EP3033608A1

EP3033608A1 - Particle sensor and method for producing a particle sensor

Info

Publication number: EP3033608A1
Application number: EP13750051.8A
Authority: EP
Inventors: Achim Trautmann; Friedjof Heuck
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2013-08-14
Filing date: 2013-08-14
Publication date: 2016-06-22
Also published as: US10126224B2; US20160195464A1; CN105452843B; CN105452843A; JP6336072B2; KR20160042893A; KR102091390B1; WO2015022028A1; JP2016530513A

Abstract

The present invention relates to a particle sensor (10) for detecting electrically conductive particles. Such a particle sensor (10) comprises a first electrode structure (14) having at least one electrode (12) and a second electrode structure (18) having at least one electrode (16), wherein the first electrode structure (14) and the second electrode structure (18) are arranged on an electrically insulating main body (22), wherein an electrical potential difference can be produced between an electrode (12) of the first electrode structure (14) and an electrode (16) of the second electrode structure (18), and wherein the main body (22) has a heating structure (28) for heating the first electrode structure (14) and the second electrode structure (18), which heating structure is at least partially surrounded by the main body (22). This makes it possible to protect the heating structure (28) and also to reduce the voltage needed to burn off particles accumulated on the electrode structures (14, 18). The present invention also relates to a method for producing a particle sensor (10).

Description

Description title

Particle sensor and method for producing a particle sensor

The present invention relates to a particle sensor with a heatable base body. The present invention further relates to a method for

Producing a particle sensor with a heatable body.

State of the art

The current legal situation writes in many countries for vehicles, which are operated with gasoline or diesel, sensors for the measurement of the

Soot particulate concentration in the exhaust gas. The detection principle known

Sensors for measuring the soot particle concentration may be based on an attachment of conductive soot particles to an electrode structure. This deposition of the electrically conductive particles may be reflected in a time decrease of the electrical resistance or in an increasing current flow between the corresponding electrodes. A measuring cycle can start with an unloaded or free sensor, which is exposed to the conductive particles in the exhaust gas. A period of time during which the electrical resistance falls below a certain threshold may serve as a measure of the particulate matter concentration in the exhaust gas. In order to be able to reuse the sensor after a prolonged accumulation of electrically conductive particles, it can be heated to burn off the deposited soot, after which another measurement cycle can begin.

For example, the sensor can be heated to the necessary burnup temperature by using large voltages and currents in an ohmic heating element. Specifically, the provision of high voltage requires a big electro-technical effort. It should be noted that thick sensors require very high voltages, but thin sensors only have limited mechanical stability.

Disclosure of the invention

The present invention relates to a particle sensor for detecting electrically conductive particles, comprising a first electrode structure having at least one electrode and a second at least one

Electrode having electrode structure, wherein the first electrode structure and the second electrode structure are arranged on an electrically insulating base body, wherein between an electrode of the first electrode structure and an electrode of the second electrode structure, an electrical

Potential difference can be generated, and wherein the base body has a heating structure for heating the first and the second electrode structure, which is at least partially enclosed by the base body.

Such a particle sensor is therefore in particular a resistive particle sensor and can be based on the property that the particles to be detected, which in particular can be formed substantially from carbon as soot particles, are in particular electrically conductive. The electrical conductivity is exploited to detect the accumulated soot particles. For this purpose, the particle sensor comprises a first electrode structure and a second electrode structure, wherein the first electrode structure and the second

Electron structure each have at least one electrode. The

In this case, electrode structures or the electrodes of the electrode structures are arranged on an electrically insulating basic body. An electrically insulating basic body may in particular be one which is formed from an electrically insulating material, or which may in principle be electrically conductive, but has an electrically insulating covering layer. In the context of the present invention, electrically insulating can be understood in particular as meaning that the specific electrical resistance is in a range of> 1 kOhm cm, whereas electrically conductive can be understood in particular if the specific electrical resistance is in a range of <1 kOhm cm is located. Furthermore, under thermally insulating in the context of the present

In particular, the invention can be understood as meaning that the thermal conductivity or thermal conductivity is in a range of <15 W / m / K, whereas thermal conductivity can be understood in particular if the thermal conductivity lies in a range of> 15 W / m / K.

If the electrode structures arranged on the base body are then exposed to a gas flow which comprises the particles to be detected, the latter attaches to the electrode structures. Thereby, when between the first electrode structure and the second electrode structure, an electrical

Potential is constructed, for example by the provision and connection of a suitable voltage source, current measurements, voltage measurements, capacitance measurements and / or resistance measurements are performed. In particular, a change in the flowing current, the prevailing voltage or the prevailing resistance statements about the accumulated particles and thus on the particle concentration in the gas stream can be made.

This measuring method can thus be based on the fact that attached electrically conductive particles have a different current flow between the electrodes

Allow electrode structures or between the

Reduce electrode resistance. As a result, a quantification of the increase in the current flow or the reduction of the electrical resistance, for example a statement about the particles deposited on the electrode structure, can be made. This may be possible in particular by observing the change in the current flow or the resistance over time.

After a certain period of measurement, accumulated particles can be removed again from the sensor or from the electrode structure in order to remove the particles

Regenerate sensor and start another measurement cycle. For this purpose, such a particle sensor has a heating structure. The heating structure serves in particular for heating the first and the second electrode structure in such a way that they can be brought to a burnup temperature which is sufficient to burn off or oxidize the deposited, in particular soot particles, and thus to remove them from the electrode structure. suitable Burning temperatures can be in a range of 500 ° C or above. For this purpose, the heating structure may be formed in particular of an electrically and thermally conductive material and serve as an ohmic heater.

In this case, the heating structure of the main body may be at least partially enclosed. In other words, the heating structure is arranged in the base body and at least partially surrounded by this or the base body material. By such integration of the heating structure in the body, which in particular of an electrically and

In particular, thermally insulating material is formed, the

Heating structure electrically isolated and chemically passivated on the other. The heating structure is thus stable against external corrosive attacks or other influences. The heating structure is mechanically particularly stable or stabilized and thermally insulated from a mechanical connection of the active measuring range, whereby a flow of heat generated, for example, in a housing by thermal conduction minimized

or can be prevented.

In addition, such a particle sensor is particularly simple and inexpensive to produce, since only a few and especially inexpensive process steps are needed.

In particular, however, the heating structure is not only thermally insulated from an anchorage or mechanical connection, but can also locate the generated heat well. In other words, the heat generated can be substantially focused on the environment of the heating structure, or the heating power can be substantially concentrated for the burn-off on the active sensor surface or the electrode structures, as a thermal decoupling from the environment and in particular from the coupling to a Housing is realized. This allows a particularly effective heating of the electrode structures for removing deposited electrically conductive particles. This makes it possible that accumulated particles can be removed with only low voltages or currents. The requirements regarding current and / or voltage for regenerating the particle sensor can thus be kept particularly low which is a great deal in the production of a particle sensor

Cost advantage can bring.

In spite of an arrangement of the heating structure in a thermally insulating main body, which may have a thermal conductivity in a range of 1 W / mK, for example, a heating of the electrode structures may be possible without difficulty, since a gradient of the heat distribution usually over the comparatively long length or Width to the height, so the areal expansion of the body material takes place, but along the height also due to the small distance between the heater layer and

Electrode structures, which may be in particular in a range of 1 μηη, sufficient heat for generating the appropriate Abbrandtemperatur can get from the heating structure to the electrode structures.

Thus, by such, also referred to as a membrane

heated body for a particle sensor even with comparatively large electrically insulating layers or substrates, such as 5 mm X 5 mm, easily burned the particles attached to the electrode structures are generated. It can be both very thin

Particle sensors or very thin body are formed, which have sufficient mechanical stability and require little power or voltage for a regeneration of the electrodes. Furthermore, a customized thermal, as well as electrical

Connection of the electrode structures as well as the heating structure, for example, to the on-board electronics of a vehicle be possible. By focusing the heating on the area of the electrode structures, a burning-off can be carried out, for example, with 12 V usual in a vehicle.

Such a particle sensor thus comprises a mechanically stable, with respect to an anchoring or connection thermally insulated and electrically resistive heating structure in a base body. The integration of the electrically resistive heater and the production of the main body or the membrane can be carried out in the same process steps. This allows the fabrication of an active stable body for a soot particle sensor based on comparatively simple and inexpensive process steps. The necessary processes are generally widely known, especially in the field of micromechanics.

Within the scope of an embodiment, the main body may be made of silicon dioxide and / or the heating structure may be made of silicon.

Such materials can be processed particularly easily by methods known per se and common in micromechanics, so that a particularly simple, sophisticated, and cost-effective production method is possible. In addition, for example, silicon dioxide has about 100 times worse thermal conductivity than silicon and further good electrical

Isolation ability, which is why it is particularly suitable as a thermal as well as electrical insulator. In addition, in this embodiment, a particularly simple manufacturing process can be made possible, in which the base body is at least partially based on, in particular, thermal

Oxidation processes can be produced. In this case, an advantage can be seen in particular in that an electrically and thermally conductive base layer can be converted at least partially chemically into an electrically and thermally insulating material which encloses the electrically resistive heater.

In the context of a further embodiment, the heating structure can be completely enclosed by the main body. In this embodiment can

Heat losses are reduced by thermal conduction particularly safe. As a result, the requirements for the current flowing during a regeneration or to the voltage applied thereto can be kept particularly low. This results in a particularly cost-effective operation and installation of such a sensor result. Furthermore, a protection of

Heating structure particularly effective against, for example, corrosive attacks possible. Completely enclosing the heating structure of the main body may in particular mean a coat-like enclosing. This can be done in the

Meaning of the present invention further that the hot

or to be heated areas of the heating structure, which are to act on the electrode structures and are arranged adjacent to these, completely embedded in the main body or enclosed by this, but corresponding connections, for example, not from need to be enclosed enclosed in the body or may be arranged outside the body.

In the context of a further embodiment, the heating structure can have a net-like line structure arranged in the main body. By means of a particularly two-dimensional net-like line structure, the area to be heated can be adapted to the field of application in a particularly advantageous manner. In particular, the network-like line structure, which may be formed in particular from silicon, assume a size and / or position corresponding to the or to the electrode structures. In this case, the line structure can cause a heating effect in particular by Joule heat or an ohmic

Resistance, which in a manner known per se, a burning or a regeneration of the electrode structures is made possible by the application of a voltage or by flowing current. In addition, a large area can be uniformly heated by a net-like structure, so that substantially no or only a slight temperature gradient over the length or over the width of the area to be heated arises. Another advantage of a net-like line structure can be seen in the fact that the corresponding line paths are well networked with each other or connected to each other. This results in the advantage that even with the interruption of individual cable paths, such as through a

Damage to the sensor, further heating can be easily possible. In this case, a network structure or a network-like structure can be understood in particular as meaning a structure which has an arrangement of a

Plurality of in particular several times interconnected

or has crosslinked pathways.

In the context of a further embodiment, the heating structure, in particular the net-like conduction structure, may comprise conduction paths which at least partially have a width which lies in a range of <500 nm.

Such pathways, which may be part of the net-like structure in particular, can cause a good heating effect even at low currents. Therefore, an operation and electrical control of a

Particle sensor in this embodiment particularly cost possible. The cable paths do not need at every point such a width or have such a cross-section, but may also be formed with a varying along its course cross-section or width, so that they need to have such a width only in a partial area.

Another advantage of such conductor paths, in particular made of silicon, may lie in the temperature-dependent electrical resistance behavior. In doped semiconductors, for example, the electrical resistance has a maximum with respect to temperature. At this maximum, the extrinsic conductivity changes to intrinsic conductivity. This maximum and the subsequent drop in electrical conductivity increase that

control engineering effort to set a defined temperature profile. The position of the maximum can be shifted to higher temperatures, for example by a high doping, or further by a very small conductor cross-section, in particular in a range of <500 nm, in particular in a range of 100 nm, for example due to a so-called minority charge carrier exclusion effect ".

In a further embodiment, a homogenization region for homogenizing the temperature of the base body may be provided, which is surrounded by the heating structure, in particular wherein the

Homogenization can be formed of electrically and / or thermally conductive material. In this embodiment, a particularly advantageous homogenization of the temperature can be generated, whereby the

Electrode structures can be heated particularly evenly. In addition, temperature peaks can be avoided, whereby damage can be avoided and the required electrical power can be minimized. In detail, the homogenization region can be a planar region in which a temperature plateau occurs, with temperatures of up to a maximum of +200 ° C. above the burnup temperature; in particular, temperatures in a range of more than 1000 ° C. can be avoided. For this purpose, the homogenization region can have a suitable areal extent and in particular have an adjustable electrically and / or thermally conductive material content. In the context of a further embodiment, the homogenization region can be surrounded by an electrically insulating region surrounded by the heating structure. In this embodiment, a temperature homogenization can be realized in particular by an adjustable in design increased thermal dissipation, or by adjusting the electrical resistance, which uses the electrical introduced heating power locally targeted.

In a further embodiment, the main body and the

Heating structure disposed in a first layer and the electrode structures are arranged in a second layer, wherein the second layer is disposed on the first layer. In this embodiment, such a sensor thus has layers or layers, which may in particular be immediately adjacent. As a result, the layer of the electrode structure can be heated particularly advantageously and without heating losses through the heating structure. In addition, a particularly compact formation of the particle sensor is possible in this embodiment. This gives a great variability in the use of such a particle sensor.

With regard to further advantages and technical features of the particle sensor according to the invention is hereby explicitly to the explanations in connection with the inventive method, the figures, as well as on

Figure description referenced.

The invention further relates to a method for producing a

Particle sensor, in particular a particle sensor according to the invention, comprising the method steps:

a) providing a base body comprising a base layer, an electrically insulating layer disposed on the base layer and an electrically conductive layer disposed on the electrically insulating layer;

b) introducing at least one recess into the electrically conductive layer for patterning the electrically conductive layer;

c) applying an electrically insulating cover layer to the electrically conductive layer; and

d) applying at least two electrode structures to the

Top layer. Such a method thus serves in particular to produce a particle sensor as described above. In the first method step a), a base body is thus initially provided which has a base layer, an electrically insulating layer arranged on the base layer and an electrically conductive layer arranged on the electrically insulating layer. The base layer may serve in particular the stability of the base body, in particular during the manufacturing process and have a large thickness. The

corresponding thickness can be selected depending on the required stability or the thickness of the electrically insulating layer and / or the electrically conductive layer. Exemplary thicknesses are in a range of about 700 μηη. In this case, the base layer may be electrically and / or thermally insulating or else preferably be electrically and / or thermally conductive. The electrically insulating layer may have a thickness approximately in the region of 1 μm. Furthermore, the electrically conductive layer arranged on the electrically insulating layer may have a thickness which lies in a range of> 5 to <100 μm. In addition, it can be advantageous from a manufacturing point of view, for example, if the electrically conductive layer and the base layer are made of the same material.

Starting from the base body, at least one, in particular a plurality of recesses, is introduced into the electrically conductive layer in the further method step b). In this case, the recess or the recesses can in particular extend to a depth which borders on the electrically insulating layer, so that the electrically insulating layer is exposed, but the thickness of which is not or not substantially changed. Such termination of the molding of the recess at a defined depth for the patterning of the electrically conductive layer can be achieved if a sufficiently high difference of the chemical or physical properties between the two layers is selected, such as between silicon and silicon dioxide and in particular with respect to the method to be selected for forming the recesses.

A suitable method for such structuring or for the introduction of recesses is for example a photolithographic process for defining the recesses and a subsequent

Deep etching (etching) process for structuring the

Recesses in the electrically conductive layer. This can be done as part of a microstructuring. For example, under a

Deep set method of forming the recesses in the electrically conductive layer, such as silicon advantageously due to chemical

Differences to the electrically insulating layer well-defined stopped. By introducing the recesses into the electrically conductive layer, which is arranged in particular opposite the base layer, for example, a net-like and in particular two-dimensional net-like structure can be created. In principle, the method step b) can serve to structure the base body and also to form, in particular, a plurality of functional areas.

If in the further method step c) a cover layer is applied to the electrically conductive layer, and in particular an electrically insulating layer as a cover layer, the recesses produced can be filled with the electrically insulating material of the cover layer, whereby a substantially flat contour surface in the region of the cover layer can be generated.

The electrically conductive layer embedded in the electrically and thermally insulating cover layer can be used below as a heating structure. In this case, the heating structure can be insulated by applying the electrically and thermally insulating covering layer in such a way that the heat generated by the heating structure can be well localized, such as in a later use on the electrode structures. In this case, the electrically insulating cover layer together with the further electrically insulating layer form the base body, which at least partially surrounds the heating structure.

In this case, the electrode structures can be applied to the cover layer in the further method step d). In this case, it may be advantageous if the electrode structures are applied in the region in which the heating structure is arranged in order to be able to focus the heat generated on the electrode structures. The electrode structures can then at a

Using a sensor thus prepared as a measuring range for detecting serve electrically conductive particles and are regenerated by the heating structures after a measuring cycle. An application of the electrode structures can by physical and / or chemical deposition, such as by evaporation or sputtering, of high-melting chemically inert

Materials such as platinum, tungsten or silicon carbide occur.

By the method described above, it is possible to integrate a heating structure in a body layer, with only a few process steps are necessary. This can be realized by using widely known and especially in the microengineering mature process. It can continue by a suitable choice of the body, the heating structure in the

Basic body are integrated, so that a final deposition and structuring of the heater structure is eliminated. Within the scope of an embodiment, a chemically convertible layer can be used as the electrically conductive layer, and the electrically insulating covering layer can be produced by a chemical conversion of the electrically conductive layer. For example, a chemical conversion may include oxidation or forming an oxide layer, or chemical conversion may include nitriding

or forming a nitride layer. In addition, the electrically insulating layer can also be easily deposited, such as by a chemical vapor deposition. In the context of the present invention, an oxide layer can be produced in particular by the chemically convertible electroconductive material which is present anyway

or oxidizable layer is exposed to an oxidizing medium, such as at high temperatures, for example> 800 to <1200 ° C, with simultaneous addition of oxygen or water vapor. As a result, the cover layer can be applied particularly simply, namely by an easily manageable oxidation of the electrically conductive material. It may be particularly advantageous that the introduced recesses are closed by the oxidation. Because the oxide can grow on the one hand into the interior of the oxidizable material and on the other hand to the outside. Furthermore, the oxidation stops automatically when all elevations in the electrically conductive are closed by the oxide layer, which procedural

Benefits, or once the process is terminated. The Furthermore, the cover layer can be applied particularly easily to the structures produced in the method by the introduction of the recesses, wherein no use of masks or the like is necessary. Because the location of the oxidation or the position of the application of the cover layer can be predetermined in a precise manner by the design of the structure in step b). The same applies to a nitration of the electrically conductive layer. Suitable reaction conditions for a nitration, such as for forming a silicon nitride layer, may include a temperature in a range of> 500 ° C to <1000 ° C with the addition of silane and ammonia.

In this context, it should be mentioned that by suitable chemical conversion of the electrically conductive layer into an electrically insulating layer, during which the material of the electrically conductive layer is consumed, structures having dimensions of> 1 μm into electrically conductive structures of 100 nm can be transferred. Since the height of the structure compared to the width during the conversion is only slightly reduced, thereby structures with extremely high

Create aspect ratios of 1: 200 (width to height).

By the method described above, it can be particularly advantageously possible in this embodiment to be able to apply electrically and in particular thermally insulating layers, which are present in particular in a thickness of> 20 μm, also by chemical conversion. This is an advantage over the known from the prior art method, since here by a conventional oxidation, for example, technically feasible layer thicknesses of up to 3 μηη are possible, or larger layer thicknesses up to 10 μηη, in particular by a deposition, such about a chemical deposition, were possible.

In the context of a further embodiment, the base layer and / or the electrically conductive layer may be formed from silicon and / or the electrically insulating layer may be formed from silicon dioxide.

In this embodiment, the base body may thus be a so-called "Silicon on insulator (SOI)" base body, or else an epitaxially grown silicon, or as a very cost-effective variant of a polycrystalline Silicon layer on an oxidized body. Made of silicon

configured layers or layers can be highly doped independently of each other, such as with phosphorus, boron, arsenic, and thus electrically very good conductivity. They are also separated from each other by a relatively thin layer of an electrically insulating material, in particular of silicon dioxide. In this embodiment, therefore, in particular cost-effective known and readily available base body can be used, which can make the manufacturing process particularly simple and inexpensive.

In a further embodiment, the at least one recess can be formed as a circular and in particular closed at the periphery opening. Circular openings can be particularly easy to produce. Furthermore, by forming circular openings, it is particularly easy to produce a net-like line structure which is particularly suitable for a heating structure of a particle sensor. The net-like conduction structure can then be formed by at least a part of the material remaining next to the openings, which is at the

Structuring in process step b) was not removed. In particular, a plurality of circular openings may be provided in the context of the present invention, wherein it is not excluded in the context of the present invention that not completely closed at the periphery openings can be provided. Furthermore, the openings

For example, have a diameter in a range of> 2 μηη to <3 μηη.

In a further embodiment, a plurality of

Recesses, in particular at circular openings, are generated, which are arranged in a hexagonal arrangement. In particular, for a hexagonal arrangement of openings or in particular of circular openings or an arrangement of the openings in a hexagonal structure, an isotropic structure can be created. Such isotropy of this structure provides, in particular, an enlarged one

Stability of the structure, as compared to anisotropic stresses, because there is no clear preference. In addition, it also allows a homogeneous

Oxide growth because it does not require orientation to the crystal directions. Furthermore, can be dispensed with a complete oxidation to integrate a heater in the position of the body. A hexagonal arrangement may in particular mean an arrangement according to a plan view of a hexagonal crystal structure.

With regard to further advantages and technical features of the method according to the invention is hereby explicitly to the explanations in connection with the particle sensor according to the invention, the figures, as well as on the

Figure description referenced.

Drawings and examples

Further advantages and advantageous embodiments of the subject invention are illustrated by the drawings and explained in the following description. It should be noted that the

Drawings are descriptive only and are not intended to limit the invention in any way. Show it

Fig. 1 is a schematic plan view of an embodiment of a

particle sensor according to the invention;

Fig. 2 is a schematic sectional view taken along the distance A-A 'of Figure 1; 3a shows a method step for producing a particle sensor in one

Cross-sectional view;

FIG. 3b shows the method step from FIG. 3a in a plan view;

4a shows a further method step for producing a particle sensor in a cross-sectional view;

4b shows the method step from FIG. 4a in a plan view;

5a shows a further method step for producing a particle sensor in a cross-sectional view;

FIG. 5b shows the method step from FIG. 5a in a plan view; FIG.

6a shows a further method step for producing a particle sensor in a cross-sectional view;

FIG. 6b shows the method step from FIG. 6a in a plan view; 7 shows a further embodiment of a partial region of a particle sensor; and

Fig. 8 shows a further embodiment of a portion of a particle sensor.

FIG. 1 shows a particle sensor 10 according to the invention. Such a particle sensor 10 may be arranged, for example, in the exhaust system of a motor vehicle. In this case, such a particle sensor 10, for example, the function of a arranged in the exhaust system of a motor vehicle

Particle filter, or determine the particle emission.

Such a particle sensor 10 thus serves in particular for detecting electrically conductive particles. In particular, the particle sensor 10 may have a first electrode structure 14 having at least one electrode 12 and a second electrode structure 18 having at least one electrode 16. In this case, the first electrode structure 14 and the second form

Electrode structure 18, an electrode system 20 from. In this case, the electrode system 20 or the electrode structures 14, 18 can form a system of comb-interdigitated interdigital electrodes, as shown in FIG. The first electrode structure 14 and the second

Electrode structure 18 are arranged on an electrically insulating base body 22. In this case, between an electrode 12 of the first

Electrode structure 14 and an electrode 16 of the second electrode structure 18, an electrical potential difference can be generated. For this purpose, for example, a voltage source, not shown, may be connected to the electrodes 12, 16. To the arranged in a gas stream particles, in particular

Soot particles to detect, the current flow generated by the potential difference or resistance or capacitance between the different electrode structures 14,18 can be determined. For this purpose, the electrode structures 14, 18 are electrically connected to an electrical connection or to an electrical outlet 24, 26.

To after a certain measurement cycle or after a certain measurement period, the deposited particles again from the

To remove electrode structures 14,18, the particle sensor 10 has a heating structure 28. In this case, the heating structure 28 can serve in particular To heat the first electrode structure 14 and the second electrode structure 18 to a combustion temperature at which the deposited particles are oxidized and thus can be removed from the electrode structures 14,18. The person skilled in the art will thus see that the heating structure 28

in particular to the size or position or

Extension of the electrode structures 14, 18 may be adapted and thus in one to the extent of the electrode system 20 corresponding

or the same or greater extent can be provided so that advantageously the entire electrode system 20 of a

Regeneration can be subjected. If necessary, the heating structure 28 can be locally replaced by a homogenization region 56, as will be explained in detail later.

The heating structure 28 may be at least partially, in particular completely, for example, surrounded by the base body 22, for example, like a coat. This is shown in particular in Figure 2, which is a

Section view along the distance A-A 'of Figure 1 shows.

In Figure 2 it can be seen that the heating structure 28 is disposed within the base body 22, or completely of the material of the

Base body 22 is surrounded.

The main body 22 may be configured, for example, of silicon dioxide, whereas the heating structure 28 may be configured, for example, of silicon. Alternative materials for the base body 22 include, for example, silicon nitride, aluminum oxide, or titanium oxide, whereas alternative ones

Materials for the heating structure 28 metals, in particular with a melting point of> 1000 ° C, such as titanium may include. Furthermore, the electrode system 20 or the electrode structures 14, 18 may be made of platinum tungsten and silicon carbide.

It can also be seen in FIG. 2 that the base body 22 and the base body 22

Heating structure 28 are arranged in a first layer 30, wherein the

Electrode structures 14, 18 are arranged in a second layer 32. In this case, the second layer 32 may be arranged on the first layer 30. In a Furthermore, in particular mechanical connections 36 for fastening and electrical contacting of the particle sensor 10 may be arranged in particular below the first layer 30 arranged third layer 34. A method of manufacturing such a particle sensor 10 is shown in the following FIGS. 3 to 6.

In a method step a), according to FIG. 3, a base body 38 is provided comprising a base layer 40, an electrically insulating layer 42 arranged on the base layer 40 and an electrically conductive layer 44 arranged on the electrically insulating layer 42. FIG. 3 shows a cross-section of the base body 38, whereas FIG. 3b shows a plan view of the base body 38 or of the electrically conductive layer 44. The electrically conductive layer 44, like the base layer 40, may be formed of silicon. The silicon may be highly doped, for example. For example, the silicon may include dopants, such as phosphorus, boron, and arsenic, where the doping level may extend to the silicon saturation limit. As a result, a particularly good electrical conductivity can be achieved. Alternative materials for the base layer include, for example, quartz, steel and titanium. The electrically insulating

Layer 42 may be configured in particular of silicon dioxide.

If the base layer 40 is formed of the same material as the upper electrically conductive layer 44, this is due to the uniformity

Process control from the process engineering point of view Advantages, since the substantially same handling steps can be used.

In a further method step b), the surface of the base body 38 or in particular the upper electrically conductive layer 44 is patterned according to FIG. For example, a photolithography

Method and a subsequent deep etching process use.

In particular, in method step b) at least one, in particular a plurality, of recesses 46 can be introduced into the electrically conductive layer 44. In this case, the electrically conductive layer 44

For example, essentially be divided into three different functional areas. In a first functional area i), the electrically conductive layer 44 can be removed substantially completely and unstructured. This may be possible by providing a very large recess 46a. By a complete removal of the electrically conductive material of the electrically conductive layer 44 in the region i), in particular of the silicon, a reduction of the thermal coupling to the base body 22 can thus be made possible. There is no electrical heating in this area. This structuring allows targeted redirecting the electrical heating power to other areas. However, this must be configured in conjunction with a reduction in the mechanical stability of the layer of electrically insulating material, in particular a silicon dioxide membrane. In other words, care should be taken that the particle sensor 10 has sufficient stability.

Furthermore, in a further functional area ii) structured

Recesses 46 b, between which projections 48 remain to be inserted. The projections 48 may serve as a heating structure 28 in a later function of the particle sensor 10 and are designed in particular as a net-like structure. It can be seen in particular in FIG. 4b that in the region ii) the recesses 46b are formed as a circular and at least partially closed opening, which are configured in a mutually hexagonal arrangement. In addition, however, the openings may in principle also have other shapes than

in particular hexagonal circular openings. Thus, the openings in particular a honeycomb structure or

Honeycomb structure are formed. Also conceivable, for example, would be squares, lines, rectangles or even spiral-shaped structures, although this enumeration is not meant to be exhaustive. Thus, in the area ii) the production of a relatively thick layer of an electrically insulating

Materials, such as in particular a silicon dioxide layer, with embedded therein or buried in this heater structure 28 in one

or two process steps take place. This allows a significant procedural advantage. A further functional region iii) essentially comprises a region 50 of untreated material of the electrically conductive layer 44 and, in the case of a function of the particle sensor 10, can be used, for example, as electrical connection 24, 26 or connection of the heating structure 28 and / or

Electrode system 20 serve. On the other hand, the region 50 of the electrically conductive layer 44 can serve a particularly homogeneous temperature distribution on or in the base body 22. In the region iii), although the surface is oxidized, but lacking the structuring, the electrically conductive layer remains with a sufficient unstructured thickness. This region can thus remain as a particularly highly thermally and electrically conductive region, in particular silicon region. In this case, the remaining silicon is separated electrically and process-technically by the electrically insulating layer 42 from the base layer 40 or the bulk. The cover layer 52, resulting from a chemical conversion, can be further reinforced by an additional deposition of a further insulating layer, which can lead to a planarization of the cover layer 52.

The fundamental possibility of realizing a plurality, in particular three, of different functional regions i), ii), iii) in a process flow as described above, thereby makes a significant difference to a completely planar deposition of the electrically insulating layer, in particular silicon dioxide. Rather, the individual functional areas in a particularly simple manner and thereby by simply

specific methods to be applied to the method to be applied, as described with respect to the individual areas, the arrangement of the functional areas is not limited to the arrangement shown. This is particularly advantageous in connection with the oxidative

Generation of an electrically insulating layer in particular as

Body material possible, as with reference to the following

Step c) is explained. Especially thick silicon dioxide layers> 1 μηη can be set very precisely and thus set an exact process control for the remaining silicon structures. In the further method step c), as shown in FIGS. 5 a and 5 b, an electrically insulating covering layer 52 can furthermore be electrically connected to the electrically conductive covering layer 52 conductive layer 44 or on the resulting from the conductive layer 44 structures, such as the projections 48 or 50 are applied, which are indicated purely schematically, however, are understandably located below the layer 52. In this case, the electrically insulating layer 52 can be applied in particular to the regions of the electrically conductive layer 44 that are left in the method step b). For example, in the case where the electrically conductive layer 44 is an oxidizable layer, the electrically insulating layer 52 may be formed by a particular thermal oxidation process. In particular, in the case of the use of silicon as an electrically conductive material, the electrically insulating cover layer 52 can be configured for example by a particular thermal oxidation process for producing silicon dioxide. Such growth of the oxide layer may in particular depend on the size and structure of the process step b).

introduced recesses 46 and the introduced structure, such as diameter and position of the circular openings take place. For example, by such a configuration, the oxidation process can be terminated automatically when no oxidizable material is exposed more or at a sufficiently short distance from the oxidizing

Atmosphere is because the diffusion through the oxide layer, for oxide layers

500 nm severely limits the oxidation rate. Thus, an oxidation can only take place where oxidizable material in a sufficiently short distance, for example <3 μηη, is present, what without the use of

For example, masks allow a defined structure.

In particular, an oxidation process may be advantageous in this process step c), since the oxide, such as the silicon dioxide, grows not only in the material to be oxidized, such as silicon, but also a part of the oxide layer also grows outward.

For example, the resulting oxide layer grows, in particular the

Silicon dioxide layer, for example, 45% into the silicon and 55% out of the silicon out. If one chooses now the form and / or size of the

Recesses 46 such as the diameter of the circular openings and their particular hexagonal closest arrangement, so in the area ii) a closed silicon dioxide layer arise in the core of a fine network In particular, highly doped silicon is buried and as a net-like

Heating structure 28 can serve.

Therefore, the inserted in a previous process step

Recesses 46 close again and the individual projections 48 may be partially or completely, depending on the design or thickness, in the oxide, in particular silicon dioxide, transferred. This way, a thick oxide layer can be produced, which may have a thickness of, for example, 20 μm. In this case, an oxide layer, for example, be used with such a thickness for the entire base body 22 and for the entire particle sensor 10, and does not need to be reduced to isolated island areas. Furthermore, it will be apparent to those skilled in the art that the base body 22 can be produced from the electrically insulating layers 42, 52.

In this method step, it is thus possible in particular to produce a net-like structure of the electrically conductive material. This is shown for example in FIG. 6a. In FIG. 6 a, it can be seen that the reticulated electrically conductive structure, which can be used in particular as heating structure 28, is formed by, in particular, hexagonal circular openings, formed for example of silicon dioxide, with electrically conductive material formed around it. The net-like line structure can be arranged in the base body 22. Furthermore, the line structure,

Have pathways that at least partially have a thickness that is in a range of <500 nm or in the range of 100 nm.

By way of example, this thickness can have the smallest conductor paths arranged approximately between circular structures. As a result, they represent at least locally or partially a high electrical resistance and can thus be used as an ohmic heater for the heating structure 28.

FIG. 6 also shows a further optional method step. In this method step, a portion 54 of the base layer 40 can be removed, such as by a backside deep etching, wherein advantageously only up to the electrically insulating layer 42 material is removed, which electrically Insulating layer 42 thus remains substantially unchanged and is exposed in this area.

The removal of the base layer 40 may have the advantage that the heat generated by the heating structure 28 can not flow into this particular thick layer, and thus heating can be localized to the desired area. As a result, such a particle sensor 10 can heat in a particularly low-energy manner and the requirements with regard to the voltage or current used are kept low.

In a further method step d), furthermore, an electrode system 20 comprising at least two electrode structures 14, 18 can be applied to the electrically insulating layer 52 or to the base body 22. This process step is known per se and can be realized for example by deposition and structuring. This process step

D) is not shown in detail in the figures.

FIG. 7 shows a further embodiment of a particle sensor 10. FIG. 7 shows that a homogenization region 56 of the main body 22 may be provided in a central area of the main body 22 for homogenizing the temperature of the main body 22 generated by the heating structure 28. The homogenization region 56 can be of the netlike type

Be surrounded heating structure 28. In this embodiment, the electrical heating power can be homogenized by unstructured regions of a thermally and / or electrically conductive material, in particular silicon. Because the

Homogenization region 56 includes a region of low electrical resistance and high thermal conductivity. In this area, in particular, the thermal resistance is low, so that the heat can flow well or can be distributed well in the base body 22 within the heating structure 28. Furthermore, there is little electrical heating due to the low electrical resistance.

In this case, the homogenization region 56 can furthermore be surrounded by an electrically insulating frame 58, which equals a closed contour lift and is produced in the same depth structuring process as the net-like heating structure, as shown in FIG. The electrically insulating frame 58, in particular configured from

Silicon dioxide, in turn, may be surrounded by the heater structure 28. In this embodiment, a temperature homogenization in the base body 22 can take place in particular by a high thermal conductivity of

Silicon surfaces, but only with small reduction of the electrical

Resistance. In this area, the heat can be concentrated in particular on the areas where it is really needed.

Thus, in the embodiments according to FIGS. 7 and 8, for example, the highly thermally conductive silicon can lead to a homogeneous temperature distribution on the electrically insulating layer 42 or the

Silicon dioxide membrane lead by either a suitable distribution of the electric resistive heating power and thermal dissipation according to Figure 7 or exclusively by a thermal dissipation according to Figure 8. Such a temperature homogenization may be advantageous because it may come to higher temperatures due to the better thermal insulation of a central region , than at the thermally better coupled membrane edges. Those shown in FIGS. 7 and 8

Homogenization regions 56 may, for example, have dimensions in a range of> 10 to <20 μm. It can be a single

Homogenization area approximately in the middle of the main body 22nd

or in the middle of the heating structure 28 may be provided, or it may be provided a plurality of homogenization regions 56, which may be arranged in a suitable manner to the temperature in the

Homogenize 22 body or evenly distributed.

Claims

claims

1 . Particle sensor for detecting electrically conductive particles,

comprising a first at least one electrode (12)

Electrode structure (14) and a second at least one electrode (16) having electrode structure (18), wherein the first electrode structure (14) and the second electrode structure (18) on an electrically insulating base body (22) are arranged, wherein between an electrode (12 ) of the first electrode structure (14) and an electrode (16) of the second

Electrode structure (18) an electrical potential difference can be generated, and wherein the base body (22) has a heating structure (28) for heating the first (14) and the second electrode structure (18), of the

Base body (22) is at least partially enclosed.

2. Particle sensor according to claim 1, wherein the base body (22) made

Silica is configured and / or the heating structure (28) is configured of silicon.

3. Particle sensor according to claim 1 or 2, wherein the heating structure (28).

is completely enclosed by the base body (22).

4. Particle sensor according to one of claims 1 to 3, wherein the heating structure (28) has a in the base body (22) arranged net-like line structure.

5. Particle sensor according to one of claims 1 to 4, wherein the heating structure (28), in particular the net-like line structure, having conductor paths, which at least partially have a width which is in a range of <500 nm. 6. Particle sensor according to one of claims 1 to 5, wherein a

Homogenization region (56) for homogenizing the temperature of Base body (22) is provided, which is surrounded by the heating structure (28), in particular wherein the homogenization region (56) is formed of electrically and / or thermally conductive material.

The particle sensor according to claim 6, wherein the homogenization region (56) is surrounded by an electrically insulating frame (58) surrounded by the heating structure (28).

Particle sensor according to one of claims 1 to 7, wherein the base body (22) and the heating structure (28) in a first layer (30) are arranged and wherein the electrode structures (14, 18) in a second layer (32) are arranged and the second layer (32) is disposed on the first layer (30).

Method for producing a particle sensor (10), comprising the method steps:

a) providing a base body (38) comprising a base layer (40), an electrically insulating layer (42) disposed on the base layer (40) and an electrically conductive layer (44) disposed on the electrically insulating layer (42);

b) introducing at least one recess (46) into the electrical

conductive layer (44) for patterning the electrically conductive layer (44);

c) applying an electrically insulating cover layer (52) on the

electrically conductive layer (44); and

d) applying at least two electrode structures (14, 18) to the cover layer (52).

The method of claim 9, wherein as the electrically conductive layer (44) a chemically convertible layer is used and wherein the electrically insulating cover layer (52) is formed by chemically transforming the electrically conductive layer (44).

1 . The method of claim 9 or 10, wherein the base layer (40) and / or the electrically conductive layer (44) are formed of silicon and / or wherein the electrically insulating layer (42) is formed of silicon dioxide.

12. The method according to any one of claims 9 to 1 1, wherein the at least one recess (46) is formed as a circular opening, in particular wherein the circular opening is closed at the periphery.

13. The method according to any one of claims 9 to 12, wherein a plurality of recesses (46), in particular at circular openings, are generated, which are arranged in a hexagonal arrangement.