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

BACKGROUND OF THE INVENTION
1. Field of the Invention

The invention is directed to a sensor for detecting electrically conductive and/or polarizable particles, in particular for detecting soot particles. The invention is also directed 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 first electrode layer and at least a second electrode layer, which is arranged between the substrate and the first electrode layer, being arranged, at least one insulation layer being formed between the first electrode layer and the at least a 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 to the second electrode layer is formed.

A sensor is preferably provided, comprising a substrate, a first electrode layer, a second electrode layer, which is arranged between the substrate and the first electrode layer, a first insulation layer being formed between the first electrode layer and the second electrode layer, at least a third electrode layer being formed between the first insulation layer and the first electrode layer, and at least a second insulation layer being formed between the at least third electrode layer and the first electrode layer, at least one opening being respectively formed in the first electrode layer, in the at least second insulation layer, in the at least third electrode layer and in the first insulation layer, the opening in the first electrode layer, the opening in the at least second insulation layer, the opening in the at least third 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 to the second electrode layer is formed.

In other words, a sensor is made available, a first and a second electrode layer being arranged horizontally one over the other and a first insulation layer, optionally at least a third electrode layer and optionally at least a second insulation layer being formed between these 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 and third electrode layers and the first and second insulation layers respectively have at least one opening, the opening in the first and third electrode layers and the opening in the first and second insulation layers 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 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 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.

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 the insulation layers. In other words, the electrode layers do not lie in one plane.

Preferably, the opening in the first electrode layer is formed at a distance from the peripheral region of the first electrode layer, the opening in the optionally at least second insulation layer is formed at a distance from the peripheral region of the second insulation layer, the opening in the optionally at least third electrode layer is formed at a distance from the peripheral region of the third electrode layer and the opening in the first insulation layer is formed at a distance from the peripheral region of the first 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 optionally third electrode layer are insulated from one another by the second insulation layer located in between. The optionally third electrode layer and the second electrode layer are insulated from one another by the first 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 for example 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.

The first insulation layer and/or the at least second 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 distance of one electrode layer from another electrode layer is set. The sensitivity of the sensor can be increased by reducing the distance between the, for example 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.

The insulation layer(s) may be formed from aluminum oxide (Al₂O₃) or silicon dioxide (SiO₂) or magnesium oxide (MgO) or silicon nitride (Si₂N₄) or glass or ceramic or any desired combinations thereof.

Preferably, the first insulation layer laterally encloses the second electrode layer. In other words, the first insulation layer can cover the side faces of the second electrode layer in such a way that the second electrode layer is laterally insulated. For example, the at least second insulation layer laterally encloses the at least third electrode layer. In other words, the second insulation layer can cover the side faces of the third electrode layer in such a way that the third electrode layer is laterally insulated.

The first electrode layer and/or the second electrode layer and/or the optionally at least third 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. In other words, a second electrode layer formed in this way can determine the depth to be etched 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 first 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 covering layer is formed on a side of the first electrode layer that is opposite from the first 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 at least second insulation layer. In a further embodiment of the invention, the covering layer may additionally laterally enclose the at least second insulation layer and the at least third 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.

In a further embodiment of the invention, the at least one covering layer may additionally laterally enclose the at least second insulation layer and the at least third electrode layer and the first insulation layer. In other words, both the side faces of the first electrode layer and the side faces of the insulation layers and electrode layers arranged thereunder may be covered by at least one 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 layers and/or of the at least third electrode layer and/or of the second electrode layer.

On the side of the first electrode layer that is facing away from the first 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, in particular at least three, electrode layers arranged one over the other. The pore sizes 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 first insulation layer, over the optionally at least third electrode layer, over the optionally at least second insulation layer and over the first electrode layer. If the sensor has a covering layer, the blind hole also extends over this covering layer. In other words, not only the first electrode layer but also the optionally at least second insulation layer, the optionally at least third electrode layer and the first 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 blind hole, the bottom of which is formed by a portion of the second electrode layer. The bottom of the blind hole may for example be formed on the upper side of the second electrode layer that is facing the first 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, of the at least second insulation layer, of the at least third electrode layer and of the first 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 blind holes, these blind holes being formed as already described. It is also conceivable that at least two passages, in particular at least two blind holes, have different cross sections, in particular different sizes of cross section, 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 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.

In a further embodiment of the invention, the openings in the first insulation layer, in the optionally at least third electrode layer, in the optionally at least second insulation layer, and in the first electrode layer may be respectively formed in a linear form or respectively formed in a meandering manner or respectively formed in a grid form or respectively formed in a spiral form. In other words, an opening in the first insulation layer, an opening in the optionally at least third electrode layer, an opening in the optionally at least second insulation layer, and an opening in the first electrode layer are respectively formed in a linear form or respectively formed in a meandering manner or respectively 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 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.

It is also possible that the at least one passage is formed as an elongate depression, a portion of the second electrode layer being formed as the bottom of the elongate depression and the elongate depression extending at least over the first insulation layer, over the optionally at least third electrode layer, over the optionally at least second insulation layer, and over the first electrode layer and over a/the optionally formed covering 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, the optionally at least second insulation layer, the optionally at least third electrode layer and the first insulation layer are respectively formed as porous, the at least one opening in the first electrode layer, the at least one opening in the optionally at least second insulation layer, the at least one opening in the optionally at least third electrode layer, and the at least one opening in the first insulation layer respectively being formed by at least one pore, the pore in the first insulation layer, the pore in the at least third electrode layer, the pore in the at least second 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 and at least third electrode layer and the first and at least second 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 layers. Both the electrode layers and the insulation layers 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. The second electrode layer is preferably formed as non-porous. 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 first 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 electrode layers, in particular the first and the optionally at least third electrode layer, and in the insulation layers. If the sensor has a covering layer, this covering layer is also preferably to be formed as porous in such a way that a pore in the covering layer, a pore in the first electrode layer, a pore in the second insulation layer, a pore in the third electrode layer and a pore in the first insulation layer form a passage to the second electrode layer.

The pore size distribution and their number in the first and optionally third electrode layer and/or the first and optionally second insulation layer and/or the covering layer(s) can be optimized with regard to the measuring or detecting tasks to be carried out.

The first and/or third electrode layer and/or the first and/or second insulation layer and, if there is one, the at least one 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.

The first electrode layer, the second electrode layer and the optionally at least third electrode layer respectively have an electrical contacting area that are free from sensor 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 or at least third electrode layer is free from insulation layers, free from electrode layers, 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 or at least third electrode layer there is neither a portion of an insulation layer nor a portion of an electrode layer, nor a portion of the passive porous filter layer.

In a further embodiment of the invention, the first electrode layer and/or the second electrode layer and/or the at least third electrode layer has strip conductor loops in such a way that the first electrode layer and/or the second electrode layer and/or the at least third 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 and/or the at least third electrode layer has at least one additional electrical contacting area that is free from sensor layers arranged over the electrode layer, that is to say the first and/or the second and/or the at least third electrode layer, 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 and/or the at least third electrode layer has two electrical contacting areas, both electrical contacting areas being free from sensor layers arranged over the electrode layer.

The formation of two electrical contacting areas on 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 and/or the at least third electrode layer has at least two electrical contacting areas. The second and/or the at least third 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 a number of insulation layers 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 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 layers also allow the size of the particles to be deduced.

According to an independent 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 (s), 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 a first electrode layer, a second electrode layer, a first insulation layer, which is arranged between the first electrode layer and the second electrode layer, optionally at least a third electrode layer, which is arranged between the first insulation layer and the first electrode layer, and optionally at least a second insulation layer, which is arranged between the third electrode layer and the first electrode layer, is produced, at least one passage that extends over the first electrode layer, the optionally at least second insulation layer, the optionally at least third electrode layer, and the first 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 also based on the idea of producing a laminate which comprises at least three electrode layers and two insulation layers, in order to introduce at least one passage 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 first insulation layer, may be formed by a chemical vapor deposition (CVD process) or a plasma-enhanced chemical vapor deposition (PECVD process).

The first 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 at least second insulation layer and/or the at least third electrode layer and/or the first insulation layer and/or the second electrode layer. Accordingly, both at least one of the insulation layers and at least one/the 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 first and third electrode layers and with the insulation layers. 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 the first insulation layer and/or the at least second 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 first insulation layer and/or the at least second insulation layer by a conditioning process or a conditioning step with phase conversion of the first insulation layer and/or the at least second 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 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, the first insulation layer and/or the at least second 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 the second electrode area and the at least third electrode area or between the at least third electrode area and the first electrode area and, in a subsequent method step, at least a portion of the first insulation layer and/or of the at least second insulation layer is removed, in particular by structured dissolving or etching or burning out, in such a way that the 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.

A laminate with a first electrode layer, a second electrode layer, a first insulation layer, which is arranged between the first electrode layer and the second electrode layer, at least a third electrode layer, which is arranged between the first insulation layer and the first electrode layer, and at least a second insulation layer, which is arranged between the third electrode layer and the first electrode layer, is produced, the first insulation layer, the at least third electrode layer, the at least second insulation layer and the first electrode layer being formed as porous layers. The pores in the first and third electrode layer and the first and second insulation layer are set in such a way that at least one pore in the first electrode layer, at least one pore in the at least second insulation layer, at least one pore in the at least third electrode layer and at least one pore in the first 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 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, over a pore in the at least second insulation layer, over a pore in the at least third electrode layer and a pore in the first insulation layer in such a way that, starting from the covering layer, at least one passage to the second electrode layer is formed. A 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 is provided, a laminate with a first electrode layer, a second electrode layer, at least a first insulation layer, which is arranged between the first electrode layer and the second electrode layer, optionally at least a third electrode layer, which is arranged between the first insulation layer and the first electrode layer, and optionally at least a second insulation layer, which is arranged between the third electrode layer and the first electrode layer, being produced, the first insulation layer, the at least third electrode layer, the at least second 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 to the second electrode layer is formed.

In other words, already during the production of the insulation layer(s) and/or the first and/or third 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/or in the second electrode layer and/or in the optionally at least third electrode layer. This is achieved by portions of the first electrode layer and/or of the second electrode layer and/or of the optionally at least third electrode layer being kept free from sensor 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 insulation layers and/or the electrode layers and/or the covering layer(s) 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 sensor layers.

As an alternative or in addition, it is possible that at least the insulation layers, 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 layers 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. 7
a+b show representation of a possible arrangement of a sensor in a fluid flow;

FIGS. 8
a+b 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. 1 a shows in a sectional representation a sensor 10 for detecting electrically conductive and/or polarizable particles, in particular for detecting soot particles. The sensor 10 comprises a substrate 11, a first electrode layer 12 and a second electrode layer 13, which is arranged between the substrate 11 and the first electrode layer 12. An insulation layer 14 is formed between the first electrode layer 12 and the second electrode layer 13. At least one opening is respectively formed in the first electrode layer 12 and in the insulation layer 14, the opening 15 in the first electrode layer 12 and the opening 16 in the insulation layer 14 being arranged one over the other, so that a passage 17 to the second electrode layer 13 is formed.

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. 1a.

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 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.

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 6f, are arranged in layers one over the other, so that passages in the form of elongate depressions 17′ and 17″ are respectively formed in a sensor.

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, 8a, 8b and 9 that it is possible that only two uppermost electrode layers have to be made accessible within a passage. In other words, in a method, preferably according to the invention, a passage 17, 17′, 17″ that is merely formed with respect to the uppermost electrode layers 12 and 51 may be formed in a sensor 10.

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, 8a, 8b 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. 10c.

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, 8a-b, 9 and FIGS. 10a-d, reference is made to the production possibilities already described, in particular to etching processes and/or laser machining processes.

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

24 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

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

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