Sensor element and method for producing a sensor element

Abstract

The invention relates to a sensor element (100) for measuring a temperature, comprising a carrier (2) and at least one functional layer (7), which comprises a material having a temperature-dependent electrical resistance. The sensor element (100) also has at least two electrodes (4a, 4b) for making electrical contact with the functional layer (7), each electrode (4a, 4b) being spiral-shaped and the electrodes (4a, 4b) being spirally guided one inside the other, wherein in each case a contact pad (10a, 10b) is arranged directly on a sub-region of one of the electrodes (4a, 4b). The sensor element (1) is designed to be directly integrated into an electrical system as a discrete component. 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. The present invention further relates to a method for producing a sensor element, preferably a temperature sensor.

[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 into MEMS (Micro Electro Mechanical System) or SESUB (Semiconductor Embedded in Substrate) 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. SMDs are predominantly used for use in power modules.

[0007] ("surface mounted device") NTC temperature sensors are used, which are soldered on. For control modules for low power, NTC chips are used as an alternative. These chips are mounted on the underside using Ag sinter paste, soldering or gluing, and the top side is contacted via a bonding wire. Metallic electrodes must be applied to make electrical contact with the NTC ceramic. According to the state of the art, thick-film electrodes, predominantly made of silver or gold pastes, are applied using a screen printing process with subsequent firing.

[0008] These current technical solutions are not suitable for the integration of electronic components into structures such as MEMS or SESUB. These systems require very small elements, typically smaller than 500 pm x 500 pm x 100 pm, which must also be integrable using suitable contacting techniques. Particular attention must be paid to the selection of a suitable electrode. The traditional soldering processes for SMD designs or wire bonding technologies for semiconductor chips (bare dies) cannot be used for this.

[0009] The increasing demands on temperature measurement accuracy also require tight tolerances in the resistance variation of such sensor elements. However, with ever smaller structures, manufacturing tolerances have an ever greater influence, causing the resulting resistance variation to exceed the required tolerances. Resistance variation can only be reduced to a limited extent through process control. Until now, thin-film NTC temperature sensors could not be manufactured with tolerances as tight as conventional designs (SMD NTC and NTC chips).

[0010] 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 with a thin-film NTC thermistor.

[0011] The object of the present invention is to describe a sensor element and a method for producing a sensor element which have improved properties.

[0012] This object is achieved by a sensor element and a method for producing a sensor element according to the independent claims.

[0013] According to one aspect, a sensor element is described. The sensor element is suitable for measuring a temperature. The sensor element is a temperature sensor.

[0014] 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.

[0015] The carrier has a top side and a bottom side. The top side is electrically insulating. Preferably, an electrically insulating layer, for example SiO2 or SiA4, is formed on the top side of the carrier. The insulating layer is formed directly on the top side of the carrier. The insulating layer can be constructed from one or more layers.

[0016] The support may have a square or rectangular basic shape. Alternatively, the support may also be hexagonal or octagonal, for example. In a preferred embodiment, the support has a honeycomb shape.

[0017] The sensor element further comprises at least one functional layer. The carrier mechanically stabilizes the functional layer. The functional layer only partially covers the carrier or the insulating layer on the upper side of the carrier. In particular, the functional layer does not extend to an edge region of the carrier.

[0018] The thickness of the functional layer is between 50 nm and 1 pm, preferably between 100 nm and 500 nm, particularly preferably between 250 nm and 400 nm. The functional layer is a thin-film functional layer.

[0019] The functional layer comprises a material (functional material) that has a specific electrical characteristic. The functional layer comprises a material with a temperature-dependent electrical resistance. The functional layer preferably comprises an NTC ceramic.

[0020] The NTC ceramic is preferably based on an oxide material in the perovskite or spinel structure type. Alternatively, the functional layer can be based on a carbide or a nitride material in the wurtzite structure type. A further alternative is a thin film of vanadium oxide or SiC. The functional layer can have a square or rectangular shape. Alternatively, the functional layer can also be hexagonal or octagonal, for example. In a preferred embodiment, the functional layer has a honeycomb shape. The shape of the functional layer is adapted to the shape of the carrier.

[0021] The sensor element further comprises at least two electrodes for electrically contacting the functional layer. Each electrode is spiral-shaped. In other words, each electrode has a curve that runs around a central point and moves away from or closer to this center depending on the observer's perspective. Each electrode can have a round spiral shape. Alternatively, the respective electrode can also have an angular, for example a rectangular, spiral shape. The spiral design results in a very space-saving configuration of the electrodes.

[0022] The electrodes are spirally intertwined or intertwined. In other words, the two electrodes form intertwined spirals, spaced apart from one another on the carrier or functional layer. The electrodes extend around a central point.

[0023] The sensor element further has at least two contact pads for electrically contacting the sensor element. The sensor element preferably has exactly two contact pads. The contact pads are directly electrically and mechanically connected to the electrodes. Each contact pad is directly connected to a partial area of ​​one of the electrodes. The contact pads are designed such that they protrude beyond a surface of the sensor element. The contact pads preferably protrude > 1 pm beyond the surface of the sensor element. The contact pads preferably protrude > 3 pm, particularly preferably > 6 pm beyond the surface of the sensor element. This facilitates the electrical connection of the sensor element. The shape of the contact pads is matched to the shape of the carrier or the functional layer.

[0024] Overall, the sensor element is very compact, allowing it to 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.

[0025] For example, the sensor element has a maximum edge length of 1000 pm, preferably < 800 pm, particularly preferably < 500 pm. The thickness of the sensor element is < 100 pm, preferably < 80 pm, particularly preferably < 50 pm. For example, the component is designed for direct integration into a MEMS structure and / or into a SESUB structure.

[0026] According to one embodiment, the sensor element also has a very narrow resistance tolerance. In other words, the sensor element has only a very small deviation range from a target resistance (nominal value of the resistance). To adjust the resistance value of the sensor element, the electrodes can be trimmed. In particular, the electrodes are continuously trimmable. This means that a predetermined resistance value (target resistance) can be achieved with pinpoint accuracy by trimming the electrodes. In particular, the electrodes can be cut to size with pinpoint accuracy in order to achieve the most exact resistance value possible.

[0027] Due to the continuously adjustable electrodes and the resulting very precise resistance adjustment, the sensor element exhibits very high temperature measurement accuracy. The sensor element preferably has a resistance tolerance comparable to the tight resistance tolerance of conventional designs such as SMD NTCs or NTC chips.

[0028] To adjust the resistance value, at least one of the spiral-shaped electrodes, preferably both electrodes, are severed, for example with the aid of a laser.

[0029] The position at which the electrodes are trimmed, or in particular severed, is crucial for the achieved resistance value. Trimming occurs at a predetermined distance from the central point around which the spiral-shaped electrodes extend. By precisely selecting the distance, continuous trimming is possible. This provides a very precise sensor element.

[0030] According to one embodiment, the functional layer is arranged on the carrier. The functional layer can be arranged directly on the carrier or the insulating layer on the carrier. This means that in this case no further component of the sensor element is arranged between the carrier and the functional layer or between the insulating layer and the functional layer. In this embodiment, the electrodes are formed directly on the functional layer. Alternatively, the electrodes can also be arranged directly on the carrier or the insulating layer. In this case, the functional layer is formed directly on the electrodes.

[0031] According to one embodiment, each electrode has a connection region. The connection region is designed to connect the respective electrode to the respective contact pad. Each contact pad is directly connected to a connection region. For example, the connection regions of the electrodes can be designed to be flatter than the remaining region of the electrodes in order to ensure optimal connection to the contact pads. The shape of the connection region (basic shape, extension) is adapted to the basic shape of the contact pads.

[0032] According to one embodiment, the sensor element has a protective layer. The protective layer can be made of oxides, nitrides, ceramics, glasses, or plastic. 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.

[0033] According to a further aspect, a method for producing a sensor element is described. Preferably, the above-described sensor element, in particular a plurality of sensor elements, 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:

[0034] 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 further components of the sensor element are subsequently formed on the top side .

[0035] 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 predetermined basic shape in a final step.

[0036] Optionally, after the provision of the carrier, an electrically insulating layer, preferably SiO2, is formed on the top side of the carrier.

[0037] B) Forming or depositing at least two electrodes on the carrier, in particular on the top side of the carrier. The deposition is carried out by a PVD ("physical vapor deposition") process, a CVD ("chemical vapor deposition") process, or galvanically. Alternatively, the deposition can also be carried out by an ALD (atomic layer deposition) process.

[0038] The electrodes are spaced apart from one another. In particular, the electrodes are spatially and electrically insulated from one another. The electrodes have a spiral structure. In particular, the electrodes are spirally guided or interwoven into one another. The electrodes extend spirally around a common center (a central point).

[0039] Alternatively, step B) can also be carried out after the following step C), which means that in this case the electrodes are applied directly to the functional layer.

[0040] C) Applying, preferably sputtering, a functional material to at least a portion of the electrodes to form a functional layer. The functional material preferably comprises an NTC ceramic based on an oxide material in the perovskite or spinel structure type. Alternatively, the functional material can also be based on a carbide or a nitride material in the wurtzite structure type. Alternatively, the functional material can comprise or represent a thin layer of vanadium oxide or SiC.

[0041] The functional layer is formed as a thin film layer. The functional layer is deposited as a full-surface thin film and then structured in a further process step, e.g., using lithography. The functional layer can be rectangular, hexagonal, or octagonal, depending on the desired final basic shape of the sensor element. After deposition, the NTC layer is not yet fully crystallized.

[0042] Alternatively, as already mentioned, step C) can also take place before step B), which means that the functional layer is applied directly to the carrier and then the electrodes are applied to the functional layer. D) Sintering of the functional layer. This serves to develop the NTC properties of the functional material and is carried out at temperatures up to 1000°C. Sintering is preferably carried out at temperatures between 500°C and 800°C, advantageously at 600°C.

[0043] The functional layer is then measured. This determines the initial tolerance range of the resistance value. At this stage of the process, for example, this is the nominal resistance value (target resistance) ± 5%. By determining how far the resistance is from the target resistance at this point, the length over which the electrodes must be severed can be determined. In particular, the distance at which the electrodes must be severed from the central point around which the spiral-shaped electrodes run is determined.

[0044] E) Adjusting the resistance value of the sensor element. This is done by trimming at least one of the electrodes using a laser. The resistance value is thereby set to a predetermined nominal value (setpoint).

[0045] To finally adjust the resistance value, material from the spiral electrodes is removed, changing the resistance of the electrodes and thus the total resistance of the sensor element. Specifically, the electrodes are severed at a predetermined distance from the point around which the electrodes extend. This can be done continuously.

[0046] The special, spiral-shaped design of the electrodes creates laser-trimmable areas, allowing for continuous resistance adjustment. Trimming increases the resistance to the desired value. This allows for a sensor element with a particularly tight resistance tolerance.

[0047] The resistance tolerance of the nominal value of the finished sensor element is maximum ± 5%, preferably maximum ± 1%, particularly preferably maximum ± 0.5%, ideally ± 0.1%.

[0048] However, if the resistance of the sensor element already corresponds to the target value, no additional adjustment of the resistance value is required.

[0049] According to one embodiment, the method further comprises the following further steps:

[0050] F) Applying a protective layer to the top side of the sensor element. The protective layer covers the top side completely except for two partial areas. The protective layer is used for structuring either

[0051] ( a ) applied over the entire surface and the free partial areas are created by a subsequent process such as lithography or laser structuring or

[0052] (b) directly applied in a structured manner by using a mask during the deposition process.

[0053] G) Forming contact pads in the areas free of the protective layer for electrical contact with the sensor element. Each contact pad is directly connected to a connection area of ​​the electrodes.

[0054] The contact pads can comprise Cu, Au, Ni, Gr, Ag, Ti, W, Pd, or Pt. The contact pads preferably comprise Au. The contact pads preferably have a layered structure with Au and Ti, with Ti applied as an adhesion layer beneath the Au layer. The contact pads preferably have a thickness of > 5 pm.

[0055] The contact pads are designed to protrude beyond a surface of the finished sensor element. Alternatively, bumps or thin electrodes can be provided. All of these possible contact elements comprise a metal, such as Cu, Au, or a solderable alloy.

[0056] According to one embodiment, the method produces a plurality of sensor elements in parallel (parallel processing). The method further comprises the following steps:

[0057] H) Separating or isolating the sensor elements.

[0058] The separation takes place in two steps:

[0059] (1) Singling in the x / y direction (length & width). This can be achieved, for example, by plasma etching or sawing and notching the functional layer and carrier. The wafer (preferably a Si wafer) from which the sensor elements are to be singulated is not sawn through, but only cut to a defined thickness.

[0060] (2) Singulation in the z-direction (height). Grinding is carried out from the back side. Through a grinding process, material is removed from the underside of the wafer down to a defined final component thickness. For this purpose, a

[0061] I) Grinding of the sensor elements from the underside, whereby material is removed from the back of the wafer up to a defined final component thickness by a grinding process, whereby the sensor elements are separated.

[0062] J) Optional plasma etching of the ground underside of the wafer to reduce, for example, microcracks. The final component shape is created during singulation. For example, the final singulated sensor element can have a rectangular, hexagonal, or octagonal basic shape. A hexagonal basic shape (honeycomb shape) proves particularly advantageous, as this allows optimal use of the space on the wafer.

[0063] The drawings described below are not to be considered to scale. Rather, individual dimensions may be enlarged, reduced, or distorted for clarity.

[0064] Elements that are identical or that perform the same function are designated by the same reference symbols.

[0065] It shows :

[0066] Figure 1 is an exploded view of a sensor element according to the prior art,

[0067] Figure 2 is a sectional view of the sensor element according to Figure 1 (prior art), Figure 3 is a plan view of an inventive

[0068] Sensor element according to a first embodiment,

[0069] Figure 4 is a plan view of the inventive

[0070] Sensor element according to another embodiment,

[0071] Figure 5 is a plan view of the inventive

[0072] Sensor element according to a further embodiment.

[0073] 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. 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] The sensor element 1 further comprises at least two contact pads 10a, 10b for electrically contacting the sensor element 1.

[0078] 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.

[0079] Due to the compact design of the individual components of sensor element 1, sensor element 1 is suitable for integration into MEMS or SESUB structures. The basic design according to Figures 1 and 2 is based on the principle of a parallel connection of individual resistors. However, with the design of sensor element 1 according to Figures 1 and 2, the resistance cannot be adapted to the specific component. Therefore, the resistance variation cannot be adjusted within the required tolerances.

[0080] Figures 3 to 5 show a plan view of a sensor element 100 according to the invention. The sensor element 100 has essentially the same components as the sensor element 1 according to Figures 1 and 2. The basic structure of the sensor element 100 corresponds to the structure of the sensor element 1 of Figures 1 and 2, as already mentioned above. With regard to the details of the components and the functioning of the sensor element 100, reference is therefore made to the above description or to the document DE 10 2020 122 923 A1. Unless otherwise stated, the reference symbols given in connection with Figures 1 and 2 also apply below.

[0081] In contrast to sensor element 1, however, the resistance of sensor element 100 according to Figures 3 to 5 can be adjusted component-specifically. For this purpose, the electrodes 4a, 4b of sensor element 100 have a spiral structure. In particular, the electrodes 4a, 4b are spirally guided or interwoven into one another.

[0082] The electrodes 4a, 4b can have a round spiral shape (Figures 3 and 4) or an angular, preferably rectangular, spiral shape (Figure 5). If the electrodes 4a, 4b have a round spiral shape (Figures 3 and 4), the sensor element 100 can, for example, have a rectangular, square or honeycomb basic shape. As can be seen from Figure 5, if the electrodes 4a, 4b have an angular spiral shape, the sensor element 100 has an angular (here rectangular) basic shape. In other words, the carrier 2 is rectangular in this case. The functional layer 7 is also rectangular in this embodiment.

[0083] The spatial separation of the two spiral-shaped electrodes ensures the electrical isolation of the electrodes (4a, 4b). The electrodes 4a, 4b extend around a central point P (center).

[0084] The electrodes 4a, 4b can be formed below the functional layer 7 (i.e., directly on the carrier 2 / the insulating layer 3). In this case, the functional layer is formed directly (i.e., without an intermediate component) on the electrodes 4a, 4b.

[0085] Alternatively, the electrodes 4a, 4b can also be formed above the functional layer 7 and in particular directly on the functional layer 7. In this case, the functional layer 7 is formed directly on the carrier 2 or the insulating layer 3.

[0086] The respective electrode 4a, 4b has a connection region 102a, 102b. The electrodes 4a, 4b are directly electrically and mechanically connected to the contact pads 10a, 10b via the connection region 102a, 102b. The connection region 102a, 102b can be flat, for example round, oval or rectangular (not explicitly shown). In particular, the connection region 102a, 102b can be flatter than a remaining region (spiral arm) of the respective electrode 4a, 4b (not explicitly shown). A shape of the connection region 102a, 102b is optimized for a shape of the contact pads 10a, 10b.

[0087] The resistance value of the sensor element 100 is adjusted by trimming the spiral-shaped electrodes 4a, 4b. Trimming is performed with the aid of a laser. The electrodes 4a, 4b are severed at a specific distance A from the point P (see the sectioned area 101 in Figures 3, 4, and 5).

[0088] The distance A is determined by previously measuring the functional layer during the manufacture of the sensor element 100, as will be described in more detail later. The electrodes 4a, 4b are severed close to an inner end of the spiral-shaped electrodes 4a, 4b, i.e., close to the central point P around which the spiral-shaped electrodes 4a, 4b extend, as can be seen from Figure 3.

[0089] By severing the electrodes 4a, 4b at a predetermined, i.e., previously determined, distance A, the resistance of the sensor element 100 can be continuously adjusted. In particular, the special structure of the electrodes 4a, 4b allows for precise trimming of the electrodes 4a, 4b. As a result, the sensor element 100 exhibits a very small deviation from the target resistance. Furthermore, the spirally intertwined electrodes 4a, 4b require very little space, resulting in a particularly compact sensor element 100.

[0090] In contrast to the basic structure shown in Figures 1 and 2, the sensor element 100 according to the invention does not necessarily have to have a rectangular basic shape, as already mentioned above. For example, the sensor element 100 and in particular the carrier 2 and the functional layer 7 can also be hexagonal (honeycomb-shaped) or octagonal, as can be seen from Figure 4. The shape of the functional layer 7 is aligned with the shape of the carrier 2 in order to enable optimal arrangement of the functional layer 7 on the carrier 2.

[0091] With a corresponding design, the shape of the contact pads 10a, 10b is also adapted to the specific component shape. Thus, in the embodiment shown in Figure 4, the contact pads 10a, 10b are smaller in size to accommodate the octagonal carrier 2. The specific spiral shape of the electrodes 4a, 4b remains unaffected.

[0092] 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 embodiment shown in Figures 3, 5, or 5. All features described in connection with the sensor element 100 therefore also apply to the method, and vice versa.

[0093] In a first step A), a carrier material is provided for forming the carrier 2 described above. During the parallel production of a plurality of sensor elements 100, a large-sized carrier (wafer) is provided, from which the individual sensor elements 100 are separated in a final step, as described below.

[0094] Preferably, the carrier material 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. Subsequently, in an optional step, an electrically insulating layer 3 is formed on the top side 11 of the carrier 2. For example, the insulating layer 3 comprises SiO2. Ideally, an insulating

[0095] Layer 3 with a thickness of up to 1.5 pm is produced on the upper side 11 of the carrier 2.

[0096] In a further step B), at least two electrodes 4a, 4b are formed / deposited on the carrier 2. The deposition is carried out by a DVD or CVD process or galvanically.

[0097] The electrodes 4a, 4b can be made of, for example, Cu, Au, Ni, Cr, Ag, Ti, Ta, W, Pd, or Pt. The electrodes 4a, 4b are designed as thin-film electrodes. The electrodes 4a, 4b are spirally structured and interwoven. The electrodes 4a, 4b extend together around a central point P.

[0098] The special structure of the electrodes 4a, 4b creates a laser-trimmable area for adjusting the resistance value of the sensor element 100.

[0099] In a further step 0), a functional material is applied to form a functional layer 7. This is done, for example, by sputtering or a spin-coating process. The functional material is first applied over the entire area and then structured in a further process (for example, by wet-chemical etching, dry etching, or laser structuring). For example, the functional layer is structured so that it has an octagonal basic shape (Figure 4). The shape of the functional layer 7 depends on the desired final shape of the sensor element 100. The functional layer 7 preferably has a thickness of between 250 nm and 400 nm.

[0100] Alternatively, step C) can also be carried out before step B), so that the functional material 7 is sputtered directly onto the carrier 2 or the insulating layer 3 of the carrier 2 and then the electrodes 4a, 4b are applied to the functional layer 7.

[0101] The functional material comprises an NTC ceramic based on an oxide material in the perovskite or spinel structure type. Alternatively, the functional material can also be based on a carbide or nitride material in the wurtzite structure type. In a further alternative, the functional material comprises or consists of thin films of vanadium oxide or SiC.

[0102] In a further step D), the functional layer 7 is subjected to a heat treatment to form the structure or properties.

[0103] Subsequently, the functional layer 7 is measured. This determines the initial resistance value of the functional layer, allowing the resistance of the sensor element to be adjusted to the target value in the next step. Using the initial resistance value, it is possible to precisely determine the distance A from point P at which the electrodes 4a, 4b must be severed in order to achieve the target resistance.

[0104] In a next step E), the resistance value is adjusted by trimming at least one of the electrodes 4a, 4b using a laser. Trimming is preferably performed in situ.

[0105] The resistance value is set to a predetermined nominal value (setpoint). By precisely setting the resistance value, the finished sensor element 100 has a very narrow resistance tolerance. To set the resistance value, the spiral-shaped electrodes 4a, 4b are severed at a very specific distance A from the point P around which the electrodes 4a, 4b run. The electrodes 4a, 4b are severed close to an inner end of the spiral-shaped electrodes 4a, 4b, i.e., close to the central point P.

[0106] In a next step F), a protective layer 8 is formed. 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 10a, 10b).

[0107] Subsequently, in step G), contact pads 10a, 10b are formed. Each contact pad 10a, 10b is directly connected to a connection region 102a, 102b of the electrodes 4a, 4b. In one embodiment, the contact pads 10a, 10b comprise metals such as Cu, Al, or Au and have a thickness of > 5 pm. In particular, the contact pads 10a, 10b protrude above the surface 13 of the sensor element 100 in the finished sensor element 100. Alternatively, bumps can be formed instead of the contact pads.

[0108] In a further step H), the sensor elements 100 are separated or isolated.

[0109] The separation takes place in two steps:

[0110] (1) Separation in the x / y direction (length and width). This can be done, for example, by plasma etching or sawing and notching of functional layer 7 and carrier 2. The wafer (for example, Si wafer) from which the sensor elements 100 are separated is not sawn through, but only sawn to a defined thickness.

[0111] (2) Singulation in the z-direction (height). Grinding is performed from the back side. Material is removed from the underside of the wafer through a grinding process until a defined final component thickness is reached.

[0112] For this purpose, a

[0113] I) Grinding the sensor elements 100 from the underside, wherein material is removed from the back of the wafer by a grinding process up to a defined final component thickness, whereby the components are separated.

[0114] J) Optional plasma etching of the ground underside of the wafer to reduce, for example, microcracks.

[0115] During singulation, the carrier 2 or the sensor element 100 acquires the specific basic shape. Either square or rectangular sensor elements 100 can be separated from the wafer, or the sensor elements 100 are separated from the wafer in the form of a honeycomb structure or an octagonal shape. In particular, a honeycomb structure enables optimal use of space on the wafer. Depending on the desired final shape of the sensor elements 100, the remaining components (in particular functional layer 7 and contact pads 10a, 10b but also spiral shape of the electrodes 4a, 4b) can be optimally adapted to the final external shape in the upstream process steps, as described, for example, in connection with Figure 4. 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 – as long as this is technically feasible.

[0116] Reference symbol list

[0117] 1 sensor element

[0118] 2 carriers

[0119] 3 I insulating layer

[0120] 4a, b Electrode

[0121] 5 electrode fingers

[0122] 6 End area

[0123] 7 Functional layer

[0124] 8 protective layer

[0125] 9 Recess

[0126] 10a, b contact pad

[0127] 11 Top of the carrier

[0128] 12 Underside of the carrier

[0129] 13 Top of the sensor element

[0130] 14 Top of the functional layer

[0131] 15 Underside of the functional layer

[0132] 100 sensor elements

[0133] 101 Average area

[0134] 102a Connection area

[0135] 102b connection area

[0136] D Thickness of the sensor element

[0137] L edge length of the beam

[0138] P point

[0139] A distance

Claims

Patent claims 1. Sensor element (100) for measuring a temperature, comprising - at least one carrier (2) with a top side (11) and a bottom side (12), wherein the top side (11) is electrically insulating, - at least one functional layer (7) comprising a material with a temperature-dependent electrical resistance, - at least two electrodes (4a, 4b) for electrically contacting the functional layer (7), wherein the respective electrode (4a, 4b) is spirally formed and wherein the electrodes (4a, 4b) are guided spirally into one another, - at least two contact pads (10a, 10b) for electrically contacting the sensor element (1), wherein the sensor element (1) is designed to be integrated as a discrete component directly into an electrical system.

2. Sensor element (100) according to claim 1, wherein the electrodes (4a, 4b) are continuously trimmable to adjust a resistance value of the sensor element (100).

3. Sensor element (100) according to claim 2, wherein at least one of the spiral electrodes (4a, 4b) is severed to adjust the resistance value.

4. Sensor element (100) according to claim 2 or 3, wherein the electrodes (4a, 4b) extend spirally around a central point (P) and wherein the electrodes (4a, 4b) are severed at a predetermined distance (A) from the point (P) to adjust the resistance value.

5. Sensor element (100) according to one of the preceding claims, wherein the respective electrode (4a, 4b) has a connection region (102a, 102b) and wherein in each case a contact pad (10a, 10b) is directly connected to a connection region (102a, 102b).

6. Sensor element (100) according to one of the preceding claims, wherein an insulating layer (3) is formed directly on the upper side (11) of the carrier (2).

7. Sensor element (100) according to claim 6, wherein the functional layer (7) is formed directly on the insulating layer (3).

8. Sensor element (100) according to one of claims 1 to 5, wherein the functional layer (7) is formed directly on the carrier (2).

9. Sensor element (100) according to one of the preceding claims, wherein the electrodes (4a, 4b) are formed directly on the functional layer (7).

10. Sensor element (100) according to one of claims 1 to 6, wherein the electrodes (4a, 4b) are formed directly beneath the functional layer (7).

11. 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 (13) of the sensor element (100) with the exception of the contact pads (10a, 10b).

12. Sensor element (100) according to one of the preceding claims, wherein the carrier (2) comprises silicon, silicon carbide, glass, AlN or Al2O3 as carrier material and / or wherein the carrier (2) has a hexagonal or octagonal basic shape.

13. Sensor element (100) according to one of the preceding claims, wherein the functional layer (7) comprises an NTC ceramic based on an oxidic material in the perovskite or spinel structure type, or wherein the functional layer (7) comprises an NTC ceramic based on a carbide or a nitride material in the wurtzite structure type, or wherein the functional layer comprises a thin film of vanadium oxide or SiC.

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

15. Sensor element (100) according to one of the preceding claims, wherein the sensor element (100) is designed for direct integration into a MEMS structure and / or into a SESUB structure.

16. A 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 at least two electrodes (4a, 4b) on the carrier (2), wherein the respective electrode (4a, 4b) is spiral-shaped; C) applying a functional material to at least a partial area of ​​the electrodes (4a, 4b) to form a functional layer (7); D) Sintering of the functional layer (7) .

17. The method of claim 16, further comprising the step: E) Adjusting a resistance value of the sensor element (100) by trimming at least one of the electrodes (4a, 4b) by means of a laser, wherein the spiral-shaped electrodes (4a, 4a) are severed to adjust the resistance value.

18. The method according to claim 17, wherein before step E) a measurement of the functional layer (7) is carried out to determine an initial resistance value of the functional layer (7).

19. The method according to claim 17 or claim 18, wherein the electrodes (4a, 4b) are arranged spirally around a central point (P) and wherein the electrodes (4a, 4b) are severed at a predetermined distance (A) from the point (P) to adjust the resistance value of the sensor element (100), the distance (A) being determined with the aid of an initial resistance value of the functional layer (7).

20. The method according to any one of claims 16 to 19, wherein step C) is carried out before step B) and wherein the electrodes (4a, 4b) are formed directly on the functional layer (7).

21. The method according to any one of claims 16 to 20, further comprising the following steps: 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 two partial areas; G) Forming contact pads (10a, 10b) in the partial areas free from the protective layer (8) for electrically contacting the sensor element (100).

22. The method according to any one of claims 16 to 21, wherein the method produces a plurality of sensor elements (100) and wherein the method further comprises the following steps: H) separating the sensor elements (100) by sawing either with a diamond saw or by a plasma etching step, so that the sensor elements (100) are not yet finally separated after this step; I) grinding the sensor elements (100) from a bottom side, wherein material is removed from the back of the wafer by a grinding process up to a defined final component thickness, whereby the sensor elements (100) are separated; J) Plasma etching of the ground underside of the wafer to reduce microcracks.

23. The method according to claim 22, wherein in step H) a hexagonal or an octagonal basic shape of the sensor element (100) is produced.

24. Method according to one of claims 16 to 23, wherein the method produces a sensor element (100) according to one of claims 1 to 15.

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