Sensor Element and Method for Producing a Sensor Element

Abstract

In an embodiment a sensor element includes at least one carrier having a top side and a bottom side, the top side being electrically insulating, at least one functional layer including a material with a temperature-dependent electrical resistance, the functional layer being arranged on the carrier, at least two electrodes arranged on the carrier at a distance from one another and at least two contact pads configured for electrically contacting the sensor element, wherein a respective contact pad is arranged directly on a partial region of one of the electrodes, wherein the sensor element is configured to measure a temperature, and wherein the sensor element is configured for direct integration into an electrical system as a discrete component.

Claims

1.-17. (canceled)

18. A sensor element comprising: at least one carrier having a top side and a bottom side, the top side being electrically insulating; at least one functional layer comprising a material with a temperature-dependent electrical resistance, the functional layer being arranged on the carrier; at least two electrodes arranged on the carrier at a distance from one another; and at least two contact pads configured for electrically contacting the sensor element, wherein a respective contact pad is arranged directly on a partial region of one of the electrodes, wherein the sensor element is configured to measure a temperature, and wherein the sensor element is configured for direct integration into an electrical system as a discrete component.

19. The sensor element according to claim 18, wherein the functional layer only partially covers the top side of the carrier.

20. The sensor element according to claim 18, wherein an insulating layer is located directly on the top side of the carrier.

21. The sensor element according to claim 18, wherein the electrodes are thin-film electrodes.

22. The sensor element according to claim 18, wherein a respective electrode has an areal end region, and wherein the respective contact pad is arranged on the areal end region of the respective electrodes.

23. The sensor element according to claim 18, wherein each electrode has a plurality of electrode fingers, and wherein the electrode fingers of the two electrodes are arranged alternately with respect to each other.

24. The sensor element according to claim 18, wherein the electrodes are arranged directly on an top side of the functional layer.

25. The sensor element according to claim 18, wherein the electrodes are arranged directly on a bottom side of the functional layer.

26. The sensor element according to claim 18, wherein the contact pads protrude from a surface of the sensor element.

27. The sensor element according to claim 18, further comprising a protective layer completely covering a top side of the sensor element except for the contact pads.

28. The sensor element according to claim 18, wherein the carrier comprises silicon, silicon carbide or glass, or wherein the carrier comprises AlN or Al.sub.2O.sub.3 as carrier material.

29. The sensor element according to claim 18, wherein the functional layer comprises an NTC ceramic based on an oxidic material in a perovskite structure type or a spinel structure type, or wherein the functional layer comprises an NTC ceramic based on a carbide or a nitride material, or wherein the functional layer comprises a thin layer of vanadium oxide or SiC.

30. The sensor element according to claim 18, wherein a thickness of the sensor element is <100 μm.

31. The sensor element according to claim 18, wherein the sensor element is designed for direct integration into a MEMS structure and/or into a SESUB structure.

32. The sensor element according to claim 18, wherein a resistance of the sensor element is adjusted by a geometry of the functional layer and/or the electrodes.

33. A method for producing a sensor element, the method comprising: providing a carrier material for forming a carrier; forming an electrically insulating layer on a top side of the carrier; forming at least two electrodes on the carrier; applying a functional material to a partial region of the electrodes to form a functional layer; sintering of the functional layer; applying a protective layer to ae top side of the sensor element, the protective layer completely covering the top side except for two partial regions, the partial regions being arranged over areal end regions of the electrodes to which contact pads are subsequently applicable; forming the contact pads in the partial regions free of the protective layer for electrical contacting of the sensor element; separating sensor elements by sawing with a diamond saw or by plasma etching so that the components are not yet finally separated; grinding the sensor elements from a bottom side, wherein a material is removed from a back side of the carrier to a defined final component thickness by grinding, wherein the carrier is a Si-wafer, and wherein the components are separated; and optionally plasma etching of the ground down bottom side of the Si-wafer to reduce micro-cracks.

34. The method according to claim 33, wherein applying the functional material is carried out before forming the at least two electrodes, and wherein the electrodes are formed directly on a top side of the functional layer.

35. A sensor element comprising: at least one carrier having a top side and a bottom side, the top side being electrically insulating; at least one functional layer comprising a material with a temperature-dependent electrical resistance, the functional layer being arranged on the carrier; at least two electrodes arranged on the carrier at a distance from one another; and at least two contact pads configured for electrically contacting the sensor element, wherein a respective contact pad is arranged directly on a partial region of one of the electrodes, wherein the electrodes are arranged directly on a bottom side of the functional layer, wherein the sensor element is configured to measure a temperature, and wherein the sensor element is configured for direct integration into an electrical system as a discrete component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings described below are not intended to be to scale. Rather, individual dimensions may be enlarged, reduced or even distorted for better representation.

[0049] Elements which are similar or which perform the same function are designated with the same reference signs.

[0050] It shows:

[0051] FIG. 1 a perspective view of a sensor element according to an embodiment,

[0052] FIG. 2 a sectional view of a sensor element according to the embodiment in FIG. 1,

[0053] FIG. 3 a process flow of the manufacturing method.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0054] FIGS. 1 and 2 show a representation of a sensor element 1 according to an embodiment. The sensor element 1 is preferably designed for measuring a temperature. The sensor element 1 is a temperature sensor. The sensor element 1 has a very compact design. A thickness D of the sensor element (see FIG. 2) is preferably <100 μm, preferably <80 μm, particularly preferably <50 μm. Therefore, the sensor element 1 is particularly well suited to be embedded directly in an electrical system as a discrete component. For example, the sensor element 1 is designed for direct integration into a MEMS structure and/or into a SESUB structure.

[0055] The sensor element 1 has a carrier 2. The carrier 2 serves to mechanically stabilize the sensor element 1. The carrier 2 has a top side 11 and a bottom side 12. The top side 11 and the bottom side 12 are arranged opposite each other.

[0056] The carrier 2 has a carrier material, preferably silicon (Si), silicon carbide (SiC) or glass (silicate or borosilicate). In an alternative embodiment, the carrier 2 has AlN or Al.sub.2O.sub.3 as the carrier material.

[0057] The top side 11 of the carrier 2 is electrically insulating. In other words, an insulating layer 3 is formed on the top side 11 of the carrier 2. For a carrier 2 made of silicon, for example, an insulating layer 3 comprising SiO.sub.2 is applied directly to the top side 11 of the carrier 2.

[0058] The insulating layer 3 has a very small thickness. The thickness of the insulating layer 3 is between 50 nm and 1 μm, preferably between 250 nm and 600 nm. Particularly preferably, the insulating layer 3 has a thickness of 500 nm.

[0059] The carrier 2 preferably has a rectangular base area. Alternatively, the carrier 2 can also be square. A maximum edge length L of the carrier 2 is 1000 μm in both cases. Preferably, the edge length L of the carrier 2 is <800 μm, particularly preferably <500 μm.

[0060] The sensor element 1 further comprises at least two electrodes 4a, 4b for electrical contacting of the sensor element 1. Alternatively, the sensor element 1 may have more than two electrodes 4a, 4b, for example three or four electrodes (not explicitly shown).

[0061] The two electrodes 4a, 4b are formed spaced apart from each other on the carrier 2. The respective electrode 4a, 4b may have a single-layer or multilayer structure. The respective electrode 4a, 4b comprises thin metal films, for example comprising Cu, Au, Ni, Cr, Ag, Ti, W, Pd or Pt. Preferably, the electrodes 4a, 4b are designed as thin film electrodes. In particular, the electrodes 4a, 4b are formed as interdigitated thin film electrodes, as described in detail below.

[0062] The respective electrode 4a, 4b is formed in a structured manner. In particular, the electrodes 4a, 4b each have an areal end region 6 and a region with electrode fingers 5. In this embodiment, the areal end region 6 of the respective electrode 4a, 4b is formed closer to a side region or to an edge of the carrier 2 than the region with the electrode fingers 5. However, both regions (end region 6 and electrode fingers 5) are preferably arranged at a distance from the edge of the carrier 2. The areal end regions 6 of the two electrodes 4a, 4b can be arranged opposite each other or at a 90° angle to each other.

[0063] In this embodiment, the region with the electrode fingers 5 is formed in a central area of the carrier 2, respectively. The areal end region 6 and the region with the electrode fingers 5 merge into one another.

[0064] The two electrodes 4a, 4b intertwine with each other in the region of the electrode fingers 5 in the central area of the carrier and form an interdigital structure there. The electrode fingers 5 of the electrodes 4a, 4b are arranged alternately. The electrical resistance of the sensor element 1 can be adjusted via the length, width and/or number of the electrode fingers 5, as well as their distance from each other.

[0065] In this embodiment, the electrodes 4a, 4b are formed directly on the top side 11 of the carrier 2 or the insulating layer 3. Alternatively (not explicitly shown), however, the electrodes 4a, 4b may also be formed on the top side 14 of a functional layer 7, as will be explained later.

[0066] The sensor element 1 further comprises a functional layer 7.

[0067] The functional layer 7 has a material with a specific electrical characteristic. The functional layer 7 has a material with a temperature-dependent electrical resistance. The functional layer 7 preferably comprises an NTC ceramic.

[0068] For example, the functional layer 7 has a ceramic based on an oxidic material in the perovskite structure type. For example, the perovskite is based on solid solutions of the composition CaMnO.sub.3, in which Ca may be wholly or partially replaced by, for example, Y, Cr, Al or La.

[0069] Alternatively, the functional layer 7 may comprise a ceramic based on a spinel structure type oxidic material. The composition of the spinel is preferably based on solid solutions of NiMn2O.sub.4, in which Ni and Mn can be replaced in whole or in part with, for example, Fe, Co, Al.

[0070] Also conceivable are functional layers 7 based on vanadium oxide, a carbidic material, for example hexagonal (Si, Ti)C, 2H, 4H or 6H, cubic SiC or based on a nitride material, for example (Al,Ti)N, CrN.

[0071] The functional layer 7 is preferably a thin film layer. In other words, the functional layer 7 has only a very small thickness. The thickness of the functional layer 7 is between 50 nm and 1 μm. Preferably, the thickness of the functional layer 7 is between 100 nm and 500 nm, particularly preferably between 250 nm and 400 nm.

[0072] The functional layer 7 only partially covers the top side 11 of the carrier 2. In other words, the functional layer 7 is not arranged over the entire surface of the carrier 2. A geometry and/or a design of the functional layer 7 is selected such that a specific resistance value of the sensor element 1 can be set therewith.

[0073] In one embodiment (not explicitly shown), the functional layer 7 is formed directly on the insulating layer 3 and thus below the electrodes 4a, 4b, for example sputtered on. In other words, the functional layer 7 is formed between the carrier 2 and the electrodes 4a, 4b. In this embodiment, the functional layer 7 is arranged on the carrier 2 in a form-fit and material-fit manner. Alternatively, the functional layer 7 is generated directly in the carrier material locally or as a layer.

[0074] For particularly tightly toleranced resistances at nominal temperature, the resistance of the sensor element 1 can be adjusted in this design with an additional trimming process. In this process, material of the electrodes 4a, 4b is partially removed by, for example, laser cutting, grinding or sawing in such a way that the resistance of the sensor element 1 is adjusted by the change in geometry.

[0075] Alternatively (see FIGS. 1 and 2), the functional layer 7 is at least partially applied to the electrodes 4a, 4b, in particular sputtered on. As can be seen from FIGS. 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. Thereby, the functional layer 7 rests directly on the region with the electrode fingers 5.

[0076] The sensor element 1 further has at least two contact pads 10a, 10b. The sensor element 1 can also have more than two contact pads, for example three or four contact pads. The contact pads 10a, 10b are adapted and arranged for electrical contacting of the sensor element 1.

[0077] The contact pads 10a, 10b are arranged directly on the areal end regions 6 of the electrodes 4a, 4b. The contact pads 10a, 10b can have a single-layer or multilayer structure. For example, Cu, Au, Ni, Cr, Ag, Ti, W, Pd or Pt can be used as materials for the contact pads 10a, 10b.

[0078] The contact pads 10a, 10b have a thickness of >400 nm, advantageously >1 μm, particularly preferably >5 μm. For integration into a SESUB structure, the contact pads 10a, 10b preferably comprise copper. In particular, the contact pads 10a, 10b are made of Cu.

[0079] The thickness of the Cu contact pads 10a, 10b is such that the contact pads 10a, 10b protrude from a surface 13 of the sensor element 1 (see in particular FIG. 2). The Cu contact pads 10a, 10b protrude at least 1 μm, preferably >3 μm, ideally >6 μm beyond the surface 13. This thickness of the Cu contact pads 10a, 10b is required for further processing in the SESUB structure in order to establish a reliable electrical connection.

[0080] The sensor element 1 may further have a protective layer 8. The protective layer 8 serves to improve the long-term stability of the sensor element 1. The protective layer 8 comprises a non-conductive material, comprising for example oxides, nitrides, ceramics, glasses or plastics, and may consist of one or more layers.

[0081] The protective layer 8 completely covers a top side of the sensor element 1 with the exception of the contact pads 10a, 10b. In particular, the protective layer 8 has recesses 9 from which the contact pads 10a, 10b protrude for electrical contacting of the sensor element 1.

[0082] The protective layer 8 is produced by a PVD or CVD process and structured by means of lithography. A thickness of the protective layer 8 is between 50 nm and 1 μm. Preferably, the thickness of the protective layer 8 is between 200 nm and 600 nm, particularly preferably between 400 nm and 500 nm.

[0083] Due to the compact design of the individual components of the sensor element 1, the sensor element 1 is excellently suited for integration in MEMS or SESUB structures.

[0084] In the following, a method for producing a sensor element 1 is described. Preferably, the method manufactures the sensor element 1 according to any one of the embodiments described above. All the features described in connection with the sensor element 1 are therefore also applicable to the method and vice versa.

[0085] In a first step A), a carrier material is provided for forming the carrier 2 described above. Preferably, the carrier material has Si, SiC or glass. Alternatively, the carrier material may comprise AlN or Al.sub.2O.sub.3. The carrier 2 has a top side 11 and a bottom side 12. Preferably, the carrier 2 has a maximum edge length L of less than 500 μm.

[0086] In a next step B), an electrically insulating layer 3 is formed on the top side 11 of the carrier 2. For example, the insulating layer 3 has SiO.sub.2. Ideally, an insulating layer 3 with a thickness of 500 nm is formed on the top side 11 of the carrier 2.

[0087] In a further step C), the formation/deposition of at least two electrodes 4a, 4b on the carrier 2 takes place. The deposition is carried out by a PVD or CVD process or galvanically. The structuring of the electrodes takes place in a subsequent process, this can be for example a lithography process or laser structuring. In this embodiment, the electrodes 4a, 4b are formed directly on the insulating layer 3.

[0088] The electrodes 4a, 4b can be formed in a single layer or in multiple layers and have for example Cu, Au, Ni, Cr, Ag, Ti, W, Pd or Pt. The electrodes 4a, 4b are formed as thin film electrodes. The electrodes 4a, 4b have a structured design and each have an areal end region 6 and a plurality of electrode fingers 5. The resistance of the sensor element can be adjusted by the geometry or design of the electrodes 4a, 4b.

[0089] In a further step D), a functional material is applied to form a functional layer 7. In this embodiment, the functional material is applied to a partial region of the electrodes 4a, 4b. This is done, for example, by sputtering or a spin-coating process. The functional material is first applied over the entire surface and then structured in a further process (for example lithography or laser structuring).

[0090] Alternatively, step D) can also be carried out before step C), so that the functional material 7 is sputtered directly onto the insulating layer 3 of the carrier 2 and then the electrodes 4a, 4b are applied to the functional layer 7.

[0091] The functional material preferably comprises an NTC ceramic based on an oxidic material in the perovskite or spinel structure type. Alternatively, the functional material may also comprise an NTC ceramic based on a carbide or a nitride type material. In another alternative, the functional material comprises or consists of thin films of vanadium oxide or SiC.

[0092] The functional layer 7 only partially covers the top side of the carrier 2 or the electrodes 4a, 4b. The resistance of the sensor element 1 can be adjusted by the geometry or design of the functional layer 7. Preferably, the functional layer 7 has a thickness between 250 nm and 400 nm.

[0093] In a further step E), contact pads 100a, 10b are formed on at least a partial region of the electrodes 4a, 4b. In each case, a contact pad 10a, 10b is formed directly on the areal end region 6 of an electrode 4a, 4b.

[0094] Preferably, the contact pads 10a, 10b have Cu and a thickness of >5 μm. In particular, in the finished sensor element 1, the contact pads 10a, 10b protrude from the surface 13 of the sensor element 1. Alternatively, bumps can be formed instead of the contact pads.

[0095] In a next step G), a protective layer 8 is formed. The protective layer 8 may comprise oxides, nitrides, ceramics or glasses and is generated by a PVD or CVD process and patterned by lithography. Ideally, the protective layer 8 has a thickness between 400 nm and 500 nm and completely covers the top side of the sensor element 1 with the exception of the contact pads 10a, 10b.

[0096] In a further step H), the sensor elements are separated. This can be done, for example, by plasma etching or sawing and notching of the functional layer 7 and carrier 2. The Si-wafer is not sawn through, but only to a defined thickness.

[0097] In a final step I), material is removed from the back of the Si wafer to a defined final component thickness by subsequent grinding from the back (a grinding process). This step results in the actual separation of the components.

[0098] FIG. 3 shows a process flow of the manufacturing process. The process is divided into eight stages S1 to S8, each of which can comprise several of the method steps A) to J) described above. The steps comprise;

[0099] S1 Provision of an Si wafer according to steps A) and B)

[0100] S2 Deposition and patterning of the electrode according to step C)

[0101] S3 Deposition and patterning of the functional layer according to step D)

[0102] S4 Sintering of the functional layer to produce the NTC properties according to step E)

[0103] S5 Deposition and structuring of the electrode as in stage S2 or corresponding to method step C). Stage S5 is alternative to stage S2, which can be omitted in this case. Thus, either stage S2 or S5 is used.

[0104] S6 Deposition and structuring of the passivation layer according to step F)

[0105] S7 Deposition and structuring of the contact pads according to step G)

[0106] S8 Separation of the individual sensor elements according to steps H) and I)

[0107] S9 Optional re-grinding of the sensor elements from the bottom side and optional plasma etching.

[0108] The description of the objects disclosed herein is not limited to the individual specific embodiments. Rather, the features of the individual embodiments can be combined with each other in any way—as far as this makes technical sense.