Sensor assembly and method for producing a sensor assembly

Abstract

The invention relates to a sensor assembly (1) for measuring a temperature, comprising: - a sensor element (2) having a ceramic material, - at least two electrodes (3a, 3b) for electrically contacting the sensor element (2), - at least two connection elements (4) each having a first end region (4a) and a second end region (4b), each connection element (4) being electrically and mechanically connected, in the first end region (4a), to the associated electrode (3a, 3b), and the second end region (4b) being designed and disposed for the electrical contacting of the sensor assembly (1), - an encasement (7), the encasement (7) completely encasing the sensor element (2), the electrodes (3a, 3b) and at least the first end region (4a), - a separate non-conductive inorganic protective layer (8), the protective layer (8) completely surrounding, with the exception of the second end region (4b), at least a region of the connection elements (4) that is free of the encasement (7). The invention also relates to a method for producing a sensor assembly (1).

Description

[0001] P2023,1149 WO N July 24, 2024 - 1 - Description Sensor arrangement and method for producing a sensor arrangement The present invention relates to a sensor arrangement, in particular a temperature sensor arrangement. The present invention further relates to a method for producing at least one sensor arrangement, preferably a temperature sensor arrangement. The constantly increasing demands on temperature sensors with regard to long-term media resistance, operating temperatures, and robustness require particularly stable sensor casings, ideally in conjunction with a reduction in response time. The highest possible dimensional accuracy is also required for the installation of encapsulated, glass-encapsulated sensors in systems, which is currently not achievable with existing additional organic-based casings.The organic coatings currently in use with high moisture and media resistance (mostly fluorine-based compounds) can significantly delay migration or corrosion of the sensor element, but cannot completely prevent it or prevent it in the long term. According to the state of the art, temperatures for monitoring and control in a wide variety of applications are primarily measured using ceramic thermistor elements (NTC), silicon temperature sensors (KTY), platinum temperature sensors (PRTD), or thermocouples (TC). NTC thermistors are the most widely used due to their low manufacturing costs. A further advantage over thermocouples and metallic resistance elements, such as Pt elements, is their pronounced negative resistance-temperature characteristic.To ensure sufficient mechanical stability and to protect against external influences, as well as to prevent corrosion from aggressive media, as well as temperature-related material changes in the NTC material caused by the gas atmosphere or in the electrode, the ceramic sensor elements are coated with a polymer or glass. The maximum operating temperatures of such elements are limited to approximately 150°C - 175°C for a pure polymer coating (epoxy-based) and approximately 260°C for a glass coating with an additional polymer layer (PFA-based). However, such sensor elements cannot be used continuously for extended periods in particularly humid environments or aggressive media.After just a short time, the polymers begin to degrade, or the different thermal expansion coefficients of the materials (ceramic - metal - polymer) lead to the formation of thin gaps between the wires and the sheath. Moisture or corrosive media can penetrate and trigger migration processes, especially when voltage is applied. To ensure their use in aggressive media, the sensor elements are installed in a plastic or stainless steel housing, for example. Potting materials are also frequently used to establish thermal contact with the element. A major disadvantage of systems constructed in this way is their delayed response time due to the additional design-related heat transfer and low thermal conductivity of the materials used.The object of the present invention is to describe a sensor arrangement and a method for producing a sensor arrangement which solve the above problems. This object is solved by a sensor arrangement and a method for producing a sensor arrangement according to the independent claims. According to one aspect, a sensor arrangement is described. The sensor arrangement is suitable for measuring a temperature. The sensor arrangement is a temperature sensor arrangement. The sensor arrangement has a sensor element. The sensor element has a ceramic material. The sensor element preferably has an NTC sensor chip. The sensor arrangement further has at least two electrodes, preferably exactly two electrodes (a first electrode and a second electrode). The electrodes serve to make electrical contact with the sensor element. The electrodes are firmly connected to a surface of the sensor element.The electrodes are preferably sputtered onto a top side and a bottom side of the sensor element. The sensor arrangement further comprises at least two, preferably exactly two, connection elements. The connection elements each have a first end region and a second end region. P2023,1149 WO N July 24, 2024 - 4 - The first end region is flattened. The respective connection element is electrically conductively and mechanically connected in the first end region to the sensor element, in particular to the respective electrode, for example by welding or brazing. The second end region is designed and arranged for electrically contacting the sensor arrangement. The second end region forms an end of the respective connection element facing away from the sensor element. The sensor arrangement further comprises a casing. The casing can, for example, comprise glass, preferably lead-free glass.In this case, the sensor arrangement is completely harmless to the environment and does not require complex hazardous waste treatment. Alternatively, the casing can also comprise a polymer, for example epoxy, polyurethane, silicone, PEEK, PFA (perfluoroalkoxy polymer) or Teflon, or even a combination of these materials. The casing completely surrounds the sensor element, the electrodes, and at least the first end region of the connection elements (hereinafter also referred to as the connection point). Furthermore, the sensor arrangement has a separate, non-conductive, inorganic protective layer. In this context, "separate" means that the protective layer represents a separate component independent of the casing. In particular, the protective layer comprises a different material and / or a different extent than the casing and / or is formed using a different process than the casing.The protective layer is non-metallic, in other words, the protective layer has no metallic conductivity. The protective layer protects the sensor arrangement and in particular also the connection elements from external influences, for example aggressive media or gases. The protective layer is corrosion-resistant and moisture-resistant. The protective layer has a small thickness. The protective layer completely surrounds at least one region of the connection elements that is free of the sheath, with the exception of the second end region. In other words, the second end region is free of the protective layer. A region of the respective connection element that is located between the second end region and the sheath is enveloped, in particular completely surrounded, by the protective layer. The protective layer is directly adjacent to the sheath.In addition, the remaining area (first end area / connection point) of the respective connection element can also be surrounded by the protective layer. In particular, it is possible for the entire sensor arrangement (sensor element, electrodes, sheath, connection elements), with the exception of the second end areas, to be enclosed by the protective layer. An extension of the protective layer along the connection elements is greater than an extension of the sheath along the connection elements. This means that the protective layer surrounds a larger (in particular longer) area of ​​the connection elements than the sheath. P2023,1149 WO N July 24, 2024 - 6 - The protective layer enables the use of the sensor arrangement even in aggressive media and at high temperatures up to 400°C. This provides a particularly durable sensor arrangement. Thanks to the specially designed protective layer, the sensor arrangement also has high electrical insulation strength.Furthermore, the sensor arrangement has short response times due to good thermal conductivity and the low thickness of the protective layer. Furthermore, the materials used make the sensor arrangement particularly cost-effective and RoHS / REACH compliant (lead-free). According to one embodiment, the protective layer is produced by an anodic process, such as anodizing in the case of an aluminum-sheathed connection element. In this case, no additional layer is applied; instead, the uppermost layer of the connection element (for example, Al, Cr, or Ni) is converted to form a (multi-layer) protective layer. In this embodiment, only the area of ​​the respective connection element located between the second end region and the sheath can be surrounded by the protective layer. The protective layer is directly adjacent to the sheath.Alternatively, the protective layer can also surround the entire sensor arrangement, including the casing, with the exception of the second end regions. By creating an anodic protective layer, very thin oxide / hydroxide layers can be produced very precisely and reproducibly with very high mechanical abrasion resistance. This results in a very precise and very robust sensor arrangement. P2023,1149 WO N July 24, 2024 - 7 - In an alternative embodiment, the protective layer can be created by a purely chemical application process or by chemical vapor deposition. In this case, the protective layer represents an additional layer that is applied to an outer side of the connection elements. Furthermore, the protective layer can also be applied to the remaining components of the sensor arrangement.In this embodiment, the protective layer can therefore also surround the entire sensor arrangement with the exception of the second end regions. The protective layer created by the methods mentioned above is inorganic. The protective layer is non-conductive. The protective layer is non-metallic. The protective layer is characterized by either purely oxidic (metal oxides), nitridic, carbide, halide, or phosphatic compounds, such as Al2O3, CuOy, CrOy, MoOy, TiO2, V. x O yor SiO2. The formed protective layer is very thin, which leads to short response times and good thermal conductivity – simultaneously accompanied by high long-term stability of the sensor arrangement. According to one embodiment, the sensor arrangement further comprises an additional hydroxide cover layer. In this context, "additional" is to be understood as meaning that the cover layer represents a stand-alone component independent of the casing and the protective layer. In particular, the cover layer comprises a different material and / or a different extent than the casing and the protective layer and / or is formed by a different method and / or by a separate / stand-alone method step compared to the casing and the protective layer. P2023,1149 WO N July 24, 2024 - 8 - The additional cover layer is formed by a further surface treatment (hydrothermal treatment) of the sensor arrangement.The cover layer is continuous. In particular, the hydroxide cover layer preferably encloses the entire sensor arrangement with the exception of the respective second end region. There are no gaps / gaps at the cover layer or between the cover layer and the other components of the sensor arrangement. The cover layer is therefore completely impermeable. The cover layer serves as an additional protective element and further increases the longevity of the sensor arrangement. Furthermore, the cover layer can achieve a better connection between the protective layer and the casing. This is particularly useful when the protective layer does not extend over the entire sensor arrangement, but is only formed over the connection elements. In this case, a gap can occur between the protective layer and the casing, which can be covered by the additional cover layer. According to one embodiment, the sensor arrangement is free of precious metals.In particular, the connection elements comprise a material free of precious metals. Furthermore, the electrodes comprise a material free of precious metals. Since the sensor arrangement is free of precious metals, it can be manufactured particularly cost-effectively. According to one embodiment, the sensor element is based on perovskites in the Y-Ca-Cr-Al-(Sn)-O system or spinels in the Ni-Co-Mn-(AlFe)-(Cu)-(Zn)-(Ca)-(Zr)-(Ti)-(Mg)-O system P2023,1149 WO N July 24, 2024 - 9 - The choice of material depends on the operating temperature and resistance characteristics. For operating temperatures up to 300°C, for example, sensor materials with a spinel structure of the general chemical formula AB2O4 or. B(A,B)O4 such as Co3-(x+y)NixMnyO4 with x = 1.32 and y = 1.32 can be used. For high application temperatures (> 300°C), high-temperature stable ceramic materials with a perovskite structure of the general chemical formula ABO3, such as the composition (Y1-xCa), are suitable. x )(Cr1-yAly)O3with x = 0.03 and 0.05 or y = 0.85. This provides a very flexible sensor arrangement that can meet the needs of a wide variety of applications. According to a further aspect, a method for producing at least one sensor arrangement is described. It should be noted that the method preferably produces a large number of sensor arrangements in parallel. For the sake of simplicity, reference will be made below essentially to one sensor arrangement. Preferably, the method produces the sensor arrangement described above. All properties disclosed in relation to the sensor arrangement or the method are also correspondingly disclosed in relation to the respective other aspect and vice versa, even if the respective property is not explicitly mentioned in the context of the respective aspect. The method comprises the following steps: A) Providing at least one sensor element.The sensor element preferably has an NTC sensor chip. The sensor element preferably has a ceramic material. P2023,1149 WO N July 24, 2024 - 10 - The sensor element is particularly preferably constructed on the basis of perovskites in the Y-Ca-Cr-Al-(Sn)-O system or spinels in the Ni-Co-Mn-(Al)-(Fe)-(Cu)-(Zn)-(Ca)-(Zr)-(Ti)-(Mg)-O system. B) Provision or formation of at least two electrodes. The electrodes are preferably sputtered onto opposite side surfaces (for example, top and bottom) of the sensor element. The electrodes serve to electrically contact the sensor element. Different metals or metal pairings, such as Al, Ni, Cu, Cr, Mo, Ti, V, or Ni-Al, Ni-Cu, Ni-Cr, Ni-Mo, or Ni-Ti, can be used for the electrodes. In particular, the electrodes are preferably free of precious metals. C) Providing at least two connection elements.The respective connection element has a first end region and a second end region. The connection elements preferably have connecting wires. The respective connection element can, for example, have a core and a sheath. The sheath can, for example, comprise Al, Cr, Ni, or Cu. The connection elements preferably comprise temperature-stable materials with a low tendency to corrosion. The connection elements are preferably free of precious metals. D) Fastening the first end region of the connection elements to the sensor element, in particular to the electrodes of the sensor element (i.e., forming the connection point). The connection elements are connected to the electrodes of the sensor element by welding or brazing. Depending on the material pairing, different welding processes can be used, such as ultrasonic welding, resistance welding, P2023,1149 WO N July 24, 2024 - 11 - thermal diffusion welding, or plasma welding.Additional hard solders are required for brazing. Before the connection elements are attached to the electrodes, the electrodes can optionally be plasma cleaned. E) Forming a casing. The casing is formed in such a way that it completely encloses the sensor element, the electrodes, and at least the first end region of the connection elements (i.e., in particular, also the connection point). The casing can comprise glass or polymer. An expansion coefficient and a melting temperature or softening temperature of a material of the casing are adapted to the expansion coefficients or melting temperatures of the materials of the connection elements and sensor element. F) Forming a protective layer. The protective layer is formed by anodizing, chemical application, or deposition from the gas phase.The protective layer is formed such that it completely surrounds at least one area of ​​the connection elements that is free of the sheath, with the exception of the second end area. The protective layer can also surround the entire sensor arrangement with the exception of the second end areas provided for contacting the sensor arrangement. The second end areas are not anodized or coated. This is ensured by masking the second end areas or subsequently stripping the second end areas. Thanks to the protective layer, the sensor arrangement can also be used at higher application temperatures up to and including 400°C and in particularly aggressive media or gases. Furthermore, by creating an anodic protective layer, very thin oxide / hydroxide layers can be produced very precisely and reproducibly with very high mechanical abrasion resistance.Such very robust sensor arrangements also have very short response times. Overall, the method produces a cost-effective, long-lasting, robust, and highly efficient sensor arrangement. According to one exemplary embodiment, a further step G) involves tempering or hydrothermal treatment to form an additional hydroxide covering layer. The hydroxide covering layer completely envelops the entire sensor arrangement with the exception of the second end region. The covering layer can further increase the longevity and robustness of the sensor arrangement. According to one exemplary embodiment, before step F), a protective lacquer is applied to the second end regions and the protective lacquer is cured. This can ensure that the second end region of the respective connecting element remains free of the protective layer.In a further step - after the formation of the protective layer - the second end regions of the connection elements provided with the protective lacquer are exposed again (stripped). The drawings described below are not to be understood as true to scale. Rather, individual dimensions may be enlarged, reduced, or distorted for better illustration. Elements that are identical or that perform the same function are designated by the same reference numerals. P2023,1149 WO N July 24, 2024 - 13 - Shown are: Figure 1: A sectional view of a sensor arrangement before the formation of a protective layer, Figure 2: A sectional view of a sensor arrangement with a protective layer according to a first exemplary embodiment, Figure 2: A sectional view of a sensor arrangement with a protective layer according to a further exemplary embodiment.Figure 1 shows a sectional view of a sensor arrangement 1 before the formation of the protective layer 8 according to the invention. The sensor arrangement 1 is a temperature sensor arrangement. The sensor arrangement 1 is specially designed for use at high temperatures up to and including 400°C. The sensor arrangement 1 is designed for use in aggressive media or gases. The sensor arrangement 1 has a sensor element 2, preferably an NTC sensor chip. The sensor element 2 has a ceramic material. In particular, the sensor element 2 is based on perovskites in the Y-Ca-Cr-Al-(Sn)-O system or on the basis of spinels in the Ni-Co-Mn-(Al)-(Fe)-(Cu)-(Zn)-(Ca)-(Zr)-(Ti)-(Mg)-O system. The choice of material for the sensor element 2 depends on the intended application temperature and the resistance characteristics. For operating temperatures up to 300°C, P2023,1149 WO N 24 can be used.July 2024 - 14 - For example, sensor materials with a spinel structure of the general chemical formula AB2O4 or B(A,B)O4, such as Co3-(x+y)NixMnyO4 with x = 1.32 and y = 1.32, can be used. For high operating temperatures (> 300°C), high-temperature-stable ceramic materials with a perovskite structure of the general chemical formula ABO3, such as the composition (Y1-xCax)(Cr1-yAly)O3 with x = 0.03 and 0.05 or y = 0.85, are suitable. Two electrodes 3a, 3b (first electrode 3a, second electrode 3b) are formed, in particular sputtered on, on opposite sides (top and bottom) of the sensor element 2. The electrodes 3a, 3b are free of precious metals. Various metals or metal pairings can be used as the material for the electrodes 3a, 3b. Examples include Al, Ni, Cu, Cr, Mo, Ti, V, or Ni-Al, Ni-Cu, Ni-Cr, Ni-Mo, or Ni-Ti. Specifically, the first (upper) electrode 3a can be made of aluminum, for example.The second (lower) electrode 4b can comprise nickel, for example. The sensor arrangement 2 further comprises two connection elements 4, for example connection wires. The connection elements 4 are free of precious metals. Preferably, the connection elements 4 comprise temperature-stable materials with a low tendency to corrosion. Connection elements 4 made of base metals, such as Ni, Al, Cu, or connection elements 4 made of steel alloys with high contents of Fe, Cr and / or Ni, as well as coated connection elements 4, such as connection elements 4 with an Fe-Ni / Cr core and a Cu sheath or an Fe-Ni / Cr core and an Al sheath, as well as connection elements 4 with an Fe-Ni / Cr core and coatings, e.g. made of Mo, Ti, V, can be used. In Figures 1 to 3, the connecting elements 4 have a core-shell structure, for example an Fe / Ni core 6 P2023,1149 WO N July 24, 2024 - 15 - and an Al shell 5 (Figure 2) or an Fe / Ni core 6 and a Cu shell 5 (Figure 3).Of course, as stated above, other materials or material combinations are also possible. The connection elements 4 have an elongated shape. In particular, an extension of the connection elements 4 along a main longitudinal axis X of the sensor arrangement (see Figure 2) is greater than an extension of the connection elements 4 in a direction transverse to the main longitudinal axis X. The connection elements 4 each have a first end region 4a and a second end region 4b. The first end regions 4a are flattened and connected to the electrodes 3a, 3b, for example by welding or brazing. In particular, a connection point between the connection elements 4 and the sensor element 2 is formed at the location of the first end regions 4a. Depending on the material used for connecting elements 4 and electrodes 3a, 3b, different welding processes can be used to connect connecting elements 4 and electrodes 3a, 3b, such asUltrasonic welding, resistance welding, thermal diffusion welding, or plasma welding. Additional brazing alloys are required for brazing. Between the first end region 4a and a central region, the respective connection element 4 transitions into a round cross-sectional shape. An opposite free end of the respective connection element 4 forms the respective second end region 4b. The second end regions 4b are designed to contact the sensor arrangement 1. The respective second end region 4b has a length l. P2023,1149 WO N July 24, 2024 - 16 - The sensor arrangement 1 further comprises a casing 7. The casing 7 completely surrounds the sensor element 2, the electrodes 3a, 3b, and the first end regions 4a of the connection elements 4, and thus also the above-mentioned connection point between the connection elements 4 and the sensor element 2. The casing 7 serves to protect the sensor arrangement 1 from external influences.The casing 7 can comprise lead-free glass or a polymer (epoxy, polyurethane, Silicon Peek, PFA or Teflon or a combination of these materials). The material provided for the casing 7 is adapted to the materials for the connection elements 4 and the sensor element 2 in terms of its expansion coefficient and melting temperature or softening temperature. According to the exemplary embodiments shown in Figures 2 and 3, the sensor arrangement 1 further comprises a protective layer 8 according to the invention. The protective layer 8 serves to increase the robustness, durability, and flexibility of the sensor arrangement 1. The protective layer 8 is further designed such that the sensor arrangement 1 has a very short response time. The protective layer 8 can be produced by an anodic process, such as anodizing in the case of aluminum-coated connection elements 4, by a purely chemical application process, or by deposition from the gas phase.The protective layer 8 comprises an inorganic material. The protective layer 8 is non-conductive. The protective layer 8 is non-metallic. P2023,1149 WO N July 24, 2024 - 17 - The protective layer 8 has an oxidized layer. The protective layer 8 preferably comprises purely oxidic (metal oxides), nitridic, carbide, halide, or phosphatic compounds. For example, the protective layer 8 comprises Al2O3, CuxOy, CrxOy, MoxOy, TiO2, VxOy, or SiO2. The protective layer 8 has a small thickness, which leads to short response times and good thermal conductivity of the sensor arrangement 1. According to the embodiment shown in Figure 2, the protective layer 8 completely surrounds the connection elements 4 in a region between the casing 7 and the second end regions 4b. The protective layer 8 preferably adjoins the casing 7 directly. The protective layer 8 envelops orsurrounds a longer (larger) area of ​​the connection elements 4 than the sheath 7. Thus, an extension A1 of the protective layer 8 along the connection elements 4 is greater than an extension A2 of the sheath 7 along the connection elements 4: A1 > A2. As mentioned above, in the exemplary embodiment shown in Figure 2, the protective layer 8 directly adjoins the sheath 7. In other words, with the exception of the second end regions 4b, every region of the sensor arrangement 1 is enveloped, either by the sheath 7 or by the protective layer 8. However, the protective layer 8 can not only enclose the connection elements 4, but can also surround the entire sensor arrangement 1 with the exception of the second end regions 4b (Figure 3). In this case, the protective layer 8 surrounds the casing 7 and the components arranged therein (sensor element 2, electrodes 3a, 3b, first end region 4a / connection point) P2023,1149 WO N 24.July 2024 - 18 - as well as the remaining area of ​​the connection elements 4 with the exception of the second end regions 4b. In every embodiment, the second end regions 4b are free of the protective layer 8 in order to enable contacting of the sensor arrangement 1. In other words, no protective layer 8 extends over the length l of the second end region 4b. According to the exemplary embodiment shown in Figure 3, the sensor arrangement 1 can furthermore have an additional hydroxide cover layer 9. The cover layer 9 is produced by an additional surface treatment of the sensor arrangement 1 and completely surrounds the sensor arrangement 1, including the casing 7 and the protective layer 8, with the exception of the second end regions 4b. The additional cover layer 9 serves to improve the connection of the protective layer 8 to the casing 7. It is completely tight and can thus cover possible gaps between the protective layer 8 and the casing 7.Specifically, a sensor arrangement 1 according to the invention can thus be constructed, for example, as follows (specific embodiment not explicitly shown): • NTC chip 2 with sputtered Ni-Al electrodes 3a, 3b; • Welded connection elements 4 (sheath wires; Fe-Ni core and Al sheath); • Pb-free glass sheath 7 (melting temperature below the melting temperature of Al, i.e. < 660°C); • Anodized (anodized) connection elements (wires) 4 after glazing and thus formation of a dense multi-layer protective layer 8 by anodizing; • Non-anodized region at the second end regions 4b for electrical contacting of the sensor arrangement 1; • Additional hydroxide cover layer 9 over the entire arrangement 1 (including glass sheath 7) with the exception of P2023,1149 WO N 24.July 2024 - 19 - second end regions 4b by hydrothermal treatment for better connection to the glass casing 7 and in particular for closing possible gaps between casing 7 and protective layer 8; • The sensor arrangement 1 thus obtained has a protective layer made of Al2O3 / AlO(OH) / Al(OH)3.Alternatively, the sensor arrangement 1 according to the invention can be constructed, for example, as follows: • NTC chip 2 with sputtered Ni-Cu electrodes 3a, 3b; • Welded connection elements 4 (sheath wires; Fe-Ni core and Cu sheath); • Glass sheath 7; • Chromium oxide protective layer 7 (galvanically produced after glazing), which surrounds the entire sensor arrangement 1 with the exception of the second end regions 4b; • Additional hydroxide cover layer 9 over the entire arrangement 1 (including glass sheath 7) with the exception of the second end regions 4b by hydrothermal treatment for better connection to the sheath 7; • Stripped wire ends (second end regions 4b) for removing the protective layer 8 / the cover layer 9 for electrical contact.The sensor arrangement 1 with a non-conductive, non-metallic, inorganic protective layer 8 has the following advantages: • Migration resistance due to the corrosion-resistant and moisture-resistant, non-conductive, inorganic protective layer 8; • High electrical insulation strength; • Short response times due to good thermal conductivity and a very thin protective layer 8; • Cost-effectiveness since no precious metals are used; • RoHS / REACH conformity (lead-free). P2023,1149 WO N July 24, 2024 - 20 - A method for producing the sensor arrangement 1 described above is described below. The method has the following steps: A) Providing the sensor element 2. The sensor element 2 preferably has an NTC sensor chip. The sensor element preferably has a ceramic material. B) Providing or forming the at least two electrodes 3a, 3b.Preferably, the electrodes 3a, 3b are sputtered onto the top and bottom of the sensor element 2. The electrodes 3a, 3b are free of precious metals. Subsequently, the electrodes 3a, 3b can (optionally) be plasma cleaned. C) Providing the connection elements 4 having the first end region 4a and the second end region 4b. The connection elements 4 have temperature-stable materials with a low tendency to corrosion. The connection elements 4 are free of precious metals. D) Fastening the first end region 4a of the connection elements 4 to the electrodes 3a, 3b of the sensor element 2 (i.e. forming the connection point) for electrically contacting the sensor element 2. Depending on the material used, different welding methods can be used as fastening methods, such as ultrasonic welding, resistance welding, thermal diffusion welding or plasma welding.Alternatively, the connection elements 4 can be fastened to the electrodes 3a, 3b by means of brazing. P2023,1149 WO N July 24, 2024 - 21 - E) Forming the casing 7 such that the casing 7 completely encloses the sensor element 2, the electrodes 3a, 3b and at least the first end region 4a of the connection elements 4 (ie in particular also the connection point). The casing 7 can comprise lead-free glass. Alternatively, the casing 7 can comprise a polymer. To form the polymer casing, a sensor head of the sensor arrangement 1 (sensor element 2 including connection point) is covered with a polymer. The polymer can comprise an epoxy, polyurethane, silicone, PEEK, PFA or Teflon or a combination of these materials. The polymer casing can be applied by a dipping process or a powder coating process. The polymer is then cured. After process step E), an arrangement as shown in Figure 1 is present.Subsequently, a protective lacquer can (optionally) be applied to the second end regions 4b and cured to ensure that the second end regions 4b remain free of the protective layer 8 during the subsequent formation of the protective layer 8 (see Figures 2 and 3). F) Formation of the protective layer 8. This can be applied or produced locally. The formation of the protective layer 8 is therefore carried out in particular by anodizing, chemical application or deposition from the gas phase. P2023,1149 WO N July 24, 2024 - 22 - During anodizing, either the entire arrangement 1 (with the exception of the second end regions 4b) or only a portion of the connection elements 4 is placed in an acid bath and voltage is then applied to form the protective layer 8. The (glass) enclosure 7 can also be placed in the acid bath. The glass corrodes and hydroxides are deposited on the surface of the casing 7.The protective layer 8 is formed such that it completely surrounds at least the area of ​​the connection elements 4 that is free of the sheath 7, with the exception of the second end region 4b (Figure 2). The protective layer 8 can also surround the entire sensor arrangement 1 with the exception of the second end regions 4b provided for contacting the sensor arrangement 1 (Figure 3). G) Annealing or hydrothermal treatment to form the additional hydroxide cover layer 9 (optional). The hydroxide cover layer 9 completely envelops the entire sensor arrangement 1 with the exception of the second end region 4b (Figure 3). The second end regions 4b are not anodized or coated as described. This is ensured, for example, by the above-mentioned protective lacquer of the second end regions 4b, which is removed again after the application of the protective layer 8 or the cover layer 9. As an alternative to using a protective lacquer, the protective layer 8 orThe cover layer 9 can also be applied using a mask. The description of the subject matter specified here is not limited to the individual specific embodiments. Rather, the features of the individual embodiments P2023,1149 WO N July 24, 2024 - 23 - can be combined with one another as desired, provided that this is technically feasible.

[0002] P2023,1149 WO N July 24, 2024 - 24 - List of reference symbols 1 Sensor arrangement 2 Sensor element 3a (First) electrode 3b (Second) electrode 4 Connection element 4a First end region 4b Second end region 5 Sheath 6 Core 7 Enclosure 8 Protective layer 9 Cover layer A1 Extension of the protective layer A2 Extension of the enclosure X Main longitudinal axis l Length of the second end region

Claims

P2023,1149 WO N July 24, 2024 - 25 - Patent claims 1. Sensor arrangement (1) for measuring a temperature, comprising - a sensor element (2) comprising a ceramic material, - at least two electrodes (3a, 3b) for electrically contacting the sensor element (2), - at least two connection elements (4), each comprising a first end region (4a) and a second end region (4b), wherein the respective connection element (4) is electrically conductively and mechanically connected to the respective electrode (3a, 3b) in the first end region (4a), and wherein the second end region (4b) is designed and arranged for electrically contacting the sensor arrangement (1), - a casing (7), wherein the casing (7) completely encloses the sensor element (2), the electrodes (3a, 3b) and at least the first end region (4a), - a separate non-conductive inorganic protective layer (8),wherein the protective layer (8) completely surrounds at least one region of the connecting elements (4) that is free from the sheath (7), with the exception of the second end region (4b).

2. Sensor arrangement (1) according to claim 1, wherein an extension (A1) of the protective layer (8) along the connecting elements (4) is greater than an extension (A2) of the sheath (7) along the connecting elements (4).

3. Sensor arrangement (1) according to one of the preceding claims, wherein the protective layer (8) completely surrounds the entire sensor arrangement (1) with the exception of the respective end region (4b). P2023,1149 WO N July 24, 2024 - 26 - 4. Sensor arrangement (1) according to one of the preceding claims, wherein the protective layer (8) is produced by an anodic process, by a purely chemical application process, or by deposition from the gas phase.

5. Sensor arrangement (1) according to one of the preceding claims, wherein the protective layer (8) comprises oxidic, nitridic, carbide, halide, or phosphatic compounds.

6. Sensor arrangement (1) according to one of the preceding claims, wherein the protective layer (8) comprises Al2O3, CuxOy, CrxOy, MoxOy, TiO2, V x O yor SiO2.

7. Sensor arrangement (1) according to one of the preceding claims, further comprising an additional hydroxide cover layer (9).

8. Sensor arrangement (1) according to claim 7, wherein the hydroxide cover layer (9) completely envelops the entire sensor arrangement (1) with the exception of the second end region (4b).

9. Sensor arrangement (1) according to one of the preceding claims, wherein the sensor arrangement (1) is free of precious metals.

10. Sensor arrangement (1) according to one of the preceding claims, P2023,1149 WO N July 24, 2024 - 27 - wherein the casing (7) comprises a glass or a polymer.

11. Sensor arrangement (1) according to one of the preceding claims, wherein the sensor element (2) comprises an NTC sensor chip.

12. Sensor arrangement (1) according to one of the preceding claims, wherein the sensor element (2) is constructed on the basis of perovskites in the Y-Ca-Cr-Al-(Sn)-O system or spinels in the Ni-Co-Mn-(Al)-(Fe)-(Cu)-(Zn)-(Ca)-(Zr)-(Ti)-(Mg)-O system.

13. Sensor arrangement (1) according to one of the preceding claims, wherein an application temperature of the sensor arrangement (1) is ≤ 400°C. 14.Method for producing at least one sensor arrangement (1) for measuring a temperature, comprising the following steps: A) providing at least one sensor element (2); B) forming at least two electrodes (3a, 3b) on a surface of the sensor element (2); C) providing at least two connection elements (4), each having a first end region (4a) and a second end region (4b); D) fastening the first end region (4a) of the connection elements (4) to the sensor element (2); E) forming a casing (7), wherein the casing (7) completely encloses the sensor element (2), the electrodes (3a, 3b) and at least the first end region (4a); F) forming a protective layer (8), wherein the protective layer (8) covers at least one region of the casing (7) free of the. P2023,1149 WO N July 24, 2024 - 28 - completely surrounds the connection elements (4) with the exception of the second end region (4b).

15. The method according to claim 14, wherein the protective layer (8) is produced by anodizing, chemical application, or deposition from the gas phase.

16. The method according to claim 14 or 15, further comprising a step G): tempering or hydrothermal treatment to form an additional hydroxidic cover layer (9).

17. The method according to claim 16, wherein the hydroxidic cover layer (9) completely surrounds the entire sensor arrangement (1) with the exception of the second end region (4b).

18. The method according to one of claims 14 to 17, wherein plasma cleaning of the electrodes (3a, 3b) takes place before the connection elements (4) are attached to the electrodes (3a, 3b).

19. The method according to any one of claims 14 to 18, wherein, prior to step F), a protective lacquer is applied to the second end regions (4b) and cured. 20.The method according to claim 19, further comprising the step of: exposing the second end regions (4b) of the connecting elements (4) provided with the protective lacquer.

21. The method according to one of claims 14 to 20. P2023,1149 WO N July 24, 2024 - 29 - wherein the first end regions (4a) are flattened and wherein the connection elements (4) are connected to the sensor element (2) by ultrasonic welding, resistance welding or plasma welding of the flattened end regions (4a) or wherein the first end regions (4a) are connected to the sensor element (2) by means of brazing.

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