Sensor for detecting electrically conductive and/or polarizable particles and method for adjusting such a sensor

Abstract

A sensor for detecting electrically conductive and/or polarizable particles, in particular for detecting soot particles, includes a substrate, a first electrode layer, and a second electrode layer, which is arranged between the substrate and the first electrode layer. An insulation layer is formed betweem the first electrode layer and the second electrode layer and at least one opening is formed in the first electrode layer and in the insulation layer, wherein the opening of the first electrode layer and the opening of the insulation layer are arranged one over the other at least in some segments in such a way that at least one passage to the second electrode layer is formed.

Claims

1. A sensor for detecting soot particles in a combustion exhaust stream, 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; an insulation layer disposed between the first electrode layer and the second electrode layer, and a first opening disposed in the first electrode layer and a second opening disposed in the insulation layer, wherein the first opening and the second opening are aligned to form a first passage to the second electrode layer, the first passage for receiving the soot particles; wherein the soot particles are detected by electrical conductivity between the first electrode layer and the second electrode layer; wherein the insulation layer laterally encloses the second electrode layer; wherein the insulation layer comprises a heat resistance of at least 850 C. in the combustion exhaust stream.

2. The sensor as claimed in claim 1, 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 insulation layer.

3. The sensor as claimed in claim 1, wherein the first electrode layer or the second 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.

4. The sensor as claimed in claim 3, 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, and wherein the second material has a higher etching resistance than the first material.

5. The sensor as claimed in claim 1, 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 insulation layer, the covering layer comprising ceramic, a glass, a metal oxide, or a combination thereof.

6. The sensor as claimed in claim 5, 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 insulation layer, the first electrode layer, or the covering layer.

7. The sensor as claimed in claim 6, wherein the blind hole has a square cross section with a surface area in a range of 33 m.sup.2-150150 m.sub.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.

8. The sensor as claimed in claim 1, further comprising a third opening disposed in the first electrode layer and a fourth opening disposed in the insulation layer, wherein the third opening and the fourth 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.

9. The sensor as claimed in claim 1, wherein the first electrode layer comprises a first electrical contact area, wherein the second electrode layer comprises a second 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, wherein the second electrical contact area is not overlaid by the insulation layer and the first electrode layer, wherein the first electrical contact area is not overlain by a covering layer, and wherein each electrical contact area is connected to a terminal pad.

10. The sensor as claimed in claim 9, wherein the first electrode layer or the second 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 or the second electrode layer comprising the strip conductor loop comprises further a third electrical contact area not overlaid by the insulation layer or an electrode layer, and wherein the third electrical contact area is connected to the terminal pad.

11. The sensor for detecting soot particles of claim 1, wherein the insulation layer consists of a thermally stable material with a high insulation resistance.

12. The sensor for detecting soot particles of claim 1, wherein the insulation layer is selected from the group consisting of 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.

13. The sensor as claimed in claim 1, wherein the first opening 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 insulation layer or the first electrode layer.

14. The sensor as claimed in claim 13, wherein the blind hole has a square cross section with a surface area in a range of 33 m.sup.2-150 150 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.

15. The sensor as claimed in claim 1, wherein the first opening is disposed in a top surface of the first electrode, the top surface being planar.

16. The sensor as claimed in claim 1, wherein a cross-sectional area of the first opening and a cross-sectional area of the second opening are identical.

17. A method of making a sensor for detecting soot particles in a combustion exhaust stream, 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; an insulation layer disposed between the first electrode layer and the second electrode layer, and a first opening disposed in the first electrode layer and a second opening disposed in the insulation layer, wherein the first opening and the second opening are aligned to form a first passage to the second electrode layer; wherein the insulation layer laterally encloses the second electrode layer; the method comprising the steps of: laminating the first electrode layer, the second electrode layer, and the insulation layer to form a laminate, the insulation layer being disposed between the first electrode layer and the second electrode layer, subsequently forming a passage through the first electrode layer and the insulation layer, and ending the passage to have a bottom formed by a portion of the second electrode layer, the passage for receiving the soot particles; wherein the soot particles are detected by electrical conductivity between the first electrode layer and the second electrode layer; wherein the insulation layer comprises a heat resistance of at least 850 C. in the combustion exhaust stream.

18. The method as claimed in claim 17, wherein the passage is formed as a blind hole by etching, plasma-ion etching, or successive etching adapted to each layer being etched.

19. The method as claimed in claim 17, wherein the passage is formed as a blind hole by etching, plasma-ion etching, or successive etching adapted to each layer being etched, and wherein the insulation layer is etching-resistant layer, the blind hole being formed in the insulation layer by a conditioning process with phase conversion of the insulation layer.

20. The method as claimed in claim 17, wherein the passage is partially formed as a blind hole by laser machining, and wherein laser machining is performed by a laser source, wavelength, a laser pulse frequency adapted individually to each layer being machined.

21. A method of making a sensor for detecting soot particles in a combustion exhaust stream, 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; an insulation layer disposed between the first electrode layer and the second electrode layer, and a first opening disposed in the first electrode layer and a second opening disposed in the insulation layer, wherein the first opening and the second opening are aligned to form a first passage to the second electrode layer, the first passage for receiving the soot particles; wherein the soot particles are detected by electrical conductivity between the first electrode layer and the second electrode layer; wherein the insulation layer laterally encloses the second electrode layer; the method comprising the steps of: laminating the first electrode layer, the second electrode layer, and the insulation layer to form a laminate, the insulation layer being disposed between the first electrode layer and the second electrode layer, wherein the insulation layer and the first electrode 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; wherein the insulation layer comprises a heat resistance of at least 850 C. in the combustion exhaust stream.

22. A sensor for detecting soot particles in a combustion exhaust stream, 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; an insulation layer disposed between the first electrode layer on a side opposite to the insulation layer; and a first opening disposed in the first electrode layer and a second opening disposed in the insulation layer; wherein the first opening and the second opening are aligned to form a first passage to the second electrode layer, the first passage for receiving the soot particles from the combustion exhaust stream; wherein the soot particles are detected by electrical conductivity between the first electrode layer and the second electrode layer; wherein the insulation layer laterally encloses a side portion of the second electrode layer; and wherein the insulation layer comprises a heat resistance of at least 850 C. in the combustion exhaust stream.

23. The sensor as claimed in claim 22, further comprising a covering layer disposed on a side of the first electrode layer opposite to the insulation layer; wherein the covering layer comprises a heat resistance of at least 850 C. in an exhaust stream.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in more detail below on the basis of exemplary embodiments with reference to the accompanying schematic drawings, in which:

(2) FIGS. 1a-c show sectional representations of various embodiments of sensors for detecting electrically conductive and/or polarizable particles;

(3) FIG. 2 shows a perspective plan view of a sensor according to the invention;

(4) FIG. 3 shows a possible formation of a second electrode layer; and

(5) FIG. 4 shows a sectional representation of a further embodiment of a sensor for detecting electrically conductive and/or polarizable particles.

DETAILED DESCRIPTION OF THE INVENTION

(6) The same reference numerals are used below for parts that are the same and parts that act in the same way.

(7) FIG. 1a 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.

(8) 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.

(9) 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).

(10) 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.

(11) 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.

(12) 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.

(13) 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.

(14) 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.

(15) 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.

(16) 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.

(17) 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.

(18) 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.

(19) 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).

(20) 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.

(21) 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.

(22) 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.

(23) 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.

(24) In a further embodiment of the invention it is conceivable that the covering layer 21 also laterally encloses the substrate 11.

(25) 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.

(26) 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.

(27) 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.

(28) 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.

(29) 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.

(30) 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).

(31) 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.

(32) 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.

(33) 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.

(34) 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.

(35) 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.

(36) 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.

(37) With regard to a possible production process in connection with the sensors 10 according to the invention of FIGS. 1a-c, 2 and 4, reference is made to the production possibilities already described, in particular etching processes.

(38) 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. 1 to 4 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

(39) 10 Sensor

(40) 11 Substrate

(41) 12 First electrode layer

(42) 13 Second electrode layer

(43) 14 Insulation layer

(44) 15 Opening in first electrode layer

(45) 16 Opening in insulation layer

(46) 17 Passage

(47) 18 Bonding agent layer

(48) 19 Side face of second electrode layer

(49) 20 Side of the first electrode layer

(50) 21 Covering layer

(51) 22 Side face of first electrode layer

(52) 23 Side face of insulation layer

(53) 34 Upper portion of covering layer

(54) 25 Side portion of covering layer

(55) 26 Side of covering layer

(56) 27 Porous filter layer

(57) 28 Bottom of blind hole

(58) 29 Opening in covering layer

(59) 30, 30 Particle

(60) 31 Side of second electrode layer

(61) 32 Peripheral region of first electrode layer

(62) 33 Electrical contacting area of first electrode layer

(63) 34 Electrical contacting area of second electrode layer

(64) 35 Additional electrical contacting area of second electrode layer

(65) 36 Strip conductor loop

(66) 37 Side of insulation layer

(67) 40 Pore in first electrode layer

(68) 41 Pore in insulation layer

(69) d Thickness of insulation layer