SENSOR FOR DETECTING ELECTRICALLY CONDUCTIVE AND/OR POLARIZABLE PARTICLES, SENSOR SYSTEM, METHOD FOR OPERATING A SENSOR, METHOD FOR PRODUCING A SENSOR OF THIS TYPE AND USE OF A SENSOR OF THIS TYPE

Abstract

A sensor for detecting electrically conductive and/or polarizable particles, in particular for detecting soot particles, includes a substrate and at least two electrode layers, a first electrode layer and at least one second electrode layer. Which is arranged between the substrate and the first electrode layer. At least one insulation layer is formed between the first electrode layer and the at least one second electrode layer and at least one opening is formed in both the first electrode layer and the at least one insulation layer. At least some sections of the opening in the first electrode layer and of the opening in the insulation layer are arranged one above the other, such that at least one passage is formed to the second electrode layer.

Claims

1.-43. (canceled)

44. A sensor for detecting soot particles, the soot particles being electrically conductive or polarizable, the sensor comprising: substrate, a first electrode layer and a second electrode layer, the second electrode layer arranged between the substrate and the first electrode layer; a first insulation layer disposed between the first electrode layer and the second electrode layer; a first opening disposed in the first electrode layer and a second opening disposed in the first insulation layer; wherein the first opening and the second opening are aligned to form a first passage to the second electrode layer.

45. The sensor as claimed in claim 44, further comprising a second insulation layer and a third electrode layer, the second insulation layer disposed between the first electrode layer and the third electrode layer, a third opening disposed in the third electrode layer and a fourth opening disposed in the second insulation layer, and wherein the third opening and the fourth opening are aligned to form a passage extension to the first passage to the second electrode layer.

46. The sensor as claimed in claim 44, wherein the first opening is distal from a peripheral region of the first electrode layer and the second opening is distal from a peripheral region of the first insulation layer, and wherein the third opening is distal from a peripheral region of the third electrode layer and the fourth opening is distal from a peripheral region of the second insulation layer.

47. The sensor as claimed in claim 45, wherein the first electrode layer, the second electrode layer, or the third electrode layer comprises a metal, a metal alloy, a high-temperature-resistant metal, a high-temperature-resistant alloy, a platinum metal, or an alloy of a metal of the platinum metals.

48. The sensor as claimed in claim 45, wherein the first electrode layer comprises a first material selected from the group of a metal, a metal alloy, a high-temperature-resistant metal, a high-temperature-resistant alloy, a platinum metal, or an alloy of platinum metals, wherein the second electrode comprises a second material selected from the group of a metal, a metal alloy, a high-temperature-resistant metal, a high-temperature-resistant alloy, a platinum metal, or an alloy of platinum metals, wherein the third electrode comprises a third material selected from the group of a metal, a metal alloy, a high-temperature-resistant metal, a high-temperature-resistant alloy, a platinum metal, or an alloy of platinum metals, and wherein the second material has a higher etching resistance than the first material or the third material.

49. The sensor as claimed in claim 44, further comprising a covering layer disposed on a side of the first electrode layer, the side of the first electrode layer facing away from the first insulation layer, the covering layer comprising ceramic, a glass, a metal oxide, or a combination thereof.

50. The sensor as claimed in claim 45, further comprising a covering layer disposed on a side of the third electrode layer, the side of the third electrode layer facing away from the first insulation layer, the covering layer comprising ceramic, a glass, a metal oxide, or a combination thereof, wherein the first passage is a blind hole, wherein a portion of the second electrode layer is a bottom of the blind hole, and wherein the blind hole extends through the first insulation layer, the first electrode layer, the second insulation layer, the third electrode layer, or the covering layer.

51. The sensor as claimed in claim 50, wherein the blind hole has a square cross section with a surface area in a range of 33 m.sup.2-150150 m.sup.2, a range of 1010 m.sup.2-100100 m.sup.2, a range of 1515 m.sup.2-5050 m.sup.2, or 2020 m.sup.2.

52. The sensor as claimed in claim 44, further comprising a fifth opening disposed in the first electrode layer and a sixth opening disposed in the first insulation layer, wherein the fifth opening and the sixth opening are aligned to form a second passage to the second electrode layer, wherein the first passage is a first blind hole having a first cross-sectional area, wherein the second passage is a second blind hole having a second cross-sectional area, and wherein the first cross-sectional area is larger than the second cross-sectional area.

53. The sensor as claimed in claim 45, wherein the first passage, the passage extension, or a combination of the first passage and the passage extension comprises a meandering shape or a spiral shape.

54. The sensor as claimed in claim 53, further comprising a covering layer disposed on a side of the third electrode layer, the side of the third electrode layer facing away from the first insulation layer, the covering layer comprising ceramic, a glass, a metal oxide, or a combination thereof, wherein the first passage is a blind hole, wherein a portion of the second electrode layer is a bottom of the blind hole, and wherein the blind hole extends through the first insulation layer, the first electrode layer, the second insulation layer, the third electrode layer, or the covering layer.

55. The sensor as claimed in claim 45, further comprising a covering layer disposed on a side of the third electrode layer, the side of the third electrode layer facing away from the first insulation layer, the covering layer comprising ceramic, a glass, a metal oxide, or a combination thereof, wherein the first electrode layer comprises a first electrical contact area, wherein the second electrode layer comprises a second electrical contact area, wherein the third electrode layer comprises a third electrical contact area, wherein the first electrical contact area is connected to the first electrode layer, the second electrical contact area is connected to the second electrode layer, the third electrical contact area is connected to the third electrode layer, wherein the second electrical contact area is not overlayed by the first insulation layer and the first electrode layer, wherein the first electrical contact area is not overlayed by the second insulation layer and the third electrode layer, wherein the third electrical contact area is not overlayed by a covering layer, and wherein each electrical contact area is connected to a terminal pad.

56. The sensor as claimed in claim 55, wherein the first electrode layer, the second electrode layer, or the third electrode layer comprises a strip conductor loop, strip conductor loop being a heating coil, a temperature-sensitive layer, a shielding electrode, or a combination thereof, wherein the first electrode layer, the second electrode layer, or the third electrode layer comprising the strip conductor loop comprises further a fourth electrical contact area not overlayed by one of the insulation layers or an electrode layer, and wherein the fourth electrical contact area is connected to the terminal pad.

57. A sensor system comprising: the sensor of claim 45, and a controller or a control circuit, the controller or the control circuit for operating the sensor in a measuring mode, in a cleaning mode, in a monitoring mode, or a combination thereof.

58. A method for controlling the sensor as claimed in claim 45, the method comprising the step of: operating the sensor in a measuring mode, in a cleaning mode, in a monitoring mode, or a combination thereof.

59. A method of making a sensor for detecting soot particles, the soot particles being electrically conductive or polarizable, the sensor comprising a substrate; a first electrode layer and a second electrode layer, the second electrode layer arranged between the substrate and the first electrode layer; a first insulation layer disposed between the first electrode layer and the second electrode layer; a second insulation layer and a third electrode layer, a third opening disposed in the third electrode layer and a fourth opening disposed in the second insulation layer, and wherein the third opening and the fourth opening are aligned to form a passage extension to the first passage to the second electrode layer, the method comprising the steps of: laminating the first electrode layer, the second electrode layer, the third electrode, the first insulation layer, and the second insulation layer to form a laminate, the first insulation layer being disposed between the first electrode layer and the second electrode layer, the second insulation layer disposed between the first electrode layer and the third electrode layer, subsequently forming a passage through the first electrode layer, the third electrode layer, the first insulation layer, and the second insulation layer, ending the passage to have a bottom formed by a portion of the second electrode layer.

60. The method as claimed in claim 59, wherein the passage is formed as a blind hole by etching, plasma-ion etching, or successive etching adapted to each layer being etched.

61. The method as claimed in claim 60, wherein the passage is formed as a blind hole or as an elongate depression by etching, plasma-ion etching, or successive etching adapted to each layer being etched, and wherein the first insulation layer or the second insulation layer is etching-resistant layer, the blind hole or a portion of the elongate depression being formed in the insulation layer by a conditioning process with phase conversion of the first insulation layer or the second insulation layer.

62. The method as claimed in claim 59, wherein the passage is formed as a blind hole, a subportion of the blind hole, an elongate depression, or a subportion of the elongate depression by irradiation, wherein irradiation is performed with electromagnetic waves, charged particles, or electrons, wherein a radiation source, a wavelength, a pulse frequency of a radiation, or energy of the charged particles being adapted individually to each layer being irradiated.

63. A method of making a sensor for detecting soot particles, the soot particles being electrically conductive or polarizable, the sensor comprising a substrate; a first electrode layer and a second electrode layer, the second electrode layer arranged between the substrate and the first electrode layer; a first insulation layer disposed between the first electrode layer and the second electrode layer; a second insulation layer and a third electrode layer, a third opening disposed in the third electrode layer and a fourth opening disposed in the second insulation layer, and wherein the third opening and the fourth opening are aligned to form a passage extension to the first passage to the second electrode layer, the method comprising the steps of: laminating the first electrode layer, the second electrode layer, the third electrode, the first insulation layer, and the second insulation layer to form a laminate, the first insulation layer being disposed between the first electrode layer and the second electrode layer, the second insulation layer disposed between the first electrode layer and the third electrode layer, wherein the first electrode layer, the second electrode layer, the third electrode, the first insulation layer, or the second insulation layer are structured by a lift-off process, an ink-jet process, a stamping process one over the other forming a passage to the second electrode layer.

64. A method of using the sensor of claim 45, the method comprising the step of: directing a flow (a) of the soot particles to not impinge perpendicularly on a plane (x, y) of the third electrode.

65. A method of using the sensor of claim 56, the method comprising the step of: detecting electrically conductive or polarizable particles, and adjusting an angle between a normal (z) to a plane (x, y) of the first electrode layer and a direction of a flow (a) of the particles is 1 degree or more, 10 degrees or more, or 30 degrees or more.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0111] The invention is explained in more detail below on the basis of exemplary embodiments with reference to the accompanying schematic drawings, in which:

[0112] FIGS. 1a-c show sectional representations of various embodiments of sensors for detecting electrically conductive and/or polarizable particles;

[0113] FIG. 2 shows a perspective plan view of a sensor according to the invention;

[0114] FIG. 3 shows a possible formation of a second electrode layer;

[0115] FIG. 4 shows a sectional representation of a further embodiment of a sensor for detecting electrically conductive and/or polarizable particles;

[0116] FIG. 5 shows a sectional representation of a further embodiment of a sensor for detecting electrically conductive and/or polarizable particles which comprises at least three electrode layers;

[0117] FIGS. 6a-f show representations of various embodiments of openings;

[0118] FIGS. 7a+b show representation of a possible arrangement of a sensor in a fluid flow;

[0119] FIGS. 8a+b show representations of various cross sections or cross-sectional profiles of passages;

[0120] FIG. 9 shows a sectional representation of undercuts in insulation layers or set-back insulation layers; and

[0121] FIGS. 10a-d show exploded representations of various embodiments of a sensor according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0122] The same reference numerals are used below for parts that are the same and parts that act in the same way.

[0123] FIG. 1 a shows in a sectional representation a sensor 10 for detecting electrically conductive and/or polarizable particles, in particular for detecting soot particles. The sensor 10 comprises a substrate 11, a first electrode layer 12 and a second electrode layer 13, which is arranged between the substrate 11 and the first electrode layer 12. An insulation layer 14 is formed between the first electrode layer 12 and the second electrode layer 13. At least one opening is respectively formed in the first electrode layer 12 and in the insulation layer 14, the opening 15 in the first electrode layer 12 and the opening 16 in the insulation layer 14 being arranged one over the other, so that a passage 17 to the second electrode layer 13 is formed.

[0124] For the purposes of a high-temperature application, the substrate 11 is formed for example from aluminum oxide (Al.sub.2O.sub.3) or magnesium oxide (MgO) or from a titanate or from steatite.

[0125] The second electrode layer 13 is connected to the substrate 11 indirectly by way of a bonding agent layer 18. The bonding agent layer 18 may be for example very thinly formed aluminum oxide (Al.sub.2O.sub.3) or silicon dioxide (SiO.sub.2).

[0126] In the exemplary embodiment, the first electrode layer 12 is formed by a platinum layer. In the example shown, the second electrode layer 13 consists of a platinum-titanium alloy (PtTi). The platinum-titanium alloy of the second electrode layer 13 is a layer that is more resistant to etching in comparison with the first electrode layer 12.

[0127] The distance between the first electrode layer 12 and the second electrode layer 13 is formed by the thickness d of the insulation layer 14. The thickness d of the insulation layer may be 0.5 m to 50 m. In the present case, the thickness d of the insulation layer is 10 m. The sensitivity of the sensor 10 according to the invention can be increased by reducing the distance between the first electrode layer 12 and the second electrode layer 13, and consequently by reducing the thickness d of the insulation layer 14.

[0128] The insulation layer 14 covers the second electrode layer 13 on the side face 19 shown, so that the second electrode layer 13 is laterally enclosed and insulated.

[0129] The passage 17 is formed as a blind hole, a portion of the second electrode layer 13 being formed as the bottom 28 of the blind hole. The blind hole or the passage 17 extends over the insulation layer 14 and over the first electrode layer 13. The passage 17 is in other words formed by the openings 15 and 16 arranged one over the other. In the embodiment shown, the openings 15 and 16 are not formed peripherally.

[0130] A soot particle 30 can enter the passage 17. In FIG. 1a, the particle 30 is lying on the bottom 28 of the blind hole, and consequently on a side 31 of the second electrode layer 13. However, the particle 30 is not touching the first electrode layer 12 in the peripheral region 32, which bounds the opening 15. As a result of the particle 30 being deposited on the bottom 28 and touching the second electrode layer 13 on the side 31, the electrical resistance is reduced. This drop in the resistance is used as a measure of the accumulated mass of particles. When a predefined threshold value with respect to the resistance is reached, the sensor 10 is heated, so that the deposited particle 30 is burned and, after being burned free, the sensor 10 can detect electrically conductive and/or polarizable particles in a next detection cycle.

[0131] FIG. 1b likewise shows in a sectional representation a sensor 10 for detecting electrically conductive and/or polarizable particles, in particular for detecting soot particles. Likewise shown are a first electrode layer 12 and a second electrode layer 13, which is arranged between the substrate 11 and the first electrode layer 12. An insulation layer 14 is formed between the first electrode layer 12 and the second electrode layer 13. With respect to the properties and the design of the openings 15 and 16, reference is made to the explanations in connection with the embodiment according to FIG. 1a.

[0132] A covering layer 21, which is for example formed from ceramic and/or glass and/or metal oxide, is formed on the side 20 of the first electrode layer 12 that is facing away from the insulation layer 14. The covering layer 21 encloses the side face 22 of the first electrode layer 12, the side face 23 of the insulation layer 14 and the side face 19 of the second electrode layer 13. The covering layer 21 consequently covers the side faces 19, 22 and 23, so that the first electrode layer 12, the second electrode layer 13 and the insulation layer 14 are laterally insulated. The covering layer 21 consequently comprises an upper portion 24, which is formed on the side 20 of the first electrode layer 12, and a side portion 25, which serves for the lateral insulation of the sensor 10.

[0133] FIG. 1c shows in a sectional representation a sensor 10 for detecting electrically conductive and/or polarizable particles, in particular for detecting soot particles. The sensor 10 comprises a substrate 11, a first electrode layer 12 and a second electrode layer 13, which is arranged between the substrate 11 and the first electrode layer 12. An insulation layer 14 is formed between the first electrode layer 12 and the second electrode layer 13. At least one opening is respectively formed in the first electrode layer 12 and in the insulation layer 14, the opening 15 in the first electrode layer 12 and the opening 16 in the insulation layer 14 being arranged one over the other, so that a passage 17 to the second electrode layer 13 is formed.

[0134] For the purposes of a high-temperature application, the substrate 11 is formed for example from aluminum oxide (Al.sub.2O.sub.3) or magnesium oxide (MgO) or from a titanate or from steatite.

[0135] The second electrode layer 13 is connected to the substrate 11 indirectly by way of a bonding agent layer 18. The bonding agent layer 18 may be for example very thinly formed aluminum oxide (Al.sub.2O.sub.3) or silicon dioxide (SiO.sub.2).

[0136] In the exemplary embodiment, the first electrode layer 12 is formed by a platinum layer. In the example shown, the second electrode layer 13 consists of a platinum-titanium alloy (PtTi). The platinum-titanium alloy of the second electrode layer 13 is a layer that is more resistant to etching in comparison with the first electrode layer 12.

[0137] The insulation layer 14 consists of a thermally stable material with a high insulation resistance. For example, the insulation layer 14 may be formed from aluminum oxide (Al.sub.2O.sub.3) or silicon dioxide (SiO.sub.2) or magnesium oxide (MgO) or silicon nitride (Si.sub.3N.sub.4) or glass.

[0138] The distance between the first electrode layer 12 and the second electrode layer 13 is formed by the thickness d of the insulation layer 14. The thickness d of the insulation layer may be 0.5 m to 50 m. In the present case, the thickness d of the insulation layer is 10 m. The sensitivity of the sensor 10 according to the invention can be increased by reducing the distance between the first electrode layer 12 and the second electrode layer 13, and consequently by reducing the thickness d of the insulation layer 14.

[0139] A covering layer 21, which is for example formed from ceramic and/or glass and/or metal oxide, is formed on the side 20 of the first electrode layer 12 that is facing away from the insulation layer 14. The covering layer 21 encloses the side face 22 of the first electrode layer 12, the side face 23 of the insulation layer 14 and the side face 19 of the second electrode layer 13. The covering layer 21 consequently covers the side faces 19, 22 and 23, so that the first electrode layer 12, the second electrode layer 13 and the insulation layer 14 are laterally insulated. The covering layer 21 consequently comprises an upper portion 24, which is formed on the side 20 of the first electrode layer 12, and a side portion 25, which serves for the lateral insulation of the sensor 10.

[0140] In a further embodiment of the invention it is conceivable that the covering layer 21 also laterally encloses the substrate 11.

[0141] A porous filter layer 27 is formed on the side 26 of the covering layer 21 that is facing away from the first electrode layer 12. The sensitivity of the sensor 10 is increased as a result of the formation of this passive porous filter or protective layer 27 which is facing the medium that is to be detected with regard to electrically conductive and/or polarizable particles, since larger particles or constituents that could disturb the measurement or detection are kept away from the first electrode layer 12 and the second electrode layer 13. Since the passage 17 is covered by the porous filter layer 27, particles can still penetrate through the pores in the porous filter layer 27, but short-circuits caused by large penetrated particles can be avoided as a result of the porous filter layer 27.

[0142] The passage 17 is formed as a blind hole, a portion of the second electrode layer 13 being formed as the bottom 28 of the blind hole. The blind hole or the passage 17 extends over the insulation layer 14, the first electrode layer 13 and over the covering layer 21. For this purpose, the covering layer 21 also has an opening 29. In other words, the passage 17 is formed by the openings 29, 15 and 16 arranged one over the other.

[0143] As a result of the choice of materials for the individual layers and the insulation of the individual layers from one another, the sensor 10 shown is suitable for a high-temperature application of up to for example 850 C. The sensor 10 can accordingly be used as a soot particle sensor in the exhaust-gas flow of an internal combustion engine.

[0144] After penetrating through the porous filter layer 27, a soot particle 30 can enter the passage 17. In FIG. 1c, the particle 30 lies on the bottom 28 of the blind hole, and consequently on a side 31 of the second electrode layer 13. However, the particle is not touching the first electrode layer 12 in the peripheral region 32, which bounds the opening 15. As a result of the particle 30 being deposited on the bottom 28 and touching the second electrode layer 13 on the side 31, the electrical resistance is reduced. This drop in the resistance is used as a measure of the accumulated mass of particles. When a predefined threshold value with respect to the resistance is reached, the sensor 10 is heated, so that the deposited particle 30 is burned and, after being burned free, the sensor 10 can detect electrically conductive and/or polarizable particles in a next detection cycle.

[0145] FIG. 2 shows a perspective view of a sensor 10. The sensor has nine passages 17. For better illustration, the porous filter layer 27 is not shown in FIG. 2. The upper portion 24 of the covering layer 21 and also the side portion 25 of the covering layer 21 can be seen. The bottoms 28 of the passages 17 are formed by portions of the second electrode layer 13. The nine passages 17 have a square cross section, it being possible for the square cross section to have a surface area of 1515 m.sup.2 to 5050 m.sup.2.

[0146] The first electrode layer 12 has an electrical contacting area 33. The second electrode layer 13 likewise has an electrical contacting area 34. The two electrical contacting areas 33 and 34 are free from sensor layers arranged over the respective electrode layers 12 and 13. The electrical contacting areas 33 and 34 are or can in each case be connected to a terminal pad (not shown).

[0147] The second electrode layer 13 has an additional electrical contacting area 35, which is likewise free from sensor layers arranged over the electrode layer 13. This additional electrical contacting area 35 may be connected to an additional terminal pad. The additional electrical contacting area 35 is necessary to allow the second electrode layer 13 to be used as a heating coil or as a temperature-sensitive layer or as a shielding electrode. Depending on the contacting assignment (see FIG. 3) of the electrical contacting areas 34 and 35, the second electrode layer 13 may either heat and burn the particle 30 or detect the particle 30.

[0148] To be able to use an electrode layer, here the second electrode layer 13, as a heating coil and/or temperature-sensitive layer and/or shielding electrode, the second electrode layer 13 has a small number of strip conductor loops 36.

[0149] In FIG. 4, a further embodiment of a possible sensor 10 is shown. The first electrode layer 12 and the insulation layer 14 are respectively formed as porous, the at least one opening 15 in the first electrode layer 12 and the at least one opening 16 in the insulation layer 14 respectively being formed by at least one pore, the pore 41 in the insulation layer 14 and the pore 40 in the first electrode layer 12 being arranged at least in certain portions one over the other in such a way that the at least one passage 17 to the second electrode layer 13 is formed. In other words, it is possible to dispense with an active or subsequent structuring of the passages, the first electrode layer 12 and the insulation layer 14 being formed as permeable to the medium to be measured. The passages 17 are represented in FIG. 4 with the aid of the vertical arrows.

[0150] The passages 17 may be formed by a porous or granular structure of the two layers 12 and 14. Both the first electrode layer 12 and the insulation layer 14 can be produced by sintering together individual particles, with pores 40 and 41 or voids for the medium to be measured being formed while they are being sintered together. Accordingly, a passage 17 that allows access to the second electrode layer 13 for a particle 30 that is to be measured or detected must be formed, extending from the side 20 of the first electrode layer 12 that is facing away from the insulation layer 14 to the side 31 of the second electrode layer 13 that is facing the insulation layer 14 as a result of the one-over-the-other arrangement of pores 40 and 41 in the first electrode layer 12 and in the insulation layer 14.

[0151] In the example shown, the second electrode layer 13 is completely enclosed on the side face 19 by the porous insulation layer 14. The second electrode layer 13 is accordingly covered on the side 31 and on the side faces 19 by the porous insulation layer 14. The porous first electrode layer 12 on the other hand encloses the porous insulation layer 14 on the side face 23 and on the side 37 facing away from the second electrode layer 13. The insulation layer 14 is accordingly covered on the side 37 and on the side faces 23 by the first electrode layer 12.

[0152] If this sensor 10 has a covering layer, this covering layer is also to be formed as porous in such a way that a pore in the covering layer, a pore 40 in the first electrode layer 12 and a pore 41 in the insulation layer 14 form a passage 17 to the second electrode layer 13.

[0153] In FIG. 5, a section through a sensor 10 for detecting electrically conductive and/or polarizable particles, in particular for detecting soot particles, is shown. The sensor 10 can in principle be used for detecting particles in gases and in liquids. The sensor 10 comprises a substrate 11, a first electrode layer 12, a second electrode layer 13, which is arranged between the substrate 11 and the first electrode layer 12, a first insulation layer 14 being formed between the first electrode layer 12 and the second electrode layer 13.

[0154] At least a third electrode layer 50 is formed between the first insulation layer 14 and the first electrode layer 12, at least a second insulation layer 60 being formed between the third electrode layer 50 and the first electrode layer 12.

[0155] According to sensor 10 of FIG. 5, therefore at least three electrode layers 12, 13, 50 and at least two insulation layers 14, 60 are formed. The first electrode layer 12 is in this case the electrode layer that is arranged furthest away from the substrate 11. The second electrode layer 13 on the other hand is connected directly to the substrate 11. It is possible that the second electrode layer 13 is connected indirectly to the substrate 11, preferably by means of a bonding agent layer.

[0156] In the embodiment according to FIG. 5, a fourth electrode layer 51 is also formed and also a third insulation layer 61. The sensor 10 consequently comprises altogether four electrode layers, to be specific the first electrode layer 12, the second electrode layer 13, and also the third electrode layer 50 and the fourth electrode layer 51. Insulation layers are respectively formed between the electrode layers (12, 13, 50, 51), to be specific the first insulation layer 14, the second insulation layer 60 and also the third insulation layer 61. The sensor 10 also comprises a covering layer 21, which is formed on the side of the first electrode layer 12 that is facing away from the substrate 11.

[0157] At least one opening 15, 16, 70, 71, 72, 73 is respectively formed in the first electrode layer 12, in the third insulation layer 61, in the fourth electrode layer 51, in the second insulation layer 60, in the third electrode layer 50 and in the first insulation layer 14. The covering layer 21 also has an opening 29. The opening 15 in the first electrode layer 12, the opening 73 in the third insulation layer 61, the opening 72 in the fourth electrode layer 51, the opening 71 in the second insulation layer 60, the opening 70 in the third electrode layer 50 and the opening 16 in the first insulation layer 14 are arranged at least in certain portions one over the other in such a way that at least one passage 17 to the second electrode layer 13 is formed.

[0158] The distance between the electrode layers 12, 13, 50 and 51 is formed by the thickness of the insulation layers 14, 60 and 61. The thickness of the insulation layers 14, 60 and 61 may be 0.1 m to 50 m. The sensitivity of the sensor 10 according to the invention can be increased by reducing the distance between the electrode layers 12, 13, 50 and 51, and consequently by reducing the thickness of the insulation layers 14, 60 and 61.

[0159] The passage 17 is formed as a blind hole, a portion of the second electrode layer 13 being formed as the bottom 28 of the blind hole. The blind hole or the passage 17 extends over the first insulation layer 14, the third electrode layer 50, the second insulation layer 60, the fourth electrode layer 51, the third insulation layer 61, the first electrode layer 12 and over the covering layer 21. In other words, the passage 17 is formed by the openings 16, 70, 71, 72, 73, 15 and 29 arranged over one another. In the embodiment shown, the openings 16, 70, 71, 72, 73, 15 and 29 are not formed peripherally. A perspective section through a passage 17 is shown.

[0160] A small soot particle 30 for example can enter the passage 17. In FIG. 5, the particle 30 is lying on the bottom 28 of the blind hole, and consequently on a side 31 of the second electrode layer 13. The particle 30 is also touching the third electrode layer 50. If the determination of particles is performed on the basis of the resistive principle, the resistance between the second electrode layer 13 and the third electrode layer 50 is measured, this resistance decreasing if the particle 30 bridges the two electrode layers 13 and 50. The size of the particle 30 is consequently relatively small.

[0161] The soot particle 30 has also entered the passage 17. The particle 30 is lying on the bottom 28 of the blind hole, and consequently on the side 31 of the second electrode layer. The particle 30 is also touching the third electrode layer 50, the fourth electrode layer 51 and also the first electrode layer 12. The particle 30 consequently bridges a number of electrode layers, in the example shown all of the electrode layers 12, 13, 50 and 51, so that the particle 30 is detected as a particle that is larger in comparison with the particle 30.

[0162] By applying different voltages to the electrode layers 12, 13, 50 and 51, different particle properties, in particular different soot properties, such as for example the diameter and/or the size of the (soot) particle and/or the charging of the (soot) particle and/or the polarizability of the (soot) particle, can be measured.

[0163] Various embodiments of openings 80 are shown in FIGS. 6a to 6f. The openings 80 may be formed both in insulation layers 14, 60 and 61 and in electrode layers 12, 50 and 51. Accordingly, the openings 80 that are shown may be an arrangement of openings 15 in a first electrode layer 12, openings 16 in a first insulation layer 14, openings 70 in a third electrode layer 50, openings 71 in a second insulation layer 60, openings 72 in a fourth electrode layer 51 and also openings 73 in a third insulation layer 61.

[0164] Preferably, the openings 80 in a laminate of the sensor 10 are formed similarly. The individual layers 12, 14, 21, 50, 51, 60 and 61 are arranged one over the other in such a way that the openings 15, 16, 29, 70, 71, 72 and 73 form passages 17. As a result of the openings shown in FIGS. 6a to 6d, elongate depressions 17 and 17 are respectively formed.

[0165] In FIG. 6a, linear openings 80 are formed, the openings 80 being formed parallel to one another and all pointing in the same predominant direction.

[0166] In FIG. 6b, a layer of the sensor 10 is subdivided into a first portion 45 and a second portion 46. All of the openings 80, 80 shown are formed as linear clearances, with both the openings 80 in the first portion 45 being formed parallel to one another, and the openings 80 in the second portion 46 being formed parallel to one another. The openings 80 in the first portion 45 run parallel in the horizontal direction or parallel to the width b of the sensor layer, whereas the openings 80 in the second portion 46 run parallel in the vertical direction or parallel to the length l of the sensor layer. The openings 80 in the second portion 46 run in a perpendicular direction in relation to the openings 80 in the first portion 45.

[0167] In FIG. 6c, likewise a number of openings 80, 80, 80 are shown in the form of elongate clearances. In a central portion 47, a number of linear openings 80 running in the vertical direction are shown, in the example shown eight openings, which are formed parallel to the length l of the sensor layer. These openings are surrounded by further openings 80, 80, forming a frame-like portion 48. First openings 80 are in this case formed parallel to the openings 80 of the central portion 47. Further openings 80 are formed perpendicularly in relation to the openings 80, 80. The openings 80 are of different lengths, so that the layer of the sensor 10 can be formed with a largest possible number of openings 80.

[0168] In FIG. 6d, a sensor layer with an elongate through-opening 80 is shown, the opening 80 running in a meandering manner.

[0169] In FIG. 6e, a further sensor layer with a number of vertically running openings 80 and a number of horizontally running openings 80 is shown. The vertical openings 80 and the horizontal openings 80 form a grid structure.

[0170] Apart from rectangular grid structures, other angular arrangements can also be produced, or geometries in which the grid or network structure has round, circular or oval shapes. Furthermore, corresponding combinations of the structures, which may be regular, periodic or irregular, can be created.

[0171] In FIG. 6f, a sensor layer with an elongate through-opening 80 is shown, the opening 80 running spirally. Apart from rectangular geometries, circular, oval geometries or combinations thereof can also be produced.

[0172] In each case a number of layers, which respectively have openings 80, 80, 80 according to an embodiment of FIG. 6a, 6b, 6c, 6d, 6e or 6f, are arranged in layers one over the other, so that passages in the form of elongate depressions 17 and 17 are respectively formed in a sensor.

[0173] As shown in FIG. 7a, a sensor 10 is introduced into a fluid flow in such a way that the direction of flow a of the particles does not impinge perpendicularly on the plane (x, y) of the electrode layers. The angle between the normal (z) to the plane (x, y) of the first electrode layer and the direction of flow of the particles is in this case at least 1 degree, preferably at least 10 degrees, particularly preferably at least 30 degrees. The particles can consequently be guided more easily into the elongate depressions 17, 17, and consequently more easily to the walls of the openings of the electrode layers 12, 50, 51 formed therein.

[0174] In FIG. 7b, a sensor 10 has thus been introduced into a fluid flow in such a way that the angle between the direction of flow a of the particles and the longitudinal axis x of the elongate depressions lies between 20 and 90 degrees.

[0175] In FIGS. 8a and 8b, a cross section which is taken perpendicularly to the sensor 10, that is to say beginning from the uppermost insulation or covering layer 21 to the substrate 11, is respectively shown. The sensors 10 of FIGS. 8a and 8b have four electrode layers, to be specific a first electrode layer 12, a second electrode layer 13 and also a third electrode layer 50 and a fourth electrode layer 51. Also formed are three insulation layers, to be specific a first insulation layer 14, a second insulation layer 60 and also a third insulation layer 61.

[0176] In the sensor 10 according to FIG. 8a, the cross-sectional profiles of two passages in the form of elongate depressions 17, 17 are shown. The left passage 17 has a V-shaped cross section or a V-shaped cross-sectional profile. The right passage 17 on the other hand has a U-shaped cross section or a U-shaped cross-sectional profile. The sizes of the openings or cross sections of the openings decrease from the covering layer 21 in the direction of the second electrode layer 13. The cross sections of the openings 29, 15, 73, 72, 71, 70 and 16 become increasingly smaller from the first cross section of an opening 29 in the direction of the lowermost cross-sectional opening 16.

[0177] With the aid of the V-shaped and U-shaped cross-sectional profiles, the measurements of round particles are improved.

[0178] In FIG. 8b it is also shown that the passages 17, 17 can have different widths. The left passage 17 has a width B1. The right passage 17 shown has a width B2. B1 is greater than B2. As a result of passages 17, 17 formed with different widths, size-specific measurements of the particles 30 can be carried out.

[0179] In FIG. 9, undercuts in insulation layers 14, 21, 60, 61 or set-back insulation layers 14, 21, 60, 61 are shown in cross section. In the case of round particles, the formation of level or smooth passage surfaces is unfavorable. The measurement of round particles can be improved by the formation of undercuts or set-back insulation layers.

[0180] The left passage 17 shown has a first insulation layer 14, a second insulation layer 60 and also a third insulation layer 61 and a covering layer 21, which also serves as an insulation layer. The insulation layers 14, 60, 61 and 21 have undercuts or clearances 90. The size of the openings 16, 71, 73 and 29 in the insulation layers 14, 60, 61 and 21 are consequently greater than the openings 70, 72 and 15 in the electrode layers 12, 50 and 51 that are respectively formed over and under the insulation layers 14, 60, 61 and 21.

[0181] This also applies in connection with the passage 17 shown on the right. In this case, the insulation layers 14, 16, 61 and 21 are formed as set-back in comparison with the electrode layers 50, 51 and 12. The openings 16, 71 or 73 in an insulation layer 14, 60 or 61 is formed larger in each case than an opening 70, 72 or 15 formed thereover in an electrode layer 50, 51 or 12 arranged over the respective insulation layer. Since the cross-sectional profile of the right passage 17 is formed in a V-shaped manner and the openings in all the layers 21, 12, 61, 51, 60, 50 and 14 become smaller in the direction of the substrate 11, the openings 16, 71, 73 and 29 in the insulation layers 14, 60, 61 and 21 are not of coinciding sizes.

[0182] It should be pointed out in connection with the sensors 10 shown in FIGS. 5, 8a, 8b and 9 that it is possible that only two uppermost electrode layers have to be made accessible within a passage. In other words, in a method, preferably according to the invention, a passage 17, 17, 17 that is merely formed with respect to the uppermost electrode layers 12 and 51 may be formed in a sensor 10.

[0183] It is also possible that a sensor 10 comprises a number of passages 17, 17, 17, at least a first passage merely reaching as far as the fourth electrode layer 51. The fourth electrode layer 51 or the second insulation layer 60 forms the bottom of this passage formed.

[0184] A second passage reaches as far as the third electrode layer 50. The third electrode layer 50 or the first insulation layer 14 forms the bottom of the passage formed. A third passage reaches as far as the second electrode layer 13. The second electrode layer 13 forms the bottom of the passage formed.

[0185] This embodiment can be carried out or can be formed independently of the features of the sensors 10 shown in FIGS. 5, 8a, 8b and 9.

[0186] The exploded representations of FIGS. 10a to 10d illustrate that a number of openings can be formed in a number of layers of the sensor 10, the layers being arranged one over the other in such a way that the openings are also formed one over the other, so that passages 17, 17 and 17 can be formed.

[0187] The sensors 10 shown comprise a substrate 11, a second electrode layer 13 arranged thereupon, a first electrode layer 12 and also a first insulation layer 14, which is arranged between the first electrode layer 12 and the second electrode layer 13. A first covering layer 21 and also a second covering layer 42 are formed on the first electrode layer 12. The first electrode layer 13 does not have an arrangement of openings for the forming of passages (see FIG. 10a).

[0188] Gaps 95 are formed within the second electrode layer 13. The first insulation layer 14 is arranged on the second electrode layer 13 in such a way that the openings 16 in the first insulation layer 14 are not arranged above the gaps 95.

[0189] On the other hand, the first electrode layer 12 is arranged in such a way that the openings 15 in the first electrode layer 12 are arranged above the openings 16 in the first insulation layer 14. With the aid of the openings 15 in the first electrode layer 12 and the openings 16 in the first insulation layer 14, passages 17 are formed, the side 31 of the first electrode layer 13 serving as the bottom 28 of the passages, in particular of blind holes and/or elongate depressions 17, 17.

[0190] In FIG. 10b, the arrangement of the openings 15 and 16 in relation to one another is shown in an enlarged representation. It can be seen that a first portion 45 and a second portion 46 with openings 15 and 16 are respectively formed both in the first insulation layer 14 and in the first electrode layer 12. The openings 15 and 16 arranged one over the other form in each case blind-hole-like passages 17.

[0191] Also in FIG. 10c, a first portion 45 and a second portion 46 are respectively formed in the first insulation layer 14 and also in the first electrode layer 12. Elongate openings 15, 16 are respectively formed in the portions 45 and 46, the elongate openings 15 and 16 being oriented in the same directions.

[0192] According to the representation of FIG. 10d it is possible that the elongate openings 15 and 16 can also be aligned perpendicularly in relation to the orientations shown in FIG. 10c.

[0193] It is pointed out that some of the sensors 10 shown (FIGS. 1a-1c, FIG. 4, FIG. 5, FIGS. 8a-b and FIG. 9) are in each case only shown as a detail. The measurement of the particles preferably takes place only in the passages 17, 17, 17 and not on side edges/side faces of the sensor and not on side faces/side edges of the sensor layers.

[0194] It is also possible that, in a further embodiment of the invention, all of the sensors 10 shown do not have an upper insulation layer/covering layer 21 and/or do not have a filter layer 27. If sensors 10 do not have an upper insulation layer/covering layer 21 and/or do not have a filter layer 27, large particles have no influence on the signal or on the measurement result.

[0195] With regard to a possible production process in connection with the sensors 10 according to the invention of FIGS. 1a-c, 2, 4, 5, 8a-b, 9 and FIGS. 10a-d, reference is made to the production possibilities already described, in particular to etching processes and/or laser machining processes.

[0196] At this stage it should be pointed out that all of the elements and components described above in connection with the embodiments according to FIGS. 1a to 10d are essential to the invention on their own or in any combination, in particular the details that are shown in the drawings.

LIST OF DESIGNATIONS

[0197] 10 Sensor [0198] 11 Substrate [0199] 12 First electrode layer [0200] 13 Second electrode layer [0201] 14 First insulation layer [0202] 15 Opening in first electrode layer [0203] 16 Opening in first insulation layer [0204] 17 Passage [0205] 17, 17 Elongate depression [0206] 18 Bonding agent layer [0207] 19 Side face of second electrode layer [0208] 20 Side of the first electrode layer [0209] 21 Covering layer [0210] 22 Side face of first electrode layer [0211] 23 Side face of insulation layer [0212] 24 Upper portion of covering layer [0213] 25 Side portion of covering layer [0214] 26 Side of covering layer [0215] 27 Porous filter layer [0216] 28 Bottom [0217] 29 Opening in covering layer [0218] 30, 30 Particle [0219] 31 Side of second electrode layer [0220] 32 Peripheral region of first electrode layer [0221] 33 Electrical contacting area of first electrode layer [0222] 34 Electrical contacting area of second electrode layer [0223] 35 Additional electrical contacting area of second electrode layer [0224] 36 Strip conductor loop [0225] 37 Side of insulation layer [0226] 40 Pore in first electrode layer [0227] 41 Pore in insulation layer [0228] 42 Second covering layer [0229] 45 First portion [0230] 46 Second portion [0231] 47 Central portion [0232] 48 Frame-like portion [0233] 50 Third electrode layer [0234] 51 Fourth electrode layer [0235] 60 Second insulation layer [0236] 61 Third insulation layer [0237] 70 Opening in third electrode layer [0238] 71 Opening in second insulation layer [0239] 72 Opening in fourth electrode layer [0240] 73 Opening in third insulation layer [0241] 80, 80, 80 Opening [0242] 90 Undercut [0243] 95 Gap [0244] a Direction of flow [0245] b Width of sensor layer [0246] l Length of sensor layer [0247] B1 Width of passage [0248] B2 Width of passage [0249] d Thickness of insulation layer [0250] x Longitudinal axis of the elongate depressions [0251] Angle between the normal to the electrode plane and the direction of flow [0252] Angle between the longitudinal axis and the direction of flow