does not occur and thus possible contamination is avoided.In the following, further various preferred embodiments of the thermoelectric switching element and of the method for producing a thermoelectric switching element are described, wherein the various embodiments can be combined with one another and correspondingly apply to embodiments of the thermoelectric switching element and to the method. Moreover, the described preferred embodiments also apply in each case to the uses of a thermoelectric switching element already described.According to a first embodiment of the thermoelectric switching element, a switching mechanism is provided which is configured to trigger on the basis of the changed material properties of the ferromagnetic material of the first layer when the Curie temperature T c of the ferromagnetic material is reached. In particular, according to this embodiment, a switching mechanism triggers c of the ferromagnetic material on the basis of the changed material properties of the ferromagnetic material of the first layer when the Curie temperature T of the ferromagnetic material is reached.The switching mechanism can be based, for example, on a magnetic circuit being closed or opened by the reversible phase transition at T c. The switching mechanism can also be based on the fact that a material parameter of the ferromagnetic material, such as the specific resistance, which is measured, for example, by means of a sensor or measuring element provided for this purpose, changes during the reversible phase transition and this change is used as a switching signal. For this purpose, the switching mechanism may include a resistance sensing element. Furthermore, the switching mechanism can contain a magnetic sensor which detects the reversible phase transition on the basis of the omission of ferromagnetism of the material of the first layer. It is also possible to use a magnetism itself, which is to be omitted or to occur during the phase transition, due to the magnetism due to the ferromagnetism of the ferromagnetic material as a switching mechanism, for example in order to stop inductive heating or (restart).According to a further embodiment of the thermoelectric switching element, a third layer is provided at least partially consisting of a metallic material and the third layer is connected to the first layer or the second layer, optionally via an intermediate layer, in particular by an adhesion bond with atomic diffusion. The optional intermediate layer can be configured in particular as an (electrically conductive) metallic layer. However, the third layer can also be directly connected to the first layer or second layer without an intermediate layer arranged therebetween. It is further possible for the third layer to be bonded to the first layer or the second layer, for example, via an intermediate layer, in which case the intermediate layer constitutes in particular an insulating intermediate layer and functions as an adhesive layer. In particular, the metallic material of the third layer differs from the materials of the first and second layers. The metallic material of the third layer preferably has a coefficient of thermal expansion that differs from the materials of the first and second layers.According to a further embodiment of the thermoelectric switching element, the third layer has at least: a resistance region at least partially consisting of a metallic material, and two conductive regions at least partially consisting of a metallic material different from the metallic material of the resistance region, wherein the conductive regions are each arranged adjacent to different sides of the resistance region and are connected to the resistance region. In addition to the one resistor region and the two conductive regions, further resistor regions and / or conductive regions can also be provided. The third layer may have a thickness of 10 mm or less, preferably 8 mm or less.In this way, a thermoelectric switching element is provided which combines, in one component, switching mechanisms based on different coefficients of thermal expansion, based on the reversible phase transition at T c and the function as a measuring resistor (shunt). In addition, still further switching mechanisms based on (thermo)electric properties of the, in particular different, materials of the thermoelectric switching element can be realized by the combination of the first, second and third layers by the thermoelectric switching element, for example based on the Seebeck effect the induction of an electric voltage in the case of a temperature difference between the contact points of the layers. In particular, for this purpose, it can be provided that the materials of the three layers are selected such that they have different electrical conductivities.According to a further embodiment of the thermoelectric switching element, the resistor region is connected to the two conductive regions in each case by an adhesion bond with atomic diffusion. In this way, inhomogeneities at the transitions between the resistor region and the conductive regions can be reduced, so that a high-quality and high-precision rated resistance can be provided by the thermoelectric switching element by the combination of the resistor region with the two conductive regions.According to a further embodiment of the switching element, the resistance region runs in each case at the boundary surface to one of the two conducting regions at an obtuse or acute angle α relative to a plane along at least one side surface of the resistance region. In this way, a reliable bond between the conducting regions, which are arranged in particular next to one another and partially overlap, and the resistor region can be achieved. In addition, further resistor regions and conductive regions can also be provided, for which the same applies in relation to the adhesion bond with atomic diffusion and in relation to the course of the boundary surfaces of the resistor region relative to one or more conductive regions. An obtuse or acute angle is understood here to mean an angle which is not rectangular, i.e. which is greater than or less than 90°. For example, an acute angle may be 89° or less and an obtuse angle may be 91° or more.According to a further embodiment of the thermoelectric switching element, the ferromagnetic material of the first layer consists at least partially of nickel (Ni) or a nickel alloy. In this way, the advantageous properties of the first layer, at least partially consisting of nickel (Ni), in particular its ferromagnetic properties, can be used, wherein at the same time, the second layer or the further layer ensures that the thermoelectric switching element can also be used in applications in which nickel or nickel-containing materials are disadvantageous, for example since their use would lead to contamination of substances, for example foods or drinking water. In particular, in such applications, the second or further layer can be in contact with the substances and preferably serve as a barrier between these and the first layer, so that contact does not occur between the substances with nickel and thus possible contamination is avoided.More preferably, the ferromagnetic material of the first layer consists of a nickel alloy. In particular, a bimetallic alloy with Ni is preferred, but alloys with Ni and two or more further elements are also possible in addition. Preferable alloying elements for a nickel alloy are, for example, copper (Cu), palladium (Pd), platinum (Pt), zinc (Zn), aluminum (Al), antimony (Sb), silicon (Si), molybdenum (Mo), gold (Au), manganese (Mn), vanadium (V), chromium (Cr), titanium (Ti), and tin (Sn). It has been found that by alloying nickel with these alloying elements, the Curie temperature T c of the alloy can be adjusted specifically to values below or above the Curie temperature T c of nickel. Moreover, the first layer may also consist substantially entirely of nickel (Ni), such that the first layer substantially has the Curie temperature T c of Ni, which is indicated in the literature at about 360° C.In particular, an alloy of nickel (Ni) with an element selected from copper (Cu), manganese (Mn), aluminum (Al) or zinc (Zn) is preferred as the ferromagnetic material of the first layer. The alloy may be a binary alloy with Ni and one of the elements mentioned. Thus, for example, the Curie temperature T c of Ni can be reduced in an advantageous manner by alloying with Mn to temperatures of below 300° C., at a Mn content of between 5 and 10 at % in the alloy, up to below 100° C., at a Mn content of between 15 and 20 at % in the alloy. The alloy may also be a ternary or quaternary alloy or an alloy comprising more than four different elements. Here, the alloying elements Cu, Mn, Al and Zn already specified are preferred alloying elements. Furthermore, an Fe-Cr-Ni-Mn alloy for the ferromagnetic material of the first layer can be provided in particular as the nickel alloy, so that the first layer can at least partially combine the advantageous properties of these elements, for example the passivating properties of Cr. More preferably, particularly as a material having a Curie temperature T c, lowered with respect to pure Ni, an Fe-Cr-Ni-Mn-Si alloy is used. A composition with a content of 10% by weight of Cr, 33% by weight of Ni, 53.5% by weight of Cr, 3% by weight of Mn and 0.5% by weight of Cr is particularly advantageous for such an alloy. It has been found that in particular alloying of 2-3 wt.% Mn in an Fe-Cr-Ni-Mn or an Fe-Cr-Ni-Mn-Si alloy is advantageous for achieving a low Curie temperature, in particular a Curie temperature of below 100° C., preferably below 50° C.According to a further embodiment of the thermoelectric switching element, the ferromagnetic material of the first layer has a Curie temperature T c of less than 360° C., preferably of less than 350° C., particularly preferably of less than 330 ° C. Thus, the thermoelectric switching element can be used in applications in which certain limit temperatures, in particular those below 360° C., or 350° C. or 330° C., are not to be exceeded. For example, use in handling temperature-sensitive substances such as organisms or foods is advantageous.The thermoelectric switching element can preferably have a Curie temperature T c in the range from 260° C. to 350° C., particularly preferably in the range from 280° C. to 300° C. These specific ranges allow dedicated temperature limitation, for example, in the context of use in heating substances, for example food, or in the case of use as a temperature regulator. However, it is also possible for the thermocouple to have a Curie temperature T c of 260° C. or below, preferably of 200° C. or below. This is particularly advantageous in the context of the preparation of foods which are temperature-sensitive, or their preparation preferably takes place at temperatures of 260° C., preferably 200° C., and below. Preferred alloying elements for the ferromagnetic material of the first layer, in particular for achieving a Curie temperature T c of 260° C. or below, preferably of 200° C. or below, are, for example, copper (Cu), manganese (Mn), aluminum (Al), indium (In), strontium (Sr), nickel (Ni), antimony (Sb), calcium (Ca), silicon (Si), gallium (Ga), germanium (Ge), palladium (Pd), vanadium (V) or iron (Fe), in particular a combination of the elements mentioned.Alternatively, it can also be provided that the ferromagnetic material of the first layer has a Curie temperature T c in the range of more than 360° C., preferably of more than 370° C., particularly preferably of more than 390° C. In this case, for example, a higher temperature at which a switching mechanism is triggered, for example, a heating operation is stopped, can be set. For this purpose, the ferromagnetic material can comprise manganese (Mn), in particular.Preferably, the metallic material of the second and / or the third layer consists essentially of a metal. In this way, a thermoelectric switching element can be achieved, the properties of which can be easily adjusted at least on the side of the second and / or third layer. This is because a material which substantially consists of a metal generally has known properties. In addition, the interaction of the materials of the layers can be determined and controlled more easily in this way.For example, the metallic material of the second and / or third layer can consist essentially of copper (Cu). Copper is distinguished by good thermal conductivity, so that good heat distribution, for example in an electronic component or a cookware, can be achieved. As a further example, it is possible for the metallic material of the second and / or third layer to consist essentially of silver (Ag). Silver is distinguished by its antibacterial or antiviral effect, so that a thermoelectric switching element with antibacterial or antiviral effect can be achieved in this way.According to a further embodiment, the metallic material of the second and / or third layer consists essentially of a metallic alloy. The use of an alloy enables greater variability and thus adaptation possibility of the material properties of the thermoelectric switching element to a specific application. Thus, various elements with their specific advantageous properties can be introduced into the material composite. For example, the metallic material of the second and / or third layer can consist essentially of a Cu alloy or an Ag alloy.Furthermore, the selection of the metallic material of the second and / or third layer from a stainless steel is preferred. Due to its advantageous properties, such as corrosion resistance, stainless steel is used in a wide variety of fields, for example in the field of cookware. In this way, a thermoelectric switching element can be achieved in which the advantageous properties of stainless steel are introduced into the composite. Such a flat composite part is suitable, for example, for uses in the context of food processing, in particular food preparation, in which the flat composite part comes into contact with foods at least on the side of the second and / or third layer, or for applications in the sanitary sector, for example in shower heads or similar devices, in which water is heated or heated water is used.It can be provided that the metallic material of the second and / or third layer is nonferromagnetic, so that the use of the thermoelectric switching element, for example as an electromagnetic component, is not influenced in this way by the magnetic properties of the material of the first layer.According to a first embodiment of the method, the second layer is provided in that: a layer at least partially consisting of a metallic material (resistive material) and two layers at least partially consisting of a further metallic material (conductive material) are provided and arranged next to one another, wherein the layer at least partially consisting of the resistive material is arranged between the two layers at least partially consisting of the conductive material in such a way that the layer at least partially consisting of the resistive material at least partially overlaps the layers at least partially consisting of the conductive material, and the layers are connected to one another in that an adhesion bond with atomic diffusion is generated in each case between the layer at least partially consisting of the resistive material and the two layers at least partially consisting of the conductive material. A composite produced by the method described, in which adjacent layers are arranged side by side in a partially overlapping manner and are connected to one another by an adhesion bond with atomic diffusion, is referred to in particular as a side-to-side (2S2) composite. In particular, such a composite has oblique boundary surfaces between the resistance material and the conductivity material. An oblique boundary surface is understood here to mean a boundary surface which runs at acute or obtuse angles relative to at least one side surface of the layer made of the resistance material.In particular, a high-resistance resistor alloy can be used as the resistor material, for example an alloy based on nickel-chromium, on copper-nickel or on iron-nickel. In particular, a material at least partially consisting of copper can be provided as the conductive material.In this way, a shunt resistor (shunt) can be realized by the second layer, which due to the adhesion bond with atomic diffusion only has a small transition zone, for example in comparison with conventionally produced, in particular welded, rated resistors. Inhomogeneities at the transition between the resistor material and the conductive material can be minimized and thus a precise measuring resistor, in particular in conjunction with further switching mechanisms, can be provided by the thermoelectric switching element.According to a further embodiment of the method, a third layer is provided at least partially consisting of a metallic material, the third layer is arranged adjacent to the first layer or to the second layer, optionally by means of an intermediate layer arranged between the third layer and the first layer or between the third layer and the second layer, and an adhesion bond with atomic diffusion is generated between the third layer and the first layer or between the third layer and the second layer, optionally in each case by means of the generation of an adhesion bond with atomic diffusion between the third layer and the intermediate layer and between the first layer and the intermediate layer or between the second layer and the intermediate layer.According to a further embodiment of the method, the adhesion bond with atomic diffusion is in each case produced by application of pressure. By applying pressure, the surfaces of the layers to be joined can be brought into intimate contact with one another over a large surface area, wherein the pressure can also be applied in conjunction with other processes, for example a forming process. The bond by the adhesion bond between the binding partners is formed by mixing by means of atomic diffusion, wherein a transition layer is formed via which a continuous adaptation of the material properties takes place. In addition, it is possible to introduce further energy in the form of heat, whereby the atomic diffusion can be enhanced. However, an adhesion bond with atomic diffusion can also be produced without additional introduction of heat. The introduction of pressure, for example by pressing the binding partners onto one another, and the introduction of further energy, for example in the form of heat, can take place simultaneously or at different times.Introduction of further energy can additionally influence the extent of the transition layer, wherein this is generally dependent on the respective materials of the binding partners. Enlarging the expansion zone and enhancing the atomic diffusion can be used in a targeted manner to influence the material properties of the thermoelectric switching element. For example, the enlargement of the expansion zone and the reinforcement of the atomic diffusion lead to a stronger intermixing of the composite material, which can promote an increased electrical conductivity and / or an increased thermal conductivity of the layers with one another.In addition, the introduction of energy and heat can specifically influence the microstructure of the composite material. For example, the materials of the layers can be recrystallized. The degree of consolidation of the materials of the layers can also be influenced.The method described above can be understood, for example, as plating, wherein in English usage the term "cladding" can be used predominantly to describe such a method. Predominantly, a metallic bond of in each case two binding partners is produced by the method described above. An adhesion bond with atomic diffusion of metallic materials with non-metallic materials, for example carbon-containing materials, or between non-metallic materials can also be produced. If no additional heat is introduced, the method can be referred to in particular as cold rolling cladding, and if additional energy is introduced in the form of heat, it can be referred to as hot rolling cladding.According to a further embodiment of the method, the adhesion bond with atomic diffusion is in each case produced by introduction of heat. It is thus also possible to produce the adhesion bond with atomic diffusion without application of pressure, but by heat application. In particular, such a method can be referred to as joining by means of introduction of heat. An example of such an embodiment of the method is the production of a composite of two or more metallic layers by means of 3D printing. In the context of this additive manufacturing method, heat is introduced into a metallic powder, in particular by means of lasers or electron beam devices, which powder can consequently be melted in a targeted manner at the locations where heat is introduced. In this way, metallic materials can be joined together at these locations where heat is introduced. Such a method can also be referred to as powder bed-based laser melting (laser metal fusion).Further features and advantages of the invention will become apparent from the following description of exemplary embodiments, with reference to the attached drawing.The drawing shows FIGS. 1 a- b show a first exemplary embodiment of a thermoelectric switching element according to the invention, FIG. 2 shows a second exemplary embodiment of a thermoelectric switching element according to the invention, FIG. 3 shows a third exemplary embodiment of a thermoelectric switching element according to the invention, and FIG. 4 shows a fourth exemplary embodiment of a thermoelectric switching element according to the invention.In the following description of the various embodiments of the invention, components and elements having the same function and the same function are provided with the same reference numerals, even if the components and elements in the various embodiments may have differences in their dimension, shape or nature.FIGS. 1 a- b show schematically in a sectional view a first exemplary embodiment of a thermoelectric switching element 2 according to the invention. FIG. 1 a shows the exemplary embodiment at room temperature and FIG. 1 b shows the exemplary embodiment at a predefined temperature T 1, which is above room temperature. The thermoelectric switching element 2 has a first layer 4, which consists of a ferromagnetic material, here essentially of a nickel (Ni) alloy, and a second layer 6, which consists essentially of a metallic material, here essentially of copper (Cu). The materials of the first layer 4 and of the second layer 6 have different coefficients of thermal expansion, wherein the coefficients of thermal expansion of the ferromagnetic material of the first layer 4 and of the metallic material of the second layer 6 are selected in such a way and the first layer 4 and the second layer 6 are arranged with respect to one another and are connected to one another in such a way that a predefined deformation of the first layer 4 and of the second layer 6 is achieved when a predefined temperature T 1 is reached.The first layer 4 and the second layer 6 are arranged two-dimensionally one above the other, are connected to one another by adhesive bonding with atomic diffusion and are formed as continuous layers in this example. The layers 4, 6 here each have constant thicknesses over the width of the illustration. However, it is also possible for the layers 4, 6 of the thermoelectric switching element 2 to vary over the width and / or length thereof. In particular, the different thermal expansion coefficients of the materials of the first layer 4 and the second layer 6 achieve a predefined deformation of the composite when a predefined temperature T 1 is reached, in such a way that the metal strip formed by the composite bends towards one direction, in particular towards the layer of the material having the lower thermal expansion coefficient. This is illustrated in FIG. 1 b. The ferromagnetic material of the first layer 4 has a low coefficient of thermal expansion than the metallic material of the second layer 6, so that the thermoelectric switching element 2 is deformed in the direction of the first layer 4 (see arrow).FIG. 1 a additionally shows a twice enlarged detail 14 of the thermoelectric switching element 2, as a result of which the adhesion bond 10 with atomic diffusion 12 of the first layer 4 with the second layer 6 can be seen. In a first enlargement 16 of the cutout 14, it can be seen that the boundary surface of the layer 4, 6 is not planar, as shown in an idealized manner in the schematic, non-enlarged view of FIG. 1 a, but rather has an irregular profile. The layers 4, 6 adjoining one another therefore have a certain roughness on the atomic level at the boundary surface, which roughness already brings about adhesion of the layers 4, 6. In a view further enlarged compared to the first enlargement 16, the second enlargement 18, further details of the interface are recognizable at the atomic level. Specifically, the atoms of the materials of the layers 4, 6 are in each case not only present on one side of the boundary surface, but rather extend into the respective other layer 4, 6 due to diffusion across the boundary surface. During cold rolling, a pressure is exerted on the layers 4, 6 to be joined by rolling, for example two rollers which are arranged above and below the layers 4, 6 lying flat one above the other, which pressure brings the layers 4, 6 into intimate contact with one another on an atomic level. At the atomic level, as shown in enlargement 18 of cutout 14, a mixing of the respective materials of layers 4, 6 takes place at the interface of layers 4, 6 by atomic diffusion 12. After plating, optionally, heating of the composite may take place to allow, among other things, further material migration.FIG. 2 shows a schematic sectional view of a second exemplary embodiment of a switching element 2 according to the invention, which has a first layer 4, wherein the first layer 4 consists of a ferromagnetic material, here substantially of a nickel (Ni) alloy, and which has a further layer 20. The further layer 20 has a resistor region 24 which is substantially composed of a high-resistance resistor alloy, and two conductive regions 26 a, 26 bwhich are each arranged adjacent to different sides of the resistor region 24 and are connected to the resistor region 24 and consist of copper (Cu). The resistor region 24 runs in each case at the boundary surface 32 a, 32 bto one of the two conductive regions 26 a, 26 bat an acute angle α relative to a plane along at least one side surface 28 of the resistor region 24. The layers 4, 20, 22 are each connected to one another by an adhesion bond 10 with atomic diffusion 12.The further layer 20 represents a shunt resistor (shunt) due to its structure comprising a resistor region 24 and two conductive regions 26 a, 26 b, wherein the two conductive regions 26 a, 26 bare used for contacting the shunt resistor. As a result of the composite with the first layer 4 made of a ferromagnetic material having a Curie temperature T c a temperature-dependent resistance is achieved.The intermediate layer 22 can also be designed as an insulating intermediate layer. In this case, the resistance of the rated resistance is not influenced by the properties of the ferromagnetic material of the first layer 4, in particular as a function of temperature. At the same time, however, the switching mechanism based on the reversible phase transition can be used when the Curie temperature T c is reached, for example as an overhitz protection, when the temperatures in the vicinity of the rated resistance (of the further layer 20) and thus the temperature of the first layer 4 reaches the temperature T c. For example, current could flow through the first layer 4 and the further layer 20 in the form of a parallel connection for this purpose, wherein the current through the first layer 4, which changes due to the change in the specific resistance of the ferromagnetic material when the Curie temperature T c is reached, can serve as a switching signal for the U-hot protection.FIG. 3 shows a schematic sectional view of a third exemplary embodiment of a switching element 2 according to the invention, which has a first layer 4 made of a ferromagnetic material and a second layer 6 made of a metallic material. The composite of the first layer 4 and the second layer 6 corresponds substantially to the composite from FIG. 1 a. In addition, in the exemplary embodiment in FIG. 3, a third layer 8 is provided, which, corresponding to the structure of the further layer 20 from FIG. 2, has a resistance region 24 and two conductive regions 26 a, 26 b. In this way, a composite of two materials with different materials with a rated resistance (shunt) corresponding to the further layer 20 is achieved, so that the different switching mechanisms can be used synergistically. By means of the first layer 4 made of a ferromagnetic material, for example, protection against overheating of the rated resistance, which is represented by the third layer 8, can be achieved. If, for example, the thermoelectric switching element that heats the layers 4, 6, 8 that are connected to one another by adhesion bonding with atomic diffusion, a switching mechanism can be brought about by reaching the Curie temperature T c of the ferromagnetic material, which switching mechanism warns about overheating or reduces or terminates a current flow or a heating process. At the same time, a temperature-dependent resistance is achieved by the bond with the first layer 4, because the specific resistance of the ferromagnetic material changes when the Curie temperature T c is reached. In addition, the different thermal expansion coefficients of at least the first layer 4 and the second layer 6 can be used to realize a switching mechanism based on the (thermo)resonance effect.FIG. 4 finally shows a schematic sectional view of a fourth exemplary embodiment of a switching element 2 according to the invention, which has a first layer 4 made of a ferromagnetic material and a second layer 6 made of a metallic material. The composite of the first layer 4 and the second layer 6 corresponds substantially to the composite from FIG. 1 a. In addition, in the exemplary embodiment in FIG. 4, a third layer 8 is provided, which has a coefficient of thermal expansion that differs from the materials of the first layer 4 and the second layer 6. In this way, a composite of materials with at least three different coefficients of thermal expansion is achieved. For example, the thermal expansion coefficient of the second layer 6 may be larger than the thermal expansion coefficient of the first layer 4 and the thermal expansion coefficient of the third layer 8 may be larger than the thermal expansion coefficient of the second layer 6, so that gradual gradation of the thermal expansion coefficients is achieved. In this way, deformation of the composite upon temperature change can be achieved, in which expansion stresses between the individual layers can be reduced, so that a more stable thermoelectric switching element 2 can be achieved.

Claims

Thermoelectric switching element (2), - having a first layer (4) at least partially consisting of a ferromagnetic material, and - having a second layer (6) at least partially consisting of a metallic material, - wherein the ferromagnetic material of the first layer (4) and the metallic material of the second layer (6) have different coefficients of thermal expansion, and - wherein the coefficient of thermal expansion of the ferromagnetic material of the first layer (4) and the coefficient of thermal expansion of the metallic material of the second layer (6) are selected and the first layer (4) and the second layer (6) are connected to one another and arranged with respect to one another in such a way that, when a predetermined temperature is reached, a predetermined deformation of the composite of the first layer (4) and the second layer (6) is achieved, characterized - in that the first layer (4) and the second layer (6) are formed by an adhesion bond (10) with atomic diffusion (12), optionally connected to one another via an intermediate layer (22).Thermoelectric switching element (2), - with a first layer (4) at least partially consisting of a ferromagnetic material, and - with a further layer (20), which at least has: - a resistance region (24) at least partially consisting of a metallic material, and - two conductive regions (26a, 26b) which at least partially consist of a metallic material different from the metallic material of the resistance region (24), - wherein the conductive regions (26a, 26b) are each arranged adjacent to different sides of the resistance region (24) and are connected to the resistance region (24), characterized in that - the first layer (4) and the further layer (20) are connected to one another by an adhesion bond (10) with atomic diffusion (12), optionally via an intermediate layer (22).Thermoelectric switching element (2) according to Claim 1 or 2, characterized - in that a switching mechanism is provided which is configured to trigger on the basis of the changed material properties of the ferromagnetic material of the first layer (4) when the Curie temperature T c of the ferromagnetic material is reached.Thermoelectric switching element (2) according to one of Claims 1 to 3, characterized - in that a third layer (8) is provided, at least partially consisting of a metallic material, and - in that the third layer (8) is connected to the first layer (4) or the second layer (6), optionally via an intermediate layer (22), in particular by an adhesion bond (10) with atomic diffusion (12).Thermoelectric switching element (2) according to Claim 4, characterized - in that the third layer (8) has at least: - a resistor region (24), which is at least partially composed of a metallic material, and - two conductive regions (26a, 26b), which are at least partially composed of a metallic material different from the metallic material of the resistor region, - wherein the conductive regions (26a, 26b) are each arranged adjacent to different sides of the resistor region (24) and are connected to the resistor region (26a, 26b).Thermoelectric switching element (2) according to one of Claims 2 to 5, characterized - in that the resistor region (24) is connected to the two conducting regions (26a, 26b) in each case by an adhesion bond (10) with atomic diffusion (12).Thermoelectric switching element (2) according to Claim 6, characterized - in that the resistance region (24) runs in each case at the boundary surface (32a, 32b) with respect to one of the two conducting regions (26a, 26b) at an obtuse or acute angle α relative to a plane along at least one side surface (28) of the resistance region (24).Thermoelectric switching element (2) according to one of Claims 1 to 7, characterized - in that the ferromagnetic material of the first layer (4) consists at least partially of nickel (Ni) or a nickel alloy.Thermoelectric switching element (2) according to one of Claims 1 to 8, characterized - in that the ferromagnetic material of the first layer (4) has a Curie temperature T c of less than 360°C, preferably of less than 350°C, particularly preferably of less than 330 °C.Use of a thermoelectric switching element (2) according to one of Claims 1 to 9 as an overhitz protection.Method for producing a thermoelectric switching element (2), in particular a thermoelectric switching element (2) according to one of Claims 1 to 9, - in which a first layer (4) is provided at least partially consisting of a ferromagnetic material, - in which a second layer (6, 20) is provided at least partially consisting of a metallic material, - in which an intermediate layer (22) is optionally provided, - in which the first layer (4) and the second layer (6, 20) are arranged adjacent to one another, optionally by means of the intermediate layer (22) arranged between the first layer (4) and the second layer (6, 20), and - in which an adhesion bond (10) with atomic diffusion (12) is produced between the first layer (4) and the second layer (6, 22), optionally in each case by means of the production of an adhesion bond (10) between the first layer (4) and the intermediate layer (6) and between the second layer (6, 22) and the intermediate layer (6), an adhesion bond (10) with atomic diffusion (12) is produced.Method according to Claim 11, - in which the second layer (20) is provided by: - providing a layer (24) at least partially consisting of a metallic material (resistance material) and two layers (26a, 26b) at least partially consisting of a further metallic material (conductive material) and arranging them next to one another, wherein the layer (24) at least partially consisting of the resistance material is arranged between the two layers (26a, 26b) at least partially consisting of the conductive material in such a way that the layer (24) at least partially consisting of the resistance material overlaps in each case at least partially with the layers (26a, 26b) at least partially consisting of the conductive material, and - connecting the layers (24, 26a, 26b) to one another by in each case connecting between the layer (24) at least partially consisting of the resistance material and the two layers (26a, 26b), at least partially consisting of the conductive material, an adhesion bond (10) with atomic diffusion (12) is produced.Method according to Claim 11 or 12, - in which a third layer (8) is provided at least partially consisting of a metallic material, - in which the third layer (8) is arranged adjacent to the first layer (4) or to the second layer (6), optionally by means of an intermediate layer (22) arranged between the third layer (8) and the first layer (4) or between the third layer (8) and the second layer (6), and - in which between the third layer (8) and the first layer (4) or between the third layer (8) and the second layer (6), optionally in each case by means of the production of an adhesion bond (10) with atomic diffusion (12) between the third layer (8) and the intermediate layer (22) and between the first layer (4) and the intermediate layer (22) or between the second layer (6) and the intermediate layer (22), an adhesion bond (10) with atomic diffusion (12) is produced.Method according to one of Claims 11 to 13, - in which the adhesion bond (10) with atomic diffusion (12) is in each case produced by application of pressure.Method according to one of Claims 11 to 13, - in which the adhesion bond (10) with atomic diffusion (12) is in each case produced by introduction of heat.

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