Sensor element for measuring temperature

Abstract

sensor element (1) for measuring a temperature - a carrier (2), - at least one functional layer (3) arranged on a top surface (2a) of the support, wherein the functional layer (3) has a material with a temperature-dependent electrical resistance, - at least one upper electrode (5), wherein a first contact area (c1) is formed between the at least one upper electrode (5) and the functional layer (3), - at least one lower electrode (4), wherein a second contact area (c2) is formed between the at least one lower electrode (4) and the functional layer (3), wherein the functional layer (3) is at least partially embedded between the at least one lower electrode (4) and the at least one upper electrode (5), and wherein the functional layer (3), the at least one upper electrode (5), and the at least one lower electrode (4) are designed and arranged such that a specific electrical resistance of the sensor element (1) is achieved. wherein the sensor element (1) has a plurality of upper electrodes (5) and a plurality of lower electrodes (4) connected in series, whereby a resistance is determined - by the size of the respective first contact area (c1) and / or - by the size of the respective second contact area (c2) and / or - by a relative position of the first contact areas (c1) and the second contact areas (c2) and / or - by a size of overlap areas (o) between first contact areas (c1) and second contact areas (c2) and / or - by a number of resistors connected in series.

Description

[0001] The present invention relates to a sensor element, preferably a temperature sensor.

[0002] To integrate passive components such as sensors, capacitors, heating elements, etc., the dimensions of modern package solutions must be adapted to the micrometer or even nanometer scale. Thin-film technologies are required to achieve such miniaturization. For processing, thin-film NTC structures are deposited onto a substrate, e.g., silicon wafers, and can be used in MEMS (Micro Electro Mechanical System) and SESUB (Semiconductor Embedded in Substrate) structures.

[0003] The state of the art in temperature monitoring and control involves the use of ceramic thermistors (NTC), silicon temperature sensors (KYT), platinum temperature sensors (PRTD), or thermocouples (TC). NTC thermistors are frequently used due to their low manufacturing costs. Furthermore, they offer an advantage over thermocouples and metallic resistors (e.g., Pt elements) due to their strongly negative resistance-temperature characteristic.

[0004] For use in power modules, surface-mounted (SMD) NTC temperature sensors are primarily used, which are mounted by soldering. For low-power control modules, NTC chips are used as an alternative. These are mounted on the underside using silver sintering paste, soldering, or adhesive, and contacted on the top side via wire bonds. To enable electrical contact, the NTC ceramic therefore requires metallic electrodes. These are typically applied as thick-film electrodes using screen printing with silver or gold paste and then baked on.

[0005] Integrating electrical components into, for example, MEMS or SESUB structures requires very small elements, typically smaller than 1000 µm x 1000 µm x 100 µm. Additionally, a compatible contacting method is needed. Conventional assembly techniques for SMD and NTC chips are unsuitable.

[0006] Document DE 10 2019 127 915 A1 describes a sensor element for measuring temperature comprising at least one carrier layer and at least one functional layer, wherein the functional layer is arranged on the top side of the carrier layer and has a material that has a temperature-dependent electrical resistance, wherein the sensor element is designed to be integrated directly into an electrical system as a discrete component.

[0007] Document US 2023 / 0040761A1 describes a temperature sensor with a further reduction in thickness. The temperature sensor comprises a first support layer, a second support layer, and a sensing element located between the first and second support layers. The sensing element includes a thermosensitive body and a first and second conduction structure electrically connected to the thermosensitive body.

[0008] Document DE 10 2022 126 526 A1 describes a sensor element for measuring a temperature, comprising at least one support, at least two electrodes, at least one functional layer comprising a material with a temperature-dependent electrical resistance, wherein the at least one functional layer is at least partially arranged between the electrodes, at least two intermediate layers comprising an insulating material, and at least two contact pads for electrically contacting the sensor element.

[0009] The object of the present invention is to describe a sensor element with improved properties.

[0010] This task is solved by a sensor element and a use of the sensor element according to the independent claims.

[0011] A sensor element is described according to one aspect. The sensor element is suitable for measuring temperature. The sensor element is a temperature sensor element. Preferably, the sensor element is an NTC (negative temperature coefficient) thermistor. The sensor element is particularly suitable for temperature monitoring and / or control in automotive applications.

[0012] The sensor element has a substrate. The substrate has a top and a bottom. The substrate can be made of silicon, silicon carbide, or glass (silicates or borosilicates). Alternatively, the substrate can be made of, for example, AlN or Al₂O₃.

[0013] The top surface of the substrate is electrically insulating. This means, for example, that a substrate containing silicon requires an insulating layer, such as SiO2. The substrate can be rectangular or square.

[0014] The sensor element further comprises at least one functional layer. The functional layer is arranged on the top surface of the substrate. The functional layer consists of a material with a temperature-dependent electrical resistance. The functional layer can be a thin film with NTC properties.

[0015] A material for the functional layer can include the following: a) Oxides: For example, perovskites (based on mixed crystals of the CaMnO3 material system, where Ca is wholly or partially replaced by Cr, Al or La) or spinel (based on mixed crystals of the NiMn2O4 material system, where Ni and / or Mn are partially replaced by Fe, Co, Al); b) Carbides, for example (Si,Ti)C, 2H, 4H or 6H, cubic SiC; c) Nitrides, for example (Al,Ti)N, CrN.

[0016] The sensor element also includes at least one upper electrode. Of course, the sensor element can also have more than one upper electrode, e.g., two upper electrodes or several upper electrodes. The at least one upper electrode can have one or more layers of thin-film metals, the materials being, for example, Cu, Au, Ni, Cr, Ag, Ti, W, Pd, or Pt.

[0017] At least one upper electrode is positioned directly above the functional layer. A contact area (i.e., the first contact area) is formed between the at least one upper electrode and the functional layer. In other words, there is an area with direct electrical and mechanical contact between the upper electrode and the functional layer.

[0018] The sensor element also includes at least one lower electrode. Of course, the sensor element can have more than one lower electrode, e.g., two lower electrodes or several lower electrodes. The at least one lower electrode can have one or more layers of thin-film metals, the materials being, for example, Cu, Au, Ni, Cr, Ag, Ti, W, Pd, or Pt.

[0019] The lower electrode can be positioned directly on the top surface of the substrate. The lower electrode is located directly beneath the functional layer. A contact area (i.e., the second contact area) is formed between the at least one lower electrode and the functional layer. In other words, there is an area with direct electrical and mechanical contact between the lower electrode and the functional layer.

[0020] The functional layer is at least partially embedded between the at least one lower electrode and the at least one upper electrode. In other words, viewed in the stacking direction of the sensor element, the functional layer is arranged between the lower and the upper electrode.

[0021] The sensor element has a specific nominal electrical resistance. The functional layer, the at least one upper electrode, and the at least one lower electrode are designed, arranged, and / or connected in such a way that a specific nominal electrical resistance of the sensor element can be achieved. In other words, the functional layer, the lower electrode, and / or the upper electrode have a specific material, a specific contact area, and / or a specific position relative to each other in order to control the resistance of the sensor element. In this way, a very precise sensor element is provided.

[0022] According to one embodiment, the sensor element has at least one insulating layer. The sensor element can have one, two, or more insulating layers. Alternatively, the sensor element can also be free of an insulating layer.

[0023] At least one insulating layer consists of a thin, non-conductive material, such as oxides, nitrides, ceramics, glasses, and polymers. The insulating layer can, for example, contain SiO2.

[0024] The following are some possible locations where an insulating layer can be applied: 1. Between the carrier and the lower electrode and / or 2. Between the lower electrode and the functional layer and / or 3. Between the functional layer and the upper electrode and / or 4. Between the upper electrode and a contact pad connected to the upper electrode.

[0025] Accordingly, there can be between zero and four insulating layers.

[0026] In other words, the insulating layer can at least partially cover the top surface of the sensor element. Additionally or alternatively, the insulating layer can at least partially cover the top surface of the lower electrode. Additionally or alternatively, the insulating layer can at least partially cover the top surface of the substrate. The insulating layer can improve the long-term stability of the sensor element.

[0027] The insulating layer can include at least one window. The insulating layer can have more than one window, e.g., two or more windows. The at least one window represents a recess in the insulating layer. The window is designed and arranged such that electrical contact between the upper electrode / lower electrode and the functional layer is permitted.

[0028] According to one embodiment, the sensor element has at least two contact pads, i.e., at least one first (upper electrode) contact pad and at least one second (lower electrode) contact pad. The contact pads facilitate the electrical connection of the sensor element to the outside.

[0029] At least one upper electrode can serve as a contact pad (i.e., as the first contact pad) of the sensor element for electrical contacting the sensor element. In this case, an additional / separate contact pad connected to the upper electrode is unnecessary. The upper electrode and the contact pad can constitute a single component of the sensor element.

[0030] Alternatively, the sensor element comprises at least one first contact pad, i.e., a separate contact pad that is electrically connected to the at least one upper electrode. In this case, the upper electrode and the contact pad represent different material layers of the sensor element.

[0031] At least one of the lower electrodes can also serve as the contact pad (i.e., the second contact pad) of the sensor element. In this case, an additional / separate contact pad connected to the lower electrode is unnecessary. The lower electrode and contact pad can form a single component of the sensor element. This is particularly suitable for wire bonding. If an insulating layer is present on the top surface of the lower electrode, the lower electrode can be connected to a wire via a window in the insulating layer.

[0032] Alternatively, the sensor element has at least one (second) contact pad that is electrically connected to the at least one lower electrode. If an insulating layer is present on the upper surface of the lower electrode, the (second) contact pad is connected to the lower electrode via a window in the insulating layer.

[0033] According to one embodiment, the resistance of the sensor element is determined / controlled by the size of the contact area between the upper electrode and the functional layer, i.e., by the size of the first contact area.

[0034] For this to work, the contact area between the lower electrode and the functional layer (second contact area) must be at least the same size as the contact area between the upper electrode and the functional layer (first contact area). Preferably, the second contact area is larger than the first contact area.

[0035] The larger contact area should be at least as large as the smaller one. Ideally, the larger contact area should have an additional length with a thickness greater than three times that of the functional layer. Ideally, the size / width of the second contact area c2 is greater than or equal to the size / width of the first contact area c1 plus three times the thickness of the functional layer.

[0036] The size of the first contact area can be controlled by the size of a window located in the insulating layer on the top of the sensor element.

[0037] According to one embodiment, the resistance of the sensor element is controlled by an area of ​​the upper electrode. This is possible, for example, if the window size in the insulating layer is larger than the area of ​​the upper electrode, or if there is no insulating layer between the upper electrode and the functional layer.

[0038] According to one embodiment, the resistance of the sensor element is determined / controlled by the size of the contact area between the lower electrode and the functional layer (i.e., the second contact area). In this case, the second contact area is smaller than the first contact area.

[0039] Ideally, the size / width of the first contact area c1 is greater than or equal to the size of the second contact area c2 plus three times the thickness of the functional layer. In other words, the width of the first contact area should be three times the thickness of the functional layer greater than the width of the second contact area.

[0040] The size of the second contact area can be controlled by the manufacturing process of the lower electrode, i.e., during the production of the sensor element. Additionally or alternatively, the size of the second contact area can be controlled by the size of a window in an insulating layer that is applied, at least partially, between the lower electrode and the functional layer.

[0041] According to one embodiment, the resistance of the sensor element is jointly controlled / determined by the upper and lower electrodes. The resistance can be limited by the size of the upper electrode and the size of the lower electrode.

[0042] In particular, the resistance is controlled by the size of the first contact area and simultaneously by the size of the second contact area. Additionally or alternatively, the resistance of the sensor element can be controlled / determined by the position of the upper and lower electrodes relative to each other, specifically by an overlap area between the upper and lower electrodes, or more precisely, by an overlap area between the first and second contact areas.

[0043] According to one embodiment, the sensor element has at least one lower electrode and at least two upper electrodes. The resistance of the sensor element can be determined / controlled by the size of the first contact areas.

[0044] Alternatively or additionally, the resistance of the sensor element can be determined / controlled by the size of the second contact area.

[0045] Alternatively or additionally, the resistance of the sensor element can be determined / controlled by a relative position of the upper electrodes and the lower electrode, and in particular by a size of the overlap areas between the upper electrodes and the lower electrode, more precisely by the size of the overlap areas between the first contact areas and the second contact area.

[0046] According to one embodiment, the sensor element comprises a plurality of upper electrodes. The sensor element also comprises a plurality of lower electrodes. The upper electrode and the lower electrodes are connected in series. This causes the current to flow through the functional layer multiple times, as if several smaller resistors were connected in series, resulting in a higher overall resistance of the sensor element.

[0047] The final resistance of the sensor element (nominal resistance) can be determined by the size of the first contact areas and / or by the size of the second contact areas. Additionally or alternatively, the resistance of the sensor element can be determined / controlled by the relative position of the upper and lower electrodes, and in particular by the size of the overlap areas between the upper and lower electrodes, more precisely by the size of the overlap areas between the first and second contact areas.

[0048] Additionally or alternatively, the resistance of the sensor element can be determined / controlled by a number of resistors connected in series. This means that the resistance is controlled by controlling the number of current passages through the functional layer.

[0049] According to one embodiment, the sensor element has a tight resistance tolerance, i.e., a small deviation range from the nominal resistance. To achieve this tight resistance tolerance, the sensor element also has at least one additional contact pad.

[0050] The additional contact pad is connected to at least one of the upper electrodes to further adjust the final resistance of the sensor element. Specifically, the additional contact pad allows for an additional / intermediate connection of at least one of the series-connected upper electrodes. This prevents unwanted / too frequent current flow through the functional layer, which would increase the overall resistance of the sensor element.

[0051] Preferably, the additional contact pad projects beyond a surface of the functional layer. In particular, the additional contact pad is not positioned directly above the functional layer, but can be offset laterally.

[0052] According to one embodiment, the sensor element has a tight resistance tolerance, i.e., a small deviation range from the nominal resistance. To achieve this tight resistance tolerance, the sensor element also includes trim electrodes. The trim electrodes are additional electrodes that provide additional electrical connections to the upper electrodes.

[0053] The trim electrodes are connected to the upper electrodes (specifically, only to certain upper electrodes). The trim electrodes connect specific upper electrodes connected in series, leaving other electrodes disconnected. This prevents unwanted or excessive current flow through the functional layer, which would increase the overall resistance of sensor element 1.

[0054] Preferably, the trim electrodes are not arranged directly above the functional layer, but offset to the side.

[0055] According to one embodiment, at least one of the trim electrodes is trimmed, i.e., electrode material is at least partially removed, e.g., by laser cutting, sawing, or grinding, to fine-tune the resistance of the final sensor element. This geometric modification allows the resistance to be altered so that it more closely matches the nominal resistance.

[0056] According to one embodiment, the sensor element has a plurality of upper electrodes and at least one lower electrode. The upper electrodes are connected in parallel. Alternatively, the sensor element can also comprise at least one upper electrode and a plurality of lower electrodes. The lower electrodes are connected in parallel. Alternatively, the sensor element can comprise a plurality of upper electrodes and a plurality of lower electrodes. The upper electrodes and the lower electrodes are connected in parallel.

[0057] The resistance of the sensor element can be determined / controlled by the size of the respective first contact area and / or by the size of the respective second contact area. Additionally or alternatively, the resistance of the sensor element can be determined / controlled by the number of upper and lower electrodes connected in parallel.

[0058] According to one embodiment, the sensor element has a tight resistance tolerance. This means that the sensor element has a very small deviation range from the nominal resistance. To achieve this tight resistance tolerance, the sensor element also has trim electrodes.

[0059] The trim electrodes are connected to top electrodes (in particular, to all top electrodes) in a row, a circle, or a spiral. The trim electrodes can also be connected to any top electrodes. Preferably, the trim electrodes are not arranged directly above the functional layer, but offset laterally. At least one of the trim electrodes can be further trimmed for fine-tuning the resistance of the final sensor element, e.g., by laser cutting, thereby eliminating certain resistances.

[0060] Another aspect describes the use of a sensor element. This sensor element can be the one described above. All characteristics described in connection with the sensor element also apply to its use. The sensor element is used for temperature monitoring and / or temperature control, e.g., in the automotive sector. Because the sensor element has a specific nominal electrical resistance and a tight resistance tolerance, very precise monitoring and / or control is enabled.

[0061] The drawings described below are not to scale. Rather, individual dimensions may be enlarged, reduced, or distorted for better illustration.

[0062] Elements that are similar or have the same function are designated with the same reference symbols.

[0063] It shows: Fig. 1 an exploded view of a sensor element according to an embodiment, Fig. 2 a sectional view of the sensor element according to Fig. 1, Fig. 3 a sectional view of the sensor element of Fig. 2 according to a further embodiment, Fig. 4 a sectional view of a sensor element according to a further embodiment, Fig. 5 a sectional view of a sensor element according to a further embodiment, Fig. 6 a cross-sectional view of the sensor element made of Fig. 5 according to a further embodiment, Fig. 7 a sectional view of a sensor element according to a further embodiment, Fig. 8 a cross-sectional view of the sensor element made of Fig. 7 according to a further embodiment, Fig. 9 a sectional view of a sensor element according to a further embodiment, Fig. 10 a sectional view of a sensor element according to a further embodiment, Fig. 11 a sectional view of a sensor element according to a further embodiment, Fig. 12 a sectional view of the sensor element made of Fig. 11 according to a further embodiment, Fig. 13 a sectional view of a sensor element according to a further embodiment, Fig. 14 a sectional view of the sensor element made of Fig. 13 according to a further embodiment, Fig. 15 a schematic top view of the sensor element according to the Fig. 13 and Fig. 14, Fig. 16 a schematic top view of a sensor element according to a further embodiment, Fig. 17 a schematic top view of a sensor element according to a further embodiment, Fig. 18 a sectional view of a sensor element according to a further embodiment, Fig. 19 a sectional view of the sensor element made of Fig. 18 according to a further embodiment, Fig. 20 a schematic top view of a sensor element according to the Fig. 18, Fig. 19.

[0064] The Fig. 1, Fig. 2 to Fig. Figure 3 shows a sensor element 1 according to a first embodiment. The sensor element 1 is a temperature sensor. The sensor element 1 is an NTC thermistor.

[0065] The sensor element 1 has a top surface 1a and a bottom surface 1b. The thickness T of the sensor element 1 is < 100 µm, preferably < 80 µm, and ideally < 50 µm. Here, the thickness T denotes an extent of the sensor element 1 in a stacking direction, i.e., the extent perpendicular to a principal extension direction of the sensor element 1.

[0066] The sensor element 1 has a carrier 2 with a top surface 2a and a bottom surface 2b. The carrier 2 preferably comprises silicon, silicon carbide, or glass (silicates or borosilicates). Alternatively, AlN or Al₂O₃ are also possible materials for the carrier 2.

[0067] The top surface 2a of the support 2 is electrically insulating. This means, for example, that a support 2 comprising silicon requires an insulating layer 6 comprising, for example, SiO2 (see e.g. Fig. 3) The thickness of the insulating layer 6 arranged on the top surface 2a of the support 2 can be between 50 nm and 1 µm, preferably between 250 nm and 600 nm. Ideally, the thickness is 500 nm. The support 2 is preferably rectangular and can be square. The edge length of the support 2 is < 1000 µm, preferably < 800 µm, and ideally < 500 µm.

[0068] The sensor element 1 also includes a functional layer 3. The functional layer 3 has a material with special electrical properties (temperature-dependent electrical resistance). The functional layer 3 is a thin film with NTC properties.

[0069] Possible materials for functional layer 3 are: a) Oxides: For example, perovskites (based on mixed crystals of the CaMnO3 material system, where Ca is wholly or partially replaced by Cr, Al or La) or spinel (based on mixed crystals of the NiMn2O4 material system, where Ni and / or Mn are partially replaced by Fe, Co, Al); b) Carbides, for example (Si,Ti)C, 2H, 4H or 6H, cubic SiC; c) Nitrides, for example (Al,Ti)N, CrN.

[0070] The thickness t of the functional layer 3 is between 1 nm and 1 µm, preferably between 100 nm and 500 nm and ideally between 250 nm and 400 nm.

[0071] Furthermore, the sensor element 1 comprises an upper electrode 5 and a lower electrode 4. Of course, the sensor element can comprise more than one upper electrode 5 / lower electrode 4, as shown in the embodiments related to the Fig. 9, Fig. 10, Fig. 11, Fig. 12, Fig. 13, Fig. 14, Fig. 15, Fig. 16, Fig. 17, Fig. 18, Fig. 19 to Fig. 20 described. The upper electrode 5 / the lower electrode 4 can have one or more layers of thin-film metals, the materials being Cu, Au, Ni, Cr, Ag, Ti, W, Pd or Pt.

[0072] The lower electrode 4 is directly on the top surface 2a of the carrier 2 ( Fig. 1 and Fig. 2) or on the insulating layer 6 arranged on the upper side 2a of the support 2 (see Fig. 3) arranged. The lower electrode 4 is arranged between the carrier 2 and the functional layer 3. The lower electrode 4 is arranged directly beneath the functional layer 3. In other words, the lower electrode 4 is at least partially in direct electrical and mechanical contact with the functional layer 3. A contact area c2 (second contact area c2) is formed between the lower electrode 4 and the functional layer 3. The second contact area c2 is the area in which the functional layer 3 rests directly on the lower electrode 4.

[0073] The upper electrode 5 is arranged on the top side of the functional layer 3, i.e., above the functional layer 3. In other words, the functional layer 3 is embedded between the upper electrode 5 and the lower electrode 4. The upper electrode 5 is at least partially in direct electrical and mechanical contact with the functional layer 3. A contact area c1 (first contact area c1) is formed between the upper electrode 5 and the functional layer 3. The first contact area c1 is the area where the upper electrode 5 rests directly on the functional layer 3.

[0074] As already mentioned, several insulating layers 6 can be present. In the embodiment according to the Fig. 1, Fig. 2 to Fig. 3 The sensor element 1 further comprises an insulating or protective layer 6, which is arranged on a top surface 1a of the sensor element 1. This insulating layer 6 covers the top surface 1a at least partially, such as the Fig. 2 can be seen from the above. An insulating layer 6 also covers a top surface of the lower electrode 4, with the exception of the contact area c2 between the lower electrode 4 and the functional layer 3. An insulating layer 6 also covers a top surface of the functional layer 3, with the exception of the contact area c1 between the upper electrode 5 and the functional layer 3.

[0075] Each insulating layer 6 has windows or recesses 7. Since there can be several insulating layers 6, there can also be several windows 7. There is a window 7 between the lower electrode 4 and the functional layer 3 ( Fig. 3) There may be another window between the lower electrode 4 and the contact pad 4a (see Fig. 1) Another window may be located between the upper electrode 5 and the functional layer 3. A window may also be located between the upper electrode 5 and the contact pad 5a (see Fig. 1 and Fig. 2) And theoretically, they can all be present at the same time. Just because one insulating layer 6 has a window 7 does not mean that another insulating layer 6 cannot also have one or more windows 7.

[0076] These windows 7 are designed and arranged to allow direct contact between the upper electrode 5 and the functional layer 3 and / or between the lower electrode 4 and the functional layer 3 and / or between the lower electrode 4 and the contact pad 4a, etc. In particular, in the Fig. 1, Fig. 2 to Fig. 3. A window 7 is arranged directly below the upper electrode 5 to allow electrical contact between the upper electrode 5 and the functional layer 3 in the first contact area c1. Another window 7 is arranged directly above the lower electrode 4 to allow electrical contact between the lower electrode 4 and a contact pad 4a, which will be described in detail later.

[0077] The respective insulating layer 6 can improve the long-term stability of the sensor element 1, particularly when the insulating layer 6 is arranged on an outer surface of the sensor element 1. The insulating layer thickness is between 50 nm and 1 µm, preferably between 200 nm and 600 nm, and ideally between 400 nm and 500 nm.

[0078] The respective insulating layer 6 consists of a thin, non-conductive material, e.g. oxides, nitrides, ceramics, glasses and polymers.

[0079] As mentioned previously, an insulating layer 6 covers the top surface 1a of the sensor element 1, with the exception of contact pads 4a and 5a, i.e., the first contact 5a and the second contact pad 4a. The contact pads 4a and 5a facilitate the electrical contacting of the sensor element 1 and have a thickness of > 100 nm, preferably > 1 µm and ideally > 5 µm. The contact pads 4a and 5a comprise one or more layers of thin-film metals with materials such as Cu, Au, Ni, Cr, Ag, Ti, W, Pd, or Pt.

[0080] For integration into SESUB structures, contact pads 4a and 5a, which contain copper, are required. The thickness of the copper pads is designed so that they form the highest points of the sensor element 1. They extend at least > 1 µm, preferably > 3 µm, and ideally > 6 µm over the remaining surface of the sensor element 1. These copper thicknesses are necessary for processing and reliable contacting in SESUB structures.

[0081] The contact pads 4a, 5a are directly connected to the electrodes 4, 5. In the embodiment according to the Fig. 1, Fig. 2 to Fig. In this embodiment, contact pad 4a is directly connected to the lower electrode 4 via the window / recess 7. Furthermore, in this embodiment, the upper electrode 5 directly functions as contact pad 5a. In other words, there is no additional first contact pad 5a connected to the upper electrode 5, as in the Fig. 1, Fig. 2 to Fig. 3 can be seen.

[0082] In an alternative embodiment (not explicitly shown), the lower electrode 4 can also function directly as contact pad 4a. In other words, in this case there is no additional second contact pad 4a connected to the lower electrode 4.

[0083] In an alternative embodiment (see Fig. 4) A special electrode material can be used to contact the functional layer 3 and the upper electrode 5 to improve adhesion (see Fig. 4) In other words: In the embodiment according to Fig. 4 A separate first contact pad 5a is provided, which electrically and mechanically contacts the upper electrode 5. The materials of the upper electrode 5 and the first contact pad 5a can be different.

[0084] In any case ( Fig. 1, Fig. 2, Fig. 3 to Fig. 4) The upper electrode 5 is directly connected via the window 7 in the insulating layer 6 to the top of the functional layer 3 to establish the contact area c1.

[0085] How the Fig. 2, Fig. 3 to Fig. As can be seen from 4, the current F flows from the second contact area 4a to the lower electrode 4, then to the functional layer 3 and via the functional layer 3 to the upper electrode 5, 5a.

[0086] The sensor element 1 has a specific resistance (nominal resistance). In the embodiment according to the Fig. 1, Fig. 2, Fig. 3 to Fig. 4 the resistance is determined and in particular limited by a size of the first contact area c1, i.e. the contact area between upper electrode 5 and functional layer 3.

[0087] To limit the resistance via the first contact area c1, the second contact area c2 must be at least the same size as the first contact area c1. Preferably, the second contact area c2 is larger than the first contact area c1, as shown in the Fig. 1, Fig. 2, Fig. 3 to Fig. Figure 4 shows that the width of the second contact area sc2 (extent of the second contact area c2 perpendicular to the stacking direction) is equal to or greater than the width of the first contact area c1 plus three times the thickness t of the functional layer 3: c2 ≥ c1 + 3t.

[0088] The size / width of the first contact area c1 is determined by the size of the window 7, which is located in the insulating layer 6 directly below the upper electrode 5. The larger the window 7, the larger the first contact area c1. The larger the first contact area c1, the lower the resistance of the sensor element 1.

[0089] If the window size is larger than the area of ​​the first contact pad 5a and / or an insulating layer 6 is missing (not explicitly shown), the resistance of the sensor element 1 can also be controlled via the area of ​​the upper electrode 5. In the embodiment according to the Fig. 1, Fig. 2 to Fig. 3 the resistance is also controlled via an area of ​​the upper electrode 5, since the upper electrode 5 acts as the first contact pad 5a.

[0090] The Fig. 5 and Fig. Figure 6 shows a sectional view of the sensor element 1 according to a further embodiment. In this embodiment, the electrical resistance is controlled via the lower electrode 4. The resistance is determined in particular by the size / width of the second contact area c2. The larger the second contact area c2, the lower the resistance of the sensor element 1.

[0091] To determine / control the resistance using the second contact area c2, the first contact area c1 must be at least the same size as the second contact area c2. Preferably, the first contact area c1 is larger than the second contact area c2 (see Fig. 5 and Fig. 6) In particular, the width of the first contact area c1 (extent of the first contact area c1 perpendicular to the stacking direction) is equal to or greater than the width of the second contact area c2 plus three times the thickness t of the functional layer 3: c1 ≥ c2 + 3t.

[0092] In this embodiment, the size of the second contact area c2 is controlled during the manufacture of the sensor element 1, in particular during the manufacture of the lower electrode 4.

[0093] As in the embodiment in Fig. Starting from the support 2, the lower electrode 4 is deposited. The contact area c2 can now be defined either by the structure of the lower electrode 4 or, as shown in the figure, by a window 7 in an insulating layer 6. To create this window 7, a SiO2 layer is deposited and, for example, a hole is etched into the SiO2. The functional layer 3 is then deposited over the hole. The lower electrode 4 is thus a planar layer, and the functional layer 3 fills the window 7. Then, an additional SiO2 layer / insulating layer 6 is deposited, and another window 7 is created for the upper electrode / contact pad 5a.

[0094] It should be noted that the figures shown are a very rough description of the layer structure and that the windows actually lead to a step in the layers above, and the layer thickness is the same regardless of the position.

[0095] The Fig. 7 and Fig. Figure 8 shows a sectional view of the sensor element 1 according to a further embodiment. In this embodiment, the resistance is controlled by both the upper electrode 5 and the lower electrode 4. More precisely, the resistance is controlled by the size of the first contact area c1 between the upper electrode 5 and the functional layer 3 and by the size of the second contact area c2 between the lower electrode 4 and the functional layer 3.

[0096] The resistance is adjusted analogously to the embodiments according to the Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5 to Fig. 6. Controlled, i.e., by the size of the contact areas c1, c2. Furthermore, the resistance can be controlled by the position of the first contact area c1 and the second contact area c2 relative to each other, in particular by an overlap area o perpendicular to the stacking direction between the first and second contact areas c1, c2, as shown in the Fig. 7 and Fig. Figure 8 shows that the larger the overlap area o, the lower the resistance.

[0097] Here too there are several insulating layers 6 and windows 7, as already mentioned in connection with the Fig. 1, Fig. 2 to Fig. 3 described. As already described above, the insulating layer 6 can be present between the lower electrode 4 and the functional layer 3 in order to control the size of the second contact area c2 via a window 7 in the insulating layer 6.

[0098] By controlling the size of the contact areas c1, c2 and / or the position of the contact areas c1, c2 relative to each other, the nominal resistance of the sensor element 1 can be precisely controlled.

[0099] In this embodiment as well, the upper electrode 5 can function as the first contact pad 5a, as in the Fig. 7 and Fig. Figure 8 shows. Alternatively, the upper electrode 5 and the first contact pad 5a can be separate material layers, analogous to Fig. 4.

[0100] The Fig. 9, Fig. 10, Fig. 11 to Fig. Figure 12 shows a cross-sectional view of the sensor element 1 according to a further embodiment. In this embodiment, the functional layer 3 is embedded between two upper electrodes 5 and a lower electrode 4. This causes the current to flow through the NTC multiple times (see current flow F). The current flows through the first upper electrode 5 (left in Figure 1). Fig. 9) through the functional layer 3 to the lower electrode 4. From the lower electrode 4, the electric current flows along the lower electrode 4 to below the second upper electrode 5 (right in Fig. 9). There, the current flows through the functional layer 3 to the upper electrode 5.

[0101] The resistance of the sensor element 1 can be controlled in the same way as in the embodiments described above, either by changing / controlling the first contact area c1, the second contact area c2, or by varying the position and size of the contact areas c1, c2. Here too, the upper electrode 5 can be an additional layer (see Fig. 11, Fig. 12) or can be simultaneous with the first contact pad 5a, i.e. the upper electrode 5 acts as the first contact pad 5a, as in the Fig. 9, Fig. 10 shown.

[0102] The Fig. 13 and Fig. Figure 14 shows a sectional view of the sensor element 1 according to a further embodiment. In this embodiment, several upper electrodes 5 and several lower electrodes 4 are used and connected in series. A plurality of upper electrodes 5 and lower electrodes 4 are present, so that a plurality of first contact areas c1 and second contact areas 2 are present, which can also be of different sizes.

[0103] The special structure causes the current to flow through functional layer 3 multiple times, as if several smaller resistors were connected in series, resulting in a larger overall resistance (see current flow F in the Fig. 13 and Fig. 14).

[0104] In this design, two factors influence the final resistance of the sensor element: First, the first and second contact areas c1, c2, as mentioned in the embodiments described above. For example, the resistance can be controlled by the size of the first contact area c1 by means of the design of the upper electrode or the window size in the insulating layer 6, or by the second contact areas c2, or by the size and position of the first and second contact areas c1, c2 simultaneously, as described above. The upper electrodes 5, in turn, can either be an additional layer (not explicitly shown) or simultaneously function as the first contact pad 5a.

[0105] The other factor controlling the resistance is the number of resistors connected in series. By limiting the number of resistors connected in series, the total resistance of sensor element 1 can be determined.

[0106] This also allows for fine-tuning of the resistance after production is complete. This fine-tuning ensures that the final sensor element 1 has a very small deviation range from its nominal resistance.

[0107] There are two options for fine-tuning: One possibility is the provision of trim electrodes 8, as in Fig. Figure 15 shows the trim electrodes 8 as separate / additional electrodes connected to certain upper electrodes 5 arranged in a row ( Fig. 15) Alternatively, the trim electrodes 8 can also be connected to certain upper electrodes arranged in a circle or spiral, or to any upper electrodes (not explicitly shown). The trim electrodes 8 are also connected to a contact pad 5a, as shown in Fig. Figure 15 shows that the trim electrodes 8 act like short-circuit electrodes. They connect certain / some upper electrodes and leave other upper electrodes 5, which are arranged between the connected upper electrodes 5, unconnected.

[0108] The more frequently the current flows through functional layer 3 (current flow F, Fig. 15), the higher the final resistance of the sensor element 1. By introducing the trim electrodes 8, it can be prevented that the current flows through the functional layer 3 more frequently than intended. Specifically, this means for the in Fig. In the embodiment shown in Figure 15, the upper electrodes 5a in the upper row can be moved further to the right using the trim electrodes 8, thus preventing a current flow F through the functional layer 3 and the upper electrodes 5a arranged between them. In this case, the overall resistance can be reduced.

[0109] For further fine-tuning, and depending on the measured resistance, the trim electrodes 8 connected to the upper electrode 5 can be additionally cut, e.g., with a laser. This means that electrode material of the trim electrodes 8 is at least partially removed to fine-tune the resistance of the final sensor element 1, e.g., by laser cutting, sawing, or grinding.

[0110] In Fig. For example, cutting the leftmost wire (number 15) would increase the resistance by the smallest increment, and each additional cut would further increase the resistance. This allows for very precise fine-tuning towards the nominal resistance of sensor element 1.

[0111] Ideally, the trim electrodes 8 are not arranged directly above the functional layer 3, but laterally, as shown in Fig. Figure 15 shows that the trim electrodes 8 are not positioned directly above the top surface of the functional layer 3.

[0112] The embodiment in Fig. Figure 15 also shows that all upper electrodes 5 contact the lower electrode 4 via the functional layer 3. However, this is not necessary, and only some of the upper electrodes 5 can be arranged on the functional layer 3 and contact the lower electrode 4, as is the case, for example, in Fig. Figure 16 shows that this would be particularly interesting for trimming electrodes by laser cutting, as it would allow for even smaller steps in fine-tuning the resistance.

[0113] The second possibility for fine-tuning the resistance of the sensor element 1 is to provide additional contact pads 9 that are connected to the upper electrodes 5 at other locations. This is shown in Fig. Figure 17 shows that the additional contact pads 9 provide another way to directly contact (certain) upper electrodes 5a without having to insert trim electrodes 8.

[0114] Depending on which additional contact pads 9 are used for the second connection, the resistance can be fine-tuned to achieve the target / nominal resistances. In the illustrated embodiment, the first contact pad 5a would be the left electrode, and the second contact pad would be either the upper left contact pad 9 (lowest resistance), the upper right contact pad 9 (slightly higher resistance), or the right contact pad 9 (highest resistance) to fine-tune the target resistances. Ideally, the contact pads 5a, 9, which are provided for the electrical contacting of the sensor element 1 with an external source, do not lie completely above the functional layer 3, but extend beyond it, as shown in Fig. 17 shown.

[0115] The Fig. 18 and Fig. Figure 19 shows a cross-sectional view of the sensor element 1 according to a further embodiment. In this embodiment, several upper electrodes 5 and one lower electrode 4 are provided and connected in parallel. This allows the current to flow through the functional layer 3 at several points simultaneously, as shown in the Fig. 18, Fig. 19 shown (see current flow F).

[0116] Here too, two factors influence the overall resistance of the sensor element: First, as described in the preceding explanations, the size and relative positions of the contact areas c1, c2.

[0117] The second factor is the number of electrodes 4, 5 connected in parallel. In this embodiment, the electrodes can also be trimmed after the sensor element 1 has been manufactured, and the resistance can be fine-tuned. An example of fine-tuning is shown in Fig. 20 shown.

[0118] The in Fig. The sensor element 1 shown in Figure 20 has a lower electrode 4 and several upper electrodes 5. In this embodiment, trim electrodes 8 are also provided, which are connected in series to all the upper electrodes 5. The trim electrodes 8 can be trimmed by laser cutting to adjust the final resistance of the sensor element 1 and thus obtain a sensor element 1 with a small deviation range from the nominal resistance. Laser cutting of the trim electrodes 8 allows individual resistances to be removed, thereby increasing the overall resistance of the sensor element 1. Preferably, the trimming takes place in an area that is not directly above the functional layer 3.

[0119] The lower electrode 4 can also be divided into several electrodes while maintaining the parallel connection. Alternatively, the structure can be mirrored with several lower electrodes 4 and one large upper electrode 5 (not explicitly shown). In this case, the upper electrode 5 can also be divided into several electrodes while maintaining the parallel connection.

[0120] The description of the items disclosed here is not limited to the individual specific embodiments. Rather, the features of the individual embodiments can be combined with one another in any way – insofar as this is technically feasible. Reference symbol list 1 sensor element 1a Top side of the sensor element 1b Underside of the sensor element 2 carriers 2a Top side of the carrier 2b Underside of the carrier 3 functional layer 4 Lower electrode 4a Contact pad / Second contact pad 5 Upper electrode 5a Contact pad / First contact pad 6 Insulation layer 7 windows 8 Trim electrode 9 Additional contact pad T Thickness of the sensor element t thickness of the functional layer o Overlap area between upper and lower electrode c1 Contact area between upper electrode and functional layer / first contact area c2 Contact area between lower electrode and functional layer / second contact area F Current flow

Claims

Sensor element (1) for measuring a temperature comprising: - a carrier (2); - at least one functional layer (3) arranged on a top surface (2a) of the carrier, wherein the functional layer (3) comprises a material with a temperature-dependent electrical resistance; - at least one upper electrode (5), wherein a first contact area (c1) is formed between the at least one upper electrode (5) and the functional layer (3); - at least one lower electrode (4), wherein a second contact area (c2) is formed between the at least one lower electrode (4) and the functional layer (3), wherein the functional layer (3) is at least partially embedded between the at least one lower electrode (4) and the at least one upper electrode (5), and wherein the functional layer (3), the at least one upper electrode (5), and the at least one lower electrode (4) are configured and arranged as follows:that a certain electrical resistance of the sensor element (1) is achieved, wherein the sensor element (1) has a plurality of upper electrodes (5) and a plurality of lower electrodes (4) connected in series, wherein a resistance is determined by: - ​​a size of the respective first contact area (c1) and / or - a size of the respective second contact area (c2) and / or - a relative position of the first contact areas (c1) and the second contact areas (c2) and / or - a size of overlap areas (o) between first contact areas (c1) and second contact areas (c2) and / or - a number of resistors connected in series. Sensor element (1) according to claim 1, comprising at least one insulating layer (6), wherein the insulating layer (6) covers at least partially a top surface (1a) of the sensor element (1) and / or at least partially a top surface of the at least one lower electrode (4) and / or at least partially a top surface (2a) of the carrier (2). Sensor element (1) according to claim 2, comprising at least one window (7), wherein the at least one window (7) is a recess in the at least one insulating layer (6), wherein the at least one window (7) is designed and arranged to enable an electrical connection between the at least one lower electrode (4) and the functional layer (3) and / or between the at least one upper electrode (5) and the functional layer (3). Sensor element (1) according to one of the preceding claims, wherein the at least one upper electrode (5) functions as a first contact pad (5a) of the sensor element (1) for electrical contacting the sensor element (1) or wherein the sensor element (1) has at least one first contact pad (5a) which is electrically connected to the at least one upper electrode (5). Sensor element (1) according to one of the preceding claims, wherein the at least one lower electrode (4) functions as a second contact pad (4a) of the sensor element (1) or wherein the sensor element (1) has at least one second contact pad (4a) which is electrically connected to the at least one lower electrode (4). Sensor element (1) according to claim 4, wherein a resistance of the sensor element (1) is determined by an area of ​​the at least one first contact pad (5a). Sensor element (1) according to one of the preceding claims, wherein a resistance of the sensor element (1) is determined by a size of the at least one first contact area (c1) formed between the at least one upper electrode (5) and the functional layer (3). Sensor element (1) according to claim 7, wherein the at least one second contact area (c2) has at least the same size as the at least one first contact area (c1). Sensor element (1) according to claim 7 or claim 8, wherein a width of the at least one second contact area (c2) is equal to or greater than a width of the at least one first contact area (c1) plus three times a functional layer thickness (t): c2 ≥ c1 + 3t. Sensor element (1) according to one of claims 7 to 9, wherein the size of the at least one first contact area (c1) is controlled by the size of a window (7) arranged in an insulating layer (6) on the top surface (1a) of the sensor element (1). Sensor element (1) according to one of claims 1 to 5, wherein a resistance of the sensor element (1) is determined by a size of the at least one second contact area (c2) and wherein the at least one second contact area (c2) is smaller than the at least one first contact area (c1). Sensor element (1) according to claim 11, wherein a width of the at least one first contact area (c1) is equal to or greater than a width of the at least one second contact area (c2) plus three times a functional layer thickness (t): c1 ≥ c2 + 3t. Sensor element (1) according to claim 11 or claim 12, wherein the size of the at least one second contact area (c2) is controlled by a manufacturing process of the at least one lower electrode (4) and / or by a size of a window (7) arranged in an insulating layer (6) that is at least partially arranged on the top side of the at least one lower electrode (4). Sensor element (1) according to one of claims 1 to 5, wherein a resistance of the sensor element (1) is determined by a size of the at least one first contact area (c1) and by a size of the at least one second contact area (c2) and / or by a position of the at least one first contact area (c1) and the at least one second contact area (c2) relative to each other. Sensor element (1) according to claim 14, wherein the resistance of the sensor element (1) is determined by the size of an overlap area (o) between the at least one first contact area (c1) and the at least one second contact area (c2). Sensor element (1) according to one of the preceding claims, having a tight resistance tolerance, wherein the sensor element (1) further comprises at least one additional contact pad (9) which is connected to at least one of the upper electrodes (5) for fine-tuning the resistance of the sensor element (1), wherein the additional contact pad (9) extends beyond a surface of the functional layer (3). Sensor element (1) according to one of claims 1 to 15, having a narrow resistance tolerance, wherein the sensor element (1) further comprises trim electrodes (8) which are connected to certain upper electrodes (5). Sensor element (1) according to claim 17, wherein at least one of the trim electrodes (8) is cut with a laser for fine-tuning the resistance of the final sensor element (1). Use of a sensor element (1) according to one of the preceding claims for temperature monitoring and / or temperature control.

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