Soot sensor and method for producing a soot sensor

Abstract

One aspect relates to a soot sensor for detecting electrically conductive and/or polarizable particles, including a substrate, an electrode layer that is formed on the substrate and that includes at least two spatially separated electrodes that engage into each other. At least one cover layer is formed on the side of the electrode layer facing away from the substrate. Multiple openings are formed in the cover layer, the openings at least partially exposing a surface of one electrode of the at least two electrodes.

Claims

1. A soot sensor for detecting electrically conductive and/or polarizable particles comprising: a substrate having a surface; at least two spatially separated and intermeshing electrodes formed on the surface of the substrate; at least one covering layer formed directly on upper surfaces of the at least two spatially separated and intermeshing electrodes, the upper surfaces facing a same direction as the surface of the substrate; and a plurality of openings provided in the covering layer that expose at least a section of a surface of an electrode of the at least two electrodes, the substrate, electrodes, covering layer and openings forming the soot sensor; wherein the at least two electrodes respectively comprise a plurality of longitudinal finger sections; wherein the plurality of openings are configured as slots and expose at least a section of an upper side of the finger sections; and wherein a longitudinal extent of the openings configured as slots are perpendicular to a longitudinal extend of the finger sections.

2. The sensor of claim 1, wherein the openings are configured in the shape of slots, and wherein the slot width of the openings is between 1.0 μm and 50.0 μm.

3. The sensor of claim 1, wherein the longitudinal extents of all of the openings in the form of slots are parallel to each other in configuration.

4. The sensor of claim 1, wherein the openings expose at least a section of the side faces of the finger sections.

5. The sensor of claim 4, wherein the openings expose at least sections of the edge regions of the upper side of the finger sections.

6. The sensor of claim 1, wherein at least sections of the surfaces of the exposed electrode sections are coated with at least one of glass fibres, particles, Al.sub.2O.sub.3particles and/or SiO2 particles.

7. The sensor of claim 1, wherein at least one electrode comprises platinum.

8. A method of producing a soot sensor for detecting particles, the method comprising: providing a substrate; forming an electrode layer on a surface of the substrate; forming at least two spatially separated and intermeshing electrodes from the electrode layer; applying a covering layer directly to upper surfaces of the at least two spatially separated and intermeshing electrodes, the upper surfaces facing a same direction as the surface of the substrate; and introducing openings in the form of slots into the covering layer using a laser in a manner such that at least a section of the surface of at least one electrode is exposed and thereby forming the soot sensor; wherein the at least two electrodes respectively comprise a plurality of longitudinal finger sections; wherein the plurality of openings configured as slots expose at least a section of an upper side of the finger sections; and wherein a longitudinal extent of the openings configured as slots are perpendicular to a longitudinal extend of the finger sections.

9. The method of claim 8 further comprising using an ultrashort pulse laser to introduce openings in the covering layer.

10. The method of claim 8, wherein forming the at least two spatially separated and intermeshing electrodes from the electrode layer is carried out using an ultrashort pulse laser.

11. The method of claim 8, wherein forming the electrode layer comprises screen printing the electrode layer.

12. The method of claim 8, wherein applying the covering layer comprises use of at least one of screen printing, thermal evaporation, and ADM (Aerosol Deposition Method).

Description

(1) The invention will now be described with the aid of exemplary embodiments with the aid of the accompanying diagrammatic drawings.

(2) In the drawings:

(3) FIGS. 1a-6b show various stages and steps of the method for the production of a sensor in accordance with the invention, wherein the steps of the method in accordance with FIGS. 6a and 6b represent alternatives to the steps 5a and 5b of the method;

(4) FIG. 7 shows a sensor in accordance with the invention in cross section; and

(5) FIG. 8 shows a sensor in accordance with the invention in use.

(6) In the following, identical parts and identically acting parts use identical reference numerals.

(7) In FIGS. 1a-6b, the views of the sensor in accordance with the invention using the letter “a” show the respective steps of the method in a top view. The views using the letter “b” show cross sections through the sensor in accordance with the respective stage or step of the method. It should be noted here that the cross sectional views are not to scale, but rather, that the applied layers are shown greatly enlarged in the direction of the perpendicular to the surface of the substrate.

(8) Firstly, the substrate 20 is shown in FIG. 1a. The substrate 20 may be produced from aluminium oxide (Al2O3) and/or zirconium oxide (ZrO2) and/or from zirconium oxide (ZrO2) with an insulation. The thickness D1 which can be seen in FIG. 1b may be 0.5-1.0 mm.

(9) In the step of the method shown in FIGS. 2a and 2b, firstly, a planar electrode layer 30 is applied to the side 21 of the substrate 20. Preferably, the electrode layer 30 is a layer of platinum. This layer may be applied in the context of a screen printing method and/or as a result of a sputtering method and/or by means of a chemical evaporation method. The thickness D2 of the electrode layer 30 may be 0.5-20.0 μm.

(10) FIGS. 3a and 3b show the structurization of the electrode layer 30. In this regard, two electrodes, namely a first electrode 31 and a second electrode 32, are produced by means of laser ablation. The two electrodes 31 and 32 are formed by removing individual sections of the previously planar electrode layer 30.

(11) The first electrode 31 comprises two finger sections 33. The second electrode 32 comprises three finger sections 34. The two electrodes 31 and 32 intermesh. In this regard, the finger sections 33 and 34 of the electrodes 31 and 32 do not come into contact. The finger sections 33 and 34 of the two electrodes 31 and 32 are essentially parallel to one another in configuration. Preferably, separations of 1.0-50.0 μm are formed between the finger sections 33 and 34. In particular, the separations A between the finger sections 33 and 34 are the same size. The electrodes 31 and 32 may also be described as interdigitated electrodes.

(12) Furthermore, the longitudinal extents LE of the finger sections 33 and 34 can be seen; they are parallel to each other in configuration.

(13) As can be seen in FIGS. 4a and 4b, a covering layer 40 is then applied to the electrode layer 30. The covering layer 40 may consist of aluminium oxide (Al2O3) and/or silicon dioxide (SiO2) and/or glass. The covering layer 40 is applied, for example, by means of a screen printing method or by means of a thermal evaporation or in the context of an ADM (Aerosol Deposition Method).

(14) The covering layer 40 is applied to the electrode layer 30 in a manner such that both the upper sides 35 of the electrodes 31 and 32 and also the side faces 36 of the electrodes 31 and 32 (see FIGS. 3a and 3b in this regard) are covered by the covering layer. In this regard, the covering layer 40 may consist of a plurality of sections disposed one above the other. Namely, formed by a first section 41 and a second section 42. The two sections 41 and 42 are formed in a manner such that a uniform thickness D3 of the covering layer 40 is applied. In this regard, the thickness of the section 42 which is applied to the side 21 of the substrate 20 is identical to the thickness D3 of the first section 41 which is applied to the upper side 35 of the electrodes 31 and 32. The thickness D3 of the covering layer 40 is preferably 0.5-20.0 μm. Because of the consistent uniform layer thickness D3, protrusions 43 are formed in the covering layer 40.

(15) FIG. 5a shows the step d) in accordance with the invention. Here, openings in the form of slots 50 are introduced into the covering layer 40. The openings 50 are introduced into the covering layer 40 by means of an ultrashort pulse laser. In the exemplary embodiment shown in FIGS. 5a and 5b, the openings in the form of slots 50 are introduced into the covering layer 40 in a manner such that the longitudinal extents LO of the openings in the form of slots 50 are parallel in configuration to the longitudinal extents LE of the electrodes 31 and 32 (see FIGS. 3a and 3b). The openings in the form of slots 50 are parallel in configuration to each other. At least sections of the upper sides 35 of the electrodes 31 and 32 are exposed by the openings in the form of slots 50. In particular, the edge regions 39 of the upper sides 35 are exposed. The edge region 39 is constituted by the sections of the upper side 35 which border the side faces 36 of the electrodes 31 and 32. By introducing the openings in the form of slots 50, the widths of the protrusions 43 and/or the sections of the covering layer 42 between the electrodes 31 and 32 are reduced.

(16) FIGS. 6a and 6b show a further embodiment of the invention. In this case, the longitudinal extents LO run perpendicular to the longitudinal extents LE of the electrodes 31 and 32. Preferably, the openings in the form of slots 50 are consistent in configuration. FIG. 6 shows a cross section along the arrow indicated in FIG. 6a. The openings in the form of slots 50 thus not only expose the upper sides 36 of the electrodes 31 and 32, but also the sides 21 of the substrate 20. Thus, in FIG. 6b, not only the upper sides 35 of the electrodes 31 and 32, but also the side faces 36 of the electrodes 31 and 32 are exposed.

(17) FIG. 7 shows a further embodiment of the invention, which is similar to that in FIG. 5b. The enlarged cross section through a sensor in accordance with the invention shows that between the electrodes 31 and 32, sections 42 of the covering layer 40 can remain despite forming openings in the form of slots 50 which in the example shown are introduced by means of ultrashort pulse laser 60. In contrast to the embodiment shown in FIG. 5b, here, the side faces of the electrodes 31 and 32 and the side faces of the remaining structures 42 and 43 of the covering layer are not perpendicular in configuration, but are inclined to the surface of the substrate 20. The edges of the electrodes 31 and 32 and the edges of the remaining structures 42 and 43 of the covering layer are rounded.

(18) A sensor 10 in accordance with the invention is also shown in FIG. 8. The direction of flow of gas S can be seen. In accordance with the invention, the sensor 10 is disposed in the flow of gas or in relation to the direction of flow of gas S in a manner such that the longitudinal extents LE of the electrodes 31 and 32 are perpendicular in orientation to the direction of flow S. The first electrode 31 in the example shown is negatively polarized, whereas the second electrode 32 is positively polarized.

(19) The openings in the form of slots 50 can also be seen; their longitudinal extents LO are configured so as to be perpendicular to the longitudinal extent LE. Because of the openings in the form of slots 50, the upper sides 35 of the electrodes 31 and 32 as well as the side faces 36 of the electrodes 31 and 32 are exposed. In the example shown, the openings in the form of slots 50 are consistent in configuration. Sections 45 of the covering layer 40 are formed between the openings in the form of slots 50. These sections 45 form comb-like prominences. Filaments 70 are particularly preferentially formed along them on the sensor 10. The stationary comb-like prominences of the covering layer 45 can act to mechanically stabilise the filaments 70 as they are formed.

(20) The filaments 70 are considered to be chains of concatenated particles, in particular chains of concatenated soot particles. The laser structurized covering layer 40 in accordance with the invention promotes the formation of filaments 70 of the soot particles which are formed between the electrodes 31 and 32. The electrodes 31 and 32 may thus be bridged together directly in a straight line by means of the sections 45. The sensitivity of the sensor in accordance with the invention is considerably increased compared with known sensors.

LIST OF REFERENCE NUMERALS

(21) 10 sensor 20 substrate 21 side 30 electrode layer 31 first electrode 32 second electrode 33 finger section of first electrode 34 finger section of second electrode 35 upper side of electrode 36 side face of electrode 39 edge region of upper side 40 covering layer 41 section of covering layer 42 section of covering layer 43 protrusion 45 section of covering layer 50 openings in the form of slot 60 ultrashort pulse laser 70 filament A separation of finger section D1 thickness of substrate D2 thickness of electrode D3 thickness of covering layer LE longitudinal extent of electrode LO longitudinal extent of opening S direction of flow of gas