EP1192459A1 - Semiconductor gas sensor with housing and method for measuring of gas concentrations - Google Patents

Semiconductor gas sensor with housing and method for measuring of gas concentrations

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Publication number
EP1192459A1
EP1192459A1 EP00938476A EP00938476A EP1192459A1 EP 1192459 A1 EP1192459 A1 EP 1192459A1 EP 00938476 A EP00938476 A EP 00938476A EP 00938476 A EP00938476 A EP 00938476A EP 1192459 A1 EP1192459 A1 EP 1192459A1
Authority
EP
European Patent Office
Prior art keywords
gas
housing
sensor element
opening
sensor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP00938476A
Other languages
German (de)
French (fr)
Inventor
Gerhard Müller
Thomas Becker
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Airbus Defence and Space GmbH
Original Assignee
EADS Deutschland GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by EADS Deutschland GmbH filed Critical EADS Deutschland GmbH
Publication of EP1192459A1 publication Critical patent/EP1192459A1/en
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • G01N27/125—Composition of the body, e.g. the composition of its sensitive layer
    • 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
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G19/00—Compounds of tin
    • C01G19/02—Oxides
    • 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
    • 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—Specially adapted to detect a particular component
    • G01N33/0037—Specially adapted to detect a particular component for NOx
    • 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—Specially adapted to detect a particular component
    • G01N33/0039—Specially adapted to detect a particular component for O3
    • 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—Specially adapted to detect a particular component
    • G01N33/004—Specially adapted to detect a particular component for CO, CO2
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02521—Materials
    • H01L21/02524—Group 14 semiconducting materials
    • H01L21/02535—Group 14 semiconducting materials including tin

Definitions

  • the present invention relates to a semiconductor gas sensor according to the preamble of claim 1, and a method for measuring gas concentrations with a semiconductor gas sensor.
  • Carbon monoxide, nitrogen oxides and ozone which is a significant burden on the environment and the human body. To reduce these loads, it is necessary to measure or analyze the gases generated during combustion. In particular, by measuring the exhaust gases during operation, pollutant emissions can be reduced by appropriate feedback.
  • Semiconductor gas sensors offer a possibility for gas analysis, in which a gas-sensitive layer, which changes its electrical resistance when exposed to certain gases, is brought to a certain measuring temperature. By measuring the electrical resistance of the sensitive layer at certain temperatures, different gas concentrations, for example of CO, NO, N0 2 or 0 3, can be determined.
  • the gas-sensitive layer is in most cases a metal oxide layer, for example made of SnO 2 .
  • a thin layer is made of Sn0 2 is arranged on a heating structure.
  • a Si0 2 layer separates a heating element from the gas-sensitive Sn0 2 layer.
  • the heating structure with the gas-sensitive layer is arranged on an Si 3 N 4 membrane, which in turn is mounted on a silicon substrate Exposure to the gas-sensitive layer with the gas Diffusion, or by flow to the sensor element.
  • the sensor element with the gas-sensitive layer is arranged in a housing.
  • the object of the present invention to provide a semiconductor gas sensor which has an improved time behavior. Furthermore, the gas sensor should be compact and inexpensive to manufacture. In addition, a method for measuring gas concentrations is to be specified, which shows an improved time behavior and enables accurate measurements.
  • the semiconductor gas sensor according to the invention comprises a heatable sensor element for measuring gas concentrations, and a housing, in the interior of which the sensor element is arranged, the housing having a first opening which connects the interior to the exterior, and wherein one or more in the housing second openings are arranged which are lower than the first opening to drive a gas flow from the second opening to the first opening by convection.
  • the second openings or gas inlet openings are preferably arranged in the lower part of the housing on its side walls, and the first opening can be arranged on the top of the housing.
  • the second opening is or are preferably the second openings are arranged at the same height or lower than the sensor element. This results in a particularly favorable gas flow in the interior of the housing.
  • the housing is preferably made of silicon using microtechnology.
  • the sensor element can be integrated in two silicon troughs which lie one above the other or opposite one another, the second opening or the second openings being formed between the mutual boundary surfaces of the troughs.
  • the first opening is formed in the silicon trough located above the sensor element.
  • the second openings, which form the gas inlet openings, are preferably formed by passages or channels located between the silicon troughs.
  • Flow-through elements for filtering or converting the gas can be arranged in the second opening or gas inlet openings.
  • the flowable element has on its inner surfaces e.g. a material that the gas flowing through converts chemically and / or catalytically before it reaches the sensor element. This allows the sensitivity of the sensor to be set or changed for different gases.
  • a method for measuring gas concentrations with a semiconductor gas sensor in which a gas flow is driven through a housing by convection, the gas flowing through the housing from the bottom up and passing a sensor element that generates a measurement signal dependent on the gas concentration.
  • FIG. 1 schematically shows a first embodiment of the semiconductor gas sensor according to the invention in a sectional view
  • Figure 2 schematically illustrates a further embodiment of the semiconductor gas sensor according to the invention.
  • the semiconductor gas sensor in a preferred embodiment of the invention comprises a sensor element 1, which is accommodated in a housing 2.
  • a housing 2 At the top 21 of the housing 2 there is an opening 3 which connects the interior 20 of the housing 2 with areas located outside the housing or with the exterior. Further openings 4a, 4b are arranged in the lower part of the housing 2.
  • the sensor element 1 In measuring operation, the sensor element 1 is heated, which is why the air or the gas warms up and rises in the areas above.
  • the gas can flow into the interior 20 from the outside through the further openings 4a, 4b, while it escapes through the opening 3 on the upper side.
  • the gas flow through the interior of the sensor is driven by convection.
  • a known sensor element is used as sensor element 1, as is described in detail, for example, in the above-mentioned article by B. Ruhland et al. It comprises a gas-sensitive layer, the electrical conductivity or resistance of which changes depending on the respective gas concentration. Metal oxide layers, in particular made of SnO 2, are suitable for this. On the sensitive layer of the Sensor element 1 means are arranged for measuring the electrical conductivity or the electrical resistance, for example in the form of a pair of contact electrodes.
  • a heating element in the form of a platinum heating resistor is over a Si0 2 layer or
  • Passivation layer coupled to the sensitive layer.
  • a Si 3 N support membrane is located underneath to support the arrangement.
  • the arrangement is stored on a wafer, in the present case on a silicon substrate.
  • Thick-film sensors possible, which deliver a measurement signal depending on the respective gas with which they come into contact.
  • the housing 2 is made of metal in the embodiment shown here. However, other materials are also possible, for example silicon.
  • the upper part of the housing 2 can also be designed as a removable cover.
  • the temperature of the sensor element 1 is set. For example, at relatively low temperatures of approx. 50 ° C to approx. 200 ° C there is a considerable sensitivity to NO 2 , whereas a suitable measuring temperature for CO is, for example, in the range from 300 ° C to 400 ° C.
  • the different sensitivities at different temperatures make it possible to determine different gas components by means of an array of sensor elements 1 which are arranged in the lower part of the chamber 1.
  • flowable elements 5a, 5b are arranged in the openings 4a, 4b, which form the gas inlet.
  • the flowable elements 5a, 5b can, depending on the measurement purpose, serve for filtering the gas and / or for chemical and / or catalytic conversion of the gas. You are on this Purpose designed as a filter or provided with passages or holes. They can also be porous.
  • a metal oxide for example Sn0 2
  • the relatively high 0 3 sensitivity that occurs with thin sensitive layers of sensor element 1 can be compensated for or reduced.
  • FIG. 2 shows schematically a cross section through a further embodiment of the present invention.
  • the sensor element 10 is integrated in a housing 40 which is made of silicon.
  • the housing 40 consists of a lower part 40a and an upper part 40b, which are each designed like a trough.
  • Both housing parts 40a, 40b are shaped like a plate, a recess or recess 41a, 41b being structured in the central region of the respective plate in order to accommodate the sensor element 10.
  • the two housing parts 40a, 40b lie one above the other in such a way that the cutouts 41a, 41b lie opposite one another and thus form the interior 50 of the housing 40.
  • At an upper side of the housing 40 there is an opening 30 which forms the gas outlet.
  • Passages 60a, 60b in the form of channels are formed between the housing parts 40a, 40b. These passages or further openings 60a, 60b form the gas inlet on the sides of the housing 40.
  • the recesses 41a, 41b or troughs and the channels 60a, 60b can be produced by typical etching techniques which are known in silicon microtechnology . This results in a particularly cost-effective production with a compact design, which is suitable for series production.

Abstract

The invention relates to a semiconductor gas sensor, for example for measuring CO, NOx, O3, etc., which comprises a heatable sensor element (1) for measuring gas concentrations, as well as a housing (2) in whose interior (20) the sensor element (1) is positioned. The housing (2) has a first opening (3) which connects the interior (20) with the exterior. The housing (2) also presents one or more second openings (4a, 4b) which are situated lower than the first opening (3) such that a gas stream is driven by convection from the second opening (4a, 4b) to the first opening (3). The semiconductor gas sensor can be made of silicon using microtechnology methods.

Description

Halbleiter-Gassensor mit Gehäuse und Verfahren zur Messung von Semiconductor gas sensor with housing and method for measuring
GaskonzentrationenGas concentrations
Die vorliegende Erfindung betrifft einen Halbleiter-Gassensor nach dem Oberbegriff des Patentanspruchs 1 , sowie ein Verfahren zur Messung von Gaskonzentrationen mit einem Halbleiter-Gassensor.The present invention relates to a semiconductor gas sensor according to the preamble of claim 1, and a method for measuring gas concentrations with a semiconductor gas sensor.
Die Messung bzw. Analyse von Gasen ist in verschiedenen Bereichen der Technik von großer Bedeutung. Z.B. entstehen bei der Verbrennung fossiler BrennstoffeThe measurement or analysis of gases is of great importance in various areas of technology. For example, arise when fossil fuels are burned
Kohlenmonoxid, Stickoxide und Ozon, was eine erhebliche Belastung der Umwelt und des menschlichen Körpers darstellt. Um diese Belastungen zu reduzieren, ist es erforderlich, die bei der Verbrennung entstehenden Gase zu messen bzw. zu analysieren. Insbesondere kann durch eine Messung der Abgase während des Betriebs der Schadstoffausstoß durch entsprechende Rückkopplung reduziert werden.Carbon monoxide, nitrogen oxides and ozone, which is a significant burden on the environment and the human body. To reduce these loads, it is necessary to measure or analyze the gases generated during combustion. In particular, by measuring the exhaust gases during operation, pollutant emissions can be reduced by appropriate feedback.
Eine Möglichkeit zur Gasanalyse bieten Halbleiter-Gassensoren, bei denen eine gassensitive Schicht, die bei Beaufschlagung mit bestimmten Gasen ihren elektrischen Widerstand ändert, auf eine bestimmte Meßtemperatur gebracht wird. Durch Messung des elektrischen Widerstands der sensitiven Schicht bei bestimmten Temperaturen lassen sich unterschiedliche Gaskonzentrationen, beispielsweise von CO, NO, N02 oder 03 bestimmen. Die gassensitive Schicht ist in den meisten Fällen eine Metalloxidschicht, beispielsweise aus Sn02.Semiconductor gas sensors offer a possibility for gas analysis, in which a gas-sensitive layer, which changes its electrical resistance when exposed to certain gases, is brought to a certain measuring temperature. By measuring the electrical resistance of the sensitive layer at certain temperatures, different gas concentrations, for example of CO, NO, N0 2 or 0 3, can be determined. The gas-sensitive layer is in most cases a metal oxide layer, for example made of SnO 2 .
Der Artikel von B. Ruhland et al, „Gas kinetic interactions of nitrous oxides with Sn02 surfaces", Sensors and Actuators B50 (1998) Seite 85 bis 94, zeigt einen derartigen Halbleiter-Gassensor. Bei diesem bekannten Gassensor ist eine dünne Schicht aus Sn02 auf einer Heizstruktur angeordnet. Eine Si02 Schicht trennt ein Heizelement von der gassensitiven Sn02 Schicht. Die Heizstruktur mit der gassensitiven Schicht ist auf einer Si3N4 Membrane angeordnet, die wiederum auf einem Siliziumsubstrat gelagert ist. Bei der Messung erfolgt die Beaufschlagung der gassensitiven Schicht mit dem Gas durch Diffusion, oder durch Anströmung des Sensorelements. Das Sensorelement mit der gassensitiven Schicht ist in einem Gehäuse angeordnet.The article by B. Ruhland et al, "Gas kinetic interactions of nitrous oxides with Sn0 2 surfaces", Sensors and Actuators B50 (1998) pages 85 to 94, shows such a semiconductor gas sensor. In this known gas sensor, a thin layer is made of Sn0 2 is arranged on a heating structure. A Si0 2 layer separates a heating element from the gas-sensitive Sn0 2 layer. The heating structure with the gas-sensitive layer is arranged on an Si 3 N 4 membrane, which in turn is mounted on a silicon substrate Exposure to the gas-sensitive layer with the gas Diffusion, or by flow to the sensor element. The sensor element with the gas-sensitive layer is arranged in a housing.
Dabei stellt sich jedoch das Problem, daß die Gasdiffusion zum Sensorelement hin durch die aufsteigende warme Luft bzw. das oberhalb des Sensorelements aufsteigende Gas behindert wird. In dem Gehäuse ergeben sich daher Gasströme, die sich nachteilig auf das Zeitverhalten des Sensors auswirken. Als Ergebnis ergeben sich lange Ansprechzeiten und zum Teil ungenaue Meßergebnisse.However, the problem arises that the gas diffusion to the sensor element is impeded by the rising warm air or the gas rising above the sensor element. There are therefore gas flows in the housing which have a disadvantageous effect on the time behavior of the sensor. The result is long response times and sometimes inaccurate measurement results.
Es ist daher die Aufgabe der vorliegenden Erfindung, einen Halbleiter-Gassensor zu schaffen, der ein verbessertes Zeitverhalten aufweist. Weiterhin soll der Gassensor kompakt ausgestaltet und kostengünstig herstellbar sein. Außerdem soll ein Verfahren zur Messung von Gaskonzentrationen angegeben werden, das ein verbessertes Zeitverhalten zeigt und genaue Messungen ermöglicht.It is therefore the object of the present invention to provide a semiconductor gas sensor which has an improved time behavior. Furthermore, the gas sensor should be compact and inexpensive to manufacture. In addition, a method for measuring gas concentrations is to be specified, which shows an improved time behavior and enables accurate measurements.
Diese Aufgabe wird gelöst durch den Halbleiter-Gassensor gemäß Patentanspruch 1 und das Verfahren zur Messung von Gaskonzentrationen gemäß Patentanspruch 10. Weitere vorteilhafte Merkmale, Aspekte und Details der Erfindung ergeben sich aus den abhängigen Ansprüchen, der Beschreibung und den Zeichnungen.This object is achieved by the semiconductor gas sensor according to claim 1 and the method for measuring gas concentrations according to claim 10. Further advantageous features, aspects and details of the invention result from the dependent claims, the description and the drawings.
Der erfindungsgemäße Halbleiter-Gassensor umfaßt ein beheizbares Sensorelement zur Messung von Gaskonzentrationen, und ein Gehäuse, in dessen Innenraum das Sensorelement angeordnet ist, wobei das Gehäuse eine erste Öffnung aufweist, die den Innenraum mit dem Außenraum verbindet, und wobei in dem Gehäuse eine oder mehrere zweite Öffnungen angeordnet sind, die tiefer liegen als die erste Öffnung, um einen Gasstrom von der zweiten Öffnung zur ersten Öffnung durch Konvektion anzutreiben. Dadurch werden die Ansprechzeiten verringert, bei einer hohen Meßgenauigkeit und geringem Aufwand.The semiconductor gas sensor according to the invention comprises a heatable sensor element for measuring gas concentrations, and a housing, in the interior of which the sensor element is arranged, the housing having a first opening which connects the interior to the exterior, and wherein one or more in the housing second openings are arranged which are lower than the first opening to drive a gas flow from the second opening to the first opening by convection. As a result, the response times are reduced, with high measuring accuracy and little effort.
Die zweiten Öffnungen bzw. Gaseintrittsöffnungen sind vorzugsweise im unteren Teil des Gehäuses an seinen Seitenwänden angeordnet, und die erste Öffnung kann an der Oberseite des Gehäuses angeordnet sein. Vorzugsweise ist die zweite Öffnung bzw. sind die zweiten Öffnungen auf gleicher Höhe oder tiefer als das Sensorelement angeordnet. Dadurch ergibt sich eine besonders günstige Gasströmung im Innenraum des Gehäuses.The second openings or gas inlet openings are preferably arranged in the lower part of the housing on its side walls, and the first opening can be arranged on the top of the housing. The second opening is or are preferably the second openings are arranged at the same height or lower than the sensor element. This results in a particularly favorable gas flow in the interior of the housing.
Vorzugsweise ist das Gehäuse aus Silizium in Mikrotechnologie gefertigt. Dabei kann das Sensorelement in zwei Siliziumwannen integriert sein, die übereinander bzw. sich gegenüber liegen, wobei die zweite Öffnung bzw. die zweiten Öffnungen zwischen den gegenseitigen Begrenzungsflächen der Wannen ausgebildet sind. Insbesondere ist die erste Öffnung in der oben gelegenen Siliziumwanne über dem Sensorelement ausgebildet. Vorzugsweise sind die zweiten Öffnungen, welche die Gaseintrittsöffnungen bilden, durch zwischen den Siliziumwannen gelegene Durchgänge oder Kanäle gebildet. Durch diese Bauweise ergibt sich eine besonders einfache und kostengünstige Herstellung, wobei der Sensor extrem kompakt realisiert werden kann.The housing is preferably made of silicon using microtechnology. In this case, the sensor element can be integrated in two silicon troughs which lie one above the other or opposite one another, the second opening or the second openings being formed between the mutual boundary surfaces of the troughs. In particular, the first opening is formed in the silicon trough located above the sensor element. The second openings, which form the gas inlet openings, are preferably formed by passages or channels located between the silicon troughs. This design results in a particularly simple and inexpensive production, the sensor being able to be implemented in an extremely compact manner.
In der oder den zweiten Öffnungen bzw. Gaseintrittsöffnungen können durchströmbare Elemente zur Filterung oder Umsetzung des Gases angeordnet sein. Dabei weist das durchströmbare Element an seinen inneren Oberflächen z.B. ein Material auf, daß das hindurchströmende Gas chemisch und/oder katalytisch umsetzt, bevor es zum Sensorelement gelangt. Dadurch kann die Empfindlichkeit des Sensors für unterschiedliche Gase eingestellt bzw. verändert werden.Flow-through elements for filtering or converting the gas can be arranged in the second opening or gas inlet openings. The flowable element has on its inner surfaces e.g. a material that the gas flowing through converts chemically and / or catalytically before it reaches the sensor element. This allows the sensitivity of the sensor to be set or changed for different gases.
Gemäß einem weiteren Aspekt der Erfindung wird ein Verfahren zur Messung von Gaskonzentrationen mit einem Halbleiter-Gassensor angegeben, bei dem ein Gasstrom durch ein Gehäuse durch Konvektion angetrieben wird, wobei das Gas das Gehäuse von unten nach oben durchströmt und an einem Sensorelement vorbeigeführt wird, das ein von der Gaskonzentration abhängiges Meßsignal erzeugt.According to a further aspect of the invention, a method for measuring gas concentrations with a semiconductor gas sensor is specified, in which a gas flow is driven through a housing by convection, the gas flowing through the housing from the bottom up and passing a sensor element that generates a measurement signal dependent on the gas concentration.
Die Erfindung wird nachfolgend beispielhaft beschrieben, wobei in den ZeichnungenThe invention is described by way of example below, in the drawings
Figur 1 eine erste Ausführungsform des erfindungsgemäßen Halbleiter-Gassensors schematisch in einer Schnittansicht zeigt; und Figur 2 eine weitere Ausführungsform des erfindungsgemäßen Halbleiter-Gassensors schematisch darstellt.FIG. 1 schematically shows a first embodiment of the semiconductor gas sensor according to the invention in a sectional view; and Figure 2 schematically illustrates a further embodiment of the semiconductor gas sensor according to the invention.
Gemäß Figur 1 umfaßt der Halbleiter-Gassensor in einer bevorzugten Ausführungsform der Erfindung ein Sensorelement 1, das in einem Gehäuse 2 untergebracht ist. An der Oberseite 21 des Gehäuses 2 befindet sich eine Öffnung 3, die den Innenraum 20 des Gehäuses 2 mit außerhalb des Gehäuses gelegenen Bereichen bzw. mit dem Außenraum verbindet. Im unteren Teil des Gehäuses 2 sind weitere Öffnungen 4a, 4b angeordnet. Im Meßbetrieb wird das Sensorelement 1 beheizt, weshalb sich in den darübergelegenen Bereichen die Luft bzw. das Gas erwärmt und aufsteigt. Durch die weiteren Öffnungen 4a, 4b kann das Gas von außen in den Innenraum 20 nachströmen, während es auf der Oberseite durch die Öffnung 3 entweicht. Der Gasstrom durch den Innenraum des Sensors wird durch Konvektion angetrieben.According to FIG. 1, the semiconductor gas sensor in a preferred embodiment of the invention comprises a sensor element 1, which is accommodated in a housing 2. At the top 21 of the housing 2 there is an opening 3 which connects the interior 20 of the housing 2 with areas located outside the housing or with the exterior. Further openings 4a, 4b are arranged in the lower part of the housing 2. In measuring operation, the sensor element 1 is heated, which is why the air or the gas warms up and rises in the areas above. The gas can flow into the interior 20 from the outside through the further openings 4a, 4b, while it escapes through the opening 3 on the upper side. The gas flow through the interior of the sensor is driven by convection.
In der hier gezeigten Ausführungsform sind die weiteren Öffnungen 4a, 4b in denIn the embodiment shown here, the further openings 4a, 4b in the
Seitenwänden des Gehäuses 2 in seinem unteren Teil angeordnet. Durch die Konvektion der erwärmten Luft bzw. des aufgeheizten Gases ergibt sich eine Kaminwirkung, die den Gasstrom zum Sensorelement 1 führt. Diese Kaminwirkung wirkt also nicht mehr der Gasdiffusion entgegen, sondern mit dieser zusammen. Durch Ausnutzung der Kaminwirkung wird die Ansprechgeschwindigkeit des Sensors erhöht. Es stellt sich also eine Pumpenwirkung ein, durch die das zu messende Gas aufgrund der Kaminwirkung in das Gehäuse 2 eingesogen wird. Das Gas erreicht aufgrund dieser Pumpenwirkung ungehindert das Sensorelement 1. Reaktionsprodukte, die aufgrund des Sensormechanismus entstehen, werden durch Ausnutzung der Konvektion bzw. der Kaminwirkung und die spezielle Anordnung der Öffnungen 3, 4a, 4b abtransportiert. Dadurch ist das Zeitverhalten des Sensors deutlich verbessert.Side walls of the housing 2 arranged in its lower part. The convection of the heated air or the heated gas results in a chimney effect which leads the gas flow to the sensor element 1. This chimney effect no longer counteracts gas diffusion, but together with it. The response speed of the sensor is increased by using the chimney effect. There is therefore a pump effect through which the gas to be measured is drawn into the housing 2 due to the chimney effect. Due to this pump effect, the gas reaches the sensor element 1 unhindered. Reaction products that arise due to the sensor mechanism are removed by utilizing the convection or the chimney effect and the special arrangement of the openings 3, 4a, 4b. This significantly improves the time behavior of the sensor.
Als Sensorelement 1 wird ein bekanntes Sensorelement verwendet, wie es z.B. in dem oben genannten Artikel von B. Ruhland et al ausführlich beschrieben ist. Es umfaßt eine gassensitive Schicht, deren elektrische Leitfähigkeit bzw. Ohnrf sehe Widerstand sich in Abhängigkeit von der jeweiligen Gaskonzentration verändert. Hierzu sind Metalloxidschichten, insbesondere aus Sn02 geeignet. An der sensitiven Schicht des Sensorelements 1 sind Mittel zur Messung der elektrischen Leitfähigkeit bzw. des elektrischen Widerstands angeordnet, z.B. in Form eines Paares von Kontaktelektroden. Ein Heizelement in Form eines Platin-Heizwiderstands ist über eine Si02-Schicht bzw.A known sensor element is used as sensor element 1, as is described in detail, for example, in the above-mentioned article by B. Ruhland et al. It comprises a gas-sensitive layer, the electrical conductivity or resistance of which changes depending on the respective gas concentration. Metal oxide layers, in particular made of SnO 2, are suitable for this. On the sensitive layer of the Sensor element 1 means are arranged for measuring the electrical conductivity or the electrical resistance, for example in the form of a pair of contact electrodes. A heating element in the form of a platinum heating resistor is over a Si0 2 layer or
Passivierungsschicht an die sensitive Schicht gekoppelt. Darunter befindet sich eine Trägermembrane aus Si3N , um die Anordnung zu unterstützen. Die Anordnung ist auf einem Wafer, im vorliegenden Fall auf einem Siliziumsubstrat, gelagert.Passivation layer coupled to the sensitive layer. A Si 3 N support membrane is located underneath to support the arrangement. The arrangement is stored on a wafer, in the present case on a silicon substrate.
Hinsichtlich des weiteren Aufbaus des bekannten Sensorelements 1 sowie seiner Funktionsweise wird ausdrücklich auf den oben genannten Artikel bezug genommen. Jedoch ist auch eine Verwendung anderer bekannter Sensorelemente wie z.B.With regard to the further construction of the known sensor element 1 and its mode of operation, reference is expressly made to the above-mentioned article. However, use of other known sensor elements such as e.g.
Dickschichtsensoren möglich, die in Abhängigkeit von dem jeweiligen Gas, mit dem sie in Kontakt geraten, ein Meßsignal liefern.Thick-film sensors possible, which deliver a measurement signal depending on the respective gas with which they come into contact.
Das Gehäuse 2 ist in der hier gezeigten Ausführungsform aus Metall gefertigt. Es sind aber auch andere Materialien möglich, beispielsweise Silizium.The housing 2 is made of metal in the embodiment shown here. However, other materials are also possible, for example silicon.
Der obere Teil des Gehäuses 2 kann auch als abnehmbarer Deckel ausgestaltet sein. Je nach dem Anwendungszweck bzw. dem zu messenden Gas wird die Temperatur des Sensorelements 1 eingestellt. Beispielsweise liegt bei relativ geringen Temperaturen von ca. 50°C bis ca. 200°C eine erhebliche N02-Empfindlichkeit vor, wohingegen eine geeignete Meßtemperatur für CO beispielsweise im Bereich von 300°C bis 400°C liegt. Durch die unterschiedlichen Empfindlichkeiten bei verschiedenen Temperaturen ist es möglich, verschiedene Gaskomponenten mittels eines Arrays von Sensorelementen 1 zu bestimmen, die im unteren Teil der Kammer 1 angeordnet sind. Andererseits ist es auch möglich, bei der Messung mit dem Sensorelement 1 verschiedene Temperaturbereiche schrittweise einzustellen, um die verschiedenen Gaskomponenten zu ermitteln bzw. zu analysieren.The upper part of the housing 2 can also be designed as a removable cover. Depending on the application or the gas to be measured, the temperature of the sensor element 1 is set. For example, at relatively low temperatures of approx. 50 ° C to approx. 200 ° C there is a considerable sensitivity to NO 2 , whereas a suitable measuring temperature for CO is, for example, in the range from 300 ° C to 400 ° C. The different sensitivities at different temperatures make it possible to determine different gas components by means of an array of sensor elements 1 which are arranged in the lower part of the chamber 1. On the other hand, it is also possible to set different temperature ranges step by step when measuring with the sensor element 1 in order to determine or analyze the different gas components.
In den Öffnungen 4a, 4b, die den Gaseinlaß bilden, sind in der bevorzugten Ausführungsform durchströmbare Elemente 5a, 5b angeordnet. Die durchströmbaren Elemente 5a, 5b können, je nach Meßzweck, zur Filterung des Gases und/oder zur chemischen und/oder katalytischen Umsetzung des Gases dienen. Sie sind zu diesem Zweck als Filter ausgestaltet bzw. mit Durchgängen oder Löchern versehen. Auch können sie porös ausgestaltet sein. Durch eine Beschichtung der inneren Oberflächen der durchströmbaren Elemente 5a, 5b mit einem Metalloxid, beispielsweise Sn02, erfolgt eine Reduktion von 03 zu 02, wenn das Gas in das Gehäuse 2 einströmt. Dadurch kann die relativ große 03-Empfindlichkeit, die bei dünnen sensitiven Schichten des Sensorelements 1 auftritt, ausgeglichen bzw. reduziert werden. Andere Beschichtungen, beispielsweise aus oxidierenden Materialien, insbesondere Palladium, bewirken eine Umwandlung von langen, stabilen Molekülen in kürzere Ketten, die besser mit einer dünnen sensitiven Schicht reagieren. In diesem Fall wird die Meßempfindlichkeit erhöht. Je nach Meßzweck sind also unterschiedliche durchströmbare Elemente 5a, 5b in den Öffnungen 4a, 4b angeordnet. Die Öffnungen 4a, 4b können aber auch frei sein, wenn eine Filterung oder Umsetzung von Gaskomponenten beim Eintritt in das Gehäuse 2 nicht erforderlich ist.In the preferred embodiment, flowable elements 5a, 5b are arranged in the openings 4a, 4b, which form the gas inlet. The flowable elements 5a, 5b can, depending on the measurement purpose, serve for filtering the gas and / or for chemical and / or catalytic conversion of the gas. You are on this Purpose designed as a filter or provided with passages or holes. They can also be porous. By coating the inner surfaces of the flowable elements 5a, 5b with a metal oxide, for example Sn0 2 , there is a reduction from 0 3 to 0 2 when the gas flows into the housing 2. As a result, the relatively high 0 3 sensitivity that occurs with thin sensitive layers of sensor element 1 can be compensated for or reduced. Other coatings, for example made of oxidizing materials, in particular palladium, bring about the conversion of long, stable molecules into shorter chains, which react better with a thin sensitive layer. In this case the sensitivity is increased. Depending on the measurement purpose, different flow-through elements 5a, 5b are thus arranged in the openings 4a, 4b. The openings 4a, 4b can also be free if filtering or conversion of gas components when entering the housing 2 is not required.
Figur 2 zeigt schematisch einen Querschnitt durch eine weitere Ausführungsform der vorliegenden Erfindung. Dabei ist das Sensorelement 10 in einem Gehäuse 40 integriert, das aus Silizium gefertigt ist. Das Gehäuse 40 besteht aus einem unteren Teil 40a und einem oberen Teil 40b, die jeweils wannenartig gestaltet sind. Beide Gehäuseteile 40a, 40b sind plattenartig geformt, wobei im mittleren Bereich der jeweiligen Platte eine Aussparung bzw. Ausnehmung 41a, 41 b herausstrukturiert ist, um das Sensorelement 10 aufzunehmen. Die beiden Gehäuseteile 40a, 40b liegen so übereinander, daß sich die Aussparungen 41a, 41 b gegenüberliegen und so den Innenraum 50 des Gehäuses 40 ausbilden. An einer Oberseite des Gehäuses 40 befindet sich eine Öffnung 30, die den Gasausgang bildet. Zwischen den Gehäuseteilen 40a, 40b sind Durchgänge 60a, 60b in Form von Kanälen ausgebildet. Diese Durchgänge bzw. weiteren Öffnungen 60a, 60b bilden den Gaseingang an den Seiten des Gehäuses 40. Die Ausnehmungen 41a, 41 b bzw. Wannen und die Kanäle 60a, 60b lassen sich durch typische Ätztechniken, die in der Silizium-Mikrotechnologie bekannt sind, erzeugen. Dadurch ergibt sich eine besonders kostengünstige Herstellung bei kompakter Bauweise, die für eine Serienfertigung geeignet ist. Figure 2 shows schematically a cross section through a further embodiment of the present invention. The sensor element 10 is integrated in a housing 40 which is made of silicon. The housing 40 consists of a lower part 40a and an upper part 40b, which are each designed like a trough. Both housing parts 40a, 40b are shaped like a plate, a recess or recess 41a, 41b being structured in the central region of the respective plate in order to accommodate the sensor element 10. The two housing parts 40a, 40b lie one above the other in such a way that the cutouts 41a, 41b lie opposite one another and thus form the interior 50 of the housing 40. At an upper side of the housing 40 there is an opening 30 which forms the gas outlet. Passages 60a, 60b in the form of channels are formed between the housing parts 40a, 40b. These passages or further openings 60a, 60b form the gas inlet on the sides of the housing 40. The recesses 41a, 41b or troughs and the channels 60a, 60b can be produced by typical etching techniques which are known in silicon microtechnology . This results in a particularly cost-effective production with a compact design, which is suitable for series production.

Claims

Patentansprüche claims
1. Halbleiter-Gassensor, mit einem beheizbaren Sensorelement (1; 10) zur Messung von Gaskonzentrationen, und einem Gehäuse (2; 40), in dessen Innenraum (20; 50) das Sensorelement angeordnet ist, wobei das Gehäuse (2; 40) eine erste Öffnung (3; 30) aufweist, die den Innenraum (20; 50) mit dem Außenraum verbindet, dadurch gekennzeichnet, daß in dem Gehäuse (2; 40) ein oder mehrere zweite Öffnungen (4a, 4b; 60a, 60b) angeordnet sind, die tiefer liegen als die erste Öffnung (3; 30), wobei die erste Öffnung (3;30) oberhalb des beheizbaren Sensorelements (1; 10) angeordnet ist, um im Betrieb durch Heizen des Sensorelements ( 1 ; 10) eine Kaminwirkung zu erzeugen.1. Semiconductor gas sensor, with a heatable sensor element (1; 10) for measuring gas concentrations, and a housing (2; 40), in the interior (20; 50) of which the sensor element is arranged, the housing (2; 40) has a first opening (3; 30) which connects the interior (20; 50) to the exterior, characterized in that one or more second openings (4a, 4b; 60a, 60b) are arranged in the housing (2; 40) are lower than the first opening (3; 30), the first opening (3; 30) being arranged above the heatable sensor element (1; 10) in order to have a chimney effect during operation by heating the sensor element (1; 10) to create.
2. Halbleiter-Gassensor nach Anspruch 1, dadurch gekennzeichnet, daß die zweiten Öffnungen (4a, 4b) im unteren Teil des Gehäuses (2) an seinen Seitenwänden angeordnet sind, und die erste Öffnung (3) an der Oberseite (21) des Gehäuses (2) angeordnet ist.2. Semiconductor gas sensor according to claim 1, characterized in that the second openings (4a, 4b) in the lower part of the housing (2) are arranged on its side walls, and the first opening (3) on the top (21) of the housing (2) is arranged.
3. Halbleiter-Gassensor nach Anspruch 1 oder Anspruch 2, dadurch gekennzeichnet, daß die zweiten Öffnungen (4a, 4b; 60a, 60b) auf gleicher Höhe oder tiefer als das Sensorelement (1; 10) angeordnet sind.3. Semiconductor gas sensor according to claim 1 or claim 2, characterized in that the second openings (4a, 4b; 60a, 60b) are arranged at the same height or lower than the sensor element (1; 10).
4. Halbleiter-Gassensor nach einem oder mehreren der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß das Gehäuse (40) aus Silizium in Mikrotechnologie gefertigt ist.4. Semiconductor gas sensor according to one or more of the preceding claims, characterized in that the housing (40) is made of silicon in microtechnology.
5. Halbleiter-Gassensor nach einem oder mehreren der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß das Sensorelement (10) in zwei Siliziumwannen (40a, 40b) integriert ist, die übereinander liegen, wobei die zweite Öffnung (60a, 60b) zwischen ihren gegenseitigen Begrenzungsflächen ausgebildet ist.5. Semiconductor gas sensor according to one or more of the preceding claims, characterized in that the sensor element (10) in two silicon troughs (40a, 40b) are integrated, which lie one above the other, the second opening (60a, 60b) being formed between their mutual boundary surfaces.
6. Halbleiter-Gassensor nach Anspruch 5, dadurch gekennzeichnet, daß die erste Öffnung (30) in der oben gelegenen Siliziumwanne (40b) über dem Sensorelement (10) ausgebildet ist.6. A semiconductor gas sensor according to claim 5, characterized in that the first opening (30) in the overhead silicon trough (40b) is formed above the sensor element (10).
7. Halbleiter-Gassensor nach Anspruch 5 oder 6, dadurch gekennzeichnet, daß die zweiten Öffnungen (60a, 60b) durch zwischen den Siliziumwannen (40a, 40b) gelegene Kanäle gebildet werden.7. A semiconductor gas sensor according to claim 5 or 6, characterized in that the second openings (60a, 60b) are formed by channels located between the silicon troughs (40a, 40b).
8. Halbleiter-Gassensor nach einem oder mehreren der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß in der zweiten Öffnung (4a, 4b), die den Gaseingang ermöglicht, ein durchströmbares Element (5a, 5b) zur Filterung und/oder Umsetzung des Gases angeordnet ist.8. Semiconductor gas sensor according to one or more of the preceding claims, characterized in that a flow-through element (5a, 5b) for filtering and / or converting the gas is arranged in the second opening (4a, 4b), which enables the gas inlet .
9. Halbleiter-Gassensor nach Anspruch 8, dadurch gekennzeichnet, daß das durchströmbare Element (5a, 5b) an seinen inneren Oberflächen ein Material aufweist, daß das hindurchströmende Gas chemisch und/oder katalytisch umsetzt, bevor es zum Sensorelement ( 10) gelangt.9. A semiconductor gas sensor according to claim 8, characterized in that the flow-through element (5a, 5b) has on its inner surfaces a material that the gas flowing through converts chemically and / or catalytically before it reaches the sensor element (10).
10. Verfahren zur Messung von Gaskonzentrationen mit einem Halbleiter-Gassensor, bei dem ein beheiztes Sensorelement(1;10) , das in einem Gehäuse angeordnet (2; 40) ist, ein über dem Sensorelement (1;10) befindliches Gas erwärmt und einen Gasstrom in der Art eines Kamins antreibt, wobei das Gas das Gehäuse (2; 40) von unten nach oben durchströmt und an dem Sensorelement (1; 10) vorbeigeführt wird, das ein von der Gaskonzentration abhängiges Meßsignal erzeugt.10. A method for measuring gas concentrations with a semiconductor gas sensor, in which a heated sensor element (1; 10), which is arranged in a housing (2; 40), heats a gas located above the sensor element (1; 10) and one Driving gas flow in the manner of a chimney, the gas flowing through the housing (2; 40) from the bottom up and past the sensor element (1; 10), which generates a measurement signal dependent on the gas concentration.
1 1. Verfahren nach Anspruch 10, dadurch gekennzeichnet, daß eine Filterung und/oder Umsetzung des Gases erfolgt, bevor es mit dem Sensorelement (1 ; 10} in Kontakt gerät. 1 1. The method according to claim 10, characterized in that a filtering and / or conversion of the gas takes place before it comes into contact with the sensor element (1; 10}.
EP00938476A 1999-04-14 2000-04-11 Semiconductor gas sensor with housing and method for measuring of gas concentrations Withdrawn EP1192459A1 (en)

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