Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/0004—Gaseous mixtures, e.g. polluted air
  • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
  • G01N33/0027—General constructional details of gas analysers, e.g. portable test equipment concerning the detector
  • G01N33/0036—General constructional details of gas analysers, e.g. portable test equipment concerning the detector specially adapted to detect a particular component
  • G01N33/0037—NOx
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
  • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
  • G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
  • G01N27/128—Microapparatus
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
  • G01N33/0004—Gaseous mixtures, e.g. polluted air
  • G01N33/0009—General constructional details of gas analysers, e.g. portable test equipment
  • G01N33/0011—Sample conditioning
  • G01N33/0013—Sample conditioning by a chemical reaction
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
  • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
  • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Definitions

• the invention relates to a layer composite with a gas-sensitive layer and a catalytically active layer, and to a micromechanical sensor element, in particular gas sensor element, with such a layer composite, according to the preamble of the independent claims.
• semiconductor sensors for the measurement of components of traffic emissions such as carbon monoxide, hydrocarbons (CH X ), nitrogen oxides (N0 X ) etc.
• semiconductor sensors in particular semiconductor sensors based on tin dioxide (Sn ⁇ 2 >) are often used, since these reduce their electrical resistance in the presence of reducing or oxidizing Change gases significantly.
• a catalyst which contains reducing gas components such as Carbon monoxide or hydrocarbons oxidized to carbon dioxide and water before they reach the actual gas-sensitive Sn0 2 layer.
• porous, catalytically active layers are used for this purpose, which are printed on the Sn0 2 layer. These layers consist of aluminum oxide (A1 2 0 3 ) as carrier material and catalytically active substances such as platinum or applied thereon Palladium.
• thick film sensors on micromechanically structured substrates are also known from the prior art, the thick films used again being based on SnO 2.
• Such micromechanical gas sensor elements have the advantage that they can be brought to operating temperature with low power and a small time constant.
• micromechanically structured base carriers are first produced, which are then provided with a known method such as dispensing or inkjet with a Sn0 2 layer in the thickness range of a few ⁇ m.
• the chip obtained is then separated by sawing, which leads to a considerable mechanical load on the applied thick layer.
• the layer composite according to the invention and the micromechanical sensor element according to the invention with such a layer composite has the advantage over the prior art that a catalytically active layer is provided which is intimately connected to the actual gas-sensitive layer and which causes the gas-sensitive layer to reduce gas components from the outside adjacent gas is not exposed.
• these gas components in the catalytically active layer have already been oxidized beforehand or have been converted into a gas which is no longer detectable by the gas-sensitive layer or which no longer influences its electrical conductivity.
• micro-mechanical sensor element of the invention when operating as a gas sensor element only is more sensitive to oxidising gas components such as N0 X, and that its output signal does not also of reducing gas components is dependent.
• the layer composite according to the invention has the advantage that it is the first time that a two-layer system can be implemented on a micromechanical sensor element. So far, thick-film systems could only be produced from a sensitive Sn0 2 layer and a catalytically active layer on so-called “hybrid sensors", ie the sensor elements explained with an Sn0 2 layer and an applied layer made of the carrier material aluminum oxide and catalytic substances applied thereon Such a layer arrangement has so far not been feasible on micromechanical sensor elements for reasons of mechanical stability. Advantageous developments of the invention result from the measures mentioned in the subclaims.
• the catalytically active layer and the gas-sensitive layer now essentially consist of the same gas-sensitive material or the same material base, namely preferably SnO 2
• the composition of the gas-sensitive layer and the catalytically active layer essentially only through the higher electrical conductivity of the gas-sensitive layer achieved by adding a doping substance and the catalytic activity of the catalytically active layer achieved by adding a catalytically active additive distinguish very well and intimately the mechanical connection of these two thick layers.
• these two layers behave mechanically like a one-layer system after their connection, for example by heat treatment such as baking or sintering, but the electrical and chemical advantages of a two-layer system, i.e. the separation of the functions "catalytic activity” and "gas sensitivity” will continue to be maintained.
• the layer composite and the micromechanical sensor element produced therewith are relatively insensitive to mechanical loads, i.e. this is compatible with the established manufacturing technology for micromechanical gas sensors and can be produced with it.
• the gas-sensitive layer has a thickness of 1 ⁇ m to 5 ⁇ m and the catalytically active layer has a thickness of 1 ⁇ m to 10 ⁇ m.
• the electrical conductivity of the catalytically active layer should be as low as possible, ie the catalytic active layer should have a significantly higher specific electrical resistance than the gas-sensitive layer. In this way, changes in the electrical conductivity of the catalytically active layer due to fluctuating compositions of the gas present have only a minor effect on the overall resistance of the sensor element or of the layer composite.
• the catalytically active layer covers the gas-sensitive layer at least on one side, since in this way it is achieved that each gas acting on the gas-sensitive layer is first diffused through the catalytically active layer before it reaches the gas-sensitive layer. This means that the gas-sensitive layer is not, or at least almost not, exposed to reducing gases.
• the invention is explained in more detail with reference to the drawing and the description below.
• the figure shows a schematic diagram of a micromechanical gas sensor element with a self-supporting membrane and an applied layer composite with a gas-sensitive layer and a catalytically active layer in section.
• FIG. 1 shows a micromechanical sensor element 5, for example a gas sensor element or an air quality sensor element.
• a dielectric layer 11 was first deposited on a support body 10, and then a cavern 17 was etched into the back of the support body 10 and extends as far as the dielectric layer 11. so that a largely self-supporting membrane 18 is formed.
• the carrier body 10 is, for example, a silicon body, while the dielectric layer is, for example, a silicon oxide layer, a silicon nitride layer or also a layer made of porous silicon.
• the dielectric layer 11 also has conventional heating elements 13 for heating a gas-sensitive layer 15 applied to the dielectric layer 11 in the region of the membrane 18, and also temperature sensor elements 12 with which the temperature of the gas-sensitive layer 15 can be determined.
• electrodes 14 are arranged on the surface of the dielectric layer 11, which are spaced apart from one another and which are each connected to the gas-sensitive layer 15, so that the electrodes 14 and associated electronic components (not shown) change the electrical conductivity of the gas-sensitive layer 15 can be determined as a function of external gas components.
• the gas-sensitive layer 15 consists of a porous SnO 2 sealing layer with a thickness between 1 ⁇ m and 5 ⁇ m, which is provided in a known manner with dopants such as tantalum to increase the electrical conductivity.
• the specific electrical resistance of the gas-sensitive layer 15 is between 50 k ⁇ cm and 200 k ⁇ cm, in particular approximately 100 k ⁇ cm.
• the gas sensitive layer 15 is further covered by a catalytically active layer 16 such that the gas sensitive Layer 15 is enclosed by the dielectric layer 11 and the catalytically active layer 16.
• the catalytically active layer 16 consists of the same material or the same material base as the gas-sensitive layer 15, ie essentially of SnO 2 , with the difference that the dopant which does not increase the electrical conductivity is added to the catalytically active layer, and that the catalytically active layer 16 instead contains a catalytically active additive, for example platinum or palladium.
• the specific electrical resistance of the catalytically active layer 16 is greater than 300 k ⁇ cm, in particular greater than 500 k ⁇ cm.
• the gas-sensitive layer 15 and the catalytically active layer 16 are intimately connected to one another, so that they behave mechanically as a single layer due to their almost the same composition.
• the micromechanical sensor element 5 is otherwise from I. Simon et al. , Sensors and Actuators, B73, (2001), pages 1 to 26, where reference is made primarily to FIG. 4 and FIGS. 8 and 9. From this, further details on the structure of the micromechanical sensor element 5 as well as on its production and function can be found, so that it can be dispensed with here, apart from the production of the layer composite from the gas-sensitive layer 15 and the catalytically active layer 16.
• high-purity SnO 2 powder is first produced from an aqueous solution.
• a first part of this Ses Sn0 2 powder is then provided with the dopants mentioned to increase the electrical conductivity, while the largest possible amount of catalytically active substances such as platinum and / or palladium is preferably added to a second part of the Sn0 2 powder.
• catalytically active substances such as platinum and / or palladium
• first starting layer is then transferred into the gas-sensitive layer 15 and the second starting layer into the catalytically active layer 16.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Combustion & Propulsion (AREA)
• Food Science & Technology (AREA)
• Medicinal Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)

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• 2001
  • 2001-07-10 DE DE10133466A patent/DE10133466B4/de not_active Expired - Fee Related
• 2002
  • 2002-06-04 US US10/483,134 patent/US20040213702A1/en not_active Abandoned
  • 2002-06-04 JP JP2003512696A patent/JP2004534253A/ja active Pending
  • 2002-06-04 WO PCT/DE2002/002024 patent/WO2003006977A2/de active Application Filing
  • 2002-06-04 EP EP02745118A patent/EP1415144A2/de not_active Withdrawn

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