EP0966675A1 - Detecteur de gaz - Google Patents

Detecteur de gaz

Info

Publication number
EP0966675A1
EP0966675A1 EP98909641A EP98909641A EP0966675A1 EP 0966675 A1 EP0966675 A1 EP 0966675A1 EP 98909641 A EP98909641 A EP 98909641A EP 98909641 A EP98909641 A EP 98909641A EP 0966675 A1 EP0966675 A1 EP 0966675A1
Authority
EP
European Patent Office
Prior art keywords
layer
fet
polymer
gas sensor
gas
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Withdrawn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
EP98909641A
Other languages
German (de)
English (en)
Inventor
Peter Alfred Payne
Krishna Chandra Persaud
John Vernon Hatfield
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.)
Osmetech PLC
Original Assignee
Osmetech PLC
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 Osmetech PLC filed Critical Osmetech PLC
Publication of EP0966675A1 publication Critical patent/EP0966675A1/fr
Withdrawn legal-status Critical Current

Links

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
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/403—Cells and electrode assemblies
    • G01N27/414—Ion-sensitive or chemical field-effect transistors, i.e. ISFETS or CHEMFETS
    • G01N27/4141—Ion-sensitive or chemical field-effect transistors, i.e. ISFETS or CHEMFETS specially adapted for gases
    • G01N27/4143—Air gap between gate and channel, i.e. suspended gate [SG] FETs

Definitions

  • This invention relates to the field of gas sensing, in particular to a gas sensor comprising an insulated gate field effect transistor (FET) in which the gate comprises a gas sensitive material, with particular, but by no means exclusive, reference to semiconducting polymers.
  • FET insulated gate field effect transistor
  • British Patent GB 2 203 553 describes an alternative technique in which changes in ac impedance are measured.
  • CHEMFETS Devices based upon chemically induced changes in electron work function, so-called CHEMFETS, have been established for about 20 years. However, there appears to have been minimal interest in the possibility of fabricating semiconducting polymer CHEMFETS; in fact, there appears to be only one report of such an application - that of Joscowicz and Janata ( M Joscowicz and J Janata, Anal. Chem. 58 (1986) 514). In this work, a rather complicated suspended gate gas sensitive Field Effect Transistor (gas FET) was described. Polymer (polypyrrole) was polymerised by connecting a suspended platinum gate mesh as the working electrode and electropolymerising around this mesh.
  • gas FET suspended gate gas sensitive Field Effect Transistor
  • the principle is essentially an adaption of the well-known technique of electropolymerisation across microgaps [5 to 20 ⁇ m] : the platinum mesh provides a plurality of such microgaps.
  • the present invention provides a semiconducting polymer insulated gate FET of straightforward design.
  • the device offers numerous advantages over conventional semiconducting polymer gas sensor based upon the measurement of resistance changes.
  • the device is of simple and more practical design compared to the device of Joscowicz and Janata, and is readily capable of supporting large (20 x 200 ⁇ m or greater) polymer coated gate dimensions.
  • the present invention also provides gas sensors comprising insulated gate FETs having other gas sensitive materials.
  • a gas sensor comprising an insulated gate FET in which the gate comprises one or more layers of a non-metallic gas sensitive material, the capacitance and/or the work function of said material being altered by exposure of said material to certain gases, and in which at least one layer of material is in direct contact with a gate insulating layer.
  • Joscowicz and Janata provides details of the likely mechanism by which the changes in capacitance and/or work function enable gas detection to be accomplished.
  • the gas sensitive material may comprise semiconducting polymer. However, it is possible to utilise a variety of other materials such as liquid crystals, metal oxides, other polymers, semi-permeable materials, silicones and ceramics.
  • a first layer of semiconducting polymer in direct contact with the gate insulating layer may be deposited by chemical polymerisation.
  • the chemical polymerisation may comprise : spin coating a gateless FET with a solution containing an oxidising agent; exposing the coated FET to monomer vapour; and etching the layer of polymer thus formed in an appropriate manner.
  • a first layer of semiconducting polymer in direct contact with the gate insulating layer may be deposited by photopolymerisation.
  • the photopolymerisation may comprise : spin coating a gateless FET with a photosensitive solution containing the monomers; exposing the coated FET to radiation of suitable wavelength to effect polymerisation and etching the layer of polymer thus formed in an appropriate manner.
  • the etching may comprise chemical etching.
  • the etching may comprise plasma etching.
  • the first layer of semiconducting polymer in direct contact with the gate insulating layer may be polypyrrole.
  • a second layer of semiconducting polymer may be deposited by electropolymerisation.
  • the first layer of semiconducting polymer in direct contact with the gate insulating layer may be etched so as to create apertures in said first layer, said apertures permitting the second layer to be deposited in direct contact with the gate insulating layer.
  • the gas sensor may be an integral part of a CMOS, PMOS or NMOS device.
  • the device may originally comprise at least one self-aligned polysilicon gate structure in which the polysilicon is removed and semiconducting polymer deposited in its place.
  • Active circuitry may be incorporated into the CMOS, PMOS or NMOS device.
  • Two insulated gate FETs may comprise a gas sensing arrangement in which the outputs of the first and second FET are differentially amplified, only the gas sensitive material or materials of the first FET being exposed to the gas.
  • the gas sensitive material or materials of the second FET may be encapsulated.
  • a method for fabricating a gas sensor comprising the steps of : providing a gateless FET; and depositing one or more layers of a non-metallic gas sensitive material to form a gate, a first layer of said material being deposited so as to be in direct contact with a gate insulating layer; in which the capacitance and/or the work function of the gas sensitive material is alterable by exposure of said material to certain gases.
  • the gas sensitive material may comprise semiconducting polymer.
  • the first layer of semiconducting polymer in direct contact with the gate insulating layer may be deposited by chemical polymerisation or photopolymerisation.
  • the method may comprise the steps of : spin coating a gateless FET with a solution containing an oxidising agent; exposing the coated FET to monomer vapour; and etching the layer of polymer thus formed in an appropriate manner.
  • the oxidising agent may be ferric chloride.
  • the method may comprise the steps of : spin coating a gateless FET with a photosensitive solution containing the monomer; exposing the coated FET to radiation of suitable wavelength to effect polymerisation; and etching the layer of polymer this formed in an appropriate manner.
  • the etching may comprise chemical etching.
  • the etching may comprise plasma etching.
  • the first layer of semiconducting polymer may be polypyrrole.
  • the method may further comprise the step of depositing a second layer of semiconducting polymer by electropolymerisation.
  • An electrical contact may be deposited onto the first layer of polymer, the electrical contact being used as a working electrode during electropolymerisation.
  • the first layer of semiconducting polymer may be etched so as to create apertures in said first layer, said apertures permitting the second layer of semiconducting polymer to be deposited in direct contact with the gate insulating layer.
  • Figure 1 shows (a) a cross sectional side view and (b) a plan view of an insulated gate FET of the present invention
  • Figure 2 shows I vs V FET response characteristics with and without the presence of gas.
  • Figure 1 depicts a cross sectional view through a gas sensor of the present invention comprising an insulated gate FET 10 in which the gate 12 comprises a layer of semiconducting polymer 12a in direct contact with a gate insulating layer 14.
  • Figure 1 depicts a pMOS FET having a p+ source region 16 and a p+ drain region 18 formed in a n " substrate 20. Electrical contacts 22, 24, 26 are made to the source, drain and gate regions respectively.
  • the gate insulating layer 14 is a thin layer of Si0 2 although other insulating materials, such as silicon nitride, may be employed. It is understood that the invention is equally applicable to the manufacture of nMOS FETs.
  • the layer of semiconducting polymer 12a is deposited by chemical polymerisation. It is this step that enables the semiconducting polymer to be deposited in direct contact with the gate insulating layer 14, in contrast to the method of Joscowicz and Janata in which a complicated suspended gate configuration was adopted.
  • the chemical polymerisation comprises: spin coating a gateless FET with a solution containing an oxidising agent; exposing the coated FET to monomer vapour; and
  • This last step ensures that polymer remains deposited only in the gate area, over the gate insulating layer 14.
  • the gate area is protected by photolithographic techniques and 'surplus' polymer is removed by plasma or chemical etching.
  • Polypyrrole is particularly suitable to act as the layer 12a, and ferric chloride is a particularly useful oxidising agent.
  • ferric chloride is a particularly useful oxidising agent.
  • Other oxidising agents, such as copper chloride, copper nitrate, would suggest themselves to skilled practitioners in the art.
  • a layer of semiconducting polymer in direct contact with the gate insulating layer 14 are within the scope of the invention.
  • the oxidising agent might be evaporated onto the surface of the FET, or spray or dip coating might be employed.
  • semiconducting polymer can be deposited by photopolymerisation.
  • the photopolymerisation can comprise : spin coating a gateless FET with a photosensitive solution containing the monomer; exposing the coated FET to radiation of suitable wavelength (probably of UV wavelengths) to effect polymerisation; and etching the layer of polymer thus formed in an appropriate manner.
  • a second layer of semiconducting polymer is deposited by electropolymerisation.
  • the second layer of polymer would be deposited onto a first layer such as polypyrrole, which acts as a excellent substrate and which adheres well to the gate insulating layer.
  • An electrical contact is deposited onto the first layer of semiconducting polymer, the electrical contact being used as a working electrode during electropolymerisation.
  • a further advantage with this method is that deposition of, for example, a metal onto deposited polymer ensures that ohmic contact is made.
  • a disadvantage is that the electropolymerisation process may attack the metal contact, which may necessitate the use of an appropriate mask prior to deposition of the second layer of polymer. Such is the case with aluminium.
  • the etching step described above is used to create apertures in the first layer of semiconducting polymer, the apertures permitting the second layer of semiconducting polymer to be electrochemically deposited in direct contact with the gate insulating layer.
  • the advantage with this approach is that it avoids any possibility of cancellation of electron work function changes of the second layer of semiconducting polymer.
  • Insulated gate FETs of the present invention may be integrated into standard CMOS technology. It is well known that CMOS devices consume low amounts of power: possible applications of CMOS insulated gate FETs include low power badge mounted gas monitoring devices. Another advantage is that "active" circuitry may be incorporated into a CMOS device. Such active circuitry might control the application of voltages to the insulated gate FET or FETs and perform data preprocessing/processing. The active circuitry might also control the electropolymerisation of the second layer of polymer.
  • Insulated gate FETs of the present invention may be produced by "retrofitting" standard CMOS devices by removing self-aligned polysilicon gate structures and then depositing polymer in the manner described above. Gate dimensions are relatively large, typically 20 x 200 ⁇ m (length x width) but polypyrrole can be successfully deposited over such a surface. The gate would be well separated from other active circuitry : the gate interconnect would have to be routed over the chip final overlglaze to rejoin the on-chip circuitry.
  • the present invention also provides a gas sensing arrangement employing two insulated gate FETs, preferably of the same semiconducting polymer or polymers in which only the polymer(s) of one FET are exposed to the gas of interest.
  • the outputs of the two FETs are differentially amplified.
  • This arrangement minimises the effect of any FET response not caused by the presence of the gas, e.g. changes in FET characteristics due to temperature drifts.
  • the polymer or polymer of the FET not exposed to the gas is encapsulated with a suitable medium, such as an epoxy resin or a photoresist.
  • Insulated gate FETs of the present invention exhibit a number of advantageous features. Arrays of FETs may be produced which can be addressed by a suitable multiplexing arrangement and which exhibit differing sensitivities towards gases.
  • the devices are inherently of relatively small dimensions.
  • the FET devices are capable of flexible operation : current or voltage mode may be employed, using ac or dc waveforms. Since the device is a transistor, the effects of the work function variations are amplified by the device.
  • Joscowicz and Janata a device is described which employs semiconducting polymer at the gate of a FET.
  • the polymer is not in direct contact with the gate insulating layer : a rather complicated "suspended gate" arrangement is used.
  • the device reported in Joscowicz and Janata is unquestionably of academic interest, however the configuration is impractical, as witnessed by the lack of any follow-up in the ten years since the publication of this paper.
  • the present invention provides a practical configuration which can be made compatible with standard CMOS technology. As a result, devices of low cost and low power consumption may be produced. Furthermore, active circuitry can be incorporated into such devices.
  • non-metallic gas sensitive materials which exhibit a change in capacitance and/or work function in the presence of gases.
  • Such materials include liquid crystals, metal oxides, other polymers such as non-conducting polymers, semi-permeable materials, silicones and ceramics.
  • the preferred methods of deposition depend upon the identity of the material selected. Exampie
  • a device according the present invention was fabricated by modifying the gate structure of a PH sensitive ISFET. Polypyrrole is deposited in the following stages:
  • the ISFET is cleaned with a suitable de-greasing solvent, rinsed in de- ionised water then methanol, and spun for 30 seconds at 2000 rpm to remove any surplus moisture;
  • the polypyrrole is then etched in the following manner:
  • aluminium is then evaporated onto the substrate and patterned using standard lithographic techniques to leave aluminium only in the gate region;
  • a plasma etch is performed in an oxygen plasma at a frequency of 400 kHZ and a power of 250W.
  • aluminium is required because the etch rates of both polypyrrole and the positive resist have been found to be very similar.
  • the use of a layer of resist between the aluminium mask and the polypyrrole is useful since it:
  • FIG. 1 shows the effect of exposure to the vapour on the Ids-Vds characteristics of the device. Substantial changes - C ⁇ 20% - are observed in drain current. The response to the vapour is fast. Furthermore, on purging with nitrogen the response returns or substantially returns to that originally observed in the absence of n-butyl acetate vapour.

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  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Molecular Biology (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

Abstract

L'invention concerne un détecteur de gaz comportant un transistor à effet de champ à grille isolée dans lequel la grille comporte une ou plusieurs couches de matière non métallique sensible au gaz - la capacité et/ou le travail d'extraction de ladite matière étant modifiés par exposition de ladite matière à certains gaz - et dans lequel au moins une couche de matière se trouve en contact direct avec une couche d'isolation de la grille.
EP98909641A 1997-03-14 1998-03-16 Detecteur de gaz Withdrawn EP0966675A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB9705278A GB9705278D0 (en) 1997-03-14 1997-03-14 Gas sensor
GB9705278 1997-03-14
PCT/GB1998/000776 WO1998041853A1 (fr) 1997-03-14 1998-03-16 Detecteur de gaz

Publications (1)

Publication Number Publication Date
EP0966675A1 true EP0966675A1 (fr) 1999-12-29

Family

ID=10809209

Family Applications (1)

Application Number Title Priority Date Filing Date
EP98909641A Withdrawn EP0966675A1 (fr) 1997-03-14 1998-03-16 Detecteur de gaz

Country Status (3)

Country Link
EP (1) EP0966675A1 (fr)
GB (1) GB9705278D0 (fr)
WO (1) WO1998041853A1 (fr)

Families Citing this family (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6575013B2 (en) 2001-02-26 2003-06-10 Lucent Technologies Inc. Electronic odor sensor
DE10110471C2 (de) 2001-03-05 2003-12-18 Siemens Ag Alkoholsensor nach dem Prinzip der Austrittsarbeitsmessung
AU2002356479A1 (en) * 2001-11-30 2003-06-10 Acreo Ab Electrochemical sensor
EP1456892A1 (fr) 2001-11-30 2004-09-15 Acreo AB Dispositif electrochimique
JP4644664B2 (ja) 2003-09-29 2011-03-02 富士フイルム株式会社 インクジェット用記録材料、インクジェット記録材料の製造方法及びインクジェット記録方法
US7276111B2 (en) 2004-02-09 2007-10-02 Seiko Epson Corporation Ink composition, inkjet recording method and recorded matter
DE102004019640A1 (de) 2004-04-22 2005-11-17 Siemens Ag Verfahren zur Erhöhung der Selektivität von FET-basierten Gassensoren
DE102004019641B4 (de) 2004-04-22 2009-10-01 Micronas Gmbh FET-basierter Gassensor
DE102004019604A1 (de) * 2004-04-22 2005-11-17 Siemens Ag Verfahren zur Minimierung von Querempfindlichkeiten bei FET-basierten Gassensoren
EP1707952A1 (fr) 2005-03-31 2006-10-04 Micronas GmbH Transistor à effet de champ comprenant un air gap et procédé de son fabrication
US7772617B2 (en) 2005-03-31 2010-08-10 Micronas Gmbh Gas sensitive field-effect-transistor

Family Cites Families (8)

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Publication number Priority date Publication date Assignee Title
DE3236757A1 (de) * 1982-10-05 1984-04-05 Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt Schaltungsanordnung mit einem ionensensitiven feldeffekttransistor (isfet) und einer auswerteschaltung
GB2145280B (en) * 1983-08-19 1987-12-02 Emi Ltd Vapour sensor
GB8428138D0 (en) * 1984-11-07 1984-12-12 Sibbald A Semiconductor devices
US4717673A (en) * 1984-11-23 1988-01-05 Massachusetts Institute Of Technology Microelectrochemical devices
DE3526348A1 (de) * 1985-07-23 1987-02-05 Fraunhofer Ges Forschung Sensoren fuer die selektive bestimmung von komponenten in fluessiger oder gasfoermiger phase
DE3688489T2 (de) * 1985-08-29 1993-09-16 Matsushita Electric Ind Co Ltd Einen feldeffekttransistor benutzender fuehler und dessen herstellungsverfahren.
US4730479A (en) * 1986-06-23 1988-03-15 The Standard Oil Company Temperature and humidity compensation for gas detection apparatus
JPS63131056A (ja) * 1986-11-20 1988-06-03 Terumo Corp Ｆｅｔ電極

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9841853A1 *

Also Published As

Publication number Publication date
GB9705278D0 (en) 1997-04-30
WO1998041853A1 (fr) 1998-09-24

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