Sensor element and method for producing a sensor element

Abstract

The invention relates to a sensor element (100) for contactlessly measuring a temperature, the sensor element comprising - at least one carrier (2) having an upper face (11) and a lower face (12), - an insulating layer (3) which is formed directly on the upper face (11) of the carrier (2), - at least a first functional layer (7a) for contactlessly measuring the temperature of an object and at least a second functional layer (7b) for the contact-based measurement of an ambient temperature, wherein each functional layer (7a, 7b) comprises a material with a temperature-dependent electrical resistance and the functional layers (7a, 7b) are arranged separately from one another on the carrier (2), - at least two electrodes (4) for electrically contacting the functional layers (7a, 7b), - at least two contact pads (10) for electrically contacting the sensor element (100), wherein each one of the contact pads (10) is arranged directly on a respective partial area of one of the electrodes (4), wherein the sensor element (100) is designed to be directly integrated, as a discrete component, into an electrical system. The invention also relates to a method for producing a sensor element (100).

Description

[0001] Description

[0002] Sensor element and method for producing a sensor element

[0003] The present invention relates to a sensor element, in particular a temperature sensor for contactless temperature measurement. The present invention further relates to a method for producing a sensor element, preferably a temperature sensor for contactless temperature measurement.

[0004] To integrate passive components such as sensors, capacitors, protective devices, or heaters into electrical systems, the dimensions must be adapted to modern packaging designs, which are in the micrometer and even nanometer scale range. To achieve this level of miniaturization, the components are deposited as thin films on carrier structures with electrical connections and described as discrete components. These novel components can be integrated, for example, into MEMS (Micro Electro Mechanical System) structures.

[0005] According to the state of the art, temperatures for monitoring and control in a wide variety of applications are mainly measured using ceramic thermistor elements

[0006] (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. The German patent application DE 10 2020 122 923 A1, the content of which is incorporated into this application by reference, describes a sensor element for temperature measurement using a thin-film NTC thermistor.

[0007] For non-contact temperature measurement of an object's temperature using an infrared sensor, it is necessary to measure the ambient temperature of the functional element (e.g., thermopile, bolometer, etc.) within the sensor. Inaccurate temperature measurement of the ambient temperature at the functional element leads to errors in interpreting the measured value. A separate element for measuring the ambient temperature is required in addition to the functional element.

[0008] The current state-of-the-art solution for ambient temperature measurement in contactless temperature sensors, such as thermopiles, is an NTC chip. This separate NTC chip must be installed in an additional process step and is therefore located at some / greater distance from the functional element.

[0009] The object of the present invention is to describe a sensor element and a method for producing a sensor element which solve the above problems.

[0010] This object is achieved by a sensor element and a method for producing a sensor element according to the independent claims.

[0011] According to one aspect, a sensor element is described. The sensor element is suitable for contactless measurement of a temperature. The sensor element is an IR (infrared) temperature sensor. In particular, the sensor element is a TF (Thin

[0012] Film" ; thin film) IR-NTC temperature sensor .

[0013] The sensor element has at least one carrier. Preferably, the sensor element has exactly one carrier. The carrier has a carrier material, preferably silicon, silicon carbide, or glass (silica or borosilicate glass). Alternatively, the carrier material can also comprise AlN or Al2O3.

[0014] The carrier has a top side and a bottom side. The top side is electrically insulating. Preferably, an insulating layer, for example SiO 2 or SiA 4 , is formed on the top side of the carrier. The insulating layer is formed directly on the top side of the carrier and can be constructed from one or more layers.

[0015] The sensor element further comprises at least one first functional layer. The first functional layer is designed and arranged for contactless temperature measurement. In particular, the first functional layer is used to measure the temperature of an object contactlessly based on its emitted radiation.

[0016] The first functional layer is formed on the carrier, in particular on the insulating layer. The carrier mechanically stabilizes the first functional layer. The first functional layer is arranged in a first region / IR region of the carrier or of the sensor element. The first region / IR region is also referred to below as the IR sensor. The sensor element furthermore has at least one second functional layer. The second functional layer is designed to measure, in particular to measure by contact, an ambient temperature. In particular, the second functional layer is designed and arranged to measure the temperature of the carrier.

[0017] The second functional layer is formed on the carrier, in particular on the insulating layer. The carrier mechanically stabilizes the second functional layer. The second functional layer is arranged in a second region / reference region of the carrier or the sensor element. The second region / reference region is also referred to below as the reference sensor.

[0018] The first and second functional layers are thin films (TF). The thickness of each functional layer is between 50 nm and 1 pm, preferably between 100 nm and 500 nm, particularly preferably between 250 nm and 400 nm.

[0019] The respective functional layer comprises a material (functional material) which has a special electrical characteristic. The respective functional layer comprises a material with a temperature-dependent electrical resistance. The respective functional layer preferably comprises an NTC ceramic. The NTC ceramic is preferably based on an oxide material in the perovskite or spinel structure type. Alternatively, the respective functional layer can be based on a carbide or a nitride material. Thin films made of vanadium oxide or SiC represent a further alternative. The two functional layers are arranged spatially separated from one another on a single carrier. The carrier therefore has two sensitive areas. In other words, according to the invention, two sensors (IR sensor and reference sensor) are combined in the smallest possible space on a single chip.There is no direct contact between the two functional layers. The two functional layers / sensors can, for example, be formed next to each other on the carrier. Alternatively, the second functional layer can surround the first functional layer. In other words, the reference sensor can be formed around the IR sensor.

[0020] By combining two sensitive areas on a single chip, the ambient temperature in the immediate vicinity of the IR sensor can be measured. This provides a particularly precise and compact sensor element.

[0021] The sensor element further comprises at least two electrodes. Preferably, the sensor element comprises at least three electrodes. In one embodiment, one of the electrodes of the first region / the IR sensor and one of the electrodes of the second region / the reference sensor can be combined. In other words, the first functional layer and the second functional layer can share a common electrode. Ideally, the sensor element comprises four electrodes.

[0022] The electrodes serve to electrically contact the functional layers. The electrodes are preferably designed as thin-film electrodes. The electrodes are formed at a distance from one another on the carrier. Two electrodes are preferably formed in the first region of the carrier and two electrodes are formed in the second region of the carrier. The electrodes preferably do not extend to an edge region of the carrier. In particular, the electrodes are preferably formed in an inner region on the carrier.

[0023] The electrodes are formed directly on the carrier or the insulating layer. In other words, the electrodes are formed below the functional layers. Alternatively, the electrodes can also be formed above the functional layers. In this case, the functional layers are formed directly on the carrier or the insulating layer.

[0024] The sensor element further comprises at least two contact pads for electrically contacting the sensor element. Preferably, the sensor element comprises at least three contact pads. In one embodiment, one of the contact pads of the first region / the IR sensor and one of the contact pads of the second region / the reference sensor can be combined. In other words, the first functional layer and the second functional layer can share a common contact pad. Ideally, the sensor element comprises four contact pads (two contact pads in the IR region and two contact pads in the reference region).

[0025] The contact pads can comprise Cu, Au, Ni, Cr, Ag, Ti, W, Pd or Pt. The contact pads preferably comprise Au. The contact pads can have a layered structure. The contact pads particularly preferably comprise Au and Ti, with Ti being formed as an adhesion layer beneath the Au layer. The contact pads are directly electrically and mechanically connected to the electrodes. One contact pad in each case is arranged directly on a partial region of at least one of the electrodes. Overall, the sensor element is very compact, i.e. it has a miniaturized design so that it can be embedded directly into an electrical system as a discrete component. The term “discrete” in this context means that the sensor element can be integrated into electrical structures as a compact and self-contained system.

[0026] For example, the sensor element has a maximum edge length (length or width) of 2000 pm, preferably < 1500 pm. The thickness of the sensor element is < 1000 pm, preferably < 700 pm, particularly preferably < 300 pm. For example, the component is designed for direct integration into a MEMS structure.

[0027] The two sensors combined in one sensor element (IR sensor and reference sensor) make it possible to determine the ambient temperature in the immediate vicinity of the IR sensor. This eliminates the need for an additional NTC chip, which would have to be assembled in an additional process step. This provides a very cost-effective, sustainable, and precise sensor element.

[0028] According to one embodiment, the sensor element further has a cavity in the carrier. In other words, a hollow space is formed in the carrier. In one embodiment, the cavity completely penetrates the carrier. In an alternative embodiment, an underside of the carrier is free of a cavity. Consequently, the underside of the carrier in this embodiment has a smooth profile. In other words, the cavity does not completely penetrate the carrier. The cavity is formed directly beneath the insulating layer. The insulating layer covers the cavity upwards (membrane structure).

[0029] The cavity is formed in the first region / IR region of the carrier or the sensor element. The cavity is located in the region of the first functional layer. In particular, the cavity is located at least partially beneath the first functional layer.

[0030] The cavity may have a smaller area than the area of ​​the first functional layer. In this context, "area" is understood to mean an extension perpendicular to a stacking direction / thickness of the sensor element. Preferably, the cavity and the first functional layer occupy the same area. Ideally, the area of ​​the cavity is larger than the area of ​​the first functional layer.

[0031] The cavity is designed and arranged to thermally decouple the first functional layer (and all other components of the sensor element formed on the first functional layer) from the carrier. This reduces thermal losses to the carrier and enables a maximized temperature change at the first functional layer. This also maximizes the resistance change.

[0032] However, complete decoupling of the first functional layer and the environment is not possible. Thus, there is always heat loss to the environment. Therefore, the temperature of the first functional layer will differ from that of the object being measured. The greater the temperature difference between the first functional layer and the environment, the greater the thermal losses. Therefore, a reference sensor (second area) for measuring the ambient temperature is necessary.

[0033] Furthermore, heat transfer through solids is significantly faster than through gases, meaning that the majority of heat loss occurs through the carrier. Consequently, the influence of the carrier is dominant compared to the rest of the environment. Therefore, it is of particular interest to determine the temperature of the carrier (and thus the environment) in order to be able to correct for thermal losses. This is done using the reference sensor / second functional layer in the immediate vicinity of the IR sensor.

[0034] According to one embodiment, a region of the carrier below the second functional layer is free of a cavity. In other words, no cavity is formed in the second region / reference region. In other words, the reference sensor has no cavity (in the carrier).

[0035] A cavity decouples the functional layer from the carrier. This delays the reaction time of the functional layer to changes in the carrier and makes it more easily affected by other influences. Without a cavity, the thermal interaction between the second functional layer and the carrier is consequently improved, and the temperature response time and stability are optimized. The thin-film structure of the functional layer has a significantly lower heat capacity than that of the carrier. This means that the carrier has a negligible influence on the carrier temperature. This also enables very precise measurement of the carrier temperature.

[0036] Overall, the design of the reference sensor without

[0037] A fast, accurate, and stable ambient temperature can be determined within the cavity. At the same time, mechanical stability is improved and design options are only minimally restricted. For example, the first and second functional layers (IR sensor and reference sensor) can be positioned closer together compared to the state of the art, there is no weight limit for the membrane on the reference sensor, etc. For example, the reference sensor can also surround the IR sensor for a more uniform determination of the ambient temperature.

[0038] According to one embodiment, the sensor element further comprises a protective layer. The protective layer can comprise oxides, nitrides, ceramics, glasses, or plastics as its material. The protective layer completely covers an upper side of the sensor element with the exception of the contact pads. For this purpose, the protective layer has recesses at the location of the contact pads. The protective layer has a thickness of between 50 nm and 1 pm, preferably between 200 nm and 600 nm, ideally between 400 nm and 500 nm. The protective layer improves the long-term stability of the sensor element.

[0039] According to one embodiment, the sensor element further comprises at least one, preferably exactly one, absorber layer. The absorber layer is formed in the first region / IR region. The second region (reference region) is free of an absorber layer.

[0040] The absorber layer is formed above the first functional layer, viewed in a stacking direction of the sensor element. The absorber layer is formed on the protective layer, in particular directly on the protective layer. The absorber layer is preferably formed congruent with the first functional layer. This means that an area of ​​the absorber layer is as large as an area of ​​the first functional layer. Alternatively, the absorber layer can also partially project beyond the first functional layer (on one side or both sides) or be smaller than it.

[0041] The absorber layer comprises a material that absorbs infrared radiation. The absorber layer is preferably made of an IR-absorbing material. Examples of materials suitable for the absorber layer include thin metal layers, dielectric materials (e.g., silicon oxide, silicon nitride, aluminum nitride, etc.), nanoporous metals, or polymers (e.g., polyimide resins, polymers with dispersed carbon particles, etc.).

[0042] The first functional layer / IR sensor measures the temperature of an object contactlessly based on its emitted radiation. The radiation is absorbed by the absorber layer, causing its temperature to change. The absorber layer is in thermal contact with the first functional layer. This changes the temperature of the first functional layer. This is expressed as a change in the material's resistance.

[0043] According to one embodiment, the sensor element further comprises at least one, preferably exactly one, reflector layer. The reflector layer is formed in the second region / reference region. The first region (IR region) is free of a reflector layer. The reflector layer is formed above the second functional layer, as viewed in a stacking direction of the sensor element. The reflector layer is formed on the protective layer. In particular, the reflector layer is formed directly on the protective layer.

[0044] The reflector layer can be congruent with the second functional layer. This means that the surface area of ​​the reflector layer is as large as the surface area of ​​the second functional layer. Alternatively, the reflector layer can partially extend beyond the second functional layer (on one side or both sides) or be smaller than it.

[0045] The reflector layer comprises a material that reflects infrared radiation. The reflector layer is preferably made of a material that reflects IR radiation. The reflector layer preferably comprises metallic materials with a sufficient thickness. For example, the same material that is used for the contact pads can also be used for the reflector layer. For example, the reflector layer comprises Cu. If the reflector layer and contact pads are made of the same material, these two components can be produced in the same process step.

[0046] The reflector layer minimizes the influence of IR radiation on the reference sensor. Because the reflector layer reflects IR radiation, the temperature of the second functional layer changes little or not at all due to IR radiation incident on the reflector layer. This results in little or no change in the resistance of the material of the second functional layer due to the incident IR radiation. Consequently, the reflector layer ensures reliable operation of the reference sensor / second functional layer. This results in a very precise sensor element.

[0047] According to one embodiment, one of the contact pads functions as a reflector layer. In other words, a contact pad formed above the second functional layer (i.e., in the second region / reference region) is designed such that it simultaneously performs the function of a contact pad and the function of the reflector layer. An additional reflector layer is thus omitted. This allows the number of process steps for manufacturing the sensor element to be reduced. In particular, the reflector layer and contact pad can be produced in the same process step in this case.

[0048] If one of the contact pads functions as a reflector layer, this does not automatically imply that the contact pad must be formed in one piece. For example, the contact pad may have several regions, one of which functions as a reflector layer. The regions may be spatially separated from one another. In other words, a gap may be formed between the regions.

[0049] According to one embodiment, the respective electrode has a flat end region. A contact pad is preferably arranged on the flat end region of at least one of the electrodes. The respective electrode preferably has a plurality of electrode fingers (interdigital structure).

[0050] According to a further aspect, a method for producing a sensor element, preferably a plurality of sensor elements, is described. Preferably, the above-described sensor element is produced by the method. All properties disclosed with respect to the sensor element or the method are also correspondingly disclosed with respect 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:

[0051] A) Providing a carrier material for forming a carrier . Preferably, the carrier material comprises Si, SiC, or glass . Alternatively, the carrier material may comprise AlN or Al2O3 . Preferably, the carrier material comprises Si . The carrier has a top side and a bottom side . The final sensor element and consequently also the carrier have a first region (IR region) and a second region (reference region).

[0052] For the sake of clarity, it should be mentioned at this point that in parallel processing, the carrier is provided in the form of a wafer in this step, from which the individual sensor elements are separated in a final step.

[0053] B ) Forming an electrically insulating layer , preferably SiO2 , on top of the carrier .

[0054] 0) Forming or depositing at least two electrodes, preferably three or four electrodes, on the insulating layer. Preferably, two electrodes are formed in the first region and two electrodes in the second region.

[0055] The electrodes are designed to be spaced apart from each other.

[0056] In particular, the electrodes are spatially and electrically isolated from each other. The electrodes preferably interlock in the form of interdigital structures.

[0057] The electrodes are formed using a DVD (physical vapor deposition) process, a CVD (chemical vapor deposition) process, or galvanically. In a further process step, the electrodes are structured.

[0058] D) Applying, preferably sputtering, a first functional material to a portion of the electrodes in the first region to form a first functional layer. Applying, preferably sputtering, a second functional material to a portion of the electrodes in the second region of the carrier to form a second functional layer. In the final sensor element, the two functional layers are formed separately from one another on the carrier.

[0059] Preferably, the functional materials of the first and second functional layers are identical. Thus, the two functional layers can be formed simultaneously on the carrier in a single step.

[0060] The functional material preferably comprises an NTC ceramic based on an oxide material with a perovskite or spinel structure. Alternatively, the functional material can also be based on a carbide or nitride material. Alternatively, the functional material can comprise or represent a thin film of vanadium oxide or SiC.

[0061] The respective functional layer is formed as a thin-film layer. The respective functional layer only partially covers the electrodes. In particular, the respective functional layer is formed such that it is spaced from the edge region of the carrier and is formed in the region of the finger structures (interdigital structures) of the electrodes.

[0062] After deposition, the respective functional layer has not yet crystallized.

[0063] E ) Sintering of the functional layers . This serves to develop the NTC properties of the functional material and is carried out at temperatures up to 1000 ° C

[0064] F) Applying a protective layer to the top side of the sensor element. The protective layer completely covers the top side except for at least two partial areas, preferably except for three or four partial areas. The partial areas are arranged at least partially over the electrodes. The partial areas are arranged in particular over the flat end areas of the electrodes, onto which the contact pads can be applied in the subsequent process step.

[0065] The protective layer is used for structuring either

[0066] ( a ) applied over the entire surface and the free partial areas are created by a subsequent process such as lithography or laser structuring or

[0067] (b) directly applied in a structured manner by using a mask during the deposition process.

[0068] G) Forming contact pads in the partial regions free of the protective layer for electrically contacting the sensor element. At least one contact pad is formed directly on the flat end region of at least one of the electrodes. The contact pads can comprise Cu, Au, Ni, Cr, Ag, Ti, W, Pd or Pt. The contact pads preferably have a layer structure comprising Au and Ti. The Au layer preferably has a thickness of < 300 nm.

[0069] As an alternative to contact pads, bumps or thin electrodes can also be used. All of these possible contact elements comprise a metal, such as Cu, Au, or a solderable alloy.

[0070] According to the invention, the method produces a sensor element for contactless temperature measurement (IR-NTC element), in which two sensitive areas are arranged on a carrier. These areas are constructed in a layer system. One area is infrared (IR) sensitive (IR sensor) and the other area is ambient temperature sensitive (reference sensor). By combining the two sensors in one component, it is possible to determine the ambient temperature in the immediate vicinity of the IR sensor. This eliminates the need for an additional NTC chip, which would have to be assembled in an additional process step.

[0071] According to one embodiment, the method further comprises the following steps:

[0072] H) Forming a reflector layer. The reflector layer is formed above the second functional layer on the protective layer, as viewed in a stacking direction of the sensor element. The reflector layer comprises a material that reflects IR radiation.

[0073] Step G) and step H) can also be combined into a single

[0074] In other words, the contact pads and the reflector layer can be formed in a single process step. This is especially true if the contact pads and reflector layer are made of the same material.

[0075] I) Forming an absorber layer. The absorber layer is formed above the first functional layer on the protective layer, as viewed in a stacking direction of the sensor element. The absorber layer comprises a material that absorbs IR radiation.

[0076] The reflector layer and absorber layer are formed spatially spaced from each other directly on the protective layer.

[0077] J) Forming a cavity in the first region of the carrier. The second region remains free of a cavity. The cavity is formed by etching from the back of the wafer down to the electrically insulating layer. Due to the selective properties of the etchant, the SiC>2 layer, for example, is not attacked.

[0078] According to one embodiment, the method produces a plurality of sensor elements. The method further comprises the following step:

[0079] K) Separating or singulating the sensor elements. This is done either with a diamond saw, by stealth dicing, or by a plasma etching step. The wafer (preferably a Si wafer) from which the individual sensor elements are to be cut is sawn or severed. The drawings described below are not to be understood as being true to scale. Rather, individual dimensions may be enlarged, reduced, or distorted for clarity.

[0080] Elements that are identical or that perform the same function are designated by the same reference symbols.

[0081] It shows :

[0082] Figure 1 is a perspective view of a

[0083] Sensor element according to the state of the art,

[0084] Figure 2 is a sectional view of the sensor element according to Figure 1 (state of the art),

[0085] Figure 3 is a perspective view of the sensor element according to the invention according to a first embodiment,

[0086] Figure 4 is an exploded view of the sensor element according to the invention according to Figure 3,

[0087] Figure 5 is a sectional view of the sensor element according to the invention shown in Figure 3,

[0088] Figure 6 is a sectional view of the sensor element according to the invention according to a further embodiment, Figure 7 is a sectional view of the sensor element according to the invention according to a further embodiment,

[0089] Figure 8 is a schematic plan view of a sensor element according to the invention according to a further embodiment.

[0090] Figures 1 and 2 show a representation of a sensor element 1 according to the prior art. The sensor element 1 serves to illustrate a basic structure of the sensor element 100 described below (Figures 3 to 7). For a detailed description of the essential features of the sensor element 1 according to Figures 1 and 2, reference is made to German patent application DE 10 2020 122 923 A1, the content of which is incorporated by reference into this application.

[0091] The sensor element 1 is an NTC thin-film temperature sensor and has a carrier 2 with a top side 11 and a bottom side 12. The top side 11 of the carrier 2 has an insulating layer 3, for example, comprising SiO2. The sensor element 1 further has at least two electrodes 4a, 4b. The two electrodes 4a, 4b are formed spaced apart from one another on the insulating layer 3 of the carrier 2 and have thin metal films.

[0092] The electrodes 4a, 4b are designed as interdigital thin-film electrodes. In particular, the electrodes 4a, 4b each have a flat end region 6 and a region with electrode fingers 5. The region with the electrode fingers 5 is formed in a central region of the carrier 2. The flat end region 6 and the region with the electrode fingers 5 merge into one another. The two electrodes 4a, 4b each engage with one another in the region of the electrode fingers 5 in the central region of the carrier 2 and form an interdigital structure there.

[0093] The sensor element 1 further has a functional layer 7 with a top side 14 and a bottom side 15. The functional layer 7 is an NTC thin film. The functional layer 7 only partially covers the insulating layer 3 on the top side 11 of the carrier 2. The functional layer 7 is preferably applied at least partially to the electrodes 4a, 4b. As can be seen from Figures 1 and 2, the electrodes 4a, 4b are formed between the carrier 2 and the functional layer 7, in particular on a bottom side 15 of the functional layer 7. The functional layer 7 lies directly on the area with the electrode fingers 5.

[0094] The sensor element 1 further comprises at least two contact pads 10a, 10b for electrically contacting the sensor element 1. The sensor element 1 can further comprise a protective layer 8. The protective layer 8 completely covers an upper side of the sensor element 1, with the exception of the contact pads 10a, 10b. The protective layer 8 has recesses 9 from which the contact pads 10a, 10b protrude for electrically contacting the sensor element 1.

[0095] Figures 3 to 8 show exemplary embodiments of a sensor element 100 according to the invention. In comparison to the sensor element 1 shown in Figures 1 and 2, the sensor element 100 is designed for the contactless temperature measurement of an object. The sensor element 100 is a TF IR-NTC temperature sensor. The sensor element 100 and thus also the carrier 2 have a first region B1 and a second region B2 (see Figures 4, 5 and 8). The first region B1 is IR-sensitive (IR sensor 101) and the second region B2 is ambient temperature sensitive (reference sensor 102). The sensor element 100 therefore combines two sensitive regions on a single chip. An additional NTC chip for determining a reference temperature is therefore superfluous.

[0096] In the exemplary embodiments according to Figures 3 to 7, the two regions B1 and B2 are located at a spatial distance from one another on the carrier 2. A region lying between the regions B1, B2 is free of functional elements of the sensor element 100. In particular, the region lying between B1 and B2 is free of functional material.

[0097] In an alternative embodiment (Figure 8), the second region B2 can also surround the first region B1. In other words, the reference sensor 102 then surrounds the IR sensor 101. In this embodiment, too, an area lying between the regions B1, B2 is free of functional elements of the sensor element 100.

[0098] The design of the individual layers in IR sensor 101 and reference sensor 102 is based on the structure of sensor element 1 according to Figures 1 and 2. Unless otherwise stated, the reference symbols used in connection with Figures 1 and 2 also apply to the following figures.

[0099] In the following, the differences between the sensor element 100 (in particular the IR sensor 101 and the reference sensor 102) and the basic structure described above are essentially explained.

[0100] (Sensor element 1) stated:

[0101] The IR sensor 101 measures the temperature of an object contactlessly based on the radiation it emits. The basic structure of the layer structure of the IR sensor 101 corresponds to the layer sequence of the TF-NTC sensor element 1 according to Figures 1 and 2. The IR sensor 101 thus has a functional material (first functional layer 7a) which is formed directly on at least a partial region of two electrodes 4. The electrodes 4 are contacted via two contact pads 10. The electrodes 4 preferably have an interdigital structure (electrode fingers 5 and flat end regions 6). This exemplary embodiment is shown in Figures 3 to 5.

[0102] Additionally, an (IR) absorber layer 21 is located on the protective layer 8. In this exemplary embodiment, the absorber layer 21 is congruent with the first functional layer 7a. This means that the absorber layer 21 and the first functional layer 7a have the same surface area (same extent in the xy direction, i.e., extent perpendicular to a stacking direction S of the sensor element 100 / perpendicular to the z direction).

[0103] However, the absorber layer 21 can also be larger than the first functional layer 7a and partially protrude beyond it (not explicitly shown). Alternatively, the absorber layer 21 can also be smaller than the first functional layer 7a (not explicitly shown).

[0104] The absorber layer 21 is thermally coupled to the first functional layer 7a and comprises an IR radiation-absorbing material. For example, the absorber layer 21 comprises a thin metal layer, a dielectric material (e.g., silicon oxide, silicon nitride, or aluminum nitride), a nanoporous metal, or a polymer (e.g., a polyimide resin or a polymer with dispersed carbon particles). The absorber layer 21 is located exclusively in the first region B1, i.e., in the region of the IR sensor 101. This means that no IR radiation-absorbing material is formed on the protective layer 8 in the second region B2.

[0105] The IR radiation impinging on the absorber layer 21 is absorbed by the absorber layer 21, resulting in a temperature change of the absorber layer 21. Due to the thermal coupling with the first functional layer 7a, this leads to a resistance change at the first functional layer 7a.

[0106] The IR sensor 101 further has a cavity 20 in the carrier 2. The cavity 20 is formed only in the first region B1. It extends neither into the second region B2 nor into the region between B1 and B2. In particular, the second region B2 (reference sensor 102) is completely free of a cavity in the carrier 2.

[0107] The cavity 20 penetrates the carrier 2 completely in the embodiment shown. Alternatively, the cavity 20 can also be designed such that it only partially penetrates the carrier 2 (not explicitly shown). In this case, the cavity does not extend from the top side 11 to the bottom side 12 of the carrier 2. The cavity 20 is formed directly beneath the insulating layer 3, as can be seen from Figures 3 to 5. Viewed in the stacking direction S, the cavity 20 is located beneath the first functional layer 7a. In the exemplary embodiment shown, an area (extension perpendicular to the stacking direction, i.e. in the xy direction) of the cavity 20 is approximately as large as an area of ​​the first functional layer 7a. However, the area of ​​the cavity 20 can also be smaller or larger than the area of ​​the first functional layer 7a (not explicitly shown).

[0108] The cavity 20 ensures that the first functional layer 7a is thermally decoupled from the carrier 2. This reduces thermal losses to the carrier 2 and enables a maximized temperature change at the first functional layer 7a. Thus, the resistance change of the first functional layer 7a is also maximized.

[0109] The second functional layer 7b is formed on the carrier 2 in close proximity to the first functional layer 7a. This layer is part of the reference sensor 102. The reference sensor 102 is designed to measure an ambient temperature and, in particular, a temperature of the carrier 2. The reference sensor 102 functions as a contact-type sensor.

[0110] The reference sensor 102 measures the temperature in the direct vicinity of the IR sensor 101. Since a complete decoupling of the IR sensor 101 (and in particular of the first functional layer 7a) from the environment is not possible, there are always losses of heat to the environment. Therefore, the temperature of the first functional layer 7a will deviate from that of the object to be measured. The greater the temperature difference between the first functional layer 7a and the environment, the greater the thermal losses. Therefore, the need for a reference sensor 102 for

[0111] Measurement of the ambient temperature is given. Furthermore, heat transfer via solids is significantly faster than via gases, meaning that the main heat loss occurs via carrier 2. Thus, the influence of carrier 2 is dominant compared to the rest of the environment. Therefore, it is of particular interest to determine the temperature of carrier 2 (and thus of the environment) in order to be able to make a correction for thermal losses.

[0112] The layer structure of the reference sensor 102 is also based on the layer structure of the TF-NTC sensor element 1 according to Figures 1 and 2. In addition, however, a reflector layer 22 is formed on the protective layer 8.

[0113] In this exemplary embodiment, the reflector layer 22 is congruent with the second functional layer 7b. This means that the reflector layer and the second functional layer 7b have an equal area (equal extent in the xy direction, i.e., extent perpendicular to a stacking direction S of the sensor element 100).

[0114] However, the reflector layer 22 can also be larger than the second functional layer 7b and partially protrude beyond it (not explicitly shown). Alternatively, the reflector layer 22 can also be smaller than the second functional layer 7b (not explicitly shown).

[0115] The reflector layer 22 comprises a material that reflects IR radiation. For example, the reflector layer 22 comprises a Cu layer with a sufficient thickness to reflect IR radiation. The reflector layer 22 can comprise the same material as the contact pads 10. The reflector layer 22 is located exclusively in the second region B2, i.e. in the region of the reference sensor 102. It does not protrude into the region lying between B1 and B2. In particular, the first region B1 (IR sensor 101) is free of a component that reflects IR radiation.

[0116] In the embodiment shown in Figures 3 to 5, the sensor element 100 has a separate reflector layer 22. In particular, the reference sensor 102 has a reflector layer 22 in addition to the contact pads 10 of the reference sensor 102. The reflector layer 22 and the contact pads 10 can be produced in a single, common process step or in separate process steps.

[0117] Alternatively, as shown in Figure 6, one of the contact pads 10 of the reference sensor 102 can also assume the function of the reflector layer 22. In other words, one of the contact pads 10 of the reference sensor 102 can be designed to reflect IR radiation (IR radiation-reflecting contact pad 10, 22 in Figure 6). A separate reflector layer 22 is omitted in this case.

[0118] For this purpose, one of the contact pads 10 of the reference sensor 102, i.e., a contact pad 10 in the second region B2, is designed such that it extends at least partially over the protective layer 8. Unlike the other contact pads 10, the contact pad 10, 22 functioning as a reflector layer is located at least partially on the protective layer 8.

[0119] Unlike what is shown in Figure 6, the contact pad 10, which assumes the function of the reflector layer 22, does not necessarily have to be formed in one piece. The contact pad 10 can, for example, also have two (or more) regions, one of which functions as the reflector layer 22 (not explicitly shown). Thus, the partial region of the contact pad 10 shown in Figure 6, which extends flatly over the protective layer 8, could also be formed as a separate region of the contact pad 10 functioning as the reflector layer 22.

[0120] The regions of the contact pad 10 can be spatially separated from one another. In other words, a gap can be formed between the regions. The explicit structure of the contact pad 10, which functions as a reflector layer 22, depends, among other things, on the manufacturing process.

[0121] The contact pad 10, 22 functioning as a reflector layer is designed such that its area approximately corresponds to the area of ​​the second functional layer 7b and is preferably larger than the area of ​​the second functional layer 7b. The thickness of the reflected contact pad 10, 22 can also be adapted, in particular increased, compared to the other contact pads 10 of the sensor element 100. In contrast to the other contact pads 10, the contact pad 10, 22 functioning as a reflector layer has IR radiation-reflecting properties.

[0122] In the exemplary embodiments according to Figures 3 to 6, reference sensor 102 and IR sensor 101 each further comprise two electrodes 4 and two contact pads 10. In total, sensor element 100 thus comprises four electrodes 4 and four contact pads 10. Each contact pad 10 is directly and mechanically connected to exactly one electrode 4 (in particular, to the flat end region 6 of the respective electrode 4).

[0123] However, it is also possible, for example, to combine one of the contact pads 10 of the IR sensor 101 and one of the contact pads 10 of the reference sensor 102 into a single contact pad (combined contact pad 103, Figure 7). Thus, the sensor element 100 according to Figure 7 has a total of four electrodes 4 and three contact pads 10. In this case, the combined contact pad 103 is electrically and mechanically connected to two electrodes 4 (one electrode 4 of the IR sensor 101 and one electrode 4 of the reference sensor 102).

[0124] Combining two electrodes 4 (one electrode of the IR sensor 101 and one electrode 4 of the reference sensor 102) into one combined electrode is also possible (not explicitly shown). Thus, a corresponding sensor element 100 would have three electrodes 4 and three or four contact pads 10.

[0125] A method for producing the sensor element 100, in particular a plurality of sensor elements 100, is described below. Preferably, the method produces a plurality of sensor elements 100 according to the embodiments shown in Figures 3 to 7. All features described in connection with the sensor element 100 therefore also apply to the method, and vice versa.

[0126] In a first step A), a carrier material is provided for forming the carrier 2 described above. The carrier material preferably comprises Si, SiC, GaN, or glass. Alternatively, the carrier material may comprise SiA1N4, AlN, or Al2O3. The carrier 2 has a top side 11 and a bottom side 12. The carrier 2 (and thus also the final sensor element 100) has the first region B1 and the second region B2.

[0127] Subsequently, in a step B), the electrically insulating layer 3 is formed on the upper side 11 of the carrier 2. For example, the insulating layer 3 comprises SiO2. Ideally, an insulating layer 3 with a thickness of up to 1.5 pm is produced on the upper side 11 of the carrier 2. The insulating layer 3 extends over the entire upper side 11 of the carrier 2 and covers the cavity 20, which is produced in a later step, at the top.

[0128] In a next step C), electrodes 4 are formed / deposited on the carrier 2. The deposition is carried out using a DVD or CVD process or galvanically. The electrodes 4 can comprise, for example, Cu, Au, Ni, Or, Ag, Ti, Ta, W, Pd, or Pt. The electrodes 4 are designed as thin-film electrodes.

[0129] Preferably, two electrodes 4 are formed in the first region B1 and two electrodes 4 in the second region B2, but other configurations are also possible, as described above.

[0130] In a further step D), functional material is applied to form the functional layers 7a, 7b. This is done, for example, by sputtering or a spin-coating process. In particular, functional material is applied in the first region B1 to produce the first functional layer 7a and in the second region B2 to produce the second functional layer 7b. The functional material can initially be applied over the entire area and then structured in a further process (for example, by wet-chemical etching, dry etching or laser structuring) to create the two functional layers 7a, 7b. The respective functional layer 7a, 7b preferably has a thickness of between 250 nm and 400 nm.

[0131] Alternatively, step D) can also be carried out before step C), so that the functional material is sputtered directly onto the insulating layer 3 of the carrier 2 and then the electrodes 4 are applied to the functional layers 7a, 7b (not explicitly shown).

[0132] The functional material comprises an NTC ceramic based on an oxide material with a perovskite or spinel structure. Alternatively, the functional material can also be based on a carbide or nitride material. In another alternative, the functional material comprises or consists of thin films of vanadium oxide or SiC.

[0133] In a further step E ), the functional layers 7a, 7b are subjected to a heat treatment (sintering) to form the structure or properties.

[0134] Subsequently, in step F), the protective layer 8 is formed. The protective layer 8 is applied such that the upper side of the sensor element 100 is completely covered by the protective layer 8 except for at least two partial regions or recesses 9 (the number of partial regions depends on the desired number of contact pads 10, preferably three or four partial regions). The partial regions are arranged at least partially over the electrodes 4. The partial regions are arranged in particular over the flat end regions 6 of the electrodes 4, onto which the contact pads 10 can be applied in the subsequent process step.

[0135] The protective layer 8 can comprise oxides, nitrides, ceramics, glasses, or polymers and is produced by means of a PVD or CVD process and structured by means of wet-chemical etching or dry etching. The protective layer 8 has a thickness of <10 pm, preferably <5 pm, particularly preferably <1 pm. Ideally, the protective layer 8 has a thickness of <1.5 pm and completely covers the upper side of the sensor element 100 (with the exception of the subsequently produced contact pads 10).

[0136] Subsequently, in step G), the contact pads 10 are formed in the partial areas free of the protective layer 8. The contact pads 10 preferably have an Au / Ti layer structure. Alternatively, bumps can be formed instead of the contact pads.

[0137] In a step H), the reflector layer 22 is then formed above the second functional layer 7b. Step G) and step H) can also be combined into a single process step. In other words, contact pads 10 and reflector layer 22 can be formed in the same process step. This applies in particular if contact pads 10 and reflector layer 22 comprise the same material.

[0138] In particular, even if a separate reflector layer 22 is not provided, one of the contact pads 10 in the second region B2 can already be formed in step G) such that it extends over the second functional layer 7b (Figure 6). However, even if a reflector layer 22 is formed in addition to the contact pads 10, this can be done in a single process step, provided the reflector layer 22 and the contact pads 10 comprise the same material.

[0139] In the next step I ) the absorber layer 21 is formed above the first functional layer 7a .

[0140] In a further step J), the cavity 20 is formed in the first region B1 of the carrier 2. The cavity 20 is formed exclusively in the first region B2. The second region B2 remains free of a cavity.

[0141] In a final step K), the sensor elements 100 are separated. This can be done, for example, by plasma etching, stealth dicing, or sawing.

[0142] The description of the objects specified here is not limited to the individual specific embodiments. Rather, the features of the individual embodiments can be combined with one another as desired—provided technically feasible.

[0143] Reference symbol list

[0144] Sensor element

[0145] 2 carriers

[0146] 3 I insulating layer

[0147] 4a, 4b electrode

[0148] 5 electrode fingers

[0149] 6 End area

[0150] 7 Functional layer

[0151] 8 protective layer

[0152] 9 Recess

[0153] 10a, 10b contact pad

[0154] 11 Top of the carrier

[0155] 12 Underside of the carrier

[0156] 13 Surface of the sensor element

[0157] 14 Top of the functional layer

[0158] 15 Underside of the functional layer

[0159] D Thickness of the sensor element

[0160] Edge length of the carrier

[0161] 100 sensor elements

[0162] 101 IR sensor

[0163] 102 Reference sensor

[0164] 103 Combined contact pad

[0165] 4 Electrode

[0166] 7a, 7b functional layer

[0167] 10 contact pad

[0168] 20 cavities

[0169] 21 Absorber layer

[0170] 22 Reflector layer

[0171] 5 Stacking direction Bl First area / IR area of ​​the carrier / sensor element

[0172] B2 Second area / reference area of ​​the wearer / the

[0173] Sensor elements

Claims

Patent claims 1. Sensor element (100) for contactless measurement of a temperature comprising - at least one carrier (2) with a top side (11) and a bottom side (12), - an insulating layer (3) formed directly on the upper side (11) of the carrier (2), - at least one first functional layer (7a) for contactless temperature measurement of an object and at least one second functional layer (7b) for contact-based measurement of an ambient temperature, wherein the respective functional layer (7a, 7b) comprises a material with a temperature-dependent electrical resistance and wherein the functional layers (7a, 7b) are arranged separately from one another on the carrier (2), - at least two electrodes (4) for electrically contacting the functional layers (7a, 7b), - at least two contact pads (10) for electrically contacting the sensor element (100), wherein in each case one contact pad (10) is arranged directly on at least a partial area of ​​one of the electrodes (4), wherein the sensor element (100) is designed to be integrated as a discrete component directly into an electrical system.

2. Sensor element (100) according to claim 1, wherein the first functional layer (7a) is formed in a first region (B1) of the carrier (2) and wherein the second functional layer (7b) is formed in a second region (B2) of the carrier (2).

3. Sensor element (100) according to one of the preceding claims, wherein the second functional layer (7b) is designed and arranged to measure a temperature of the carrier (2).

4. Sensor element (100) according to one of the preceding claims, further comprising a cavity (20) in the carrier (2), wherein the cavity (20) is located below the insulating layer (3) and wherein the cavity (20) is formed in a first region (B1) of the sensor element (100) and at least partially below the first functional layer (7a).

5. Sensor element (100) according to one of the preceding claims, wherein a region of the carrier (2) below the second functional layer (7b) is free of a cavity.

6. Sensor element (100) according to one of the preceding claims, further comprising a protective layer (8), wherein the protective layer (8) completely covers an upper side of the sensor element (100) with the exception of the contact pads (10).

7. Sensor element (100) according to one of the preceding claims, further comprising at least one absorber layer (21), wherein the absorber layer (21) is formed above the first functional layer (7a) as seen in a stacking direction (S) of the sensor element (100).

8. Sensor element (100) according to claim 7 and claim 6, wherein the absorber layer (21) is formed on the protective layer (8).

9. Sensor element (100) according to claim 7 or 8, wherein the absorber layer (21) is in thermal contact with the first functional layer (7a).

10. Sensor element (100) according to one of claims 7 to 9, wherein the absorber layer (21) comprises a material which absorbs infrared radiation.

11. Sensor element (100) according to one of the preceding claims, further comprising at least one reflector layer (22), wherein the reflector layer (22) is formed above the second functional layer (7b) as seen in a stacking direction (S) of the sensor element (100).

12. Sensor element (100) according to claim 11 and claim 6, wherein the reflector layer (22) is formed on the protective layer (8).

13. Sensor element (100) according to claim 11 or 12, wherein the reflector layer (22) comprises a material which reflects infrared radiation.

14. Sensor element (100) according to one of claims 11 to 13, wherein the reflector layer (22) and the contact pads (10) comprise the same material.

15. Sensor element (100) according to one of claims 11 to 14, wherein one of the contact pads (10) functions as a reflector layer.

16. Sensor element (100) according to one of the preceding claims, wherein the respective electrode (4) is designed as a thin-film electrode, wherein the respective electrode (4) has a flat end region (6), wherein at least one contact pad (10) is arranged on the flat end region (6) of at least one of the electrodes (4) and wherein the respective electrode (4) has a plurality of electrode fingers (5).

17. Sensor element (100) according to one of the preceding claims, wherein a thickness (D) of the sensor element (1) is < 1000 pm.

18. Sensor element (100) according to one of the preceding claims, wherein the sensor element (1) is designed for direct integration into a MEMS structure.

19. Sensor element (100) according to one of claims 2 to 18, wherein the first region (B1) represents an IR sensor (101) and the second region (B2) represents a reference sensor (102), and wherein the second region (B2) surrounds the first region (B1).

20. Method for producing at least one sensor element (100) comprising the following steps: A) providing a carrier material for forming a carrier (2); B) forming an insulating layer (3) on an upper side (11) of the carrier (2); C) forming at least two electrodes (4) on the insulating layer (3); D) applying a functional material in a first region (B1) and in a second region (B2) of the carrier (2) to form at least two functional layers (7a, 7b) separated from one another; E) sintering the functional layers (7a, 7b); F) applying a protective layer (8) to an upper side of the sensor element (100), wherein the protective layer (8) completely covers the upper side except for at least two partial areas, wherein the partial areas are arranged at least partially above the electrodes (4); G) Forming at least two contact pads (10) in the partial areas free from the protective layer (8) for electrically contacting the sensor element (100).

21. The method of claim 20, further comprising the steps of: H) forming a reflector layer (22), wherein the reflector layer (22) is arranged above the second functional layer when viewed in a stacking direction (S) of the sensor element (100) (7b) is formed; I) Forming an absorber layer (21), wherein the absorber layer (21) is formed above the first functional layer (7a) as seen in a stacking direction (S) of the sensor element (100).

22. The method according to claim 21, wherein the contact pads (10) and the reflector layer (22) are produced in the same process step.

23. The method according to any one of claims 20 to 22, further comprising the step: J) forming a cavity (20), wherein the cavity (20) is formed in the first region (B1) and wherein the second region (B2) remains free of a cavity.

24. Method according to one of claims 20 to 23, wherein the method comprises a plurality of sensor elements (100) is produced and wherein the method further comprises the following step: K) separating the sensor elements (100) by means of a diamond saw or by a plasma etching step.

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