CROSS REFERENCE TO RELATED APPLICATIONS

This Utility Patent Application claims priority under 35 U.S.C. § 371 to International Application Serial No. PCT/EP2017/083701, filed Dec. 20, 2017, which claims the benefit of EP Patent Application No. EP 16206130.3, filed Dec. 22, 2016; which are both incorporated herein by reference.

The invention relates to a sensor for detecting electrically conductive and/or polarizable particles, in particular a soot sensor, comprising a substrate, an electrode layer formed on the substrate with at least two spatially separated and intermeshing electrodes, wherein at least one covering layer is formed on the side of the electrode layer facing away from the substrate. Furthermore, the invention relates to a method for the production of a sensor in accordance with the invention, in particular a soot sensor.

Sensors, for example with comb-like electrode structures, are used in order to measure soot concentrations in an exhaust gas flow from internal combustion engines. An exemplary electrode structure or an exemplary sensor is described in WO 2006/111386 A1. The drop in the electrical resistance due to the increasing soot deposit is measured between the electrodes. The sensor can be regenerated when the soot deposits are too severe by constructing a heating element on or in the soot sensor.

In order to increase the sensitivity of the soot sensor, the intermeshing electrodes should have as small a distance separating them as possible. In WO 2014/135450 A1, a small separation of this type is produced by individualizing the platinum electrodes by laser ablation of the platinum layer which has been applied over the entire surface, and thus electrode separations of less than 50 μm can be produced in this manner.

Because the concentration of soot in the exhaust gas flow from internal combustion engines is reducing, increasing the sensitivity of the sensor further would be desirable, without at the same time system modifying the sensor size or the principle of sensor production used up to now.

The underlying objective of the invention is to provide a further developed sensor, in particular a soot sensor, which has a higher sensitivity. A further objective of the present invention is to provide a further developed method for the production of a sensor in accordance with the invention.

In accordance with the invention, in respect of the sensor this objective is achieved by the features of claim1. In respect of the method for the production of a sensor, in particular a soot sensor, the objective is achieved by the features of claim9.

The invention arises from the notion of providing a sensor for the detection of electrically conductive and/or polarizable particles, in particular a soot sensor, wherein the sensor comprises a substrate, an electrode layer formed on the substrate with at least two mutually spatially separated and intermeshing electrodes, wherein at least one covering layer is formed on the side of the electrode layer facing away from the substrate.

In accordance with the invention, a plurality of openings is provided in the covering layer, which expose at least a section of a surface of an electrode, in particular of the at least two electrodes. It has been shown that the sensitivity of the sensor is increased when the covering layer, which covers large portions of the sensors, in particular large portions of the electrode layer, is structurized in an appropriate manner, in particular laser-structurized.

The substrate is preferably produced from aluminium oxide (Al2O3) and/or zirconium oxide (ZrO2) and/or from zirconium oxide (ZrO2) with insulation and/or other oxide ceramics. In a preferred embodiment of the invention, the substrate has a thickness of 0.5-1.0 mm.

An electrode layer is provided on one side of the substrate. This electrode layer comprises at least two electrodes which are spatially separated from each other and intermeshing.

Electrodes of this type may be comb electrodes and/or intermeshing electrodes. The at least two electrodes do not touch each other. Moreover, electrode sections of a first electrode are disposed in recesses of electrode sections of the second electrode, but without coming into contact with each other. Preferably, at least one of the electrodes is produced from platinum. The thickness of the electrode layer is preferably 0.5-20.0 μm.

The covering layer may, for example, be formed from aluminium oxide (Al2O3) and/or silicon dioxide (SiO2) and/or glass. Preferably, the covering layer has a thickness of 0.5 μm-20.0 μm.

In accordance with the invention, a plurality of openings is provided in the covering layer which are preferably in the form of slots. The term “openings in the form of slots” should be understood to mean that their length is greater than the width.

It is possible for the openings in the form of slots to be configured so as to be parallel to each other. In particular, it is possible for the openings in the form of slots to have a uniform pattern. This means that a plurality of rows of openings in the form of slots are disposed one beside the other, wherein the rows preferably each have the same distances between them.

The slot width of the openings is preferably between 1.0 μm and 50.0 μm.

The electrodes preferably comprise a plurality of longitudinal finger sections. In this regard, the finger sections of the at least two electrodes are preferably disposed parallel to each other.

The longitudinal extent of the openings in the form of slots may be parallel and/or perpendicular in configuration to the longitudinal extent of the finger sections, wherein the longitudinal extents of all of the openings in the form of slots are preferably parallel to each other in configuration. In other words, in a preferred embodiment of the invention, the covering layer is configured in a manner such that all of the longitudinal extents of the openings in the form of slots are either parallel or perpendicular to the longitudinal extent of the finger sections.

Particularly preferably, the openings in the form of slots are introduced into the covering layer in a manner such that the longitudinal extents of the openings in the form of slots are configured so as to be perpendicular to the finger sections of the electrodes. In other words, the longitudinal extents of the openings in the form of slots are configured so as to be perpendicular to the longitudinal extent of the finger sections.

Preferably, sections of the covering layer remain between the openings in the form of slots.

When using a sensor in accordance with the invention, filaments, in particular soot filaments, i.e. successive rows of particles or soot particles, are formed between the at least two electrodes. Filaments or soot filaments of this type grow from a negatively polarized electrode to a positively polarized electrode, preferably in the direction in which the gas is flowing. Preferably, a sensor is disposed in a flow of gas in a manner such that the direction of the gas flow runs perpendicular to the longitudinal extent of the finger sections. The sections formed between the openings in the form of slots or the remaining sections of the covering layer mechanically stabilize the described soot filaments. This results in a preferential filament formation, and thus in an enhanced sensitivity.

The filaments, in particular the soot filaments, may be described as chains of concatenated particles, in particular as chains of concatenated soot particles.

The formation of filaments, in particular soot filaments between adjacent electrodes, in particular between adjacent comb electrodes, reduces the electrical resistance if the filament makes contact with both electrodes. The sensitivity of the sensor is determined by the formation of the (soot) filaments.

In the particular case of the particularly preferred embodiment in which the longitudinal extents of the openings in the form of slots are configured so as to be perpendicular to the longitudinal extent of the finger sections, soot filaments may be formed or may grow along the remaining sections of the covering layer on the direct path between the at least two electrodes.

The openings, in particular the openings in the form of slots, may expose at least a section of the side faces of the finger sections and/or at least a section of the upper side of the finger sections. In other words, the uncovered or exposed surface of at least one electrode is a section of the upper side and/or of the side face of the electrode.

The “side faces of the finger sections” should be understood to mean the faces of the electrode which are configured so as to be (essentially) perpendicular to the substrate or perpendicular to the covering layer. Preferably, the side faces are configured so as to be (essentially) parallel to each other. The “upper side of the finger section” should be understood to mean the side which faces in the direction of the covering layer. At least on an intermediate product of the sensor or in an intermediate stage of the production of the sensor, the upper sides of the finger sections are covered, preferably completely covered, with the covering layer.

In a further embodiment of the invention, the openings, in particular in the form of slots, may expose at least sections of the edge regions of the upper side of the finger sections. The “edge region of the upper side” should be understood to mean the region of the upper side which is joined to the side faces of the finger sections.

In a further embodiment of the invention, at least sections of the surfaces of the exposed electrode sections may be coated with glass fibres and/or with particles, in particular with aluminium oxide particles (Al2O3) and/or with silicon dioxide particles (SiO2).

In a further aspect, the invention concerns a method for the production of a sensor in accordance with the invention, in particular a soot sensor in accordance with the invention. The method in accordance with the invention is characterized by the following steps of the method:a) providing a substrate,b) forming an electrode layer with at least two spatially separated and intermeshing electrodes on the substrate,c) applying a covering layer to the electrode layer,d) introducing openings, in particular 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.

In step d), i.e. when introducing openings, in particular in the form of slots, an ultrashort pulse laser is used in particular. In particular, the ultrashort pulse laser is a picosecond or femtosecond laser. With an ultrashort pulse laser of this type, it is possible to introduce openings in the form of slots into the covering layer with line widths of 1.0 to 50.0 μm.

When forming an electrode layer, it is initially possible in step b) to firstly apply a planar electrode layer to the substrate and then to structurize the electrode layer. A planar electrode layer may, for example, be applied by using a deposition method such as, for example, screen printing and/or sputtering and/or thermal evaporation. The subsequent structurization of the electrode layer may, for example, be carried out using a laser, in particular using an ultrashort pulse laser. In particular, in order to produce small distances between the individual electrodes, in particular between the individual finger sections of the electrodes, advantageously, an ultrashort pulse laser is used.

Alternatively, it is possible to produce the electrode layer by means of screen printing. In particular, metal pastes may initially be applied using screen printing in order to form a subsequent electrode structure.

The covering layer, in particular a ceramic covering layer, may be applied using screen printing and/or thermal evaporation and/or using an ADM (Aerosol Deposition Method). In accordance with the invention, following application of the covering layer, openings, in particular openings in the form of slots, are introduced using an ultrashort pulse laser.

Particularly preferably, the covering layer with a plurality of openings, in particular openings in the form of slots, is a laser structurized covering layer.

A further, subordinate aspect of the invention concerns the use of a sensor in accordance with the invention for the detection of electrically conductive and/or polarizable particles, in particular for the detection of soot particles.

In particular, the invention concerns the use of a sensor in accordance with the invention in an exhaust gas system, in particular in an exhaust gas system, of an internal combustion engine.

The sensor in accordance with the invention is preferably disposed in the exhaust gas pipe in a manner such that the direction of gas flow is orientated perpendicular to the longitudinal extents of the finger sections of the electrodes. The (soot) filaments described above are in particular formed from a negatively polarized electrode in the direction of the positively polarized electrode in the direction of flow of the gas. The sections of the covering layer which are formed between the openings, in particular openings in the form of slots, mechanically stabilise the (soot) filaments. Because of this, the preferential (soot) filament formation occurs. This brings about an enhanced sensitivity of the sensor in accordance with the invention.

Particularly preferably, the sensor in accordance with the application in accordance with the invention or the disposition in the exhaust gas pipe is configured in a manner such that the longitudinal extents of the openings in the form of slots are perpendicular in configuration to the longitudinal extent of the finger sections. In a configuration of the openings in the form of slots of this type, the (soot) filaments can grow along the remaining covering layer sections in a path which is directly between the at least two electrodes. The remaining covering layer sections may also be described as aluminium oxide (Al2O3) bridges if the covering layer consists of aluminium oxide.

The (soot) filaments described preferably form along the edges and/or comb-like bridges of the exposed covering layer. Furthermore, the (soot) filaments are formed in the “lee” or in the dead zone of the flow of local peaks on the topology of the covering layer.

