WO2013034352A1

WO2013034352A1 - Method for producing a sensor element

Info

Publication number: WO2013034352A1
Application number: PCT/EP2012/064393
Authority: WO
Inventors: Jens Schneider; Lothar Diehl; Sascha Klett; Gerhard Schneider
Original assignee: Robert Bosch Gmbh
Priority date: 2011-09-06
Filing date: 2012-07-23
Publication date: 2013-03-14
Also published as: CN103765203A; CN103765203B; DE102011082175A1

Abstract

A method is proposed for producing a sensor element (10) for detecting at least one property of a gas in a measurement space, more particularly for detecting a gas component in the gas or a temperature of the gas. The method comprises the following steps: providing a sintered solid electrolyte (12), arranging a heating element (18) on or in the solid electrolyte (12), and the conjoint thermal treatment of the solid electrolyte (12) and the heating element (18).

Description

Description title

METHOD FOR MANUFACTURING A SENSOR ELEMENT

State of the art

A large number of sensor elements and methods for detecting at least one property of a gas in a measuring gas space are known from the prior art. This can basically be any physical and / or chemical

Properties of the gas, wherein one or more properties can be detected. The invention is described below in particular with reference to a qualitative and / or quantitative detection of a gas component of the gas, in particular with reference to a detection of an oxygen content in the gas. The oxygen content can be detected, for example, in the form of a partial pressure and / or in the form of a percentage. Alternatively or additionally, however, other properties of the gas are detectable, such as the

Temperature of the gas.

For example, such sensor elements can be configured as so-called lambda probes, as they are known, for example, from Konrad Reif (ed.): Sensors in

Motor vehicle, 1. Edition 2010, pp. 160-165. With broadband lambda probes, in particular with planar broadband lambda probes, for example, the

Determined oxygen concentration in the exhaust gas in a wide range and thus be closed to the air-fuel ratio in the combustion chamber. The air ratio λ describes this air-fuel ratio.

In particular, ceramic sensor elements are known from the prior art, which are based on the use of electrolytic properties of certain solids, ie ion-conducting properties of these solids. In particular, these solids can be ceramic solid electrolytes, such as, for example, zirconium dioxide (ZrO ₂ ), in particular yttrium-stabilized zirconium dioxide (YSZ) and / or Scandium-doped zirconia (ScSZ), which may contain minor additions of aluminum oxide (Al ₂ O ₃ ) and / or silicon oxide (Si0 ₂ ).

Due to its measuring principle, the lambda probe usually has to be first heated to its operating temperature, since the solid electrolyte becomes conductive only at temperatures above 350 ° C. for oxygen ions. The operating temperature is

usually in the range of 600 ° C to 900 ° C.

The lambda probes therefore usually have a heating element which serves to heat the solid electrolyte and the electrodes. This heating element is usually applied to a solid electrolyte or to a solid electrolyte layer in the green state, i. in an unsintered state, applied, for example, glued or printed. Subsequently, the solid electrolyte is arranged together with the one

Heating element sintered to a permanent adhesion of the heating element to the

To ensure solid electrolyte.

Motorized two-wheelers are very common in Asian countries. Significant tightening of emissions regulations is planned in these countries over the next few years. This results in a great need for sensor elements, in particular stoichiometric lambda probes, for mixture control in the internal combustion engines of these two-wheelers. The requirements for lambda sensors for small motor vehicles, such as motorcycles, for example, differ significantly from the requirements for lambda sensors for motor vehicles. In particular, the sensor elements for small motor vehicles must be designed even more cost-effective and physically smaller. Furthermore, the temperature resistance of the various components, such as solid electrolyte, probe body or cable exit, must be at least as high as in sensor elements for motor vehicles, since the small motor vehicles usually use cheaper engine concepts, which have a worse combustion and thus cause a lower efficiency. Therefore, it comes to long periods of operation in full load operation, so that the sensor elements are exposed to correspondingly high exhaust gas temperatures.

Lambda sensors for motor vehicles, especially automobiles, and commercial vehicles have a comparatively large heating element with a high power consumption. A low-impedance, high-performance heater, as used in such lambda probes would be too large for small-sized vehicles and because of the additional cost problematic for a high-performance heater output stage as well as for heat-efficient heat dissipation from the control unit.

Disclosure of the invention

Therefore, a sensor element is proposed for detecting at least one property of a gas in a measurement gas space, in particular for detecting a gas component in the gas or a temperature of the gas, and a method for its production, which is more compact in its construction than previously known

Sensor elements for motor vehicles is and especially for small motorized

Vehicles, especially two-wheelers, such as motorcycles, is suitable.

The method according to the invention for producing such a sensor element comprises the following steps, preferably in the order given:

Providing a sintered solid electrolyte,

Arranging a heating element on or in the solid electrolyte, and common thermal treatment of the solid electrolyte and the

Heating element.

The heating element may be disposed in or on the solid electrolyte in an unsintered state, and the thermal treatment may be sintering. Of the

Solid electrolyte may include an insulating layer on which the heating element is disposed, and the heating element may be coated with an insulating layer or a protective glaze prior to sintering. The coefficient of thermal expansion of the insulating layer of the solid electrolyte may differ from the coefficient of thermal expansion of the insulating layer of the heating element by at most 10%, preferably at most 5% and particularly preferably at most 2%, for example by 1%. The insulating layer of the solid electrolyte may have a thickness of 2 μηη to 100 μηη, preferably 5 μηη to 75 μηη and more preferably from 10 μηη to 50 μηη have. The heating element can be arranged by printing, rolling, brushing or painting on or in the solid electrolyte. The heating element can also be arranged in a sintered state on or in the solid electrolyte and the thermal treatment can be a tempering. The heating element can be attached by gluing or mechanical bonding,

in particular pressing, be arranged on or in the solid electrolyte. The

Heating element can with the solid electrolyte by means of a high temperature resistant material be connected, in particular by means of a glass ceramic, a ceramic adhesive or a glass frit. For bonding the heating element to the solid electrolyte, it is possible to use an adhesive which is applied to the solid electrolyte by brushing, painting, printing, spraying or as a decal. The adhesive may have a thickness of from 2 μηη to 300 μηη and preferably from 5 μηη to 250 μηη and more preferably from 10 μηη to 200 μηη.

The sensor element may have a maximum length of 55 mm, preferably a maximum of 45 mm and more preferably a maximum of 40 mm, and a maximum width of 8 mm, preferably not more than 7 mm and more preferably not more than 6 mm, for example a length of 35 mm and a Width of 5 mm. The heating element may have a cold total resistance of 6 Ω to 22 Ω, and preferably from 8 Ω to 20 Ω. The heating element may be an electrical heating element with a power consumption of a maximum of 5 W, preferably a maximum of 4 W and more preferably a maximum of 3.5 W, at an operating voltage of 13 V, for example 4 W.

In the context of the present invention, a solid electrolyte is to be understood as meaning a body or article having electrolytic properties, that is to say having ion-conducting properties. In particular, it may be a ceramic solid electrolyte. In particular, the solid electrolyte may be in the form of a solid electrolyte layer or of several

Be formed solid electrolyte layers. In the context of the invention, a layer is to be understood as meaning a uniform mass in areal extent with a certain height which lies above, below or between other elements. An electrode in the context of the present invention is generally understood to mean an element which is capable of contacting the solid electrolyte in such a way that a current can be maintained by the solid electrolyte and the electrode. Accordingly, the electrode may comprise an element to which the ions can be incorporated in the solid electrolyte and / or removed from the solid electrolyte. Typically, the electrodes comprise a noble metal electrode, which may, for example, be applied to the solid electrolyte as a metal-ceramic electrode or otherwise be in communication with the solid electrolyte.

Typical electrode materials are platinum cermet electrodes. However, other precious metals, such as gold and / or palladium, are in principle applicable. In the context of the present invention, a heating element is generally to be understood as meaning an element which is capable of heating the solid electrolyte and the electrodes to their functional temperature. The heating element can a

Supply line and have a heating area. Usually, at least one electrode is arranged on or in the solid electrolyte. The heating element is separated from the electrode either by the solid electrolyte, a solid electrolyte layer or additional insulation. A heating region of the heating element is to be understood as that region of the heating element which overlaps the electrode in the direction of this layer structure. For example, in a planar structure of a lambda probe, the overlap in a direction perpendicular to the

Layers of planar construction can be seen. The heating area is usually located in an end region of the solid electrolyte. A supply region is to be understood as that region of the heating element which serves to transport the energy for heating the solid electrolyte and the electrode into the heating region.

A cold resistance in the context of the present invention is to be understood as the electrical resistance measured at 20 ° C. According to this definition, the total cold resistance is understood to mean the electrical resistance of the entire heating element, which is composed of the resistance of the heating region and the resistance of the supply region.

An insulating layer is to be understood in the context of the present invention as an electrically insulating layer. Such a layer usually comprises

Alumina, silicon carbide (SiC), aluminum nitride (AIN), magnesium oxide (MgO), barium steatite, steatite, cordierite or other commercial ceramic insulating materials.

In the context of the present invention, a protective glaze is to be understood as meaning a glaze which may contain aluminum, silicon and / or barium and serves to protect a component against external influences, such as, for example, thermal stresses, mechanical effects or damage by electrical voltage.

In the context of the present invention, a coefficient of thermal expansion is to be understood as a characteristic value which describes the behavior of a substance with respect to changes in its dimensions in the case of temperature changes. In particular, this is the ratio between the relative volume increase dV / V, ie Volume change compared to the initial volume, and to understand the temperature change dT of a body, so that the characteristic value has the unit 1 / K.

A high-temperature resistant material is to be understood as meaning a material which is at a temperature, such as its state, in particular its state of aggregation

especially in an exhaust tract of an internal combustion engine, i.

Temperatures up to 1000 ° C, not changed. In particular, such materials remain dimensionally stable even at such temperatures and do not start to flow and / or melt or react. Examples of such materials are in particular

Glass ceramic, ceramic adhesive or glass frits. The term frit is a

Intermediate to understand in the production of glass or ceramic melts. The glass frit is formed, for example, by superficial melting of glass powder, whereby the glass grains cake together. Both the powder and the resulting material is called a frit. In some manufacturing processes, the resulting material is additionally quenched. The result is a porous material. Finally, it is easy to produce a powder from the quenched material by grinding, which is also called a frit.

For the purposes of the present invention, among the platinum metal group according to the general definition of chemistry are the elements of groups 8 to 10 of the 5th period, i. the light platinum metals ruthenium (Ru), rhodium (Rh), palladium (Pd), and the 6th period, i. to understand the heavy platinum metals osmium (Os), iridium (Ir), platinum (Pt). In the context of the present invention, sintering is to be understood as meaning a process for the production of materials and / or workpieces in which fine-grained, ceramic substances are heated to temperatures below their melting temperatures, usually under elevated pressure. When sintering mostly granular or powdery substances are mixed and then joined together by heating. In contrast to the pure melt, however, no or at least not all starting materials are melted. It is therefore a primary molding process. The powder masses are first brought into the shape of the desired workpiece. This is done either by compression of the powder masses or by shaping and subsequent drying.

Here, at least a minimum cohesion of the powder particles must be given. If this cohesion is not given, a binder must be used. This so-called green compact is subsequently heat treated below the Melting temperature compacted and cured. In the technical field of the present invention, sintering takes place at temperatures of 900 ° C to 1400 ° C.

In the context of the present invention, tempering is to be understood as meaning the heating of a solid to a temperature below the melting temperature. This happens over a long period of time, which can span several hours. Due to the increased mobility of the atoms of the solid structure defects can be compensated and the crystal structure in the near and far order can be improved. In this way, the process of melting and cooling to adjust the crystal structure can be avoided. In the technical field of the present invention, the annealing is carried out at a temperature of at most 1000 ° C, preferably at a temperature of 400 ° C to 800 ° C.

The invention is basically suitable for any internal combustion engine having at least one ceramic sensor element for detecting at least one parameter of an exhaust gas of an internal combustion engine, in particular at least one lambda sensor and / or at least one NOx sensor and / or at least one HC sensor, wherein the ceramic sensor element has at least one heating element for heating the ceramic sensor element. In particular, the internal combustion engine may comprise a gasoline engine and / or a diesel engine. Alternatively or additionally, the internal combustion engine may also comprise a hybrid drive, for example with a gasoline engine and / or at least one diesel engine and additionally at least one electric motor. The ceramic sensor element may in particular be a lambda probe or comprise a lambda probe. The lambda probe can be designed, for example, as a finger probe or as a planar lambda probe, that is to say for example as a lambda probe with a laminar structure. For example, jump probes and / or broadband lambda probes can be realized. Alternatively or additionally, the ceramic

Sensor element also comprise at least one other type of ceramic sensor element, for example, a NOx sensor.

The ceramic sensor element may comprise at least one electrochemical cell. In the context of the present invention, an electrochemical cell is to be understood as meaning an element which comprises at least two electrodes and at least one solid electrolyte which connects the electrodes. A temperature of Ceramic sensor element can be determined for example by means of a determination of an internal resistance of the electrochemical cell. In a ceramic sensor element with a Nernst cell, the temperature of the ceramic

Sensor element can be detected for example by means of a determination of the internal resistance of the Nernst cell.

The heating of the ceramic sensor element and / or the power supply of the heating element can be effected by means of an electrical energy source, such as the battery in a vehicle.

The production method according to the invention differs from the methods known from the prior art by the following features: printing, rolling, brushing or painting, such as by means of a stencil

A heater structure on a sintered ceramic substrate, such as a sensor element of an exhaust probe, using an ink or paste with platinum or platinum compound as an electrical conductor and a scaffolding portion for stabilizing the heater structure, and a subsequent coating with a thin oxide insulating layer or protective glaze, such as aluminum , Silicon and / or barium fractions, and a subsequent process step for the firing of the heater structures and the protective glaze. Alternatively, it is also possible by sticking or mechanical

Connecting a prefabricated heating element on or in the prefabricated sintered solid electrolyte body to produce the sensor element. This is conceivable, for example, by surface or partial bonding with a high-temperature-resistant material which is subjected to a temperature treatment together with the solid electrolyte, for example a glass ceramic, a ceramic adhesive or a glass frit. By joint assembly of the heating element and the solid electrolyte body and by heat transfer by radiation and convection, the connection is permanently guaranteed. By using a heating element, preferably from the support material alumina, silicon carbide, aluminum nitride, barium steatite, steatite, cordierite or other common ceramic insulating materials, this is

high temperatures. The use of a heating element with a

high temperature stable Heizleitermaterial, such as platinum, rhodium, palladium, gold, chromium, tungsten, molybdenum or corresponding alloys, is possible. In particular, the heating element can basically be realized as a co-sintered or subsequently sintered platinum-metal group structure. In particular, the heating element is a weak heating element for bridging cold

Operating conditions, such as during idle, with a

Power consumption of a maximum of 5 W, while lambda probes for motor vehicles more than 7 W are common. The inrush current does not exceed 2 A to minimize the requirement for a sensor element controller. A light-emitting behavior of the probe of up to 30 seconds is unproblematic for exhaust gas probes for small motor vehicles, since the majority of the pollutant amount is not formed here in the starting phase, but within the corresponding driving cycle. The use of

Metals of the platinum group metal for the structure of the heating element is due to the high thermal load of hot exhaust gases, which may be up to about 1000 ° C at full load required. The heating element is formed in particular from platinum cermet and may correspond to the prior art material composition, but is designed with a high support framework proportion and thin meander and lead structures to a total cold resistance of 8 Ω to 20 Ω. It suffices in this case to design the heat output in such a way that, when heating in a cold ambient temperature, i. at temperatures from -20 ° C to -40 ° C, one

Sensor element temperature of a maximum of 750 ° C is reached.

In particular, a sensor element with a maximum length of 40 mm and a maximum width of 6 mm is proposed, which has an integrated heating element, the minimum cold resistance at 20 ° C from 8 Ω to 20 Ω and a

Power consumption of 5 W when applying an operating voltage of 13 V has. Characterized in that according to the invention, the heating element to an already

finished, i. sintered solid electrolyte bodies is applied, can be arranged on such a solid electrolyte body differently designed heating elements. This is particularly advantageous in the case when the heating element itself is already completed, i. is sintered, so that any combination of different heating elements can be arranged on the same type of solid electrolyte bodies.

Brief description of the drawings

Further optional details and features of the invention will become apparent from the following description of preferred embodiments, which are shown schematically in the figures. Show it: Figure 1 is a cross-sectional view of a sensor element of a first

Embodiment, Figure 2 is a cross-sectional view of a sensor element of a second

Embodiment and

Figure 3 is a cross-sectional view of a sensor element of a third

Embodiment.

Embodiments of the invention

Figure 1 shows a cross-sectional view of a first embodiment of a

Sensor element 10 according to the invention can be used for the detection of physical and / or chemical properties of a gas, wherein one or more properties can be detected. The invention is described below in particular with reference to a qualitative and / or quantitative detection of a gas component of the gas, in particular with reference to a detection of an oxygen content in the gas. The oxygen content can be detected, for example, in the form of a partial pressure and / or in the form of a percentage. In principle, however, other types of gas components are also detectable, for example nitrogen oxides, hydrocarbons and / or hydrogen. Alternatively or additionally, however, other properties of the gas can be detected. The invention can be used in particular in the field of vehicle technology, in particular in the field of small motor vehicles, such as

Motorcycles, so that it may be in the sample gas chamber in particular an exhaust tract of an internal combustion engine of a motorcycle and the gas in particular an exhaust gas. The sensor element 10 is described as an exemplary component of a planar lambda probe, but is not limited to this type of lambda probe, but can also be designed as a finger probe. Since this lambda probe has a compact design for use in small motor vehicles, the sensor element 10 has, for example, a length, ie a dimension in the direction of the view of FIG. 1 of not more than 50 mm, in particular not more than 45 mm and particularly preferably not more than 40 mm, and a width, ie a dimension from left to right or vice versa the Figure 1 of a maximum of 10 mm, in particular a maximum of 8 mm and more preferably a maximum of 6 mm, on. In the example of FIG. 1, the sensor element 10

for example, a length of 35 mm and a width of 5 mm. Therefore, the view of FIG. 1 is a view of a cross section perpendicular to a longitudinal direction of the sensor element 10.

The sensor element 10 has a solid electrolyte 12 which is yttrium-stabilized

Zirconium dioxide with, for example, 6 to 10% by weight of yttrium oxide contains a first electrode 14 facing a measuring gas space, a second electrode 16, a heating element 18 and a reference channel 20. In the case of lambda probes, a pumped reference can be problematic for small motor vehicles, for which reason a probe design with air reference and a corresponding effect on low heating power requirement is preferred in the example shown. A high heat output is not required for the small motor vehicle exhaust probes. Further details regarding the power consumption of the heating element 18 will be discussed in more detail later.

The heating element 18 is arranged to heat the electrodes 14, 16 and the solid electrolyte 12. The electrodes 14, 16 are connected to one another via the solid electrolyte 12 and can form a Nernst cell and / or electrochemical cell. It is also possible to provide further functional layers, for example further electrodes, a conductor track, a diffusion barrier, a diffusion gap, a further heating element and / or an oxygen pumping cell. These functional layers may be incorporated or integrated in the solid electrolyte 12. The optional Nernst cell in the solid electrolyte 12 is preferably provided to measure the respective residual oxygen content in a combustion exhaust gas and from this the ratio of

To control combustion air to fuel for further combustion so that neither a fuel nor an excess of air occurs.

On a side of the solid electrolyte 12 opposite the first electrode 14 there is a first insulating layer 22 having a thickness of from 2 μm to 100 μm, preferably from 5 μm to 75 μm, and particularly preferably from 10 μm to 50 μm.

For example, the first insulating layer 22 may have a thickness of 30 μm. The first insulating layer 22 is made of alumina in the main component. Alternatively or additionally, however, silicon carbide, aluminum nitride, barium steatite, steatite or cordierite can be used for the first insulating layer 22. The heating element 18 is arranged on the first insulating layer 22. The heating element 18 is of a second Insulating layer 24 or protective glaze covered or coated so that the

Heating element 18 between the first insulating layer 22 and the second insulating layer 24 is embedded. The second insulating layer 24 has the same thickness as the first insulating layer 22 for a symmetrical arrangement of the heating element 18 between the first insulating layer 22 and the second insulating layer 24. However, it is understood that the first insulating layer 22 and the second insulating layer 24 may have a different thickness. A variation of the thickness may be required, for example, depending on the mounting position or the specific field of application. The production of the sensor element 10 takes place in such a way that a solid electrolyte 12 in a green state, i. an unsintered state, in a manner known per se, for example by the thick-film technique and / or the film lamination technique and / or a screen printing method and / or a spraying method with the functional layers, in particular the electrodes 14, 16 and the reference channel 20, but also with the first insulating layer 22 is provided. In particular, the first insulating layer 22 is applied with a thickness such that the first insulating layer 22 after sintering has the above-mentioned thickness, i. a thickness of 30 μηη after sintering. The first insulating layer 22 may be applied to the solid electrolyte by, for example, printing, rolling, brushing or painting or the like. In particular, the first insulating layer 22 is formed such that its coefficient of thermal expansion deviates from the later-applied second insulating layer 24 by a maximum of 10%, preferably not more than 5% and particularly preferably not more than 2%, for example by 1%. The setting of the respective

Thermal expansion coefficients can be carried out by additions of silica, calcium oxide, magnesium oxide, barium oxide or other metal oxides. Furthermore, it is possible and advantageous to adapt the modulus of elasticity of the first

Insulating layer 22 to the elastic modulus of the second applied later

Insulating layer 24 by targeted introduction of porosity make. The porosity can be achieved by introducing a pore-forming agent, which usually consists of

Carbon based materials is to be adjusted. This volatilizes or burns during sintering, preferably residue-free, leaving behind cavities. The solid electrolyte 12 is then together with the electrodes 14, 16, the

Reference channel 20 and the first insulating layer 22 sintered. The sintering can

for example, at a temperature of 900 ° C to 1400 ° C, over several hours. A thus finished, ie already sintered, solid electrolyte 12 with the already arranged thereon electrodes 14, 16, the introduced reference channel 20 and the applied first insulating layer 22 is then for a subsequent

Process step for arranging a heating element 18 is provided. In this case, the heating element 18 is applied to the first insulating layer 22 of the sintered solid electrolyte 12

printed, rolled up, brushed or painted, such as applied by a paste or ink, or as a prefabricated decal by the so-called transfer technique. The heating element 18 is preferably made of metals from the

Platinum metal group, such as platinum, rhodium, palladium, gold, or even transition metals, e.g. Chromium, tungsten or molybdenum, or their alloys. In particular, the geometry of the heating element 18 of the solid electrolyte 12 is adapted to the requirements of the assembly. In particular, the heating element 18 may be designed such that the electrical power input is mainly in the heating area, i. in the region of a measuring cell of the sensor element 10, is implemented. The

Measuring cell is the area of the heating element 18, which overlaps with the electrodes 14, 16. This can be done by a corresponding design of the electrical resistance of the heating element 18, in which in the heating area, i. the area of

Measuring cell, for example, a resistance of 8 Ω to 20 Ω, for example, 10 Ω, is provided and in a supply range, a resistance of 1 Ω to 3 Ω is provided. This can be done, for example, by the heating conductor having a smaller cross-section in the heating region than in the supply region. The heating element 18 is then coated with the second insulating layer 24 or protective glaze, which can also be applied as a paste or ink or as a prefabricated decal. Subsequently, a drying process and then a thermal treatment, such as a renewed sintering process, such as at a temperature of 900 ° C to 1250 ° C, over several hours. The second insulating layer 24 or the protective glaze is made of a similar material as the first insulating layer 22, which is burned due to its composition at low temperature together with the heating element 18 and so permanently adheres to the first insulating layer 22. The first insulating layer 22 and the second insulating layer 24 are preferably made thin with said thicknesses and made of a material such as alumina, which is electrically insulating and a high

Thermal conductivity has formed. FIG. 2 shows a cross-sectional illustration of a sensor element 10 according to a second embodiment. Below are just the differences to the first

Embodiment described, wherein like components have the same reference numerals. The sensor element 10 likewise has a solid electrolyte 12, wherein a heating element 18 is arranged on one side of the solid electrolyte 12 opposite the first electrode 14. In particular, the heating element 18 is embedded in an insulating layer 22 and fixedly attached to the solid electrolyte 12 by means of an adhesive 26. In particular, the adhesive 26 is arranged as a layer, the layer thickness of the adhesive 26 being 2 .mu.m to 300 .mu.m, preferably 5 .mu.m to 250 .mu.m, and particularly preferably 10 .mu.m to 200 .mu.m, for example 50 .mu.m. The adhesive 26 is made of a

high temperature resistant material. Alternatively, another high-temperature resistant material suitable for permanently attaching the heating element 18 and the insulating layer 22 to the solid electrolyte 12, such as one, may be used

Glass ceramic or a glass frit.

The production of the sensor element 10 takes place in such a way that a solid electrolyte 12 in a green state, i. an unsintered state, in a conventional manner by, for example, the thick-film technique and / or the Folienlaminiertechnik and / or a screen printing process and / or a spray process with the functional layers, in particular the electrodes 14, 16 and the reference channel 20, is provided. The solid electrolyte 12 is then together with the electrodes 14, 16 and the

Reference channel 20 sintered. The sintering can be carried out for example at a temperature of 900 ° C to 1400 ° C for several hours.

Such a finished, i. already sintered solid electrolyte 12 with the electrodes 14, 16 already arranged thereon and the introduced reference channel 20 is then used for a subsequent method step for arranging a heating element 18

provided. On the first electrode 14 opposite side of the

Solid electrolyte 12, an adhesive 26 is applied, for example, brushed, for example by a brush or a squeegee, printed, for example by screen printing or pad printing, sprayed or glued as a decal. The

Layer thickness of the adhesive 26 is chosen so that it is 2 μηη to 300 μηη, preferably 5 μηη 250 μηη and more preferably 10 μηη to 200 μηη, for example, 50 μηη after a thermal treatment, which will be described below.

Optionally, for applying the adhesive 26, a material development or Adaptation of existing material systems may be required. For example, a ceramic adhesive, a glass ceramic or glass frits can be used. In particular, an adhesive 26 is used, which after a thermal described later

Treatment has a coefficient of thermal expansion which is identical to the coefficient of thermal expansion of the solid electrolyte 12 and the heating element 18 or, if this is not technically possible, has a coefficient of thermal expansion which substantially the arithmetic mean between the

Thermal expansion coefficient of the solid electrolyte 12 and the heating element 18 has. For example, if the solid electrolyte 12 has a

Thermal expansion coefficient of 10 x 10 ^"6 1 / K and the heating element 18 a

Thermal expansion coefficient of 6 x 10 ^"6 1 / K, so an adhesive 26 is used, which has a thermal expansion coefficient of 8 x 10 ^{" 6} 1 / K after a thermal treatment. On the adhesive 26, a prefabricated heating element 18, which is embedded in an insulating layer 22, applied, ie, the heating element 18 and the insulating layer 22 are in a sintered state. The embedding of the heating element 18 in the insulating layer 22 can be effected, for example, by applying the heating element 18 to a first part of the insulating layer 22, for example by printing or brushing on a paste, and then applying a second part of the insulating layer 22 covering the heating element 18 , By a subsequent sintering process from the first part and the second part of the insulating layer 22 is a monolithic composite, so that the two parts are no longer distinguishable and a single insulating layer 22 is present with the heating element 18 therein. The above

Thermal expansion coefficient for the heating element refers to the composite of the insulating layer 22 and the heating element embedded therein 18. The insulating layer 22 thus serves as a support for the heating element 18, since it carries the heating element 18, in particular carries in itself. As a support material for the heating element 18, for example, a material may be used which preferably consists of aluminum oxide, silicon carbide, aluminum nitride, magnesium oxide, silicon oxide, barium steatite, steatite and / or cordierite or other commercially available ceramic insulating materials. These materials are electrically insulating and have a high thermal conductivity. The material used for the heating element 18 is preferably platinum, rhodium, palladium, gold, chromium, tungsten, molybdenum or their alloys. In particular, the geometry of the heating element 18 of the solid electrolyte 12 is adapted to the requirements of the assembly. The insulating layer 22 has, for example, a thickness of 60 μηη and is thus preferably made thin. In particular, the heating element 18 can be designed in such a way that the electrical power input is converted mainly in the heating area, ie the part of the heating element 18 which will be located in a region of a measuring cell of the sensor element 10. The measuring cell is the area of the solid electrolyte 12 which overlaps with the electrodes 14, 16.

Subsequently, the solid electrolyte 12, the adhesive 26, and the insulating layer 22 with the heating element 18 embedded therein are subjected to a thermal treatment. This takes place for example as heat treatment at a temperature of at most 1000 ° C., preferably at a temperature of 400 ° C. to 800 ° C., for example at 600 ° C. for 12 hours, and thus at a lower temperature than a sintering process. The

Heat transfer takes place by heat radiation and convection. One

co-sintering of the solid electrolyte 12, the adhesive 26, and the insulating layer 22 with the heating element 18 embedded therein is not required in this embodiment because the solid electrolyte 12 and the heating element 18 have already undergone a sintering process in their separate production. The heat treatment is preferably used to cure the adhesive 26 so that it the insulating layer 22 and the

Solid electrolyte 12 permanently connects. FIG. 3 shows a cross-sectional view of a sensor element 10 according to a third embodiment. The following are merely the differences to the second

Embodiment described, wherein like components have the same reference numerals.

The sensor element 10 of the third embodiment also has a solid electrolyte 12 and a first electrode 14 and a second electrode 16 and one therein

arranged reference channel 20. The heating element 18 is embedded in an insulating layer 22 on an opposite side of the first electrode 14

Solid electrolyte 12 is arranged. The difference from the second embodiment is that no adhesive is provided for bonding between the solid electrolyte 12 and the insulating layer 22, i. the insulating layer 22 with the embedded therein

Heating element 18 is attached to the solid electrolyte 12 without adhesive.

In contrast to the second embodiment, no adhesive 26 is used to produce the sensor element 10 of the third embodiment, but the finished solid electrolyte 12, ie the sintered solid electrolyte 12, becomes with the electrodes 14, 16 already arranged thereon and the reference channel 20 introduced therein provided. The completion of the solid electrolyte 12 and the mentioned

Functional layers are carried out, for example, as in the second embodiment. The insulating layer 22 with the heating element 18 embedded therein is in a

finished condition, i. sintered state on the electrode 14

opposite side of the solid electrolyte 12 is arranged. Subsequently, the solid electrolyte 12 and the insulating layer 22 mounted thereon are mechanically connected. This can be done, for example, by arranging the solid electrolyte 12 with the insulating layer 22 arranged thereon in a molding tool and subsequent pressing. The force applied for pressing is below the material strength of the solid electrolyte 12 and the insulating layer 22 with the embedded therein

Heating element 18 and may for example be 50 kN. By pressing it comes to a compression, in particular in the area of the contact surfaces of the

Solid electrolyte 12 and the insulating layer 22 so that they are superficially pressed into each other depending on the applied force. Subsequently, the solid electrolyte 12 and the insulating layer 22 connected thereto are removed from the mold and subjected to a thermal treatment. This takes place for example as heat treatment at a temperature of at most 1000 ° C., preferably at a temperature of 400 ° C. to 800 ° C., for example at 600 ° C. for 12 hours, and thus at a lower temperature than a sintering process. The heat transfer takes place by heat radiation and convection. A common sintering of the solid electrolyte 12 and the insulating layer 22 with the heating element 18 embedded therein is in this

Embodiment not required because the solid electrolyte 12 and the heating element 18 have already been subjected to a sintering process in their separate production. The tempering is preferably used to stabilize the mechanical connection between the solid electrolyte 12 and the insulating layer 22. This also leads to a permanent bonding of the solid electrolyte 12 with the insulating layer 22. An eventual air gap between the insulating layer 22 and the solid electrolyte 12 may by a correspondingly stronger design the heating power of the heating element 18 can be compensated. In addition, it may be advantageous to plan flat the contact surfaces of the insulating layer 22 and the solid electrolyte 12 or at least one of them prior to mechanical bonding. As a result, the forces during pressing act more uniformly on the contact surfaces of the insulating layer 22 and the solid electrolyte 12 and the connection between them is equally stable over the entire contact surfaces. For all the aforementioned embodiments, a heating element 18 is used, which has a total cold resistance of 8 to 20 Ω. Furthermore, all have

Sensor elements have a maximum length of 55 mm, preferably 45 mm, more preferably a maximum of 40 mm, and a maximum width of 8 mm, preferably not more than 7 mm and more preferably not more than 6 mm, for example a length of 35 mm and a width of 5 mm ,

It is to be expressly understood that all features disclosed in the specification and claims should be considered as separate and independent of each other for purposes of original disclosure as well as for the purpose of limiting the claimed invention independently of the feature combinations in the embodiment and / or claims , It is explicitly stated that all

Range indications or indications of groups of units every possible

Intermediate value or any subgroup for the purpose of the original one

Disclosure as well as for the purpose of limiting the claimed invention, in particular also as a limit of a range indication.

Claims

Claims 1. Method for producing a sensor element (10) for detecting at least one property of a gas in a measurement gas space, in particular for detecting a gas component in the gas or a temperature of the gas, comprising the steps:

Providing a sintered solid electrolyte (12),

- Arranging a heating element (18) on or in the solid electrolyte (12), and common thermal treatment of the solid electrolyte (12) and the heating element (18).

2. Method according to the preceding claim, wherein the heating element (18) in

an unsintered state is disposed on or in the solid electrolyte (12) and the thermal treatment is sintering.

3. The method according to any one of the preceding claims, wherein the solid electrolyte (12) comprises an insulating layer (22) on which the heating element (18) is arranged, and the heating element (18) before the thermal treatment with an insulating layer (24) and / or a protective glaze is coated.

4. The method according to the preceding claim, wherein the

Thermal expansion coefficient of the insulating layer (22) of the solid electrolyte (12) of the coefficient of thermal expansion of the insulating layer (24) of the heating element (18) by a maximum of 10%, preferably at most 5% and more preferably at most 2%, deviates, for example by 1%.

5. The method of claim 3 or 4, wherein the insulating layer (22) of the solid electrolyte (12) after the common sintering with the heating element (18) has a thickness of 2 μηη to 100 μηη, preferably 5 μηη to 75 μηη and particularly preferably of 10 μηη to 50 μηη, has.

6. The method according to any one of the preceding claims, wherein the heating element (18) by printing, rolling, brushing or painting on the solid electrolyte

(12) is arranged.

A method according to claim 1, wherein the heating element (18) is disposed in a sintered state on or in the solid electrolyte (12) and the thermal treatment is annealing.

8. The method according to the preceding claim, wherein the heating element (18) by gluing or mechanical bonding, in particular pressing, on or in the solid electrolyte (12) is arranged.

9. The method according to the preceding claim, wherein the heating element (18) is connected to the solid electrolyte (12) by means of a high temperature resistant material, in particular a glass ceramic, a ceramic adhesive (26) or a glass frit

10. The method of claim 8 or 9, wherein for bonding the heating element (18) with the solid electrolyte (12), an adhesive (26) is applied by brushing, brushing, printing, spraying or as a decal applied to the solid electrolyte (12) becomes.

1 1. Method according to the preceding claim, wherein the adhesive (26) after sintering has a thickness of 2 μηη to 300 μηη and preferably 5 μηη to 250 μηη and particularly preferably from 10 μηη to 200 μηη having.

12. The method according to any one of the preceding claims, wherein the heating element (18) has a total cold resistance of 6 ohms to 22 ohms, and preferably from 8 ohms to 20 ohms.

13. The method according to any one of the preceding claims, wherein the heating element (18) is an electrical heating element with a power consumption of a maximum of 5 W, preferably 4 W and more preferably 3.5 W, at an operating voltage of 13 V, for example, a power consumption of 5 W.

14. The method according to any one of the preceding claims, wherein the sensor element (10) has a maximum length of 55 mm, preferably at most 45 mm and still

more preferably not more than 40 mm and a maximum width of 8 mm, preferably not more than 7 mm and more preferably not more than 6 mm, for example a length of 35 mm and a width of 5 mm.