WO1998041853A1 - Gas sensor - Google Patents
Gas sensor Download PDFInfo
- Publication number
- WO1998041853A1 WO1998041853A1 PCT/GB1998/000776 GB9800776W WO9841853A1 WO 1998041853 A1 WO1998041853 A1 WO 1998041853A1 GB 9800776 W GB9800776 W GB 9800776W WO 9841853 A1 WO9841853 A1 WO 9841853A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- layer
- fet
- polymer
- gas sensor
- gas
- Prior art date
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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Abstract
Description
Claims
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP98909641A EP0966675A1 (en) | 1997-03-14 | 1998-03-16 | Gas sensor |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9705278A GB9705278D0 (en) | 1997-03-14 | 1997-03-14 | Gas sensor |
GB9705278.1 | 1997-03-14 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1998041853A1 true WO1998041853A1 (en) | 1998-09-24 |
Family
ID=10809209
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/GB1998/000776 WO1998041853A1 (en) | 1997-03-14 | 1998-03-16 | Gas sensor |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP0966675A1 (en) |
GB (1) | GB9705278D0 (en) |
WO (1) | WO1998041853A1 (en) |
Cited By (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1235070A1 (en) * | 2001-02-26 | 2002-08-28 | Lucent Technologies Inc. | Electronic odor sensor |
WO2003046540A1 (en) * | 2001-11-30 | 2003-06-05 | Acreo Ab | Electrochemical sensor |
WO2003047009A1 (en) * | 2001-11-30 | 2003-06-05 | Acreo Ab | Electrochemical device |
DE102004019604A1 (en) * | 2004-04-22 | 2005-11-17 | Siemens Ag | Method for minimizing cross sensitivities in FET based gas sensors |
US7276111B2 (en) | 2004-02-09 | 2007-10-02 | Seiko Epson Corporation | Ink composition, inkjet recording method and recorded matter |
US7459732B2 (en) | 2005-03-31 | 2008-12-02 | Micronas Gmbh | Gas-sensitive field-effect transistor with air gap |
US7553458B2 (en) | 2001-03-05 | 2009-06-30 | Micronas Gmbh | Alcohol sensor using the work function measurement principle |
US7707869B2 (en) | 2004-04-22 | 2010-05-04 | Micronas Gmbh | FET-based gas sensor |
US7772617B2 (en) | 2005-03-31 | 2010-08-10 | Micronas Gmbh | Gas sensitive field-effect-transistor |
US7992426B2 (en) | 2004-04-22 | 2011-08-09 | Micronas Gmbh | Apparatus and method for increasing the selectivity of FET-based gas sensors |
EP2436740A1 (en) | 2003-09-29 | 2012-04-04 | Fujifilm Corporation | Ink for inkjet printing, ink set for inkjet printing, inkjet recording material and producing method for inkjet recording material, and inkjet recording method |
Citations (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE3236757A1 (en) * | 1982-10-05 | 1984-04-05 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Circuit arrangement containing an ion-sensitive field-effect transistor (ISFET) and an evaluation circuit |
DE3424129A1 (en) * | 1983-08-19 | 1985-03-07 | Emi Ltd., Hayes | STEAM SENSOR |
EP0181206A2 (en) * | 1984-11-07 | 1986-05-14 | National Research Development Corporation | Semiconductor devices |
EP0185941A2 (en) * | 1984-11-23 | 1986-07-02 | Massachusetts Institute Of Technology | Polymer-based microelectronic pH-sensor |
WO1987000633A1 (en) * | 1985-07-23 | 1987-01-29 | Fraunhofer-Gesellschaft Zur Förderung Der Angewand | Sensors for selective determination of components in liquid or gaseous phase |
EP0214805A2 (en) * | 1985-08-29 | 1987-03-18 | Matsushita Electric Industrial Co., Ltd. | Sensor using a field effect transistor and method of fabricating the same |
US4730479A (en) * | 1986-06-23 | 1988-03-15 | The Standard Oil Company | Temperature and humidity compensation for gas detection apparatus |
EP0345347A1 (en) * | 1986-11-20 | 1989-12-13 | Terumo Kabushiki Kaisha | Fet electrode |
-
1997
- 1997-03-14 GB GB9705278A patent/GB9705278D0/en active Pending
-
1998
- 1998-03-16 EP EP98909641A patent/EP0966675A1/en not_active Withdrawn
- 1998-03-16 WO PCT/GB1998/000776 patent/WO1998041853A1/en not_active Application Discontinuation
Patent Citations (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE3236757A1 (en) * | 1982-10-05 | 1984-04-05 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Circuit arrangement containing an ion-sensitive field-effect transistor (ISFET) and an evaluation circuit |
DE3424129A1 (en) * | 1983-08-19 | 1985-03-07 | Emi Ltd., Hayes | STEAM SENSOR |
EP0181206A2 (en) * | 1984-11-07 | 1986-05-14 | National Research Development Corporation | Semiconductor devices |
EP0185941A2 (en) * | 1984-11-23 | 1986-07-02 | Massachusetts Institute Of Technology | Polymer-based microelectronic pH-sensor |
WO1987000633A1 (en) * | 1985-07-23 | 1987-01-29 | Fraunhofer-Gesellschaft Zur Förderung Der Angewand | Sensors for selective determination of components in liquid or gaseous phase |
EP0214805A2 (en) * | 1985-08-29 | 1987-03-18 | Matsushita Electric Industrial Co., Ltd. | Sensor using a field effect transistor and method of fabricating the same |
US4730479A (en) * | 1986-06-23 | 1988-03-15 | The Standard Oil Company | Temperature and humidity compensation for gas detection apparatus |
EP0345347A1 (en) * | 1986-11-20 | 1989-12-13 | Terumo Kabushiki Kaisha | Fet electrode |
Cited By (14)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6575013B2 (en) | 2001-02-26 | 2003-06-10 | Lucent Technologies Inc. | Electronic odor sensor |
EP1235070A1 (en) * | 2001-02-26 | 2002-08-28 | Lucent Technologies Inc. | Electronic odor sensor |
US7553458B2 (en) | 2001-03-05 | 2009-06-30 | Micronas Gmbh | Alcohol sensor using the work function measurement principle |
WO2003046540A1 (en) * | 2001-11-30 | 2003-06-05 | Acreo Ab | Electrochemical sensor |
WO2003047009A1 (en) * | 2001-11-30 | 2003-06-05 | Acreo Ab | Electrochemical device |
US7482620B2 (en) | 2001-11-30 | 2009-01-27 | Acreo Ab | Electrochemical device |
EP2436740A1 (en) | 2003-09-29 | 2012-04-04 | Fujifilm Corporation | Ink for inkjet printing, ink set for inkjet printing, inkjet recording material and producing method for inkjet recording material, and inkjet recording method |
US7276111B2 (en) | 2004-02-09 | 2007-10-02 | Seiko Epson Corporation | Ink composition, inkjet recording method and recorded matter |
US7707869B2 (en) | 2004-04-22 | 2010-05-04 | Micronas Gmbh | FET-based gas sensor |
US7946153B2 (en) | 2004-04-22 | 2011-05-24 | Micronas Gmbh | Method for measuring gases and/or minimizing cross sensitivity in FET-based gas sensors |
US7992426B2 (en) | 2004-04-22 | 2011-08-09 | Micronas Gmbh | Apparatus and method for increasing the selectivity of FET-based gas sensors |
DE102004019604A1 (en) * | 2004-04-22 | 2005-11-17 | Siemens Ag | Method for minimizing cross sensitivities in FET based gas sensors |
US7459732B2 (en) | 2005-03-31 | 2008-12-02 | Micronas Gmbh | Gas-sensitive field-effect transistor with air gap |
US7772617B2 (en) | 2005-03-31 | 2010-08-10 | Micronas Gmbh | Gas sensitive field-effect-transistor |
Also Published As
Publication number | Publication date |
---|---|
EP0966675A1 (en) | 1999-12-29 |
GB9705278D0 (en) | 1997-04-30 |
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