US20170356868A1

US20170356868A1 - 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

Info

Publication number: US20170356868A1
Application number: US15/539,522
Authority: US
Inventors: Tim Asmus; Karlheinz Wienand; Stefan Dietmann; Martin Kunz
Original assignee: Heraeus Sensor Technology GmbH
Current assignee: Yageo Nexensos GmbH
Priority date: 2014-12-23
Filing date: 2015-12-23
Publication date: 2017-12-14
Also published as: TWI621841B; WO2016102178A1; TWI631325B; CN107407624B; WO2016102636A1; CN107532986A; CN107430053B; JP2018500567A; US20180328832A1; TW201629459A; CN107532986B; KR20170101270A; EP3237879A1; EP3237881A1; EP3237881B1; JP2018500566A; JP6514336B2; JP2018508751A; EP3237880B1; EP3237880A1

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.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a sensor for detecting electrically conductive and/or polarizable particles, in particular for detecting soot particles. The invention also relates to a sensor system, to a method for operating a sensor, to a method for producing a sensor for detecting electrically conductive and/or polarizable particles and to a use of a sensor of this type.

2. Discussion of the Related Art

The prior art discloses sensors comprising a sensor carrier, with electrodes and heating structures being arranged on this sensor carrier in a planar arrangement. In a detecting mode of operation, polarizable and/or electrically conductive particles are deposited on this planar arrangement. The deposited particles bring about a reduction in the resistance between the electrodes, this drop in the resistance being used as a measure of the mass of deposited particles. When a predefined threshold value with respect to the resistance is reached, the sensor arrangement is heated by the heating structures, so that the deposited particles are burned and, after the cleaning process, the sensor can be used for a further detection cycle.
DE 10 2005 029 219 A1 gives a description of a sensor for detecting particles in an exhaust-gas flow of internal combustion engines, the electrode, heater and temperature-sensor structures having been applied to a sensor carrier in a planar arrangement. One disadvantage of this sensor arrangement is that the electrodes to be bridged have a necessary minimum length in order to be able to arrive at an acceptable sensitivity range when measuring conductive or polarizable particles, such as for example soot. However, a certain size of the sensor component is necessary for this, in order to be able to arrange the minimum length for the electrodes to be bridged. This is accompanied by corresponding cost disadvantages in the production of these sensor components.
The invention is based on the object of providing a further-developed sensor for detecting electrically conductive and/or polarizable particles, in particular for detecting soot particles, the sensor being minimized with regard to its size, so that the aforementioned disadvantages can be overcome.
The object of the present invention is also to provide a sensor system, a method for operating a sensor and a method for producing a sensor of this type.

SUMMARY OF THE INVENTION

This object is achieved according to the invention by a sensor for detecting electrically conductive and/or polarizable particles, in particular for detecting soot particles.
The invention is based on the idea of providing a sensor for detecting electrically conductive and/or polarizable particles, in particular for detecting soot particles, comprising a substrate and at least two electrode layers, a second electrode layer being arranged between the substrate and a first electrode layer, at least one insulation layer being formed between the first electrode layer and the second electrode layer and at least one opening being respectively formed in the first electrode layer and in the at least one insulation layer, the opening in the first electrode layer and the opening in the insulation layer being arranged at least in certain portions one over the other in such a way that at least one passage, in particular in the form of an elongate depression, to the second electrode layer is formed.
In other words, a sensor is made available, at least a first and a second electrode layer being arranged horizontally one over the other and at least one insulation layer being formed between the two electrode layers. In order to form a passage to the second electrode layer, so that particles to be detected, in particular soot particles, can reach the second electrode layer with the aid of the passage, both the first electrode layer and the at least one insulation layer respectively have at least one opening, the opening in the first electrode layer and the opening in the insulation layer being arranged at least in certain portions one over the other, so that the passage is formed or can be formed.
Particles can accordingly reach the second electrode layer by way of at least one passage only from one side of the sensor, to be specific from the side of the sensor that is made to be the closest to the first electrode layer. The electrically conductive and/or polarizable particles accordingly lie on a portion of the second electrode layer.
The sensor according to the invention comprises at least two electrode layers and at least one insulation layer, at least one insulation layer preferably always being formed between two electrode layers. It is possible that the sensor comprises more than two electrode layers and more than one insulation layer, also in this situation one insulation layer, optionally also more than one insulation layer, always being formed between two electrode layers.
The electrode layers are arranged one over the other, in particular in layers one over the other, the electrode layers being respectively kept at a distance from one another by means of at least one insulation layer. In other words, the electrode layers do not lie in one plane.
An elongate depression should be understood as meaning such a depression that is longer than it is wide. In other words, the length of the depression is greater than the width of the depression. An elongate depression may also be referred to as a groove or as a trench or as a channel.
The sensor according to the invention may for example comprise at least three electrode layers and at least two insulation layers, an insulation layer preferably always being formed between two electrode layers.
An insulation layer may also consist of two or more sublayers, which may be arranged next to one another and/or one over the other. Two or more sublayers of an insulation layer may consist of different materials and/or comprise different materials.
An electrode layer may also consist of two or more sublayers, which may be arranged next to one another and/or one over the other. Two or more sublayers of an electrode layer may consist of different materials and/or comprise different materials.
It is possible that the sensor comprises more than three electrode layers and more than two insulation layers, also in this situation an insulation layer preferably always being formed between two electrode layers. From now on, the expression “at least third electrode layer” should be understood as meaning that a fourth and/or fifth and/or sixth and/or seventh and/or eighth and/or ninth and/or tenth electrode layer may also be intended instead of the stated third electrode layer.
From now on, the expression “at least second insulation layer” should be understood as meaning that a third and/or fourth and/or fifth and/or sixth and/or seventh and/or eighth and/or ninth insulation layer may also be intended instead of the stated first or second insulation layer.
The sensor according to the invention may in other words comprise a laminate which comprises at least three electrode layers and at least two insulation layers. The electrode layer closest to the substrate is referred to as the second electrode layer, the electrode layer at the maximum distance from the substrate is referred to as the first electrode layer. Between the first electrode layer and the second electrode layer there is for example at least a third electrode layer, at least one insulation layer being respectively formed between two electrode layers.
Preferably, the opening in the at least first electrode layer is formed at a distance from the peripheral region of the first electrode layer and the opening in the at least one insulation layer is formed at a distance from the peripheral region of the insulation layer. The openings are accordingly preferably not formed in a peripheral position, or not formed at the side peripheries of the layers concerned.
The first electrode layer and the second electrode layer are insulated from one another by the insulation layer located in between. Such a structure allows a very sensitive sensor of a smaller overall size in comparison with sensors of the prior art to be formed.
The second electrode layer, formed for example with a flat extent, is indirectly or directly connected to the substrate. An indirect connection of the second electrode layer to the substrate may take place by means of a bonding agent, in particular a bonding agent layer. The bonding agent may also be formed in an insular manner between the substrate and the second electrode layer. For example, a drop-like formation of the bonding agent/the bonding agent layer is possible. A bonding agent layer may be formed between the second electrode layer and the substrate.
The bonding agent, in particular the bonding agent layer, may for example consist of an aluminum oxide (Al₂O₃) or a silicon dioxide (SiO₂) or a ceramic or a glass or any desired combinations thereof. The bonding agent layer is preferably formed very thin, and consequently only has a small thickness.
At least one insulation layer may have a thickness of 0.1 to 50 μm, in particular of 1.0 μm to 40 μm, in particular of 5.0 μm to 30 μm, in particular of 7.5 μm to 20 μm, in particular of 8 μm to 12 μm. With the aid of the thickness of the insulation layer(s), the respective distance of a first electrode layer from another electrode layer is set. The sensitivity of the sensor can be increased by reducing the distance between the preferably flat-extending electrode layers, located one over the other. The smaller the thickness of the insulation layer is formed, the more sensitive the sensor is made.
It is also possible that the thickness(es) of the electrode layers and/or the thickness(es) of the insulation layer(s) of a substrate vary.
At least one insulation layer may be formed from aluminum oxide (Al₂O₃) or silicon dioxide (SiO₂) or magnesium oxide (MgO) or silicon nitride (Si₂N₄) or glass or ceramic or a metal oxide or any desired mixture thereof.
Preferably, the at least one insulation layer laterally encloses the second electrode layer. In other words, the insulation layer can cover the side faces of the second electrode layer in such a way that the second electrode layer is laterally insulated.
At least the first electrode layer and/or at least the second electrode layer is formed from a conductive material, in particular from metal or an alloy, in particular from a high-temperature-resistant metal or a high-temperature-resistant alloy, particularly preferably from a platinum metal or from an alloy of a platinum metal. The elements of the platinum metals are palladium (Pd), platinum (Pt), rhodium (Rh), osmium (Os), iridium (Ir) and ruthenium (Rh). Nonprecious metals such as nickel (Ni) or nonprecious metal alloys such as nickel/chromium or nickel/iron may also be used.
It is possible that at least one electrode layer is formed from a conductive ceramic or a mixture of metal and ceramic. For example, at least one electrode layer may be formed from a mixture of platinum grains (Pt) and aluminum oxide grains (Al₂O₃). It is also possible that at least one electrode layer comprises silicon carbide (SiC) or is formed from silicon carbide (SiC). The stated materials and metals or alloys of these metals are particularly high-temperature-resistant and are accordingly suitable for the forming of a sensor element that can be used for detecting soot particles in an exhaust-gas flow of internal combustion engines.
In a further embodiment of the invention, the second electrode layer is formed from a conductive material, in particular from a metal or an alloy, that has a higher etching resistance than the conductive material, in particular the metal or the alloy, of the first electrode layer. This has the advantage that the second electrode layer can be formed in a production process as a layer stopping the etching process/removal process. In other words, a second electrode layer formed in this way can determine the depth to be etched/removed of a passage that is for example to be introduced into the sensor structure.
On the side of the first electrode layer that is facing away from the insulation layer there may be formed at least one covering layer, which is formed in particular from ceramic and/or glass and/or metal oxide. In other words, the at least one covering layer is formed on a side of the electrode layer that is opposite from the insulation layer. The covering layer may serve as a diffusion barrier and additionally reduces an evaporation of the first electrode layer at high temperatures, which in an exhaust-gas flow for example may be up to 850° C.
The at least one covering layer may laterally enclose the first electrode layer. In a further embodiment of the invention, the covering layer may additionally laterally enclose the insulation layer. In other words, both the side faces of the first electrode layer and the side faces of the insulation layer(s) arranged thereunder may be covered by at least covering layer. It is also conceivable that the covering layer additionally laterally encloses the second electrode layer. The lateral enclosing part or lateral enclosing region of the covering layer may accordingly reach from the first electrode layer to the second electrode layer. This brings about a lateral insulation of the first electrode layer and/or of the insulation layer and/or of the second electrode layer.
It is possible that at least one covering layer does not completely cover the uppermost electrode layer, in particular the first electrode layer. In other words it is possible that at least one covering layer only covers certain portions of the uppermost electrode layer, in particular the first electrode layer. If the uppermost electrode layer is formed as a heating layer, it is possible that only the portions of the heating loop/heating coil are covered by the at least one covering layer.
On the side of the first electrode layer that is facing away from the insulation layer or on the side of the covering layer that is facing away from the first electrode layer there may be additionally formed at least one porous filter layer. With the aid of a porous filter layer of this type, large particle parts can be kept away from the arrangement of at least two electrode layers arranged one over the other. At least one of the pores or a number of pores in the filter layer are designed so as to ensure a passage through the filter layer that particles of the corresponding size can pass. The pore size of the filter layer may be for example >1 μm. Particularly preferably, the pore size is formed in a range from 20 μm to 30 μm. The porous filter layer may for example be formed from a ceramic material. It is also conceivable that the porous filter layer is formed from an aluminum oxide foam. With the aid of the filter layer, which also covers the at least one passage to the second electrode layer, the large particles, in particular soot particles, that disturb the measurement can be kept away from the at least one passage, so that such particles cannot cause a short circuit.
The at least one passage to the second electrode layer may for example be formed as a blind hole, a portion of the second electrode layer being formed as the bottom of the blind hole and the blind hole extending at least over the insulation layer and over the first electrode layer. If the sensor has a covering layer, the passage, in particular the blind hole and/or the elongate depression, also extends over this covering layer. In other words, not only the first electrode layer but also the insulation layer and the covering layer then have an opening, these openings being arranged one over the other in such a way that they form a passage, in particular a blind hole or an elongate depression, the bottom of which is formed by a portion of the second electrode layer. The bottom of the blind hole or of the elongate depression may for example be formed on the upper side of the second electrode layer that is facing the insulation layer. It is also conceivable that the second electrode layer has a depression that forms the bottom of the blind hole.
The opening cross section of the blind hole is formed by the peripheral portions of the first electrode layer and of the insulation layer and, if there is one, of the covering layer that bound the openings. The opening cross section of the at least one blind hole may be round or square or rectangular or lenticular or honeycomb-shaped or polygonal or triangular or hexagonal.
Other types of design, in particular free forms, are also conceivable. For example, it is possible that the blind hole has a square cross section with a surface area of 3×3 μm²to 150×150 μm², in particular of 10×10 μm²to 100×100 μm², in particular of 15×15 μm²to 50×50 μm², in particular of 20×20 μm².
In a development of the invention, the sensor may have a multiplicity of passages, in particular a multiplicity of blind holes and/or elongate depressions, these blind holes and/or elongate depressions being formed as already described. It is also conceivable that at least two passages, in particular two blind holes and/or two elongate depressions, have different cross sections, in particular cross sections of different sizes, so that a sensor array with a number of zones can be formed, in which a number of measuring cells with blind-hole cross sections of different sizes and/or depression cross sections of different sizes can be used. Parallel detection of electrically conductive and/or polarizable particles, in particular of soot particles, allows additional items of information concerning the size of the particles or the size distribution of the particles to be obtained.
The sensor comprises for example a number of passages in the form of elongate depressions, the passages being arranged in the manner of a grid.
In a further embodiment of the invention it is possible that the at least one passage in the form of an elongate depression runs in a meandering manner. In other words, at least one elongate depression may be formed in a meandering manner. The form of the elongate depression may also be formed spirally.
At least one passage, in particular an elongate depression, may have at least in certain portions a V-shaped and/or U-shaped and/or half-round cross section. Such cross sections or cross-sectional profiles improve the measuring of round particles. Furthermore, the golf ball effect is avoided by such cross sections or cross-sectional profiles.
The width of the elongate depressions at the uppermost edge of the depression may lie in the range from 0.1 to 500 μm, preferably in the range from 1 to 200 μm, particularly preferably in the range from 4 to 100 μm. The width of the elongate depressions in the vicinity of the first electrode (layer) may lie in the range from 0.1 to 200 μm, preferably in the range from 0.1 to 100 μm, particularly preferably in the range from 1 to 50 μm. The width of the elongate depressions can vary and it is possible to change the width in certain portions on a sensor. This likewise allows findings to be made about the size of the particles measured, since for example large particles do not enter narrow depressions.
If a number of passages in the form of elongate depressions are formed in a sensor, they may be formed as oriented in one or more predominant directions.
In a further embodiment of the invention, the openings in the at least one insulation layer and at least one electrode layer may be respectively formed in a linear form or respectively formed in a meandering manner or formed in a spiral form or respectively formed in a grid form.
In other words, an opening in the insulation layer and an opening in the electrode layer are respectively formed in a linear form or respectively formed in a meandering manner or formed in a spiral form or respectively formed in a grid form. The openings in the individual layers are preferably formed similarly, so that a passage, in particular in the form of an elongate depression, can be formed. The openings do not necessarily have to have exactly coinciding cross sections or exactly coinciding sizes of cross section. It is possible that, beginning from the second electrode layer, the cross sections of the openings respectively become greater in the direction of the first electrode layer. The basic forms of the openings are preferably formed similarly, so that all of the openings are formed either in a linear form or in a meandering manner or in a spiral form or in a grid form.
In a further embodiment of the invention it is possible that the sensor has a number of passages that are formed in a linear form and/or a meandering manner and/or a spiral form and/or a grid form.
If the second electrode layer has the form of a meander or the form of a loop, the at least one passage of the sensor is formed in such a way that the passage does not end in a gap or an opening in the form of the meander or the form of the loop. The at least one passage of the sensor is formed in such a way that a portion of the second electrode layer forms the bottom of the passage.
In one embodiment of the invention it is possible that the at least one opening in the at least one insulation layer forms an undercut and/or a clearance in the passage. In other words, the insulation layer may be formed as set back in the passage in comparison with an electrode layer arranged over the insulation layer and an electrode layer arranged under the insulation layer. A lateral clearance in the opening in at least one insulation layer may also be formed as round and/or V-shaped. The forming of an undercut or of an insulation layer set back in the passage improves the measuring of round particles. Particles, in particular round particles, are fed to the electrode layers in such a way that a good electrical contact is made possible.
In other words, the opening in the at least one insulation layer may be larger than the openings in the electrode layers arranged over and under the insulation layer.
The elongate depression may also be referred to as a trench and/or groove and/or channel.
In a further embodiment of the invention it is possible that the sensor comprises both at least one passage in the form of a blind hole, which is formed as round and/or square and/or rectangular and/or lenticular and/or honeycomb-shaped and/or polygonal and/or triangular and/or hexagonal, and at least one passage in the form of an elongate depression, which is formed in a linear form and/or a meandering manner and/or in a spiral form and/or in a grid form.
In a further embodiment of the invention, the first electrode layer and the insulation layer are respectively formed as porous, the at least one opening in the first electrode layer and the at least one opening in the insulation layer respectively being formed by at least one pore, the pore in the insulation layer and the pore in the first electrode layer being arranged at least in certain portions one over the other in such a way that the at least one passage to the second electrode layer is formed. In other words, it is possible to dispense with an active or subsequent structuring of the passages, the first electrode layer and the insulation layer being formed as permeable to the medium to be measured.
This can be made possible for example by a porous or granular structure of the at least two layers. Both the first electrode layer and the insulation layer can be produced by sintering together individual particles, with pores or voids for the medium to be measured being formed while they are being sintered together. Accordingly, at least one passage that allows access to the second electrode layer for a particle that is to be measured or detected must be formed, extending from the side of the first electrode layer that is facing away from the insulation layer to the side of the second electrode layer that is facing the insulation layer as a result of the one-over-the-other arrangement of pores in the first electrode layer and in the insulation layer. If the sensor 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 in the first electrode layer and a pore in the insulation layer form a passage to the second electrode layer.
The pore size distribution in the at least first electrode layer and/or the insulation layer(s) and/or the covering layer(s) can be optimized with regard to the measuring or detecting tasks to be carried out.
The first electrode layer and/or the insulation layer and, if there is one, the covering layer may have portions with different pore sizes in such a way that a sensor array with a number of zones of different pore sizes is formed. Parallel detection with portions of layers of different pore sizes allows a “fingerprint” of the medium that is to be analyzed or detected to be measured. Accordingly, further items of information concerning the size of the particles to be measured or the size distribution of the particles to be measured can be obtained. Equally, the number of pores per unit area or volume may be varied and the accessibility to electrodes or electrode portions is thereby controlled, whereby the sensitivity of the sensor to certain particle sizes can be set.
At least the first electrode layer and the second electrode layer can respectively have an electrical contacting area that are free from sensor and/or insulation layers arranged over the respective electrode layers and are or can in each case be connected to a terminal pad. The electrode layers are connected or can be connected to terminal pads in such a way that they are insulated from one another. For each electrode layer there is formed at least one electrical contacting area, which is exposed in the region of the terminal pads for the electrical contacting. The electrical contacting area of the first electrode layer is free from a possible covering layer and free from a passive porous filter layer. In other words, above the electrical contacting area of the first electrode layer there is neither a portion of the covering layer nor a portion of the filter layer.
The electrical contacting area of the second electrode layer is free from the insulation layer, from the first electrode layer, and also free from a possibly formed covering layer and free from a passive porous filter layer. In other words, on the electrical contacting area of the second electrode layer there is neither a portion of the insulation layer nor a portion of the first electrode layer, a portion of the insulation layer or a portion of the passive porous filter layer.
In a further embodiment of the invention, at least the first electrode layer and/or the second electrode layer has strip conductor loops in such a way that the first electrode layer and/or the second electrode layer is formed as a heating coil and/or as a temperature-sensitive layer and/or as a shielding electrode. The first electrode layer and/or the second electrode layer has at least one additional electrical contacting area that is free from electrode layers, that is to say the at least a first/second electrode layer, arranged sensor layers and insulation or filtration or auxiliary layers and is connected or can be connected to an additional terminal pad. In other words, the first electrode layer and/or the second electrode layer has two electrical contacting areas, both electrical contacting areas being free from layers arranged thereover.
The formation of two electrical contacting areas for an electrode layer is necessary whenever this electrode layer is formed as a heating coil and/or temperature-sensitive layer and/or as a shielding electrode. Preferably, the second electrode layer has at least two electrical contacting areas. The second electrode layer is preferably formed not only as a heating coil but also as a temperature-sensitive layer and as a shielding electrode. By appropriate electrical contacting of the electrical contacting area, the electrode layer can either heat or act as a temperature-sensitive layer or shielding electrode. Such a formation of the electrode areas allows compact sensors to be provided, since one electrode layer can assume a number of functions. Accordingly, no separate heating coil layers and/or temperature-sensitive layers and/or shielding electrode layers are necessary.
During the heating of at least one electrode layer, measured particles or particles located in a passage of the sensor may for example be burned away or burned off.
To sum up, it can be stated that a very accurately measuring sensor can be made available as a result of the structure according to the invention. The forming of a/a number of thin insulation layers allows the sensitivity of the sensor to be increased significantly.
Furthermore, the sensor according to the invention can be made much smaller than known sensors. The formation of the sensor in a three-dimensional space allows a number of electrode layers and/or one/a number of insulation layer(s) to be built as a smaller sensor. Furthermore, significantly more units can be formed on a substrate or a wafer during the production of the sensor. This structure is consequently accompanied by a considerable cost advantage in comparison with normally adjacent planar-constructed structures.
A further advantage of the sensor according to the invention is that the cross sections of the passages can be dimensioned in such a way that specific particles of specific sizes cannot enter the passages. It is also possible that the cross sections of a number of passages can be of different sizes, so that only specific particles of corresponding particle sizes are allowed access into individual passages.
The sensor according to the invention may be used for detecting particles in gases. The sensor according to the invention may be used for detecting particles in liquids. The sensor according to the invention may be used for detecting particles in gases and liquids or gas-liquid mixtures. When the sensor is used for detecting particles in liquids, it is not always possible however to burn off or burn away the particles.
In the case of known sensors, the sensors are arranged in one plane and engage in one another. In the case of the present sensor, it is not necessary for the electrode structures to engage in one another, since the individual electrode layers are formed at a distance from one another as a result of the formation of insulation layers between the electrode layers. The electrode layers of the sensor according to the invention are not connected to one another, but lie one over the other, separated by at least one insulation layer. There is a “non continuous loop” between at least a first electrode layer and at least a second electrode layer. The at least two electrode layers are not twisted together or entwined. At least two electrode layers can only be electrically connected to one another by a soot particle located in at least one passage.
With the aid of at least three formed electrode layers, it is possible during a measurement of particles for example to deduce the particle size or to detect the particle size. If a particle bridges only two electrode layers arranged one over the other, the size of the particle is smaller than a particle that bridges more than two electrode layers. Different formations of the thickness of the insulation layer(s) also allow the size of the particles to be deduced.
According to a further aspect, the invention relates to a sensor system, comprising at least one sensor according to the invention and at least one controller, in particular at least one control circuit, which is formed in such a way that the sensor can be operated in a measuring mode and/or in a cleaning mode and/or in a monitoring mode.
The sensor according to the invention and/or the sensor system according to the invention may have at least one auxiliary electrode. Between an auxiliary electrode and an electrode layer and/or between an auxiliary electrode and a component of the sensor system, in particular the sensor housing, there may be applied such an electrical potential that the particles to be measured are electrically attracted or sucked in by the sensor and/or the sensor system. Preferably, such a voltage is applied to the at least one auxiliary electrode and to at least one electrode layer that particles, in particular soot particles, are “sucked into” the at least one passage.
The sensor according to the invention is preferably arranged in a sensor housing. The sensor housing may for example have an elongate tube form. The sensor system according to the invention may accordingly also comprise a sensor housing.
Preferably, the sensor and/or the sensor in the sensor housing and/or the sensor housing is formed and/or arranged in such a way that the sensor, in particular the uppermost layer of the sensor, or the layer of the sensor that is arranged furthest away from the substrate, is arranged obliquely in relation to the direction of flow of the fluid. The flow in this case does not impinge perpendicularly on the plane of the electrode layers. Preferably, the angle α between the normal to the plane of the first electrode layer and the direction of flow of the particles is at least 1 degree, preferably at least 10 degrees, particularly preferably at least 30 degrees. Also preferred is an arrangement of the sensor in which the angle β between the direction of flow of the particles and the longitudinal axis of for example elongate depressions lies between 20 and 90 degrees. In this embodiment, the particles to be detected more easily enter the passages, in particular blind holes or elongate depressions, in the sensor, and thereby increase the sensitivity.
The controller, in particular the control circuit, is preferably formed in such a way that the electrode layers of the sensor are interconnected with one another. Such voltages may be applied to the electrode layers or individual electrode layers that the sensor can be operated in a measuring mode and/or in a cleaning mode and/or in a monitoring mode.
According to an independent aspect, the invention relates to a method for controlling a sensor according to the invention and/or a sensor system according to the invention.
The method according to the invention allows the sensor to be operated according to choice in a measuring mode and/or in a cleaning mode and/or in a monitoring mode.
In the measuring mode, a change in the electrical resistance between the electrode layers or between at least two electrode layers of the sensor and/or a change in the capacitances of the electrode layers can be measured.
With the aid of the method according to the invention, particles can be detected or measured on the basis of a measured change in resistance between the electrode layers and/or by a measurement of the change in impedance and/or by a measurement of the capacitance of the electrode layer(s). Preferably, a change in resistance between the electrode layers is measured.
In the measuring mode, an electrical resistance measurement, that is to say a measurement on the resistive principle, may be carried out. This involves measuring the electrical resistance between two electrode layers, the electrical resistance decreasing if a particle, in particular a soot particle, bridges at least two electrode layers, which act as electrical conductors.
It applies in principle in the measuring mode that, by applying different voltages to the electrode layers, different properties of the particles to be measured, in particular soot particles, can be detected. For example, the particle size and/or the particle diameter and/or the electrical charging and/or the polarizability of the particle can be determined.
If at least one electrode layer is also used or can be connected as a heating coil or heating layer, an electrical resistance measurement may additionally serve the purpose of determining the point in time of the activation of the heating coil or heating layer. The activation of the heating coil or heating layer corresponds to a cleaning mode to be carried out.
Preferably, a decrease in the electrical resistance between at least two electrode layers indicates that particles, in particular soot particles, have been deposited on or between the electrodes (electrode layers). As soon as the electrical resistance reaches a lower threshold value, the activation of the heating coil or heating layer takes place. The particles are in other words burned off. With an increasing number of burnt-off particles or burnt-off particle volume, the electrical resistance increases. The burning off is preferably carried out for such a time until an upper electrical resistance value is measured. Reaching an upper electrical resistance value is taken as an indication of a regenerated or cleaned sensor. A new measuring cycle can subsequently begin or be carried out.
Alternatively or in addition, it is possible to measure a change in the capacitances of the electrode layers. An increasing loading of the arrangement of electrode layers leads to an increase in the capacitance of the electrode layers. The arrangement of particles, in particular soot particles, in at least one passage of the sensor leads to a charge transfer or a change in the permittivity (ε), which leads to an increase in the capacitance (C). In principle: C=(ε×A)/d, where A stands for the active electrode area of the electrode layer and d stands for the distance between two electrode layers.
The measuring of the capacitance may be carried out by way of example by:

- determining the rate of voltage increase with a constant current and/or
- applying a voltage and determining the charging current and/or
- applying an AC voltage and measuring the current profile and/or
- determining the resonant frequency by means of an LC oscillating circuit.

The described measurement of the change in the capacitances of the electrode layers may also be carried out in connection with a monitoring mode to be carried out.
According to OBD (on-board diagnosis) regulations, all parts and components that are relevant to exhaust gas must be checked for their function. The functional check is to be carried out for example directly after starting a motor vehicle.
For example, at least one electrode layer may be destroyed, this being accompanied by a reduction in the active electrode area A. Since the active electrode area A is directly proportional to capacitance C, the measured capacitance C of a destroyed electrode layer decreases.
In the monitoring mode, it is alternatively or additionally possible to form the electrode layers as conductor circuits. The conductor circuits may be formed as closed or open conductor circuits, which can be closed on demand, for example by a switch. It is also possible to close the electrode layers by way of at least one switch to form at least one conductor circuit, it being checked in the monitoring mode whether a test current is flowing through the at least one conductor circuit. If an electrode layer has a crack or is damaged or destroyed, no test current would flow.
According to an independent aspect, the invention relates to a method for producing a sensor for detecting electrically conductive and/or polarizable particles, in particular a method for producing a described sensor according to the invention.
The method comprises that a laminate with at least a first electrode layer and a second electrode layer and at least one insulation layer, which is arranged between the first electrode layer and the second electrode layer, is produced, at least one passage, in particular in the form of an elongate depression, that extends over the first electrode layer and the insulation layer being subsequently introduced into the laminate, the bottom of the passage being formed by a portion of the second electrode layer.
The method is based on the idea of producing a laminate which comprises at least a first electrode layer, a second electrode layer and at least one insulation layer, in order to introduce at least one passage, in particular in the form of an elongate depression, into this laminate. The passage serves as access to the second electrode layer for the particles to be detected, in particular soot particles.
The production of the laminate and/or of the individual layers of the laminate may take place by a thin-film technique or a thick-film technique or a combination of these techniques. As part of a thin-film technique to be applied, a vapor depositing process or preferably a cathode sputtering process may be chosen. As part of a thick-film process, a screen-printing process is conceivable in particular.
At least one insulation layer and/or at least one covering layer, which is formed on the side of the first electrode layer that is facing away from the insulation layer, may be formed by a chemical vapor deposition (CVD process) or a plasma-enhanced chemical vapor deposition (PECVD process).
The at least one insulation layer may be produced in such a way that it laterally encloses the second electrode layer. An optionally present covering layer may likewise be produced in such a way that it laterally encloses the first electrode layer and/or the insulation layer and/or the second electrode layer. Accordingly, both the at least one insulation layer and the at least one covering layer may form an additional lateral enclosure.
The passage may for example be formed as a blind hole or as an elongate depression, the at least one blind hole or a subportion of the blind hole or the at least one elongate depression or a subportion of the elongate depression being introduced into the laminate by at least one removing or etching process, in particular by a plasma-ion etching process, or by a number of successively carried out removing or etching processes which is adapted to the layer of the laminate that is respectively to be etched or to be removed.
In other words, a blind hole or an elongate depression may be introduced into the laminate in such a way that, for example for each layer to be penetrated or to be etched or to be removed, a process that is optimum for this layer is used, and consequently a number of etching or removing steps that are to be successively carried out are carried out.
It is also conceivable that the blind hole or a subportion of the blind hole or the elongate depression or a subportion of the elongate depression may be made in a chemical etching process from the liquid or vapor phase. The first electrode layer preferably consists of a metal, in particular a platinum layer, which is relatively easy to etch through or to etch.
In one possible embodiment of the method according to the invention it is possible that the etching process stops at the second electrode layer if the second electrode layer is produced from a material that is more resistant to etching in comparison with the at least first electrode layer and with the at least one insulation layer. If the laminate or the sensor comprises an additional covering layer, the second electrode layer also comprises a material that is more resistant to etching in comparison with this covering layer. For example, the second electrode layer is produced from a platinum-titanium alloy (Pt/Ti). It is also conceivable that the second electrode layer consists of a layer filled with metal oxides.
In a further embodiment of the method according to the invention it is possible that at least one insulation layer is formed as a layer stopping the etching process and, in a further step, a subportion of the blind hole or a subportion of the elongate depression is introduced into the at least one insulation layer by a conditioning process or a conditioning step with phase conversion of the at least one insulation layer.
In a further embodiment of the method according to the invention it is possible that the at least one passage and/or a passage is formed as a blind hole or as an elongate depression and this blind hole or the at least one blind hole or a subportion of the blind hole or this elongate depression or the at least one elongate depression or a subportion of the elongate depression is introduced into the laminate by a process of irradiating with electromagnetic waves or charged particles (electrons), the radiation source and/or the wavelength and/or the pulse frequency of the radiation being adapted to the layer of the laminate that is respectively to be machined.
It is preferably possible that the at least one passage and/or a passage is formed as a blind hole or as an elongate depression and this blind hole or the at least one blind hole or a subportion of the blind hole or this elongate depression or the at least one elongate depression or a subportion of the elongate depression is introduced into the laminate by a laser machining process, in particular by means of an ultrashort pulse laser, the laser source and/or the wavelength and/or the pulse frequency of the laser and/or the energy of the charged particles and/or the species of the charged particles being adapted to the layer of the laminate that is respectively to be machined. Particularly preferably, an ultrashort pulse laser is a femto laser or a pico laser.
One further possibility for producing the passage that is formed as a blind hole or as an elongate depression is consequently the partial removal of the laminate by means of a laser. Laser sources with different wavelengths and/or pulse frequencies that are respectively made to suit the material to be removed can be used. Such a procedure has the advantage that, by making them suit the material of the layer that is to be removed, the respectively individual laser machining steps can be carried out quickly, so that overall an improved introduction of passages and/or blind holes and/or elongate depressions into the laminate is obtained. The use of an ultrashort pulse laser proves to be particularly advantageous.
Apart from electromagnetic radiation, charged or uncharged particles can however also be used for removing the electrode layers and/or insulation layers. Thus, apart from electron beams, other charged or uncharged particles can also be used for the ablation. This may be carried out with or without masks that contain the structural information to be transferred.
In a further embodiment of the method according to the invention it is possible that, when producing the laminate, at least one insulation layer is created over the full surface area, in particular by a screen-printing process or spraying-on process or immersion process or spin-coating process, between two electrode areas and, in a subsequent method step, at least a portion of the insulation layer is removed, in particular by structured dissolving or etching or burning out, in such a way that the at least one passage is formed in the sensor.
Such a method corresponds to the lost mold principle. Accordingly, it is possible, especially in the case of thermally stable materials, to perform structuring by the lost mold principle. A lost mold serves for creating a passage from the first electrode layer to the second electrode layer. The at least one insulation layer or insulating layer is created between the electrode layers from a thermally stable material, a portion of this insulation layer preferably being removed by dissolving or etching or burning out after the application of the first electrode layer. As a result of this, the first electrode layer located thereover is also removed. If a covering layer is formed, the portion of the covering layer that is located over the removed portion of the insulation layer is also removed by the dissolving or etching or burning out of the portion of the insulation layer.
Preferably, after the introduction of a passage and/or a blind hole and/or an elongate depression into the laminate, at least one passive porous filter layer is applied on the covering layer. The passive porous filter layer is formed for example by an aluminum oxide foam. This is also formed over the at least one passage or over the at least one blind hole or over the at least one elongate depression.
In a further independent aspect, the invention relates to a method that serves for producing a sensor for detecting electrically conductive particles and/or polarizable particles, in particular a sensor.
A laminate with at least a first electrode layer and a second electrode layer and at least one insulation layer, which is arranged between the first electrode layer and the second electrode layer, is produced, the insulation layer and the first electrode layer being formed as porous layers. The pores in the first electrode layer and the insulation layer are set in such a way that at least one pore in the first electrode layer and at least one pore in the insulation layer are arranged at least in certain portions one over the other, so that at least one passage to the second electrode layer is produced.
If the sensor has a covering layer, this at least one covering layer is also applied to the first electrode layer with a pore size and porosity, at least one pore in the covering layer being arranged at least in certain portions over a pore in the first electrode layer and/or a pore in the insulation layer in such a way that, starting from the covering layer, at least one passage to the second electrode layer is formed. At least one passive porous filter layer may finally be applied to the covering layer.
In a further independent aspect, a method for producing a sensor for detecting electrically conductive particles and/or polarizable particles, in particular for producing a sensor, is provided, a laminate with at least a first electrode layer and a second electrode layer and at least one insulation layer, which is arranged between the first electrode layer and the second electrode layer, being produced, the insulation layer and the first electrode layer being structured, in particular created by a lift-off process and/or an ink-jet process and/or in a stamping process, in such a way that, as a result of the structured application of the individual layers one over the other, a passage, in particular in the form of an elongate depression, to the second electrode layer is formed.
In other words, already during the production of the at least one insulation layer and/or the at least first electrode layer, such a structure that has openings or clearances is produced, a number of openings that are arranged at least in certain portions one over the other forming at least one passage to the second electrode layer. If the sensor has a covering layer, this covering layer may also be applied in an already structured form to the first electrode layer.
In the case of all of the described processes for producing a sensor for detecting electrically conductive and/or polarizable particles, it is necessary that an electrical contacting area is respectively formed in the first electrode layer and in the second electrode layer. This is achieved by portions of the first electrode layer and of the second electrode layer being kept free from layers arranged over the respective electrode layers. This may take place on the one hand by the electrical contacting areas being produced by removing and/or etching away and/or lasering away sensor layers arranged thereover. It is also conceivable that the at least one insulation layer and/or at least the first electrode layer and/or the covering layer are applied to one another in a structured form, so that the electrical contacting areas are already kept free during the production of the individual electrode layers.
As an alternative or in addition, it is possible that at least the insulation layer(s), preferably all of the layers, of the laminate of the sensor are produced by means of an HTCC (high temperature cofired ceramics) process. The insulation layer(s) is/are produced by combining powder, for example ceramic powder, metal powder, aluminum oxide powder and glass powder, and also an amount of binder and solvent, which together form a homogeneous liquid mass. This mass is applied to a film strip, so that green sheets are formed. The drying of the green sheets subsequently takes place. The dried green sheets may be cut and/or punched and/or shaped, in particular provided with openings. Subsequently, the green sheets may for example be rolled up and transported for further processing.
The electrode layers may for example be produced on the green sheet by printing, in particular by screen printing or stencil printing, from metal pastes. Alternatively, thin metal films may be produced and correspondingly prestructured.
Once the various substrate, electrode and insulation layers have been created, the green sheets are arranged in the desired sequence and positioned in exact register one over the other, pressed and joined together by thermal treatment. The binder may be of an organic or inorganic nature and during the thermal treatment either turns into a stable material or combusts or evaporates. The particles thereby fuse firmly to one another by melting and/or sintering processes during the thermal treatment. In this way, the three-dimensional structure of the sensor is formed or produced.
In a further embodiment of the invention it is conceivable that, when producing the laminate, the electrical contacting areas are covered with the aid of stencils, so that the electrical contacting areas cannot be coated with other sensor layers.

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

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

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;

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

FIGS. 7a and 7b show representation of a possible arrangement of a sensor in a fluid flow;

FIGS. 8a and 8b show representations of various cross sections or cross-sectional profiles of passages;

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

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

DETAILED DESCRIPTION OF THE INVENTION

The same reference numerals are used below for parts that are the same and parts that act in the same way.
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.
For the purposes of a high-temperature application, the substrate 11 is formed for example from aluminum oxide (Al₂O₃) or magnesium oxide (MgO) or from a titanate or from steatite.
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 (Al₂O₃) or silicon dioxide (SiO₂).
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 (Pt—Ti). 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.
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 μm to 50 μm. In the present case, the thickness d of the insulation layer is 10 μm. 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.
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.
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.
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.
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. 1 a.
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.
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.
For the purposes of a high-temperature application, the substrate 11 is formed for example from aluminum oxide (Al₂O₃) or magnesium oxide (MgO) or from a titanate or from steatite.
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 (Al₂O₃) or silicon dioxide (SiO₂).
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 (Pt—Ti). 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.
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 (Al₂O₃) or silicon dioxide (SiO₂) or magnesium oxide (MgO) or silicon nitride (Si₃N₄) or glass.
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 μm to 50 μm. In the present case, the thickness d of the insulation layer is 10 μm. 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.
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.
In a further embodiment of the invention it is conceivable that the covering layer 21 also laterally encloses the substrate 11.
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.
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.
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.
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.
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 15×15 μm²to 50×50 μm².
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 μm to 50 μm. 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
In FIG. 6d , a sensor layer with an elongate through-opening 80 is shown, the opening 80 running in a meandering manner.
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.
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.
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.
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 6 f, 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.
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 α 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.
In FIG. 7b , a sensor 10 has thus been introduced into a fluid flow in such a way that the angle β between the direction of flow a of the particles and the longitudinal axis x of the elongate depressions lies between 20 and 90 degrees.
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.
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.
With the aid of the V-shaped and U-shaped cross-sectional profiles, the measurements of round particles are improved.
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.
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.
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.
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.
It should be pointed out in connection with the sensors 10 shown in FIGS. 5, 8 a, 8 b 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.
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.
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.
This embodiment can be carried out or can be formed independently of the features of the sensors 10 shown in FIGS. 5, 8 a, 8 b and 9.
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.
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 ).
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.
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″.
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.
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.
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. 10 c.
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.
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.
With regard to a possible production process in connection with the sensors 10 according to the invention of FIGS. 1a-c , 2, 4, 5, 8 a-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.
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

10 Sensor
11 Substrate
12 First electrode layer
13 Second electrode layer
14 First insulation layer
15 Opening in first electrode layer
16 Opening in first insulation layer
17 Passage
17′, 17″ Elongate depression
18 Bonding agent layer
19 Side face of second electrode layer
20 Side of the first electrode layer
21 Covering layer
22 Side face of first electrode layer
23 Side face of insulation layer
34 Upper portion of covering layer
25 Side portion of covering layer
26 Side of covering layer
27 Porous filter layer
28 Bottom
29 Opening in covering layer
30, 30′ Particle
31 Side of second electrode layer
32 Peripheral region of first electrode layer
33 Electrical contacting area of first electrode layer
34 Electrical contacting area of second electrode layer
35 Additional electrical contacting area of second electrode layer
36 Strip conductor loop
37 Side of insulation layer
40 Pore in first electrode layer
41 Pore in insulation layer
42 Second covering layer
45 First portion
46 Second portion
47 Central portion
48 Frame-like portion
50 Third electrode layer
51 Fourth electrode layer
60 Second insulation layer
61 Third insulation layer
70 Opening in third electrode layer
71 Opening in second insulation layer
72 Opening in fourth electrode layer
73 Opening in third insulation layer
80, 80′, 80″ Opening
90 Undercut
95 Gap
a Direction of flow
b Width of sensor layer
l Length of sensor layer
B1 Width of passage
B2 Width of passage
d Thickness of insulation layer
x Longitudinal axis of the elongate depressions
α Angle between the normal to the electrode plane and the direction of flow
β Angle between the longitudinal axis and the direction of flow

Claims

What is claimed is:

1.-43. (canceled)

44. 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; and

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, wherein the first passage is in a form of an elongate depression.

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

47. The sensor as claimed in claim 44, 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.

48. The sensor as claimed in claim 44,

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.

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 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.

51. The sensor as claimed in claim 44,

further comprising a plurality of holes in each of the first electrode layer and the first insulation layer being aligned to form a plurality of passages, each passage of the plurality of passages comprising an elongate depression, the plurality of passages being arranged in a grid.

52. The sensor as claimed in claim 44, wherein the first passage comprises a meandering shape or a spiral shape.

53. The sensor as claimed in claim 44, wherein the elongate depression comprises a V-shape, a U-shape, or a half-round cross sectional shape.

54. The sensor as claimed in claim 44, wherein the second hole forms an undercut or a clearance in the first passage.

55. The sensor as claimed in claim 44,

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 arranged at least in certain portions one over the other 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.

56. The sensor as claimed in claim 44,

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 overlayed by the insulation layer and the first electrode layer,

wherein the first electrical contact area is not overlayed by a covering layer, and

wherein each electrical contact area is connected to a terminal pad.

57. The sensor as claimed in claim 56,

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 overlayed by the insulation layer or an electrode layer, and

wherein the third electrical contact area is connected with the terminal pad.

58. The sensor as claimed in claim 57, wherein the first passage does not lie over a gap between portions of the strip conductor loop and a second strip conductor loop of the second electrode layer.

59. The sensor as claimed in claim 44, wherein the first electrode layer or the second electrode layer is at a different electrical potential than an ambient environment.

60. A sensor system comprising:

the sensor of claim 44, 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.

61. A method for controlling the sensor as claimed in claim 44, 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.

62. A method of making a sensor for detecting soot particles, the soot particles being electrically conductive or polarizable, the sensor comprising

a substrate;

an insulation layer disposed between the first electrode layer and 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, the passage comprising an elongate depression, and

ending the passage to have a bottom formed by a portion of the second electrode layer.

63. The method as claimed in claim 62,

wherein the elongate depression is formed by etching, in plasma-ion etching, or successive etching adapted to each layer being etched,

wherein the insulation layer is etching-resistant layer, and

wherein a portion of the elongate depression in the insulation layer is formed by a conditioning process with phase conversion of the insulation layer.

64. The method as claimed in claim 62,

wherein the elongate depression is formed by etching, in plasma-ion etching, or successive etching adapted to each layer being etched, and

wherein the insulation layer is etching-resistant layer, the elongate depression being formed in the insulation layer by a conditioning process with phase conversion of the insulation layer.

65. The method as claimed in claim 62,

wherein the elongate depression is partially formed by laser machining, and

wherein laser machining is performed by a laser source, wavelength, a laser pulse frequency adapted individually to each of the first electrode layer, the second electrode layer, and the insulation layer.

66. A method of making a sensor for detecting soot particles, the soot particles being electrically conductive or polarizable, the sensor comprising

a substrate;

the method comprising the steps of:

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, the passage being in a form of an elongate depression.

67. A method of using the sensor of claim 44, 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 first electrode layer or the second electrode layer.

68. A method of using the sensor of claim 44, the method comprising the step of:

detecting electrically conductive or polarizable particles, and

adjusting an angle α between a normal (z) to a plane (x, y) of the first electrode layer and a direction of a flow (a) of the particles to 1 degree or more, 10 degrees or more, or 30 degrees or more.

69. A method of using the sensor of claim 44, the method comprising the step of:

detecting electrically conductive or polarizable particles, and

adjusting an angle β between a direction of flow (a) of the particles and a longitudinal axis (x) of the elongate depression to between 20 and 90 degrees.