Sensor Element and Method for Manufacturing a Sensor Element

Abstract

In an embodiment a sensor element includes a carrier having an electrically insulating material, a top side and a bottom side, an NTC thermistor arranged on the top side of the carrier and at least two first electrodes configured for electrically contacting the sensor element, wherein the first electrodes are arranged on the top side of the carrier, wherein the sensor element is configured to measure a temperature, and wherein the sensor element is configured for direct integration in an electrically insulating manner.

Claims

1.-27. (canceled)

28. A sensor element comprising: a carrier comprising an electrically insulating material, a top side and a bottom side; an NTC thermistor arranged on the top side of the carrier; and at least two first electrodes configured for electrically contacting the sensor element, wherein the first electrodes are arranged on the top side of the carrier, wherein the sensor element is configured to measure a temperature, and wherein the sensor element is configured for direct integration in an electrically insulating manner.

29. The sensor element according to claim 28, wherein the sensor element is configured for the direct integration onto a conductor path of a power module in the electrically insulating manner.

30. The sensor element according to claim 28, wherein the electrically insulating material of the carrier comprises a ceramic based on AlN, Si.sub.3N.sub.4, Al.sub.2O.sub.3, low temperature cofired ceramics (LTCC) or Zirconia Toughened Aluminum Oxide (ZTA) materials.

31. The sensor element according to claim 28, wherein coefficients of thermal expansion of a carrier material and a material of the NTC thermistor are matched.

32. The sensor element according to claim 28, wherein the NTC thermistor is an SMD NTC thermistor, and wherein the sensor element further comprises a protective layer arranged at least around the NTC thermistor.

33. The sensor element according to claim 28, wherein a respective first electrode comprises a plurality of layers, and wherein the respective first electrode comprises Cu, Ni, Pd and/or Au.

34. The sensor element according to claim 33, wherein at least one layer of the respective first electrode is a thick film, and wherein at least one further layer of the respective first electrode is a thin film.

35. The sensor element according to claim 28, wherein a respective first electrode has a first area for electrically contacting with the sensor element by wire bonding or soldering, and wherein the respective first electrode has a second area for contacting with the NTC thermistor by soldering.

36. The sensor element according to claim 35, wherein the first area and the second area are interconnected by a connecting area.

37. The sensor element according to claim 28, wherein a respective first electrode of the two first electrodes is arranged directly on the top side of the carrier, wherein the NTC thermistor is arranged directly on the respective first electrode, wherein the NTC thermistor has a metallization located on a top side of the NTC thermistor, and wherein the metallization forms a second one of the two first electrodes.

38. The sensor element according to claim 37, wherein the NTC thermistor is a chip NTC thermistor.

39. The sensor element according to claim 37, wherein the metallization is configured for electrical contacting of the sensor element by wire bonding.

40. The sensor element according to claim 37, wherein the metallization has at least one layer containing nickel.

41. The sensor element according to claim 40, wherein the layer is arranged directly at a ceramic base body of the NTC thermistor.

42. The sensor element according to claim 40, wherein the layer further comprises a proportion of vanadium.

43. The sensor element according to claim 37, wherein the metallization comprises a plurality of layers arranged directly one above the other.

44. The sensor element according to claim 28, further comprising at least one second electrode arranged on the bottom side of the carrier, wherein the second electrode is multi-layered and comprises Cu, Ni, Pd and/or Au, or wherein the second electrode comprises at least one layer of Ag.

45. The sensor element according to claim 44, wherein the second electrode is arranged over an entire surface on the bottom side of the carrier.

46. The sensor element according to claim 44, wherein the second electrode is arranged such that a free edge is formed on the bottom side of the carrier.

47. The sensor element according to claim 44, wherein the second electrode has a metallization on a top side.

48. The sensor element according to claim 44, further comprising at least one adhesion promoting layer arranged between a respective first electrode and the carrier and/or between the second electrode and the carrier.

49. A method for manufacturing a sensor element, the method comprising: providing a carrier material for forming the carrier; applying at least two first electrodes to a top side of the carrier material; applying at least one second electrode to a bottom side of the carrier material; and arranging an NTC thermistor on the top side of the carrier material, wherein the NTC thermistor is soldered onto a partial area of the at least two first electrodes.

50. The method according to claim 49, wherein a respective first electrode has a multilayer structure and comprises Cu, Ni, Pd and/or Au.

51. The method according to claim 49, wherein the first electrodes are applied to the top side of the carrier material by a combined process of sputtering, CVD process, PVD process and/or electrodeposition.

52. The method according to claim 49, further comprising forming a metallization on the bottom side of the second electrode, wherein the metallization is applied by a CVD process, a PVD process and/or by electrodeposition.

53. A method for manufacturing a sensor element, the method comprising: providing a carrier material for forming the carrier; applying at least a first electrode on a top side of the carrier material; applying at least one second electrode to a bottom side of the carrier material; and arranging an NTC thermistor on the first electrode, wherein the NTC thermistor is applied to a partial area of the first electrode, and wherein the NTC thermistor has a metallization which functions as a further first electrode.

54. The method according to claim 53, wherein the NTC thermistor is a chip NTC thermistor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0130] The drawings described below are not to be understood as being to scale. Rather, individual dimensions may be enlarged, reduced or even distorted for better representation.

[0131] Elements that are similar to each other or that perform the same function are designated with the same reference signs.

[0132] FIG. 1 shows a side view of a sensor element according to an embodiment;

[0133] FIG. 2 shows a top perspective view of a sensor element according to a further embodiment;

[0134] FIG. 3 shows a perspective bottom view of the sensor element according to FIG. 2;

[0135] FIG. 4 shows a schematic representation of the layer structure of a first electrode;

[0136] FIG. 5 shows a top view of a sensor element according to a further embodiment; and

[0137] FIG. 6 shows a perspective view of a part of the sensor element (NTC chip thermistor) according to FIG. 5.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0138] FIG. 1 shows a sensor element 1 according to a first embodiment. The sensor element 1 is preferably designed to measure a temperature. The sensor element 1 is a temperature sensor. The sensor element 1 is designed to be processed with conventional AVT, such as soldering, silver sintering and/or wire bonding, which are standardly used in the power module manufacturing.

[0139] The sensor element 1 has a carrier 2. The carrier 2 has a good thermal conductive and electrically insulating material. Preferably, the carrier 2 is a ceramic carrier. Preferably, the carrier 2 has a ceramic based on Al.sub.2O.sub.3, LTCC or ZTA materials. Alternatively, the carrier may have AlN or Si.sub.3N.sub.4 as the carrier material.

[0140] The carrier 2 has a top side 2a and a bottom side 2b. The bottom side 2b is the side of the carrier 2 which faces a printed circuit board in the installed state of the sensor element 1.

[0141] The carrier 2 is rectangular. According to an embodiment, the carrier 2 has a width B (see FIG. 2), where 1.5 mm≤B≤2 mm. Preferably, the width B=1.6 mm. Of course, other (smaller or larger) widths are also conceivable, for example 0.5 mm≤B≤2 mm.

[0142] According to an embodiment, the carrier 2 has a thickness or height H (see FIG. 2), where 0.3 mm≤H≤0.5 mm. Preferably, the height H=0.4 mm. However, other (smaller or larger) heights are also conceivable, for example 0.1 mm≤H≤1.0 mm.

[0143] According to an embodiment, the carrier 2 has a length L (see FIG. 2), where 3.0 mm≤L≤4.0 mm. Preferably, the length L=3.5 mm. Smaller and larger embodiments are also conceivable, for example 1 mm≤L≤4 mm.

[0144] In other words, the sensor element 1 or the carrier 2 has very compact dimensions and is thus ideally suited for integration on a printed circuit board.

[0145] The sensor element 1 further comprises at least two first or upper electrodes 4 and at least one second or lower electrode 5. The second or lower electrode 5 is preferably a pure metallization and has no electrical function.

[0146] The at least two first electrodes 4 are formed on the top side 2a of the carrier 2. The first electrodes 4 are formed and arranged to enable electrical contacting of the sensor element 1 using conventional AVT (preferably wire bonding or soldering).

[0147] The respective first electrode 4 is formed in a structured manner. The respective first electrode 4 has, for example, the materials Cu, Ni, Pd and/or Au. The respective first electrode 4 has a multilayer structure (see FIG. 4). In particular, a bottom layer 10 of the first electrode 4 comprises Cu. The bottom layer 10 is the layer of the first electrode 4 which is formed directly or immediately on the top side 2a of the carrier 2. A first middle layer 11 of the first electrode 4 has Ni. The first middle layer 11 is directly adjacent to the bottom layer 10. A second middle layer 12 of the first electrode 4 has, for example, Pd. The second middle layer 12 is directly adjacent to the first middle layer 11. A top layer 13 of the first electrode 4 has Au. The top layer 13 is directly adjacent to the second middle layer 12. The top layer 13 forms the top side or outer side of the respective first electrode 4.

[0148] The layers 10, 11, 12, 13 are thin or thick films, depending on the material. The bottom layer 10 (Cu) and the first middle layer 11 (Ni) are preferably designed as thick films. The top layer 13 (Au) and the second middle layer 12 (Pd) are preferably thin films 12. The layer sequence and thickness are selected in such a way that, in particular, a reliable soldering and Al thick-wire bonding process is made possible.

[0149] The layer thicknesses vary from ≤1 μm to ≤20 μm, whereby the Cu and Ni layers 10, 11 designed as thick films can each be up to 20 μm thick. The Pd and Au layers 12, 13 each have a layer thickness of ≤1 μm.

[0150] The individual layers 10, 11, 12, 13 of the respective first electrode 4 are applied to the top side 2a of the carrier 2 by a combined process of sputtering, CVD process, PVD process and/or electrodeposition.

[0151] The two first electrodes 4 are arranged separately from each other. The electrodes 4 are configured in such a way that a free area is formed on the top side 2a, i.e. an area which is free of electrode material. In particular, the first electrodes 4 do not extend to the edge of the top side 2a.

[0152] The respective first electrode 4 has a first area (bond pad 4a) and a second area (solder pad 4b). The first area 4a is formed larger than the second area 4b. The first area 4a has an extension D1 parallel to a longitudinal axis L (see FIG. 2) of the sensor element 1, where 0.2 mm≤D1≤1.5 mm. Preferably, the extension D1=0.9 mm. The first area 4a has an extension D2 perpendicular to the longitudinal axis L of the sensor element 1, where 0.2 mm≤D2≤2.0 mm. Preferably, the extension D2=1.1 mm.

[0153] The two areas 4a, 4b merge into each other. In particular, the two areas 4a, 4b are linked or connected to each other by a web-shaped connecting area 4c.

[0154] The two first electrodes 4 are oriented on the top side 2a in such a way that the two second areas/solder pads 4b are arranged opposite one another along a transverse axis Q of the carrier 2, thereby enabling an NTC thermistor 3 to be soldered on. The transverse axis Q is perpendicular to the longitudinal axis L (FIG. 2). In particular, the second areas 4b are formed in a central area of the top side 2a.

[0155] Optionally, a solder resist can also be applied to both ridges of the electrode on the top side 2a of the carrier 2.

[0156] The sensor element 1 has the NTC thermistor 3 mentioned above. The NTC thermistor 3 in this embodiment is an SMD NTC thermistor. For simplicity, the term “NTC thermistor 3” will be used in the following in connection with the embodiment according to FIGS. 1 to 3 instead of “SMD NTC thermistor 3”.

[0157] Alternatively (see embodiments according to FIGS. 5 and 6), the NTC thermistor 3 may also be a chip NTC thermistor 3. For simplicity, the term “NTC thermistor 3” is used instead of “chip NTC thermistor 3” in connection with the embodiment according to FIGS. 5 and 6.

[0158] The NTC thermistor 3 has a top side 3a and a bottom side 3b (for this, see the embodiment according to FIG. 6). The NTC thermistor 3 has a height h of 0.2 mm≤h≤0.7 mm.

[0159] The NTC thermistor 3 is arranged on the surface of the sensor element 1. Preferably, the NTC thermistor 3 is an EIA 0402 or EIA 0201 SMD NTC. Alternatively, the NTC thermistor 3 may also be an EIA 01005 SMD NTC.

[0160] Preferably, the NTC thermistor 3 according to FIG. 1 (SMD NTC thermistor, variant 1) is soldered onto the top side 2a of the carrier 2. In particular, the NTC thermistor 3 is soldered onto the second areas 4b or solder pads 4b of the first electrodes 4. Consequently, the NTC thermistor 3 is arranged in the central area of the top side 2a of the carrier 2.

[0161] In order to avoid damage to the junctions between the NTC thermistor 3 and the carrier 2 due to cyclic temperature changes and thermomechanical stresses occurring in the process, the expansion coefficients of the carrier material and the ceramic material of the NTC thermistor 3 are matched to each other.

[0162] In the embodiment according to FIGS. 1 to 4, the sensor element 1 further has a protective layer or protective sheath 9 (glob top). The protective sheath 9 preferably completely encases at least the NTC thermistor 3. As a result, the NTC thermistor 3 is optimally protected against external influences.

[0163] Electrical contacting of the sensor element 1 is achieved by wire bonding (preferably Al thick wire bonding) of the first electrodes 4, in particular the first areas or bond pads 4a. Damage to the NTC ceramic can thus be avoided. The reliability of the sensor element 1 in contrast to prior art NTC thermistors is thus increased. The NTC thermistor 3 is also contacted by the wire bonding through the web-shaped connecting area 4c between the first area 4a and the second area 4b.

[0164] The second electrode 5 is disposed on the bottom side 2b of the carrier 2. The second electrode 5 is designed and arranged to be applied directly to the conductive path of a power module using conventional AVT (preferably soldering or silver sintering).

[0165] The second electrode 5 may be formed in multiple layers or in a single layer. For example, the second electrode 5 may have only one or more Ag layers (thin film electrode). Alternatively, the second electrode 5 can also have a layer structure analogous to the layer structure of the respective first electrode 4 (see also FIG. 4).

[0166] Preferably, the second electrode 5 is formed over the entire surface. In other words, the second electrode 5 extends completely or almost completely over the entire bottom side 2b of the carrier 2. However, a free edge 6 can also be formed on the bottom side 2b. In this case, the second electrode 5 does not extend to the edge of the bottom side 2b of the carrier 2.

[0167] A metallization 7, preferably an Ag metallization, is formed on the bottom side or outer side of the second electrode 5 in this embodiment. The metallization 7 can be formed via a CVD process, a PVD process or by electrodeposition onto the second electrode 5. The metallization 7 enables the direct connection of the sensor element 1 to the printed circuit board by using a silver sintering process. A metallization 7 is used in particular if the second electrode 5 has a layer structure analogous to the respective first electrode 4. If the second electrode 5 is designed as an Ag thin-film electrode, metallization 7 can also be omitted.

[0168] Furthermore, an adhesion promoting layer 8, for example a Ti layer, can be formed between the first electrode 4 and/or the second electrode 5 and the carrier 2. In this case, the electrode 4, 5 is formed directly on the adhesion promoting layer 8. This enables a particularly good bonding of the electrodes 4, 5 to the carrier 2.

[0169] According to a further embodiment, the sensor element 1 can also be formed without a second/lower electrode 5 in order to simplify the structure.

[0170] According to a further embodiment, the sensor element 1 may also be designed for thin wire bonding. In this example, the NTC thermistor 3 is preferably an SMD EIA 01005. Preferably, in this embodiment, the carrier 2 has the following dimensions: 0.1 mm≤H≤1 mm; 0.5 mm≤B≤2.0 mm; 1.0 mm≤L≤2.0 mm. Preferably, the first area 4a of the respective first electrode 4 has the following dimensions: 0.1 mm≤D1≤1.1 mm; 0.1 mm≤D2≤1.1 mm.

[0171] Compared to the prior art, the insulating sensor element 1 enables an application directly on the conductor path of a power module. Due to the special electrode structure, contacting with Al thick wire is possible without damaging the NTC ceramic as well as with increased reliability in contrast to prior art NTC thermistors. In addition, the mechanical stability of the sensor element 1 is increased by using ceramic carrier materials based on e.g. AlN, Si.sub.3N.sub.4, Al.sub.2O.sub.3, LTCC or ZTA materials.

[0172] FIGS. 2 and 3 show a perspective top view (FIG. 2) and a perspective bottom view (FIG. 3), respectively, of a sensor element 1 according to a further embodiment.

[0173] In contrast to the sensor element 1 according to FIG. 1, the sensor element here does not have a protective sheath 9. Furthermore, the sensor element 1 is designed without metallization 7 and without an adhesion promoting layer 8. For all further features of the sensor element 1, reference is made to the description in connection with FIG. 1.

[0174] In the following, a method for manufacturing a sensor element 1 is described. Preferably, the method produces the sensor element 1 according to one of the embodiments described above (FIGS. 1 to 3). All features described in connection with the sensor element 1 are therefore also applicable to the method and vice versa.

[0175] In a first step A), a carrier material is provided for forming the carrier 2. The carrier material exhibits good thermal conductivity. The carrier material has an electrically insulating material. The carrier material comprises a ceramic. Preferably, the carrier material comprises a ceramic based on Al.sub.2O.sub.3, LTCC or ZTA materials. Alternatively, the carrier material may also comprise AlN or Si.sub.3N.sub.4.

[0176] In a further step B), the deposition of the at least two first electrodes 4 on the top side 2a of the carrier material takes place. This is done by a combined process of sputtering, CVD process, PVD process and/or electrodeposition. In this process, multi-layered first electrodes 4 are formed. In particular, the respective first electrode 4 has a layered structure consisting of a bottom layer 10, two middle layers 11, 12 and a top layer 13.

[0177] First, the bottom layer 10 is deposited on the top side 2a of the substrate, for example by electroplating. Preferably, the bottom layer 10 comprises Cu. Preferably, the bottom layer 10 is a thick film. Preferably, the bottom layer 10 has a thickness between 1 μm and 20 μm, particularly preferably between 3 μm and 15 μm.

[0178] Subsequently, the first middle layer 11 is formed on the bottom layer 10, for example by electroplating. The first middle layer 11 has Ni. Preferably, the first middle layer 11 is a thick film. Preferably, the first middle layer 11 has a thickness between 1 μm and 20 μm, particularly preferably between 3 μm and 7 μm.

[0179] Subsequently, the second middle layer 12 is formed on the first middle layer 11, for example by means of sputtering. The second middle layer 12 has, for example, Pd. Preferably, the second middle layer 12 is a thin film. Preferably, the second middle layer 12 has a thickness of ≤1 μm.

[0180] Last, the top layer 13 is formed on the second middle layer 12, for example by sputtering. The top layer 13 has Au. The top layer 13 forms the top side or outer side of the respective first electrode 4. Preferably, the top layer 13 is a thin film. Preferably, the top layer 13 has a thickness of ≤1 μm.

[0181] In an alternative embodiment, a further step takes place prior to step B), in which the adhesion promoting layer 8 is applied to the top side 2a of the carrier material. Subsequently, in this embodiment, the first electrodes 4 are formed on the adhesion promoting layer 8.

[0182] In a further step C), the second electrode 5 is applied to the bottom side 2b of the carrier material. This can also be done by a combined process of sputtering, CVD process, PVD process and/or electrodeposition. The resulting second electrode 5 has a multilayer structure, for example analogous to the structure of the respective first electrode 4.

[0183] Alternatively, however, the second electrode 5 may have only one or more layers of Ag. In this case, the second electrode 5 is applied to the bottom side 2a of the carrier material.

[0184] In an alternative embodiment, a further step in which the adhesion promoting layer 8 is applied to the bottom side 2b of the carrier material takes place before step C). Subsequently, in this embodiment, the second electrode 5 is formed on the adhesion promoting layer 8.

[0185] In an alternative embodiment, step C) may be omitted so that no second electrode 5 is deposited on the bottom side 2b of the carrier material.

[0186] In an alternative further step, a metallization 7 may be formed on the bottom side or outer surface of the second electrode 5. The metallization is applied to the second electrode 5 via a CVD process, a PVD process or by electrodeposition.

[0187] In a next step D), the arrangement of the NTC thermistor 3 on the top side 2a of the carrier material takes place. In particular, the NTC thermistor 3 is soldered onto a partial area (second area 4b or solder pad 4b) of the at least two first electrodes 4.

[0188] In a further step, a protective layer or protective sheath 9 is applied. The protective sheath 9 preferably comprises a polymer. Preferably, the protective sheath 9 consists of a polymer. The protective sheath 9 preferably completely encases the NTC thermistor 3.

[0189] Subsequently, the direct bonding of the sensor element 1 to a conductor path of a printed circuit board can take place, in particular by means of a conventional AVT, preferably by soldering or Ag-sintering of the second electrode 5.

[0190] Furthermore, the first electrodes 4 and the NTC thermistor 3 can now be contacted. This is also done by means of a conventional AVT, preferably by wire bonding (preferably Al thick wire bonding) or soldering.

[0191] FIG. 5 shows a sensor element 1 according to a further embodiment. In contrast to the embodiments shown in FIGS. 1 to 3, the NTC thermistor 3 here is a chip NTC thermistor. Furthermore, in contrast to the embodiments shown in FIGS. 1 to 3, only one electrode 4 is formed here directly on the top side 2a of the carrier 2. In the following, this electrode will be referred to as the first upper electrode 4. The first upper electrode 4 is constructed analogously to the first electrodes 4 described above. In particular, the first upper electrode has a multilayer structure.

[0192] The first upper electrode 4 is applied to the top side 2a of the carrier in such a way that an edge region of the carrier 2 is free of the first upper electrode 4 (free edge 44). The free edge 44 has a width of 0.05 to 0.25 mm.

[0193] Alternatively, however, the first upper electrode 4 may completely cover the top side 2a of the carrier 2 (not explicitly shown). In this case, an area of the first upper electrode 4 is (1.25±0.75) mm×(2.25±1.25) mm.

[0194] The NTC thermistor 3 does not completely cover the first upper electrode 4. As can be seen from FIG. 5, the NTC thermistor 3 is arranged in an edge region of the first upper electrode 4. In other words, a partial area 45 of the first upper electrode 4 is free of the NTC thermistor 3. This partial area 45 serves as a first bond pad.

[0195] The NTC thermistor 3 has a metallization 40. The metallization 40 is a thin film metallization. The metallization 40 is formed on the top side 3a of the NTC thermistor 3, preferably sputtered on. A further metallization 40 can be arranged on a further, opposite side of the NTC thermistor (bottom side 3b) (FIG. 6).

[0196] The metallization 40 on the top side 3a of the NTC thermistor 3 serves as a further bonding pad for an Al-thick wire contacting of the sensor element 1. In other words, the metallization 40 of the NTC thermistor 3 functions as a second upper electrode 4. This ensures an electrical contacting of the sensor element 1 in a simple way.

[0197] The metallization 40 is a layered electrode with several layers 41, 42 (FIG. 6). The layers 41, 42 are sputtered, for example. The metallization 40 has a layer 41 which is applied directly to the ceramic of the base body 43 (FIG. 6). The layer 41 contains nickel, for example with a proportion of vanadium, or consists of these metals.

[0198] The layer 41 can again be formed in multiple layers (not explicitly shown). A bottom layer of the layer 41 is, for example, in direct contact with the ceramic. The bottom layer includes, for example, chromium or consists of chromium. The layer 41 may further comprise a top layer deposited on the bottom layer. The top layer contains, for example, nickel with a portion of vanadium or consists of these metals.

[0199] The layer 41 has, for example, a thickness in the range of 0.2 μm to 10 μm. Preferably, the thickness is in the range of 0.3 μm to 2 μm. This thickness can apply to both a single-layer and a multilayer layer 41.

[0200] A further layer 42 (top layer) is applied to the layer 41. For example, the top layer 42 serves as corrosion protection for the layer 41, in particular to prevent oxidation. The top layer contains, for example, silver, gold, copper or aluminium or consists of one of these materials. The top layer has, for example, a thickness in the range from 0.05 μm to 20 μm.

[0201] All further features of the sensor element 1, in particular the second or lower electrode 5, the metallization 7 and the adhesion promoting layer 8 are implemented analogously to the embodiments described further above.

[0202] In the following, a method for manufacturing a sensor element 1 according to the embodiment of FIGS. 5 and 6 is described.

[0203] In a first step A), a carrier material for forming the carrier 2 is provided. The carrier material exhibits good thermal conductivity. The carrier material exhibits an electrically insulating material. The carrier material comprises a ceramic. Preferably, the carrier material has a ceramic based on AlN, Si.sub.3N.sub.4, Al.sub.2O.sub.3, LTCC or ZTA materials.

[0204] In a further step B), the deposition of one of the two first electrodes 4 (first upper electrode 4) on the top side 2a of the carrier material takes place. This is done by a combined process of sputtering, CVD process, PVD process and/or electrodeposition. In this process, a multilayer first upper electrode 4 is formed. In particular, the first upper electrode 4 has a layered structure consisting of a bottom layer 10, two middle layers 11, 12 and a top layer 13 (FIG. 4). The layer structure of the first upper electrode 4 is analogous to the layer structure of the first electrodes described above.

[0205] The first upper electrode 4 can be applied over the entire surface of the top side 2a. Alternatively, the first upper electrode 4 is applied in such a way that an edge region of the carrier 2 remains free (free edge 44).

[0206] In an alternative embodiment, a further step in which the adhesion promoting layer 8 is applied to the top side 2a of the carrier material takes place before step B). Subsequently, in this embodiment, the first upper electrode 4 is formed on the adhesion promoting layer 8.

[0207] In a further step C), the second or lower electrode 5 is applied to the bottom side 2b of the carrier material. This can also be done by a combined process of sputtering, CVD process, PVD process and/or electrodeposition. The resulting second electrode 5 has a multilayer structure, for example analogous to the structure of the respective first electrode 4. Alternatively, however, the second electrode 5 may have only one or more layers Ag.

[0208] In an alternative embodiment, a further step takes place prior to step C), in which the adhesion promoting layer 8 is applied to the bottom side 2b of the carrier material. Subsequently, in this embodiment, the second electrode 5 is formed on the adhesion promoting layer 8.

[0209] In an alternative further step, a metallization 7 can be formed on the bottom side or outer surface of the second electrode 5. The metallization is applied to the second electrode 5 via a CVD process, a PVD process or by electrodeposition.

[0210] In an alternative embodiment, the application of the second electrode 5 to the bottom side 2b of the substrate is omitted. In this case, the sensor element 1 is bonded by means of adhesive bonding.

[0211] In a next step D), the NTC thermistor 3 is arranged on a partial area of the first upper electrode 4. In particular, the NTC thermistor 3 is soldered onto an edge area of the first upper electrode 4. The NTC thermistor 3 has a metallization 40 on the top side 3a, which functions as the second upper electrode 4.

[0212] Subsequently, the direct bonding of the sensor element 1 to a conductor path of a printed circuit board can take place, in particular by means of a conventional AVT, preferably by soldering or Ag-sintering of the second electrode 5.

[0213] Furthermore, the first or upper electrodes 4, 40 can now be contacted. This is also done by means of a conventional AVT, preferably by wire bonding (preferably Al thick wire bonding) or soldering.

[0214] The description of the objects disclosed herein is not limited to the individual specific embodiments. Rather, the features of the individual embodiments may be combined with one another in any desired manner—to the extent that this is technically feasible.