WO2000020850A1 - Multi-sensor device for gravimetric chemical measurements by means of resonant piezoelectric layers by thick film technology - Google Patents

Multi-sensor device for gravimetric chemical measurements by means of resonant piezoelectric layers by thick film technology Download PDF

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Publication number
WO2000020850A1
WO2000020850A1 PCT/EP1999/006957 EP9906957W WO0020850A1 WO 2000020850 A1 WO2000020850 A1 WO 2000020850A1 EP 9906957 W EP9906957 W EP 9906957W WO 0020850 A1 WO0020850 A1 WO 0020850A1
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Prior art keywords
substrate
sensors
titanate
compounds
thick film
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PCT/EP1999/006957
Other languages
French (fr)
Inventor
Vittorio Ferrari
Daniele Marioli
Andrea Taroni
Original Assignee
Universitá Degli Studi Di Brescia
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Publication date
Application filed by Universitá Degli Studi Di Brescia filed Critical Universitá Degli Studi Di Brescia
Priority to AU64662/99A priority Critical patent/AU6466299A/en
Publication of WO2000020850A1 publication Critical patent/WO2000020850A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/036—Analysing fluids by measuring frequency or resonance of acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01G—WEIGHING
    • G01G3/00—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances
    • G01G3/12—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances wherein the weighing element is in the form of a solid body stressed by pressure or tension during weighing
    • G01G3/13—Weighing apparatus characterised by the use of elastically-deformable members, e.g. spring balances wherein the weighing element is in the form of a solid body stressed by pressure or tension during weighing having piezoelectric or piezoresistive properties
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/025—Change of phase or condition
    • G01N2291/0256—Adsorption, desorption, surface mass change, e.g. on biosensors

Definitions

  • the present invention relates to a device for detecting, measuring and monitoring a plurality of gaseous and/or vapor state analytes, based on resonant piezoelectric elements, by means of a thick film technology.
  • a device for detecting, measuring and monitoring a plurality of gaseous and/or vapor state analytes, based on resonant piezoelectric elements by means of a thick film technology.
  • the availability of chemical sensors having a good metrologic performance and low realization cost is required by many application situations.
  • the detection of gaseous compounds and vapors in the air is an object of deep and topical interest for the environment monitoring, and for measurements in domestic and industrial environments .
  • Object of this invention is to provide a device for the detection, measurement and monitoring of gaseous and/or vapor state analytes different from one another and present at the same time in given environments, with high sensitivity and high selectivity and specificity.
  • Another object of the invention is to provide a flexible, low cost multi-sensor device for gravimetric chemical measurements.
  • a device for detecting and measuring gaseous and/or vapor state analytes, based on resonant piezoelectric layers which device, according to the present invention, comprises: - a substrate, a plurality of sensors made from piezoelectric elements based on compounds of polarized ferroelectric ceramics, realized by means of a thick film technology on said substrate and coated with sensitive coatings suitable to selectively and reversibly absorb said analytes, at least a heating element incorporated in said substrate, provided with a suitable regulation circuit apt to thermostate said substrate, suitable circuits being also provided for the amplification, transmission and elaboration of the signals emitted by the sensors and suitable means for the treatment and electronic data processing and/or software.
  • said substrate is made from alumina.
  • the substrate may be also made from any other suitably insulated material, such as an enameled metal material, for instance enameled steel or the like.
  • said compounds of ferroelectric ceramics are made from lead zirconate-titanate, and are realized by silk-screen printing on said substrate from alumina.
  • the thick film technology allows to realize electronic devices and circuits by means of silk-screen printing processes of pastes having specific and different properties on suitable substrates, followed by thermal cycles to stabilize the mechanical and functional properties of the deposits.
  • the base material employed as an active phase for the preparation of the piezoelectric elements is lead zirconate-titanate of various compositions and particle sizes .
  • a binder is added to the powder lead zirconate- titanate, generally made from lead oxide (PbO) powder or vitreous compounds, to promote the compacting of lead zirconate-titanate and its adhesion to the substrate during firing.
  • the mixture made from lead zirconate-titanate and the binder is then dissolved in a liquid carrier made from an organic solvent and a thickener, typically ethyl cellulose in terpineol, to obtain a fluid compound having the right rheology to allow silk-screen printing. After the printing, the layers are dried at about 150 °C and then submitted to a firing process at about 950°C.
  • the piezoelectric activity is induced in the layers by means of a polarization process, namely the application of an electric field in the order of 4-5 MV/m for about 10 minutes, at a temperature near the Curie one (the typical values employed range from 100 to 200°C) , followed by the return to ambient temperature with the applied field.
  • a polarization process namely the application of an electric field in the order of 4-5 MV/m for about 10 minutes, at a temperature near the Curie one (the typical values employed range from 100 to 200°C) , followed by the return to ambient temperature with the applied field.
  • the piezoelectric and mechanical characteristics of the film depend on the composition of the paste and the mean particle size of the powders (typically comprised
  • the lead zirconate-titanate based resonant sensor on alumina substrate allows to detect small mass amounts integral with the vibrating structure through the decrease in the resonance frequency of the product, and can therefore advantageously detect a chemical species by means of the sensitization of the resonator with a material capable of reversibly absorbing the analyte of interest, with ensuing variation in its own mass.
  • the material that makes up said sensitive coatings that cover said piezoelectric elements and that are capable of reversibly absorbing the analyte of interest is generally a polymeric material, selected according to the analyte to be detected and measured.
  • the substrate from alumina has an active role in the determination of the resonance frequency measured, which is not due to the piezoelectric layer only, but to the substrate/piezoelectric layer whole which constitutes therefore a composite resonator: in fact, it has been found that a reduction in the thickness of the substrate leads to an increase in resonance frequency and, correspondingly, in mass sensitivity.
  • piezoelectric layer having a thickness of about 100 ⁇ m
  • the frequency is of about 6,5 MHz and the sensitivity of -450 kHz/ g, which value is a remarkable result.
  • the device according to the invention is a gravimetric multi-sensor on one only substrate.
  • Each microbalance of the whole is typically coated with a different sensitive material, so as to obtain for each analyte a range of different and complementary responses, to allow the detection through a suitable electronic processing and/or software.
  • the methods for processing response signals are complementary to the gravimetric multi-sensor system according to the present invention.
  • the device according to the invention comprises a substrate 1 from alumina of 2.5 x 2.5 cm.
  • Four resonant piezoelectric layer sensors 2a, 2b, 2c and 2d from lead zirconate-titanate having a circular shape are present on substrate 1, near the corners of said substrate 1.
  • the piezoelectric element 2a is coated with poly(N- vinylpyrrolidone) and is sensitive to relative humidity; element 2b is coated with poly (amidoamine) and is sensitive to sulfur dioxide; element 2c is coated with polystyrene and is sensitive to aromatic hydrocarbons (e.g., toluene), while element 2d is coated with poly (ethylenglicole) and is sensitive to aliphatic hydrocarbons (for instance, hexane) .
  • the meander-shaped, metal-based heating element 3 is also present in the central region of the substrate, according to a cross-geometry, to optimize symmetry.
  • sensor 2b of the example is sensitive to S0 2 , but not only to it; in particular the sensitivity to S0 2 is appraisably affected, for instance, by the content of relative humidity of the environment (sensed by 2a) . This fact is due to the complexity of the chemical reactions involved in the analyte detection process which prevents an absolute response specificity.
  • the device according to the present invention provides an economical way to solve such problem as, to go back to the specific example, one would not be able to tell, from the response of the individual sensor 2b, if said response is originated by S0 2 , humidity or a mixture of the same.
  • the response of 2a allows to determine the humidity content and therefore to separate from the signal of 2b only the contribution due to S0 2 .
  • the device according to the invention provides with respect to those of the known art - are in particular the following ones: - the resonant piezoelectric layer sensing elements are planar, hence they need no additional and particular working steps; the realization of multi-sensor matrices is technically easy and economical; - thermostating carefully all the matrix of the multi- sensor matrix is technically feasible and advantageous, as the thick film technology often allows to realize heating elements having widely variable geometries and sizes, and their localization on the same high thermal conductivity alumina substrate whereon sensors are placed maximizes the effectiveness of temperature regulation, keeping power consumption low;
  • the system is miniaturized, compact, sturdy, without moving parts and has a low realization cost, even by reduced production volumes.

Abstract

A device for sensing and measuring gaseous and/or vapor state analytes based on resonant piezoelectric layers, comprising a substrate from alumina (1), a plurality of sensors (2a, 2b, 2c, 2d) made from lead zirconate-titanate based piezoelectric elements, realized by means of a thick film technology on said substrate (1) and coated with sensitive coatings suitable to selectively and reversibly absorbing said analytes, at least a heating element (3) suitable to thermostate said substrate (1), as well as suitable circuits for the amplification, transmission and elaboration of the signals emitted by the sensors and suitable means for the treatment and electronic data processing and/or software.

Description

MULTI-SENSOR DEVICE FOR GRAVIMETRIC CHEMICAL MEASUREMENTS BY MEANS OF RESONANT PIEZOELECTRIC LAYERS BY THICK FILM TECHNOLOGY
DESCRIPTION The present invention relates to a device for detecting, measuring and monitoring a plurality of gaseous and/or vapor state analytes, based on resonant piezoelectric elements, by means of a thick film technology. As is known, the availability of chemical sensors having a good metrologic performance and low realization cost is required by many application situations. In particular, the detection of gaseous compounds and vapors in the air is an object of deep and topical interest for the environment monitoring, and for measurements in domestic and industrial environments .
The problem of chemical detection by means of electric output sensors is, as is well-known, a complex one, since it is extremely difficult to realize selective devices for the anlytes of interest, and it is substantially impossible to reach the response specificity. Object of this invention is to provide a device for the detection, measurement and monitoring of gaseous and/or vapor state analytes different from one another and present at the same time in given environments, with high sensitivity and high selectivity and specificity. Another objet of the invention is to provide a flexible, low cost multi-sensor device for gravimetric chemical measurements. These and still other objects and related advantages which will be stressed by the following description, are achieved by a device for detecting and measuring gaseous and/or vapor state analytes, based on resonant piezoelectric layers, which device, according to the present invention, comprises: - a substrate, a plurality of sensors made from piezoelectric elements based on compounds of polarized ferroelectric ceramics, realized by means of a thick film technology on said substrate and coated with sensitive coatings suitable to selectively and reversibly absorb said analytes, at least a heating element incorporated in said substrate, provided with a suitable regulation circuit apt to thermostate said substrate, suitable circuits being also provided for the amplification, transmission and elaboration of the signals emitted by the sensors and suitable means for the treatment and electronic data processing and/or software.
More particularly, said substrate is made from alumina. The substrate may be also made from any other suitably insulated material, such as an enameled metal material, for instance enameled steel or the like. Preferably, said compounds of ferroelectric ceramics are made from lead zirconate-titanate, and are realized by silk-screen printing on said substrate from alumina. As is known, the thick film technology allows to realize electronic devices and circuits by means of silk-screen printing processes of pastes having specific and different properties on suitable substrates, followed by thermal cycles to stabilize the mechanical and functional properties of the deposits. The base material employed as an active phase for the preparation of the piezoelectric elements is lead zirconate-titanate of various compositions and particle sizes .
A binder is added to the powder lead zirconate- titanate, generally made from lead oxide (PbO) powder or vitreous compounds, to promote the compacting of lead zirconate-titanate and its adhesion to the substrate during firing. The mixture made from lead zirconate-titanate and the binder is then dissolved in a liquid carrier made from an organic solvent and a thickener, typically ethyl cellulose in terpineol, to obtain a fluid compound having the right rheology to allow silk-screen printing. After the printing, the layers are dried at about 150 °C and then submitted to a firing process at about 950°C. After the firing, the piezoelectric activity is induced in the layers by means of a polarization process, namely the application of an electric field in the order of 4-5 MV/m for about 10 minutes, at a temperature near the Curie one (the typical values employed range from 100 to 200°C) , followed by the return to ambient temperature with the applied field. The piezoelectric and mechanical characteristics of the film depend on the composition of the paste and the mean particle size of the powders (typically comprised
between 1 and 10 μm) , the firing heat treatments, which
concur as a whole to defining the microstructure of the layer and the polarization conditions. The lead zirconate-titanate based resonant sensor on alumina substrate allows to detect small mass amounts integral with the vibrating structure through the decrease in the resonance frequency of the product, and can therefore advantageously detect a chemical species by means of the sensitization of the resonator with a material capable of reversibly absorbing the analyte of interest, with ensuing variation in its own mass. The material that makes up said sensitive coatings that cover said piezoelectric elements and that are capable of reversibly absorbing the analyte of interest is generally a polymeric material, selected according to the analyte to be detected and measured. It has been found that the substrate from alumina has an active role in the determination of the resonance frequency measured, which is not due to the piezoelectric layer only, but to the substrate/piezoelectric layer whole which constitutes therefore a composite resonator: in fact, it has been found that a reduction in the thickness of the substrate leads to an increase in resonance frequency and, correspondingly, in mass sensitivity. For a
piezoelectric layer having a thickness of about 100 μm
on a substrate of 250 μm, the frequency is of about 6,5 MHz and the sensitivity of -450 kHz/ g, which value is a remarkable result.
The device according to the invention is a gravimetric multi-sensor on one only substrate. Each microbalance of the whole is typically coated with a different sensitive material, so as to obtain for each analyte a range of different and complementary responses, to allow the detection through a suitable electronic processing and/or software. The methods for processing response signals are complementary to the gravimetric multi-sensor system according to the present invention.
The parasitic influence of the operating temperature on the resonance frequency of the sensors according to the present invention is drastically reduced by means of a thermostating system. Such system employs a heating element silk-screen printed on the substrate, controlled by a regulation electronic circuit that keeps the temperature of the substrate at about 50°C, independently on ambient temperature. The electronic systems have been eliminated from the substrate which houses the sensors, as they are a disturbing heat source whose amount is not constant in time and which have not a uniform space distribution. The temperature control system allows to markedly improve the stability of the resonance frequencies, the mass resolution and the minimum detectability threshold of the gaseous analytes of interest . The invention will be described in the following with reference to the attached drawing, solely given by way of non limiting illustration of the invention, and wherein: Figure 1 shows a device according to the present invention, comprising four resonant gravimetric sensors .
With reference to such figure, the device according to the invention comprises a substrate 1 from alumina of 2.5 x 2.5 cm. Four resonant piezoelectric layer sensors 2a, 2b, 2c and 2d from lead zirconate-titanate having a circular shape are present on substrate 1, near the corners of said substrate 1.
The piezoelectric element 2a is coated with poly(N- vinylpyrrolidone) and is sensitive to relative humidity; element 2b is coated with poly (amidoamine) and is sensitive to sulfur dioxide; element 2c is coated with polystyrene and is sensitive to aromatic hydrocarbons (e.g., toluene), while element 2d is coated with poly (ethylenglicole) and is sensitive to aliphatic hydrocarbons (for instance, hexane) . On substrate 1, the meander-shaped, metal-based heating element 3 is also present in the central region of the substrate, according to a cross-geometry, to optimize symmetry.
The number of 4 sensors is merely indicative and, being not limited by any substantial constraint but the one of ensuring a symmetric arrangement of the sensors with respect to the heating elements, may be varied, in particular increased according to needs. It must be taken into account that there unavoidably exists a tendency towards cross-sensitivity between the different sensors. In other words, sensor 2b of the example is sensitive to S02, but not only to it; in particular the sensitivity to S02 is appraisably affected, for instance, by the content of relative humidity of the environment (sensed by 2a) . This fact is due to the complexity of the chemical reactions involved in the analyte detection process which prevents an absolute response specificity. Being a multi-sensor device, the device according to the present invention provides an economical way to solve such problem as, to go back to the specific example, one would not be able to tell, from the response of the individual sensor 2b, if said response is originated by S02, humidity or a mixture of the same. However, the response of 2a allows to determine the humidity content and therefore to separate from the signal of 2b only the contribution due to S02.
Through a suitable processing of the signals coming from the multiplicity of sensors, it is possible to exploit the information redundancy associated to non selective responses to obtain a reliable estimate of the composition of the atmosphere being examined. The higher the number of the sensors of the whole - insofar as allowed by the relative increase in the complexity of the system - the higher the detail by which said composition can be re-constructed.
Further advantages which the device according to the invention provides with respect to those of the known art - are in particular the following ones: - the resonant piezoelectric layer sensing elements are planar, hence they need no additional and particular working steps; the realization of multi-sensor matrices is technically easy and economical; - thermostating carefully all the matrix of the multi- sensor matrix is technically feasible and advantageous, as the thick film technology often allows to realize heating elements having widely variable geometries and sizes, and their localization on the same high thermal conductivity alumina substrate whereon sensors are placed maximizes the effectiveness of temperature regulation, keeping power consumption low;
- the system is miniaturized, compact, sturdy, without moving parts and has a low realization cost, even by reduced production volumes.

Claims

1. A device for sensing and measuring gaseous and/or vapor state analytes based on resonant piezoelectric layers, which device, according to the present invention, comprises:
- a substrate (1) ;
- a plurality of sensors (2a, 2b, 2c, 2d) made from piezoelectric elements based on polarized ferroelectric ceramic compounds, realized with a thick film technology on said substrate (1) , and coated with sensitive coatings suitable for selectively and reversibly absorbing said analytes;
- at least a heating element (3) incorporated in said substrate (1) , provided with a suitable regulation circuit, suitable to thermostate said substrate (1) , suitable circuits being also provided for the amplification, transmission and elaboration of the signals emitted by the sensors and opportune means for the treatment and electronic data processing and/or software.
2. The device according to claim 1, characterized in that said substrate (1) is made from alumina.
3. The device according to claim 1, characterized in that said substrate (1) is made from an insulated material, such as enameled steel.
4. The device according to claim 1, characterized in that said compounds of ferroelectric ceramics comprise lead zirconate-titanate.
5. The device according to claim 4, characterized in that said compounds of ferroelectric ceramics comprise, besides lead zirconate-titanate, binders such as lead oxide and/or vitreous compounds .
6. The device according to claims 1-5, characterized in that said piezoelectric elements made from lead zirconate-titanate are realized by silk-screen printing on said alumina substrate.
7. The device according to claim 1, characterized in that said heating element is silk-screen printed on said alumina substrate.
8. The device according to claim 1, characterized in that it is thermostated to 50°C by means of said heating element.
PCT/EP1999/006957 1998-10-07 1999-09-21 Multi-sensor device for gravimetric chemical measurements by means of resonant piezoelectric layers by thick film technology WO2000020850A1 (en)

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IT002153 IT1302616B1 (en) 1998-10-07 1998-10-07 MULTISENSOR DEVICE FOR GRAVIMETRIC CHEMICAL MEASUREMENTS USING PIEZOELECTRIC RESONANT THICK FILM TECHNOLOGY.
ITMI98A002/153 1998-10-07

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WO2006078229A1 (en) * 2004-10-17 2006-07-27 Board Of Regents Of The University And Community College System Of Nevada Self-sensing array of microcantilevers for chemical detection
GB2432001A (en) * 2003-10-17 2007-05-09 Nevada System Of Higher Education Self-sensing array of microcantilevers for chemical detection
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US10156585B2 (en) 2003-03-11 2018-12-18 Board Of Regents Of The Nevada System Of Higher Education, On Behalf Of The University Of Nevada, Reno Cantilevered probes having piezoelectric layer, treated section, and resistive heater, and method of use for chemical detection

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US7498721B2 (en) 2003-02-05 2009-03-03 Brunel University Resonant sensor assembly
US10156585B2 (en) 2003-03-11 2018-12-18 Board Of Regents Of The Nevada System Of Higher Education, On Behalf Of The University Of Nevada, Reno Cantilevered probes having piezoelectric layer, treated section, and resistive heater, and method of use for chemical detection
GB2432001A (en) * 2003-10-17 2007-05-09 Nevada System Of Higher Education Self-sensing array of microcantilevers for chemical detection
US8524501B2 (en) 2003-10-17 2013-09-03 Board Of Regents Of The Nevada System Of Higher Education Self-sensing array of microcantilevers for chemical detection
GB2432001B (en) * 2003-10-17 2009-04-15 Nevada System Of Higher Education Self-sensing array of microcantilevers for chemical detection
US7279131B2 (en) 2004-07-01 2007-10-09 Uop Llc Method and apparatus for mass analysis of samples
US7533587B2 (en) 2004-07-01 2009-05-19 Uop Llc Method and apparatus for mass analysis of samples
US7533586B2 (en) 2004-07-01 2009-05-19 Uop Llc Method and apparatus for mass analysis of samples
US10473636B2 (en) 2004-10-01 2019-11-12 Board Of Regents Of The Nevada System Of Higher Education, On Behalf Of The University Of Nevada Cantilevered probe detector with piezoelectric element
US8713711B2 (en) 2004-10-01 2014-04-29 Board Of Regents Of The Nevada System Of Higher Education, On Behalf Of The University Of Nevada Cantilevered probe detector with piezoelectric element
US7694346B2 (en) 2004-10-01 2010-04-06 Board Of Regents Of The Nevada System Of Higher Education On Behalf Of The University Of Nevada Cantilevered probe detector with piezoelectric element
US8434161B1 (en) 2004-10-01 2013-04-30 Board Of Regents Of The Nevada System Of Higher Education, On Behalf Of The University Of Nevada Cantilevered probe detector with piezoelectric element
US8434160B1 (en) 2004-10-01 2013-04-30 Board Of Regents Of The Nevada System Of Higher Education, On Behalf Of The University Of Nevada Cantilevered probe detector with piezoelectric element
WO2006078229A1 (en) * 2004-10-17 2006-07-27 Board Of Regents Of The University And Community College System Of Nevada Self-sensing array of microcantilevers for chemical detection
FR2931550A1 (en) * 2008-05-20 2009-11-27 Commissariat Energie Atomique DEVICE FOR THE GRAVIMETRIC DETECTION OF PARTICLES IN A FLUID MEDIA COMPRISING AN OSCILLATOR BETWEEN TWO FLUIDIC CHANNELS, A METHOD FOR PRODUCING THE SAME, AND METHOD FOR THE IMPLEMENTATION OF THE DEVICE
FR2931549A1 (en) * 2008-05-20 2009-11-27 Commissariat Energie Atomique DEVICE FOR THE GRAVIMETRIC DETECTION OF PARTICLES IN A FLUID ENVIRONMENT, COMPRISING AN OSCILLATOR CROSSED BY A FLUIDIC VEIN, METHOD FOR PRODUCING THE SAME AND METHOD FOR IMPLEMENTING THE DEVICE
US8746048B2 (en) 2008-05-20 2014-06-10 Commissariat A L'energie Atomique Et Aux Energies Alternatives Device for the gravimetric detection of particles in a fluid medium, comprising an oscillator between two fluid channels
US8844340B2 (en) 2008-05-20 2014-09-30 Commissariat a l'Energie et aux Energies Alternatives Device for the gravimetric detection of particles in a fluid medium, comprising an oscillator over which a fluid stream flows, production process and method of employing the device
WO2009141515A1 (en) * 2008-05-20 2009-11-26 Commissariat A L'energie Atomique Device for the gravimetric detection of particles in a fluid medium, comprising an oscillator between two fluid channels, production process and method of employing the device
WO2009141516A1 (en) * 2008-05-20 2009-11-26 Commissariat A L'energie Atomique Device for the gravimetric detection of particles in a fluid medium, comprising an oscillator over which a fluid stream flows, production process and method of employing the device
RU2486498C2 (en) * 2011-08-03 2013-06-27 Федеральное государственное военное образовательное учреждение высшего профессионального образования "Военный авиационный инженерный университет" (г. Воронеж) Министерства обороны Российской Федерации Method to measure relative air humidity

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ITMI982153A1 (en) 2000-04-07
IT1302616B1 (en) 2000-09-29

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