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WO1999019719A1 - Nanocrystalline sensor and a production method - Google Patents

Nanocrystalline sensor and a production method Download PDF

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Publication number
WO1999019719A1
WO1999019719A1 PCT/EP1998/006439 EP9806439W WO9919719A1 WO 1999019719 A1 WO1999019719 A1 WO 1999019719A1 EP 9806439 W EP9806439 W EP 9806439W WO 9919719 A1 WO9919719 A1 WO 9919719A1
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Prior art keywords
sensor
nanoparticles
metal oxide
sensors
substrate
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PCT/EP1998/006439
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German (de)
French (fr)
Inventor
Patrick Keller
Jörg-Uwe MEYER
Hans Ferkel
Werner Riehemann
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Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV
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Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV
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Publication of WO1999019719A1 publication Critical patent/WO1999019719A1/en
Anticipated expiration legal-status Critical
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    • 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
    • G01N27/127—Composition of the body, e.g. the composition of its sensitive layer comprising nanoparticles
    • 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
    • G01N33/004—CO or CO2

Definitions

  • the invention relates to a sensor, which is preferably intended for gas analysis and in particular for detecting carbon dioxide, with a layer containing at least one sensitive metal oxide, and to a method based on laser ablation.
  • sensors are developed and used for a wide variety of purposes. For example, there are currently pressure sensors, acceleration sensors, heat sensors and gas sensors. Gas sensors are used to determine and monitor the concentration of certain gases in the air. The carbon dioxide content of the room air is particularly important for the control of air conditioning and ventilation systems. The use of CO 2 sensors is also a prerequisite for the continuous control of biological and chemical processes in bio- and environmental technology as well as for climate monitoring in greenhouses, in order to influence the composition of the atmosphere to be monitored with additional devices. Further areas of application can be expected, for example, in the investigation of the combustion of fossil fuels, in occupational safety and health and in agriculture.
  • Solid state sensors detect the concentration of gases by their adsorption through sensitive layers, which usually consist of semiconducting materials, in particular metal oxides.
  • sensitive layers which usually consist of semiconducting materials, in particular metal oxides.
  • the adsorption of gas molecules on the sensor surface increases or decreases the number of free charge carriers and therefore results in a changed resistance or a changed conductivity of the sensitive layer.
  • Dipole moments of the adsorbed gas molecules also change the dielectric constant and thus also the capacitance of the sensor layer. Based on the known measurement of these changes, conclusions can be drawn about the amount of gas adsorbed and thus about the corresponding gas concentration of the surrounding room air.
  • conductivity and dielectric constant of the sensitive layer are measured at AC voltage.
  • the layer itself is usually located on a substrate surface covered with two electrodes, the electrodes usually being arranged in the form of two interdigitated comb structures, the so-called interdigital structure.
  • the conventional metal oxide sensors are very robust and therefore in demand for use even under rough conditions, but they have a disadvantageously low sensitivity.
  • they are provided with a heating device on the back of the substrate and operated at local temperatures of several hundred degrees Celsius. This results in a high energy consumption of the sensors, which is all the more serious as such sensors are to be used for continuous continuous monitoring.
  • the low sensitivity of the metal oxide must be compensated for by a correspondingly large sensor area in order to obtain evaluable and reliable measurement results. So far, this has stood in the way of a miniaturization of such solid-state sensors that is desirable per se.
  • the achievement of this object is specified for a sensor in claim 1 and for the manufacturing method in claim 5. Further developments of the invention are the subject of the dependent claims.
  • the object is achieved for a sensor in that the metal oxide consists of nanoparticles with typical grain sizes between preferably 3 and 30 nanometers.
  • the active surface of the sensor is increased considerably compared to conventional sensors, which results in a significantly higher sensitivity. This makes it possible to reduce the sensor area; in addition, the sensor according to the invention can also be operated at substantially lower operating temperatures of below 300 ° C. and thus more cost-effectively.
  • a first embodiment provides that the nanoparticles essentially contain barium titanate (BaTi0 3 ), and a further embodiment that the nanoparticles also contain at least one of the additives CuO, La 2 0 3 and CaC0 3 .
  • This system is particularly suitable for the detection of C0 2 .
  • the nanoparticles are embedded in an organic matrix.
  • An organic binder can be used if the sensitive material is not applied directly to the sensor substrate in the manner described below, but instead is applied using one of the common thick-film processes, such as the screen printing process.
  • the object is achieved according to the invention in that nanoparticles are produced and evaporated in situ on a substrate or the like.
  • the use of laser ablation according to the invention is directed to the nanoparticles produced thereby.
  • the composition of the nanoparticles can be influenced by the targeted control of the process parameters and by the composition of the starting materials.
  • Evaporation in situ ie during laser ablation, offers the advantage of direct application of the sensitive material from the substrate without first having to separate a powder, as in the case of the screen printing process, then mixing it with a binder and then applying it in a further step.

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

Abstract

The invention relates to a sensor preferably for analyzing gas, especially for detecting carbon dioxide. Said sensor has at least one layer containing sensitive metal and a laser ablation contact method. According to the invention, the metal oxide consists of nanoparticles with typical particle sizes preferably ranging from 3 to 30 nanometers in order to increase the sensitivity of the metal oxide sensor and to increase the operation of said sensor with a smaller sensor surface and at a temperature less than 300 DEG C. In addition, nanoparticles are created and are vapor deposited in situ on a substrate or the like with the assistance of the inventive method.

Description

Nanokristalliner Sensor und Herstellungsverfahren Nanocrystalline sensor and manufacturing process

B E S C H R E I B U N GDESCRIPTION

Technisches GebietTechnical field

Die Erfindung bezieht sich auf einen vorzugsweise zur Gasanalyse und insbesondere zum Kohlendioxidnachweis bestimmten Sensor mit einer mindestens ein sensitives Metalloxid enthaltenden Schicht sowie auf ein auf Laserablation beruhendes Verfahren.The invention relates to a sensor, which is preferably intended for gas analysis and in particular for detecting carbon dioxide, with a layer containing at least one sensitive metal oxide, and to a method based on laser ablation.

Stand der TechnikState of the art

In der Sensortechnik werden Sensoren für die unterschiedlichsten Zwecke entwickelt und eingesetzt, so gibt es derzeit beispielsweise Drucksensoren, Beschleunigungssensoren, Wärmesensoren und Gassensoren. Gassensoren dienen dazu, die Kontentration bestimmter Gase in der Luft zu ermitteln und zu überwachen. Insbesondere der Kohlendioxidgehalt der Raumluft ist für die Steuerung von Klima- und Be- lüftungsanlagen von Bedeutung. Auch bei der kontinuierlichen Kontrolle biologischer und chemischer Prozesse in der Bio- und Umwelttechnologie sowie bei der Klimaüberwachung in Gewächshäusern ist der Einsatz von CO2-Sensoren Voraussetzung, um durch zusätzliche Vorrichtungen die Zusammensetzung der zu überwachenden Atmosphäre zielgerichtet zu beeinflussen. Weitere Anwendungsgebiete sind beispielsweise bei der Untersuchung der Verbrennung fossiler Brennstoffe, im Arbeitsschutz und in der Landwirtschaft zu erwarten.In sensor technology, sensors are developed and used for a wide variety of purposes. For example, there are currently pressure sensors, acceleration sensors, heat sensors and gas sensors. Gas sensors are used to determine and monitor the concentration of certain gases in the air. The carbon dioxide content of the room air is particularly important for the control of air conditioning and ventilation systems. The use of CO 2 sensors is also a prerequisite for the continuous control of biological and chemical processes in bio- and environmental technology as well as for climate monitoring in greenhouses, in order to influence the composition of the atmosphere to be monitored with additional devices. Further areas of application can be expected, for example, in the investigation of the combustion of fossil fuels, in occupational safety and health and in agriculture.

Zur Gasanalyse und insbesondere zum C02-Nachweis sind verschiedene Sensorarten entwickelt worden. Infrarotmeßgeräte nutzen die Ab-Various types of sensors have been developed for gas analysis and especially for C0 2 detection. Infrared measuring devices use the

BESTATIGUNGSKOPΪE sorption von Infrarotstrahlung durch C02 für eine Konzentrationsbestimmung, besitzen allerdings eine hohe Querempfindlichkeit gegenüber Wasserdampf mit ähnlichem Absorptionsbereich wie Kohlendioxid. Auch Polymersensoren, bei denen eine Wechselwirkung mit CO2 in gleicher Weise wie durch Feuchteeinfluß zu einer Massenänderung und damit zu einer auszuwertenden Frequenzverschiebung führen kann, sind für den selektiven Nachweis von C02 ungeeignet. Elektrochemische Zellen, in denen erhöhter C02-Gehalt infolge eines verschobenen Carbonat- gleichgewichts durch eine pH-Wertänderung nachgewiesen werden kann, sind infolge langer Ansprechzeiten nachteilhaft.BESTATIGUNGSKOPΪE sorption of infrared radiation by C0 2 for a concentration determination, but have a high cross sensitivity to water vapor with a similar absorption range as carbon dioxide. Also polymer sensors, in which an interaction with CO 2 in the same way as through the influence of moisture can lead to a mass change and thus to a frequency shift to be evaluated, are unsuitable for the selective detection of CO 2 . Electrochemical cells in which an increased CO 2 content can be detected due to a shifted carbonate balance due to a change in pH are disadvantageous due to the long response times.

Festkörpersensoren weisen die Konzentration von Gasen durch deren Adsorption durch sensitive Schichten nach, die üblicherweise aus halbleitenden Materialien, insbesondere Metalloxiden, bestehen. Durch die Adsorption von Gasmolekülen an der Sensoroberfläche erhöht oder verringert sich die Anzahl freier Ladungsträger und hat daher einen veränderten Widerstand bzw. eine veränderte Leitfähigkeit der sensitiven Schicht zur Folge. Durch Dipolmomente der adsorbierten Gasmoleküle wird auch die Dielektrizitätskonstante und damit auch Kapazität der Sensorschicht verändert. Aufgrund der an sich bekannten Messung dieser Veränderungen lassen sich Rückschlüsse auf die adsorbierte Gasmenge und somit auf die entsprechende Gaskonzentration der umgebenden Raumluft ziehen. Zur Verhinderung von Polarisierungserscheinungen werden Leitfähigkeit und Dielektrizitätskonstante der sensitiven Schicht bei Wechselspannung gemessen. Die Schicht selbst befindet sich üblicherweise auf einer mit zwei Elektroden bedeckten Substratoberfläche, wobei die Elektroden meist in Form zweier ineinandergreifender Kammstrukturen, der sogenannten Interdigitalstruktur, angeordnet sind. Die herkömmlichen Metalloxidsensoren sind zwar sehr robust und dadurch für den Einsatz gerade auch unter rauhen Bedingungen gefragt, besitzen jedoch eine nachteilhaft geringe Sensitivität. Um deren Empfindlichkeit zu erhöhen, werden sie mit einer Heizvorrichtung auf der Substratrückseite versehen und bei lokalen Temperaturen von mehreren hundert Grad Celsius betrieben. Dies hat einen hohen Energieverbrauch der Sensoren zur Folge, der um so schwerer wiegt, als derartige Sensoren zu kontinuierlichen Dauerüberwachung eingesetzt werden sollen. Zudem muß die geringe Sensitivität des Metalloxids durch eine entsprechend große Sensorfläche ausgeglichen werden, um auswertbare und zuverlässige Meßergebnisse zu erhalten. Dies steht bislang einer an sich wünschenswerten Miniaturisierung solcher Festkörpersensoren im Wege.Solid state sensors detect the concentration of gases by their adsorption through sensitive layers, which usually consist of semiconducting materials, in particular metal oxides. The adsorption of gas molecules on the sensor surface increases or decreases the number of free charge carriers and therefore results in a changed resistance or a changed conductivity of the sensitive layer. Dipole moments of the adsorbed gas molecules also change the dielectric constant and thus also the capacitance of the sensor layer. Based on the known measurement of these changes, conclusions can be drawn about the amount of gas adsorbed and thus about the corresponding gas concentration of the surrounding room air. To prevent polarization phenomena, conductivity and dielectric constant of the sensitive layer are measured at AC voltage. The layer itself is usually located on a substrate surface covered with two electrodes, the electrodes usually being arranged in the form of two interdigitated comb structures, the so-called interdigital structure. The conventional metal oxide sensors are very robust and therefore in demand for use even under rough conditions, but they have a disadvantageously low sensitivity. To increase their sensitivity, they are provided with a heating device on the back of the substrate and operated at local temperatures of several hundred degrees Celsius. This results in a high energy consumption of the sensors, which is all the more serious as such sensors are to be used for continuous continuous monitoring. In addition, the low sensitivity of the metal oxide must be compensated for by a correspondingly large sensor area in order to obtain evaluable and reliable measurement results. So far, this has stood in the way of a miniaturization of such solid-state sensors that is desirable per se.

Darstellung der ErfindungPresentation of the invention

Angesichts dieser Unzulänglichkeiten herkömmlicher Sensoren ist es Aufgabe der Erfindung, einen Metalloxidsensor bereitzustellen, der bei niedrigeren Temperturen betrieben werden kann und so mit einem wesentlich verminderten Energiebedarf auskommt, der ferner aufgrund eines sensitiveren Materials miniaturisiert werden und so womöglich auch kostengünstiger hergestellt werden kann. Schließlich ist es Aufgabe der Erfindung, ein Verfahren bereitzustellen, mit dem ein solcher Sensor hergestellt werden kann.In view of these shortcomings of conventional sensors, it is an object of the invention to provide a metal oxide sensor that can be operated at lower temperatures and thus manages with a significantly reduced energy requirement, which can also be miniaturized due to a more sensitive material and can thus also be manufactured more cost-effectively. Finally, it is an object of the invention to provide a method with which such a sensor can be produced.

Die erfindungsgemäße Lösung dieser Aufgabe ist für einen Sensor im Anspruch 1 und für das Herstellungsverfahren im Anspruch 5 angegeben. Weiterbildungen der Erfindung sind Gegenstand der abhängigen Ansprüche. Die Aufgabe wird erfindungsgemäß für einen Sensor dadurch gelöst, daß das Metalloxid aus Nanopartikeln mit typischen Korngrößen zwischen vorzugsweise 3 und 30 Nanometern besteht.The achievement of this object is specified for a sensor in claim 1 and for the manufacturing method in claim 5. Further developments of the invention are the subject of the dependent claims. The object is achieved for a sensor in that the metal oxide consists of nanoparticles with typical grain sizes between preferably 3 and 30 nanometers.

Durch den erstmaligen Einsatz nanokristalliner Materialien als sensitive Schicht wird die aktive Oberfläche des Sensors gegenüber herkömmlichen Sensoren erheblich vergrößert, was eine deutlich höhere Sensitivität zur Folge hat. Dadurch wird es möglich, die Sensorfläche zu verkleinern; zudem kann auch der erfindungsgemäße Sensor bei wesentlich niedrigeren Betriebstemperaturen von unter 300°C und somit kostensparender betrieben werden.By using nanocrystalline materials as a sensitive layer for the first time, the active surface of the sensor is increased considerably compared to conventional sensors, which results in a significantly higher sensitivity. This makes it possible to reduce the sensor area; in addition, the sensor according to the invention can also be operated at substantially lower operating temperatures of below 300 ° C. and thus more cost-effectively.

Eine erste Ausführungsform sieht vor, daß die Nanopartikel im wesentlichen Bariumtitanat (BaTi03) enthalten, und eine weitere Ausführungsform, daß die Nanopartikel ferner mindestens eines der Additive CuO, La203 und CaC03 enthalten. Dieses System ist insbesondere für den Nachweis von C02 geeignet. Entsprechend einer weiteren Ausführungsform ist vorgesehen, daß die Nanopartikel in eine organische Matrix eingebettet sind. Die Verwendung eines organischen Bindemittels bietet sich an, wenn das sensitive Material nicht in der nachfolgend beschriebenen Weise direkt auf das Sensorsubstrat aufgetragen wird, sondern nach einem der gängigen Dickschichtverfahren, etwa dem Siebdruckverfahren, aufgetragen wird.A first embodiment provides that the nanoparticles essentially contain barium titanate (BaTi0 3 ), and a further embodiment that the nanoparticles also contain at least one of the additives CuO, La 2 0 3 and CaC0 3 . This system is particularly suitable for the detection of C0 2 . According to a further embodiment it is provided that the nanoparticles are embedded in an organic matrix. An organic binder can be used if the sensitive material is not applied directly to the sensor substrate in the manner described below, but instead is applied using one of the common thick-film processes, such as the screen printing process.

Für das Herstellungsverfahren wird die Aufgabe erfindungsgemäß dadurch gelöst, daß Nanopartikel erzeugt und in situ auf ein Substrat oder dergleichen aufgedampft werden.For the production process, the object is achieved according to the invention in that nanoparticles are produced and evaporated in situ on a substrate or the like.

Während die Laserablation üblicherweise zur Abtragung von Substratmaterial eingesetzt wird und die so behandelte Oberfläche des Sub- strats das eigentliche Verfahrenserzeugnis ist, ist die erfindungsgemäße Anwendung der Laserablation auf die dadurch erzeugten Nanopartikel gerichtet. Durch die gezielte Steuerung der Prozeßparameter und durch die Zusammensetzung der Ausgangsstoffe kann die Zusammensetzung der Nanopartikel beeinflußt werden. Die Aufdampfung in situ, d. h. während der Laserablation, bietet den Vorteil der direkten Auftragung des sensitiven Materials aus das Substrat, ohne daß ein Pulver wie im Falle des Siebdruckverfahrens erst separiert, dann mit einem Bindemittel gemischt und nachfolgend in einem weiteren Schritt aufgebracht werden muß. While laser ablation is usually used to remove substrate material and the surface of the sub- Strats is the actual product of the process, the use of laser ablation according to the invention is directed to the nanoparticles produced thereby. The composition of the nanoparticles can be influenced by the targeted control of the process parameters and by the composition of the starting materials. Evaporation in situ, ie during laser ablation, offers the advantage of direct application of the sensitive material from the substrate without first having to separate a powder, as in the case of the screen printing process, then mixing it with a binder and then applying it in a further step.

Claims

P A T E N T A N S P R Ü C H E PATENT CLAIMS 1. Sensor zur Gasanalyse und insbesondere zum Kohlendioxidnachweis bestimmter Sensor mit einer mindestens ein sensitives Metalloxid enthaltenden Schicht, dadurch gekennzeichnet, daß das Metalloxid ans Nanopartikeln mit typischen Korngrößen zwischen vorzugsweise 3 und 30 Nanometern besteht.1. Sensor for gas analysis and in particular for carbon dioxide detection certain sensor with a layer containing at least one sensitive metal oxide, characterized in that the metal oxide consists of nanoparticles with typical grain sizes between preferably 3 and 30 nanometers. 2. Sensor nach Anspruch 1 , dadurch gekennzeichnet, daß die Nanopartikel im wesentlichen Ba- riumtitanat (BaTi03) enthalten.2. Sensor according to claim 1, characterized in that the nanoparticles essentially contain barium titanate (BaTi0 3 ). 3. Sensor nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die Nanopartikel ferner mindestens eines der Additive CuO, La203 und CaC03 enthalten.3. Sensor according to claim 1 or 2, characterized in that the nanoparticles further contain at least one of the additives CuO, La 2 0 3 and CaC0 3 . 4. Sensor nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß die Nanopartikel in eine organische Matrix eingebettet sind.4. Sensor according to one of claims 1 to 3, characterized in that the nanoparticles are embedded in an organic matrix. 5. Auf Laserablation beruhendes Verfahren, dadurch gekennzeichnet, daß Nanopartikel erzeugt und in situ auf ein Substrat oder dergleichen aufgedampft werden. 5. A method based on laser ablation, characterized in that nanoparticles are generated and evaporated in situ on a substrate or the like.
PCT/EP1998/006439 1997-10-10 1998-10-12 Nanocrystalline sensor and a production method Ceased WO1999019719A1 (en)

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DE19744857.7 1997-10-10
DE1997144857 DE19744857A1 (en) 1997-10-10 1997-10-10 Nanocrystalline sensor and manufacturing process

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WO2000073534A1 (en) * 1999-05-28 2000-12-07 Ultramet Low temperature metal oxide coating formation
WO2002036204A2 (en) 2000-10-31 2002-05-10 Marat Vadimovich Evtukhov Integral life support system

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US6237397B1 (en) * 1999-10-06 2001-05-29 Iowa State University Research Foundation, Inc. Chemical sensor and coating for same
FR2816756B1 (en) * 2000-11-15 2003-10-31 Univ Paris Curie PROCESS FOR OBTAINING A POLYMER COMPOSITION DOPED WITH NANOPARTICLES FOR THE PRODUCTION OF POLYMER COMPOSITE MATERIALS, DEVICE FOR ITS IMPLEMENTATION, COMPOSITION AND MATERIALS OBTAINED
JP3735686B2 (en) 2001-10-30 2006-01-18 独立行政法人理化学研究所 Method for producing metal oxide ferroelectric particle crystal
DE102004019639A1 (en) * 2004-04-22 2005-11-17 Siemens Ag FET-based gas sensor

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000073534A1 (en) * 1999-05-28 2000-12-07 Ultramet Low temperature metal oxide coating formation
WO2002036204A2 (en) 2000-10-31 2002-05-10 Marat Vadimovich Evtukhov Integral life support system

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