METHOD FOR PRODUCING A SENSOR AND SENSOR

Abstract

One aspect relates to a method for producing a sensor, in particular a temperature sensor, with at least one electrically conductive layer and at least one additional layer, in particular a passivation layer and/or an insulation layer. According to one aspect, the electrically conductive layer and/or the additional layer, in particular the passivation layer and/or the insulation layer, are produced by aerosol deposition (aerosol deposition method, ADM).

Claims

1-18. (canceled)

19. A method for producing a temperature sensor comprising at least one electrically conductive layer and at least one additional layer, the at least one additional layer comprising at least one of a passivation layer and an insulation layer, characterized in that the electrically conductive layer and/or the at least one additional layer is produced by aerosol deposition (aerosol deposition method, ADM).

20. The method of claim 19, further comprising: a) providing a sensor carrier; b) directly or indirectly applying the at least one electrically conductive layer on the sensor carrier; and c) applying the at least one additional layer by aerosol deposition (ADM).

21. The method of claim 20, further comprising using, in the aerosol deposition in (c), a powder of: a) aluminium oxide (Al.sub.2O.sub.3) with a purity of the base materials of at least 94 wt. % and/or b) magnesium oxide (MgO) with a purity of the base materials of at least 94 wt. % and/or c) magnesium titanate in the compositions Mg.sub.2TiO.sub.5, MgTiO.sub.3, or MgTi.sub.2O.sub.5, with a total purity of the base materials of at least 98 wt. % and/or d) binary zirconia alloys (ZrO.sub.2) with the stabilizers yttrium oxide, in particular 0 wt. % to 20 wt. % yttrium oxide, and/or CaO, and in particular 0 wt. % to 15 wt. % CaO, and/or MgO, in particular 0 wt. % to 15 wt. % MgO, with a total purity of the base materials of at least 98 wt. % and/or e) ternary alloys (zirconia ZrO.sub.2) as specified in d) with further additives formed of Nb.sub.2O.sub.5, in particular 0 wt. % to 30 wt. % Nb.sub.2O.sub.5, and/or Ta.sub.2O.sub.5, in particular 0 wt.-% to 30 wt. % Ta.sub.2O.sub.5, with a total purity of the base materials of at least 98 wt. %.

22. The method of claim 21, further comprising using, in that in the aerosol deposition in (c), a powder with a purity of the base materials of at least 95%, wherein in particular the powder of aluminium oxide (Al.sub.2O.sub.3) and/or magnesium oxide (MgO) and/or zirconium oxide (zirconia (ZrO.sub.2), which in particular is stabilized, is used with a purity of the base materials of at least 95% or any mixture thereof.

23. The method of claim 20, further comprising using, in the aerosol deposition, in (c), an inert gas comprising one of helium (He), argon (Ar), nitrogen (N.sub.2), and oxygen (O.sub.2) as the carrier gas, and a temperature treatment of not more than 150 C.

24. The method of claim 20, characterized in that the at least one electrically conductive coating is structured, or applied indirectly or directly on the sensor carrier in a structured form.

25. A temperature sensor, comprising: at least one electrically conductive layer; and at least one additional layer comprising one of a passivation layer and an insulation layer characterized in that the at least one additional layer is produced by aerosol deposition (aerosol deposition method, ADM).

26. The sensor of claim 25, characterized in that at least one layer produced using aerosol deposition comprises: a) aluminium oxide (Al.sub.2O.sub.3) with a purity of the base materials of at least 94 wt. % and/or b) magnesium oxide (MgO) with a purity of the base materials of at least 94 wt. % and/or c) magnesium titanate in the compositions Mg.sub.2TiO.sub.5, MgTiO.sub.3 or MgTi.sub.2O.sub.5 with a total purity of the base materials of at least 98 wt. % and/or d) binary zirconia alloys (ZrO.sub.2) with the stabilizers yttrium oxide, in particular 0 wt. % to 20 wt. % yttrium oxide, and/or CaO, and in particular 0 wt. % to 15 wt. % CaO, and/or MgO, in particular 0 wt. % to 15 wt. % MgO, with a total purity of the base materials of at least 98 wt. % and/or e) ternary zirconia alloys (ZrO.sub.2) as specified in d) with further additives formed of Nb.sub.2O.sub.5, in particular 0 wt. % to 30 wt. % Nb.sub.2O.sub.5, and/or Ta.sub.2O.sub.5, in particular 0 wt.-% to 30 wt. % Ta.sub.2O.sub.5, with a total purity of the base materials of at least 98 wt. %.

27. The sensor of claim 25, characterized in that at least one layer produced using aerosol deposition consists of at least 95% aluminium oxide (Al.sub.2O.sub.3).

28. The sensor of claim 27, characterized in that the specific electrical resistance of at least one Al.sub.2O.sub.3 layer produced by means of aerosol deposition at a temperature of 600 C. is at least 10.sup.10 Ohm cm.

29. The sensor of claim 25, characterized in that at least one layer produced by means of aerosol deposition has a thickness of 100 nm-50 m.

30. The sensor of claim 25, characterized in that at least one layer produced by means of aerosol deposition (ADM) has a hardness of at least 6 Gpa.

31. The sensor of claim 25, characterized in that at least one layer produced by means of aerosol deposition (ADM) is moisture tight.

32. The sensor of claim 25, characterized by a sensor support, comprising: a) aluminium oxide (Al.sub.2O.sub.3) with a purity of the base materials of at least 94 wt. % and/or b) magnesium oxide (MgO) with a purity of the base materials of at least 94 wt. % at least 94 wt. % and/or c) magnesium titanate in the compositions Mg.sub.2TiO.sub.5, MgTiO.sub.3 or MgTi.sub.2O.sub.5 with a total purity of the base materials of at least 98 wt. % and/or d) binary zirconia alloys (ZrO.sub.2) with the stabilizers yttrium oxide, in particular 0 wt. % to 20 wt. % yttrium oxide, and/or CaO, and in particular 0 wt. % to 15 wt. % CaO, and/or MgO, in particular 0 wt. % to 15 wt. % MgO, with a total purity of the base materials of at least 98 wt. % and/or e) ternary zirconia alloys (ZrO.sub.2) as specified in d) with further additives formed of Nb.sub.2O.sub.5, in particular 0 wt. % to 30 wt. % Nb.sub.2O.sub.5, and/or Ta.sub.2O.sub.5, in particular 0 wt.-% to 30 wt. % Ta.sub.2O.sub.5, with a total purity of the base materials of at least 98 wt. %.

33. The sensor of claim 25, characterized in that at least one electrically conductive coating preferably consists of metal, in particular of platinum (Pt) and/or rhodium (Rh) and/or iridium (Ir) and/or palladium (Pd) and/or gold (Au) and/or tungsten (W) and/or tantalum (Ta) and/or nickel (Ni) and/or copper (Cu) and/or of an alloy of the specified metals.

34. The sensor of claim 25, characterized by at least two electrically conductive layers, wherein between the at least two electrically conductive layers of at least one layer is produced by means of aerosol deposition.

35. The sensor of claim 25, characterized by at least two electrically conductive layers, wherein the electrically conductive layers are connected to each other via at least one measuring bridge.

36. The sensor of claim 25 used in a vehicle for measuring a temperature and/or particle quantities and/or soot particle quantities and/or reaction heat and/or a gas content and/or a gas flow.

Description

[0098] Hereafter, the invention is described in greater detail with reference to the appended schematic drawings. They show:

[0099] FIG. 1-3 Results of comparative temperature drift measurements on a sensor according to the invention in comparison to known sensors;

[0100] FIG. 4a+4b plan views of Al.sub.2O.sub.3 layers, wherein the Al.sub.2O.sub.3 layer of FIG. 4a is produced using a PVD process and the Al.sub.2O.sub.3 layer of FIG. 4b by ADM;

[0101] FIGS. 5a-5c differently designed sensors;

[0102] FIGS. 6a-6d differently designed sensors with insulation and covering layer; and

[0103] FIGS. 7a-7c differently designed sensors with a plurality of insulation layers and/or covering layers.

[0104] FIGS. 1-3 show the extent to which the temperature drift of a sensor according to the invention can be positively influenced in comparison to known sensors that are produced using standard methods.

[0105] The sensor according to the invention comprises an electrically conductive layer of platinum and a passivation layer of aluminium oxide (Al.sub.2O.sub.3). The aluminium oxide layer is produced by means of aerosol deposition.

[0106] FIGS. 1-3 show a comparison with respect to differently applied Al.sub.2O.sub.3 passivation layers. The first three bars each relate to sensors that have an Al.sub.2O.sub.3 layer applied using a screen printing method.

[0107] The bars 4-6 on the other hand relate to Al.sub.2O.sub.3 layers applied by means of aerosol deposition (ADM).

[0108] Bars 7-9 by contrast relate to Al.sub.2O.sub.3 layers applied to a platinum structure using PVD (Physical Vapor Deposition) methods.

[0109] The design of the sensors, i.e. the platinum layers, the layer thickness and dimensions, were identical. Temperature-change tests were carried out with the finished sensors. To that end, the sensors were placed into a chamber furnace using an apparatus and then removed from the chamber furnace again. As soon as the sensors were outside the chamber furnace they were also blown with air, so that a rapid cooling was obtained.

[0110] The graphic of FIG. 1 shows the temperature drift in Kelvin after 12,000 cycles at 0 C. The graphic in FIG. 2 shows the temperature drift in Kelvin after 12,000 cycles measured at 100 C. The graphic in FIG. 3 shows the temperature drift in Kelvin after 12,000 cycles measured at 900 C.

[0111] It is clear to see that at all the temperatures, i.e. at 0 C. and at 100 C. and at 900 C., the sensors that have a passivation layer of Al.sub.2O.sub.3 which was applied using aerosol deposition (ADM) show a significantly lower drift.

[0112] These test results confirm that passivation layers produced using aerosol deposition (ADM), in particular Al.sub.2O.sub.3 layers, significantly improve a sensor, the requirements regarding the stability being exceeded by several times.

[0113] The following table lists a comparison of the electrical resistances of the insulation layers produced in different ways. To produce this models were assembled in which the Al.sub.2O.sub.3 insulation layer was applied between two platinum electrode areas, firstly by means of aerosol deposition and secondly by screen printing methods. The thickness of the layers was 9 microns in each case.

TABLE-US-00001 Insulation Insulation resistance resistance In GOhm at room In GOhm Al.sub.2O.sub.3 using temperature at 250 C. 1) ADM method 7.0 + 3.08 25.7 3.95 2) Screen-printing method 0.4 0.16 2.1 0.34

[0114] It is found that at room temperature, the layer produced using aerosol deposition has an electrical insulation resistance 17 times higher than the layer produced by screen printing, i.e. the ADM layer insulates substantially better.

[0115] At 250 C., the layer produced by aerosol deposition (ADM) has a 12 higher value of insulation resistance compared to a screen-printed layer.

[0116] FIG. 4a shows an Al.sub.2O.sub.3 layer which is produced conventionally using a PVD process. Cracks are visible. These arise after the temperature treatment due to shrinkage caused by the phase transformation from gamma to alpha.

[0117] FIG. 4b shows an Al.sub.2O.sub.3 layer which is produced by ADM. The Al.sub.2O.sub.3 powder exists as o-phase during the production of the layer. Since ADM is a cold coating method, no phase transformation takes place. No cracks are produced during the temperature treatment.

[0118] Due to the low porosity, the absence of cracks and low levels of defects, a very dense ADM layer is obtained that has both a high electrical insulation resistance with a good thermal heat conductivity.

[0119] Due to the positive properties described, such as the high electrical insulation resistance combined with good thermal conductivity, layers produced by ADM are particularly well suited for constructing multi-layer systems, in which ADM layers alternating with conductive layers or structures are used for constructing sensors.

[0120] FIG. 5a shows a simple sensor design. An ADM layer 2 is applied to a substrate carrier 1. Due to the very good insulation resistance, the ADM layer 2 acts as an insulating layer if metals or oxides, such as stabilized zirconium oxide, with low electrical resistance are used as the substrate carrier material.

[0121] This design is also applied as a balancing layer when the substrate carriers 1 has a rough, topographical, porous or defective surface, or if defects such as cracks or small holes are present in the surface. Proven materials for forming this ADM layer, as described above, are oxides or mixed oxides, preferably Al.sub.2O.sub.3 or MgO. On the insulation layer 2 at least one conductive structure or surface 3 is applied, which preferably consists of platinum, gold, nickel or a CrNi alloy.

[0122] The insulation layer 2 can also be used to influence the adhesion of the conductive surface or structure 3.

[0123] FIG. 5b shows a structure in which at least one conductive layer or structure 3 is applied to a substrate carrier 1. Proven materials for use as the substrate carrier material are Al.sub.2O.sub.3 or stabilised ZrO.sub.2. The conductive layer or structure 3 preferably consists of platinum, gold, nickel or a CrNi alloy.

[0124] The conductive layer or structure 3 is covered by an ADM layer 4. Al.sub.2O.sub.3 is a proven material for use as the coating material. The ADM layer 4 acts as a protection or passivation layer, because layers thus produced are very dense and have a low gas permeability. Non-covered areas of the conductive layer or structure 3 are used here as a connection surface for electrical contacting. This structure would be used as a temperature resistor or heating resistor.

[0125] FIG. 5c shows a structure which represents a combination of FIG. 5a and FIG. 5b. The conductive layer or structure 3, which is made of platinum, gold, nickel or a CrNi-alloy, for example, is embedded between two ADM layers 2 and 4. This structure contains the advantages of the insulation layer 2 and the covering or the passivation layer 4 and is used as a temperature resistor or heating resistor.

[0126] The following design examples show the advantages of the layers produced with ADM particularly well. The layers produced thus have a low porosity, are free of cracks and low in defects and have a very high density. A particularly proven material as an ADM layer is Al.sub.2O.sub.3, since these layers have a high electrical insulation resistance combined with good thermal conductivity. Depending on the application, layer thicknesses in the range of 0.5 to 50 m are practical. Layer thicknesses of 5 to 10 m have proven particularly successful.

[0127] FIG. 6a shows an extension of the structure of FIG. 5b. The ADM layer 5 covering the first conductive surface or structure 3 here is an insulation layer on which an additional conductive surface or structure 6 is applied. The insulation layer material consists of Al.sub.2O.sub.3, MgO or a mixture of the two materials. Al.sub.2O.sub.3 has proven particularly successful.

[0128] The conductive surface or structure 6 shown here is implemented as a resistance loop and represents a heater. The structure is used, for example, as a flow or mass flow sensor based on the anemometer principle, in which a conductive structure 3 is used as a temperature resistance and the other conductive structure 6 is used as a heating resistor. The property measured is the proportional heat loss.

[0129] FIG. 6b shows the extension of the sensor structure of FIG. 6a. In addition, the top layer is an ADM layer applied as a passivation layer 7 and protects the conductive surface or structure 6 underneath it against corrosive attack.

[0130] FIG. 6c shows a design variant of FIG. 6a, where in this case the upper conductive layer or structure 6 is implemented as a double electrode structure in the form of an IDE structure. This structure can be used as a conductivity sensor. The IDE structure is used to measure the resistance between the electrodes when it is immersed in a liquid or a gas stream. Deposits on the sensor surface can also be measured by resistive measurement.

[0131] FIG. 6d shows an extension of the sensor structure of FIG. 6c. In addition, the topmost layer is an ADM layer applied as an insulation or passivation layer 7. The sensor functions described in FIG. 6c can be evaluated by means of capacitive measurements or impedance measurements.

[0132] FIG. 7a shows a sensor design with three conductive surfaces or structures 3, 6 and 9 on a substrate carrier 1. The conductive surfaces or structures 3, 6 and 9 are at least one temperature resistance, one heating resistor and one electrode structure. The conductive surfaces or structures 3, 6 and 9 are electrically insulated from each other by at least one ADM layer 5, 8 in each case. This structure can be used as a conductivity sensor, wherein for the IDE structure for measuring the conductivity, at least one heating structure is used for temperature controlling the sensor. A resistance structure can be used for temperature measurement.

[0133] FIG. 7b shows a further embodiment of FIG. 7a, which as a top layer additionally contains an ADM layer as an insulation or passivation layer 10. With this structure a surface deposit on the top ADM layer 10 can be detected using a capacitive measurement or impedance measurement.

[0134] FIG. 7c shows an extension of the embodiment of FIG. 7a, with an additional layer 11 being applied above the IDE structure. This layer 11 is used as a functional layer, which changes the electrical properties in response to particular gases. This structure can be used as a gas sensor.

LIST OF REFERENCE NUMERALS

[0135] 1 substrate carrier [0136] 2 insulation layer (I) by (ADM) [0137] 3 conductive layer (I) or structure(s) [0138] 4 covering layer (I) by ADM [0139] 5 insulation layer (II) by (ADM) [0140] 6 conductive layer (II) or structure(s) [0141] 7 covering layer (II) by ADM [0142] 8 insulation layer (III) by (ADM) [0143] 9 conductive layer (III) or structure(s) [0144] 10 covering layer (III) by ADM [0145] 11 functional layer