WO1990015323A1 - Surface type microelectronic gas and vapor sensor - Google Patents

Surface type microelectronic gas and vapor sensor Download PDF

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Publication number
WO1990015323A1
WO1990015323A1 PCT/US1990/003127 US9003127W WO9015323A1 WO 1990015323 A1 WO1990015323 A1 WO 1990015323A1 US 9003127 W US9003127 W US 9003127W WO 9015323 A1 WO9015323 A1 WO 9015323A1
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electrode
set forth
electrolytic medium
microsensor
electrodes
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PCT/US1990/003127
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French (fr)
Inventor
Takaaki Otagawa
Marc J. Madou
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Sri International
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Priority to US36165689A priority
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Publication of WO1990015323A1 publication Critical patent/WO1990015323A1/en

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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means
    • G01N27/26Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/403Cells and electrode assemblies
    • G01N27/404Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors
    • G01N27/4045Cells with anode, cathode and cell electrolyte on the same side of a permeable membrane which separates them from the sample fluid, e.g. Clark-type oxygen sensors for gases other than oxygen

Abstract

The present invention is concerned with electrode structures and microsensors having fast response times and high sensitivity and to methods using such structures and/or microsensors. This is accomplished by utilizing a solid electrolytic medium (26) on the active area of the sensor which has a plurality of holes (27) through it exposing a plurality of regions (28) of the sensing electrode (18). Generally the thickness of the solid electrolytic medium is restricted to be no more than about 10 microns so that the holes are formed when the electrolytic medium is deposited.

Description

Description

. Surface Type Microelectronic Gas And Vapor Sensor

Cross-Reference

This application is a continuation-in-part of copending application Serial No. 73,712 filed July 15, 1987.

Technical Field The present invention relates to a surface conforming microsensor structure which is capable of analyzing a gas mixture for one or more specific components thereof, or for one or more gases dissolved in a liquid, and to analysis methods using such a sensor.

Background Art

A number of gas sensors are known to the art. For example, U.S. Patent 4,227,,984,. issued to Dempεey, et al, discloses a potentiostated 3-electrode solid polymer electrolyte (SPE) gas sensor. The sensor structure disclosed in this patent has catalytic sensing and counter electrodes on opposite sides of a solid polymeric electrolyte membrane. Miniaturization of such a structure is extremely difficult. Long term stability of the electrode-SPE interface is quite poor due to the swelling nature of the SPE. Still further, such a sensor is not readily adapted to the formation of arrays which can measure a number of different gaseous species or which can provide redundancy in the measurement of one or more gaseous species. Further yet, the construction of such sensors is relatively expensive. Surface conforming substantially planar sensors are also known to the art. For example, M. Koudelka describes a planar "Clark-type" oxygen sensor in "Sensors and Actuators", 9 (1986) 249-258. Also, M. Koudelka and A. Grisel, describe such a planar sensor in "Miniaturized "Clark-type" Oxygen Sensor" as reported in Proceedings of Transducers 85 (Philadelphia, Pennsylvania, June 1985). The sensor or sensors described by Koudelka and by Koudelka and Grisel are in the nature of planar 2-electrode oxygen sensors fabricated using standard integrated circuit (IC) technology. The sensors consist of a silver cathode and a silver/silver chloride/chloride ion reference anode. The electrodes are in a planar orientation upon a silicon dioxide layer upon a silicon substrate. An electrolytic medium, in the nature of a hydrogel layer, completely covers the electrodes and their surfaces to a substantial depth, generally at least about 40 to 50 microns. A silicon rubber membrane, generally 25 to 50 microns thick, having pores which are porous to oxygen encapsulates the hydrogel layer and the electrodes. While the planar sensor just described has a number of advantages it is not as sensitive as would be desired and does not have as fast a response time as would be desired since the analyte gas must pass through the hydrogel layer to reach the sensing electrode.

The present invention is directed to overcoming one or more of the problems as set forth above.

Disclosure Of Invention

In accordance an embodiment of the present invention an improved electrode structure is set forth. The improved electrode structure includes a first electrode having an outfacing surface. A solid electrolytic medium covers the outfacing surface, the electrolytic medium havingaplurality of holes therethrough exposing a plurality of regions of the outfacing surface which are not covered by the electrolytic medium.

In accordance with an alternative embodiment of the present invention a microsensor structure is set forth comprising a substrate having a substrate lSurface having an active area. A first electrode is upon the substrate surface, the first electrode having a sensing portion on the active area. The sensing portion has an outfacing surface facing away from the substrate. A solid electrolytic medium lδovers the outfacing surface, the solid electrolytic medium having a plurality of holes therethrough exposing a plurality of regions of the outfacing surface which are not covered by the electrolytic medium. A second electrode is in contact with the

2§lectrolytic medium and is free from contact with the first electrode.

In accordance with another embodiment yet of the present invention an improvement is set forth in a method of determining the concentration of a

2f>articular gaseous species which comprises contacting the species with an microsensor having a substrate having a sensing electrode and a reference electrode on a surface thereof, the sensing electrode being covered by a solid electrolytic medium, and measuring

3Ghe electrochemical effect of the species on the sensing electrode. The improvement comprises utilizing a solid electrolytic medium having a plurality of holes therethrough exposing a plurality of regions of the sensing electrode. grie Description Of Drawings

The invention will be better understood by reference to the figures of the drawings wherein like numbers denote like parts throughout and wherein: 5 Figure 1 illustrates, in top view, a microsensor in accordance with an embodiment of the present invention with an electrode thereon in accordance with an embodiment of the present invention; 0 Figure 2 is a sectional view taken along the lines II-II of Figure 1;

Figure 3 is a view similar to Figure 1 but showing an array of microsensors in accordance with the present invention on a single substrate; and 5 Figure 4 is an enlarged partial cross- sectional view taken in the area IV-IV of Figure 1.

Best Mode For Carrying Out Invention

The present invention relates to a microsensor 10 as seen in one embodiment in Figure 1. ϋttιe microsensor 10 includes a substrate 12 having a substrate surface 14 having an active area 16 upon which electrochemical reactions occur. The substrate may be made of any of a number of materials. For example, the substrate may be made of Sn insulative material, that is, a dielectric material, such as a non-conducting plastic or glass. Alternatively, the substrate can be made of a semiconducting material such as silicon or even of a conducting material so long as an appropriate dielectric material defines the substrate surface 14. For example, Figure 4 shows a substrate 12 which is made of a semiconductor material, namely silicon, and wherein the substrate surface 14 is formed by IC processing techniques of a dielectric material, namely silicon dioxide. Silicon nitride or another insulative material can alternatively be used.

A first electrode 18 is on the substrate surface 14. The first electrode 18 has a sensing portion 20 on the sensing area 16 of the substrate surface 14. The sensing portion 20 has an infacing surface 22 (see Figure 2) facing the substrate surface 14 and an outfacing surface 24 facing away from the substrate surface 14. A solid electrolytic lmedium 26 covers the outfacing surface 24 of the first electrode 18. The solid electrolytic medium 26 (see Figure 1) has a plurality of holes 27 therethrough which expose a plurality of regions 28 of the outfacing surface 24. Thus, the regions 28

ISre not covered by the electrolytic medium. The exposed regions 28 of the first electrode 18, the solid electrolytic medium 26 and the surrounding gas phase form a 3-boundary sensing boundary 29 (Figure 4). Having the regions 28

2§xposed in this manner leads to an extremely fast response time for the first electrode 18 and also to extremely high sensitivity. Generally, the solid electrolytic medium 26 is of a thickness upon the outfacing surface 24 of no more than about 10

2microns, preferably no more than about 5 microns . However, the specific extension of the solid electrolytic medium 26 is not critical so long as the holes 27 exist and expose the regions 28. The criticality lies in having the regions 28 exposed to

3fiorm the 3-phase sensing boundary 29. Generally, th eelectrolytic medium 26 will inherently have holes 27 exposing the regions 28 if it is laid down relatively thinly. However, a thicker solid electrolytic medium can be used and the holes 27 can be produced

35therwise, for example, by using a laser, chemically, by mechanical punching, etc. A second (counter) electrode 30 is in contact, with the electrolytic medium 26 and free from contact with the first electrode 18. In the particular embodiment illustrated the second δlectrode 30 is upon the substrate surface 14.

Xn accordance with an embodiment of the present invention a third (reference) electrode 32 may also be in contact with the electrolytic medium 26 and free from contact with the first electrode 18 lfind the second electrode 30. Generally, the third electrode 32 will also be in contact with the substrate surface 14.

In accordance with preferred embodiments of the present invention the first electrode 18, lfenerally the sensing electrode, the second electrode 30, generally the counter electrode, and the third electrode 32, generally the reference electrode, as well, when present, are adjacent to one another. A first-second electrode gap 34 of generally no more

2fihan about 50 microns is advantageously present, preferably no more than about 10 microns, more preferably no more than about 5 microns and still more preferably no more than about 2 microns. Indeed, sub-micron (less than about 1 micron) gaps

2Sre particularly preferred. When there is a third electrode 32, as well, the gap 36 between the first electrode 18 and the third electrode 32 is conveniently no more than about 100 microns, although this is a far less important restrain and

3§ignificantly larger gaps can be present. The size of the gap 38 between the third electrode 32 and the second electrode 30 is also of no criticality.

A dielectric wall 40 will generally be present surrounding the active area 16 and the

3§lectrolytic medium 26. A barrier 42 (Figure 2) can be present which covers the electrolytic medium 26, the barrier 42 having openings through which an analyte gas can pass. In certain instances the barrier 42 can selectively pass a gaseous species of interest while excluding possibly interferine Species. Generally, the barrier 42 will be in the nature of a polymeric material and more particularly will often be in the nature of a membrane which is gas permeable but aqueous solution impermeable. Note that the membrane need not have actual pores leading 16o its gas permeable nature. For example, the analyte gas may dissolve in the membrane and migrate therethrough to the electrolytic medium. In such instances, the entire microsensor 10 can be inserted in an aqueous solution and dissolved gases therein lδhan form a gas phase, e.g., within the barrier 42 and can be measured. This is the case even if the electrolytic medium 26 abuts the membrane since the analyte is in effect a gas, or gas-like, as it exits the membrane. The microsensor 10 can be utilized, 2fior example, in vivo in blood to analyze for blood gases on a continuous basis.

Figure 3 illustrates an embodiment of the present invention wherein a plurality of the microsensors 10 are upon the substrate surface 14 of 2fihe single substrate 12. By proper selection of the chemistries of the various electrodes 18,30,32 and of the barrier 42, for each of the sensors 10, one can provide an overall structure which is useful for analyzing for a number of different gaseous species 3§t once, and/or can provide redundancy in measuring for one or more gaseous species.

An aqueous reservoir 43 (Figure 2) can be included in the substrate 12 in liquid flow contact with the electrolytic medium 26 to keep the 3δlectrolytic medium 26 from drying out and thereby inactivating the microsensor 10. Such an aqueous reservoir 43 can be used in conjunction with all embodiments of the invention.

The first electrode 18 can be made of any of a number of materials, for example platinum, gold, iilver, other platinum group metals, or other desired metals to provide detection of desired species. The first electrode 18, and along with it the second electrode 30, and the third electrode 32, when present, can be formulated by vapor deposition, l§puttering, or the like. Generally, such techniques as are utilized in the IC art are applicable to formulate a microsensor 10 in accordance with the present invention. This can lead to the formation of the controlled size gaps 34,36 and 38, which gaps

154,36,38 can be made quite small in size (below 5 microns and even, with care, below 1 micron) . The contacts ends 44,46,48 of the electrodes 18,30 and 32, respectively, can be formulated on an appropriate contacts area of the substrate 12.

20 What is being done in the embodiment just described is to reduce to zero the time of diffusion of the gaseous species through the electrolytic medium 26 so that the limiting factor on the response time of the microsensor structure 10 is the rate of

2migration of the ionic moiety between the electrodes 18 and 30. It should be recognized that migration of the analyte from the environment to the microsensor structure 10 or through the barrier 42 may in practice be slower thaan operation of the

3microsensor structure 10. In addition, the electrodes 18 and 30 are placed close enough together so that the time of ionic migration is very small whereby the overall time of response of the microsensor structure 10 is very small. 35 The time of diffusion through the electrolytic medium is, in accordance with the present invention, reduced to zero. Basically, the electrolytic medium 26, the first electrode 18 and the gas phase form a 3-phase sensing boundary. Since there is no diffusion at all through the electrolytic medium, the time of such diffusion is, by definition, zero. In such an instance it is desirable to place the first and second electrodes as close together as possible since the only thing then limiting the response time of the microsensor structure is the lGime of diffusion of an ionic moiety, generally hydrogen ion, from one electrode to the other. It should be noted that reducing the separation of the electrodes, alone, without reducing the time of diffusion of the gaseous species through the lδlectrolytic medium, has almost no effect since the time of diffusion of the gaseous species through the electrolytic medium is generally significantly longer than the time of migration of an ionic moiety from one electrode to the other.

20 Another method of keeping the solid polymer electrolyte film hydrated is to provide a water absorption overlayer over the solid polymer electrolyte film. The analyte gas, for example CO and/or CO„ , can pass through the overlayer. The

25verlayer may be, for example, a hydroscopic polymer such as cellulose acetate butyrate. Or, a hydroscopic salt, for example lithium chloride and/or lithium bromide, may be incorporated in the solid polymer electrolyte film.

30 Specially selected solid polymer electrolyte films may be used which are themselves hydroscopic or which have a particularly high density of sulfonate groups. An example is poly(sodium 4- styJrenesulfonate) , [ -]

Figure imgf000011_0001
n. This

3βolymer is very hydrophilic whereby signals from the sensor are made humidity independent. This particula polymer may also have its property tailored, for example by mixing with Nafion (a trademark of DuPont) polymer, so as to assure that it is not too hydrophilic or too fragile to stick to a Substrate. Such techniques as are discussed above serves to make a solid polymer electrolyte film highly proton conductive or sodium conductive.

Any of a number of different types of solid electrolytic media 26 can be utilized. For l§xample, the solid electrolytic medium 26 can be a hydrogel. Preferable, however, particularly for voltaπtmetric measurements, are solid electrolytes, including solid polymeric electrolytes such as Nafion (a trademark of DuPont) which is part of a class of

1Solid polymeric ion exchangers which conduct ions upon exposure to water. Probably the best known examples are membranes made from polystyrene with fixed negative sites (sulfonate, carboxylate or phosphonate) or fixed positive sites (quaternary

2&mmonium ax quaternary phosphonium) . Selection as far as ions are concerned with these materials is almost exclusively on the basis of charge and for ions with the same charge discrimination is very slight. For voltammetric sensing the use of

2δhese materials is new. Other examples of solid polymeric electrolytes besides Nafion (which is a perfluorinated ionomer) are sulfonated styrene- divinyl benzene resins and divinyl napthalene sulfonic acid polymer.

30 Such polymers are characterized chemically and physically in that they have a hydrophobic nature with ionic (hydrophilic) clusters inside. They conduct ions upon hydration. They exclude co-ions up to the Donnan failure point at which stage ions of

3Both types can penetrate into the resin. Neutral molecules can diffuse readily through such membranes and especially large organic molecules can dissolve within the more hydrophobic resins.

Resins can also be used as reference solutions (see, for example, French patent publication No. 2,158,905). These ion exchange resins have been used as the electrolytic medium for a potentiometric CO_ sensor (see, for example, U.S. Patent 3,730,868) .

Useful gels for incorporation within the l§ensor structure include, without limitation: methylcellulose, polyvinyl alcohol, agar, carboxycellulose, gelatin, agarose, deionized gelatin, polyacrylamide, polyvinyl pyrrolidone, hydroxyethylacrylate, hydroxyethylmethacrylate, and lfiolyacrylic acid. They are characterized in that they constitute thickened (more viscous) solutions. They are hydrophilic in natural and include synthetic polymeric film forming materials.

The electrolytic medium 26 can alternatively 2Be selected from a family of inorganic oxide solid proton conductors, e.g., hydrogen uranyl phosphate, protonated J"-alumina, zirconium phosphates or antimonic acids.

Means (e.g., the barrier 42) is usually provided for encapsulating the electrolytic medium 26 and the sensing electrode 18. In the embodiments illustrated the barrier 42 can be any convenient polymer. It is generally preferred that the encapsulation material be such as to be impermeable to water vapor so that the water content of the solid polymer electrolyte 26 remains relatively constant whereby the properties of the gas sensor remain relatively constant with time. The barrier 42 may be, for example, in the nature of a membrane. The barrier 42 provides entry into the microsensor 10 of a selected moiety in response to contact of a selected species with its outfacing surface 45. Either the selected species will pass through the barrier 42 and will then constitute the selected moiety, or contact of the selected species with the Barrier 42 will lead to the introduction of a different moiety into the microsensor 10. The barrier 42. is generally at least substantially impermeable to the electrolytic medium 26 to prevent escape and/or mixing with any analyte solution l§xterior of the barrier 42.

The barrier 42 may encapsulate the entire microsensor 10. Alternatively, the barrier 42 may only cover the sensing area 16, or part or all of the substrate surface 14. It may be desirable to lencapsulate the remainder of the microsensor 10, or even all of the microsensor 10 including the barrier 42, as a protection against contamination. Generally, an inert encapsulating layer (not shown) will serve the purpose. The encapsulating layer,

2θhen present, must provide access (via, for example, pores or holes therethrough) to the barrier 42. It can be formulated as can the barrier 42.

A number of materials may serve as the. barrier 42. For example, the barrier 42 can comprise

2S gas permeable liquid impermeable membrane. This is useful in the situation wherein the sensor is used in a liquid to detect dissolved gases, for example, if the microsensor 10 is utilized in blood.

Other types of materials for utilizing as

36he barrier 42 are teflon membranes, silicone rubber membranes, silicon polycarbonate rubber membranes, mylar, nylon 6, polyvinyl alcohol, polyvinyl chloride, methylcellulose, cellulose acetate, high density polyethylene, polystyrene, natural rubber, 3Sluorosilicone, dimethylsilicon rubber, any appropriately perforate photoresist polymer, and dimethylsilicon. It is generally preferred that the membranes utilized be solution castable so as to make fabrication of the membrane more easily accomplished.

5 The barrier 42 can be constructed by, for example solution casting, separate casting on a different substrate and physical transfer, heat shrinking in place, solution casting utilizing an ink-jet printer, spin coating, or dip coating. If lϋhe barrier 42 is in the nature of uniform latex microspheres, made for example of polystyrene, styrene-butydiene, or Teflon (trademark of DuPont), such microspheres can be placed in position utilizing an ink-jet like technique, by dipping, by solvent 1Spraying, or the like. If the barrier 42 is of the nature of or includes activated carbon or similar materials it can be placed in position by ink-jet type printing, solvent casting, or the like. If the barrier includes, for example, permanganate coated 2§lumina or other substance which serves to remove nitric oxide, it can be placed in position similarly to the carbon particles.

Various types of sensing electrodes 18 can be used. These include, for example, electrodes 18 25f platinum, platinum black, silver, gold, iridium, palladium, palladium/silver, iridum dioxide, platinum black/paladium, platinum oxide, and mixtures thereof, electronically conductive polymers, and generally any of the electrodes normally utilized in 3§lectro- chemical measurements. A sensing electrode 18 will generally be chosen which is responsive to a particular gaseous species. Various conventional materials can be utilized as the counter electrode 30 3Snd as the reference electrode 32. Table 1 sets forth, as examples only, a short list of gases, and electrochemical systems which have been used to determine them.

Also in accordance with the present invention an improvement is set forth in a method of determining the concentration of a particular gaseous species which comprises contacting the species with a sensor having a substrate having a sensing electrode and a reference electrode on a surface thereof, the electrode being covered by a solid electrolytic l edium, and measuring the electrochemical effect of the species on the sensing electrode. The improvement comprises utilizing a solid electrolytic medium 26 having holes 27 therethrough exposing a plurality of regioins 28 of the sensing electr5ode

158. The method may further include providing a counter electrode as the second electrode 30, all as set forth above, and utilizing the counter electrode 30 along with the sensing electrode 18 and the reference electrode 32 when measuring the

2§lectrochemiσal effect. The various electrodes 18, 30 and 32 are preferably constructed and positioned as set forth above.

The microsensor 10 in accordance with-the invention can be constructed, generally, following

2fihe techniques of the IC industry. For example, the metals, can be deposited by sputtering or evaporation, electron-beam or ohmic evaporation onto a resist masked substrate 12 or by a lift-off technique. These techniques are particularly useful for

3βroviding closely placed sensing electrodes 18 and counter electrodes 30 with very small interelectrode gaps. Solid polymer electrolytes, when used, can be provided by using lift off technology or ink-jet printer like technology. As noted previously, i fthe

3fihickness of the solid polymer electrolyte is sufficiently limited this will lead to formation of the holes 27. Hydrogels, when used, can be provided as are solid polymer electrolytes. In such an instance it will generally be necessary to form the needed holes 27.

5 While the substrate surface 14 is illustrated as being planar it should be recognized that the invention is not limited to such a structure. Thus, the first electrode 18 usually generally conforms with the substrate surface 14, whatever its shape, planar, spherical, or the like. The electrochemical analysis which can be measured in accordance with the method of the present invention includes voltammetric, potentiometric, coloumbic, conductometric and AC analysis. 5 In accordance with the present invention the microsensors of the invention can be used for differential pulse voltometry (DPV) methods. In such a technique potential is scanned and the resultant current response is differentiated, thereby generating more information from a single sensor. The use of the DPV technique to achieve required selectivity is a direct application of the characteristic thermodynamic potentials of the. gases being analyzed. Note that certain gases of ≥nterest, for example CO, H , C-Hj-OH, NO, and NO,,, have characteristic thermodynamic potentials of, respectively, -103, 0, 87, 957 and 1093 mV vs NHE. In practice, however, each reaction requires an additional potential called overpotential, the amount βf which depends on electrocatalyst, in order to proceed at a measurable rate.

This technique is useful if the gas to be sensed exists in a mixture containing several reactive components that exhibit close thermodynamic 3£otential (e.g., CO, H2 and C2H OH) . If one considers a simple example wherein a mixture of gas A and gas B exists, gas A and gas B will exhibit current vs potential curves with different limiting currents I. and IR. By differentiating the current versus potential curves one obtains two sharp, βlearly separated peaks with characteristic potentials, E and BR. The peak current values are proportional to the gas concentrations. Thus the DPV technique can provide the potential-control and selectivity for a microsensor through precise lmeasurements of the peak values. These are closely related to the thermodynamic potentials of the gases and are characteristics of each gaseous species.

In addition, the nature of this technique allows the microelectrochemical sensor to rezero lδhe background several times each second, thereby limiting any background drift. Also, this technique improves the sensitivity because the DPV current readout eliminates most of the capacitive charging current and provides an especially good signal to

2noise ratio.

The invention will be better understood by reference to the following experimental sections.

Instrumentation and Experimental Procedure The experimental setup included a

2 icroprocessor-controlled gas-handling system (Tylan Co.). Premixed gas mixtures, 200 ppm CO in air, 100 ppm N0„ in air, 100 ppm NO in N_ , 1000 ppm ethanol in » (primary standard grade, manufactured by Union Carbide Company Linde Division, South San Francisco,

30alifornia, and distributed by Almac Cryogenic, Inc.), were used to evaluate the microelectronic gas sensors, and hydrocarbon-free air was used as a blank (background) gas. The sample gas (200 ppm CO) and the blank gas (air or N_) were introduced to a

3Stainless-steel gas-sensor chamber at a nominal flow 3 rate of 150 cm /min using flowmeters. The sensor potential is controlled by a PAR Model 173 potentiostat equipped with a PAR Model 175 Universal Programmer. For low current (less than 1 μA) measurements, an in-vivo voltammograph (Bioanalytical Systems, Inc. Model CV 37) is used. A (Hewlett- Packard Model 7644A) X-Y-t recorder records signals as a function of time.

Humidified gas samples were prepared as needed by passing dry gas samples through a humidifier prior to entering the gas chamber. The humidifier comprises three Gore-Tex (Type A, 3 mm ID, pore size 2 μm, porosity 50 percent) porous Teflon tubes with three different lengths, approximately 1, 2 and 3 cm, which are equilibrated with water vapor pressure at room temperature, and provide approximate humidity values of 10 to 15, 20 to 25 and 35 to 40 percent relative humidity (RH) , respectively. The relative humidity of the gas mixture was determined by placing a humidity sensor (General Eastern

Instruments Corp. Model 800B humidity and temperature indicator) in the gas line right after the gas chamber.

Industrial Applicability The present invention provides a novel electrode structure 18, a novel microsensor 10, and an improved method of determining the concentration of gaseous species. All of the above is useful in analyzing for any one gaseous species among other gaseous species, or, in accordance with certain embodiments, with other gaseous species which are dissolved in a fluid, for example a body fluid such as blood. Extremely fast response time is provided along with extremely high sensitivity. Uses include the foillowwing: portable environmental gas analyzers, detection of hazardous gases, fire alarms, gas leak detectors, alarm badges for safety inspectors, monitoring and regulating exhaust gases from engines, oiol furnaces or industrial burners, βontrol of indoor air quality, and gas chromatography detectors, amongothers. And, construction is relatively inexpensive utilizing standard IC techniques.

While the invention has been described in lβonnection with specific embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of lfihe invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope

2θf the invention and the limits of the appended claims.

Claims

ClaimsThat Which Is Claimed Is;
1. An electrode structure, comprising: a first electrode having a sensing portion; and a solid electrolytic medium covering said outfacing surface, said electrolytic medium having a plurality of holes therethrough exposing a pluraality of regions of said sensing portion.
2. An electrode structure as set forth in claim 1, wherein said electrolytic medium is of a thickness upon said outfacing surface of no more than about 10 microns.
3. An electrode structure as set forth in claim 1, further including: a barrier covering said electrolytic medium, said barrier being permeable to an analyte gas.
4. An electrode structure as set' forth in claim 3, further including: an aqueous reservoir in flow contact with said electrolytic medium.
5. A microsensor structure, comprising: a substrate having a substrate surface having an active area; a first electrode on with said substrate surface, said first electrode having a sensing portion on said active area, said sensing portion having an infacing surface facing said substrate surface and an outfacing surface facing away from said substrate surface; a solid electrolytic medium covering said outfacing surface,said electrolytic medium having a plurality of holes therethrough exposing a plurality of regions of said outfacing surface; and a second electrode in ion conductive contact with said electrolytic medium and free from contact with said first electrode.
6. A microsensor as set forth in claim 5, further including: a barrier covering said electrolytic medium, said barrier being permeable to an analyte gas.
7. A microsensor structure as set forth in claim 6, wherein said barrier is water impermeable.
8. A microsensor as set forth in claim 6, further including: an aqueous reservoir in flow contact with said electrolytic medium.
9. A microsensor structure as set forth in claim 5, further including: a dielectric wall extending outwardly from said substrate surface about said active area and said electrolytic medium.
10. A microsensor structure as set forth in claim 5, wherein said substrate is of a dielectric material.
11. A microsensor as set forth in claim 5, wherein said second electrode is on said substrate surface and wherein said first and second electodes are adjacent one another and are separated by a first-second electrode gap of no more than about 50 microns.
12. A microsensor as set forth in claim 11, further including: a barrier covering said electrolytic medium, said barrier being permeable to an analyte gas.
13. A microsensor as set forth in claim 12, wherein said member is water impermeable.
14. A microsensor as set forth in claim 5, further including: a third electrode in contact with said electrolytic medium and free from contact with. said first and second electrodes.
15. A microsensor as set forth in claim 14, wherein said first electrode is a sensing electrode, said second electrode is a counter electrode and said third electrode is a reference electrode.
16. A microsensor as set forth in claim 15, wherein said second and third electrodes are on said substrate surface, wherein said first and second electrodes are adjacent one another and are separated by a first-second electrode gap of no more than about 50 microns.
17. A microsensor structure as set forth in claim 5, further including: a plurality of said first electrodes and a plurality of said second electrodes, each of said first electrodes being on said substrate, said first electrodes each being in contact with a respective one of a corresponding plurality of solid electrolytic mediums, said electrolytic mediums being electrically isolated from one another.
18. In a method of determining the concentration of a particular gaseous species which comprises contacting the species with a sensor having a substrate having a sensing electrode and a counter electrode on a surface thereof, the electrodes being covered by an electrolytic medium, and measuring the electrochemical effect of said species on said sensing electrode, the improvement comprising: utilizing as said electrolytic medium a solid electrolytic medium having a plurality of holes therethrough exposing a plurality of regions of said sensing electrode.
19. A method as set forth in claim 18, wherein said method f rther includes: providing a reference electrode as a third electrode on said surface and utilizing said reference electrode along with said sensing and counter electrode when measuring said effect.
20. A method as set forth in claim 18, further including: positioning said sensing and counter electrodes adjacent one another and separated by a sensing-counter electrode gap of no more than about 50 microns.
21. A method as set forth in claim 20, wherein said solid electrolytic medium is of a thickness upon said outfacing surface of no more than about 10 microns.
22. A method as set forth in claim 21, wherein said solid electrolytic medium comprises a solid polymer electrolyte.
PCT/US1990/003127 1989-06-02 1990-06-01 Surface type microelectronic gas and vapor sensor WO1990015323A1 (en)

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Cited By (8)

* Cited by examiner, † Cited by third party
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WO1994029708A1 (en) * 1993-06-03 1994-12-22 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Electrochemical sensor
US5466605A (en) * 1993-03-15 1995-11-14 Arizona Board Of Regents Method for detection of chemical components
DE19546047C1 (en) * 1995-12-09 1997-02-06 Draegerwerk Ag An electrolyte for an electrochemical measuring cell
WO1997013143A1 (en) * 1995-10-06 1997-04-10 The Board Of Trustees Of The University Of Illinois Electrochemical sensors for gas detection
US5985673A (en) * 1994-12-22 1999-11-16 Arizona Baord Of Regents Method for regeneration of a sensor
FR2795017A1 (en) * 1999-06-21 2000-12-22 Eastman Kodak Co Device for controlling the atmosphere of an ink reservoir applied to the ink-jet
EP1590658A2 (en) * 2003-01-16 2005-11-02 Perkinelmer Las, Inc. Electrochemical sensor having improved response time
EP1623218A2 (en) * 2003-05-09 2006-02-08 MST Technology GmbH Electrode comprising material to help stabilize oxide of catalyst for electrochemical sensor

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US5891395A (en) * 1993-03-15 1999-04-06 Arizona Board Of Regents, A Body Corporate Of The State Of Arizona, Acting For And On Behalf Of Arizona State University Chemical switch for detection of chemical components
US5466605A (en) * 1993-03-15 1995-11-14 Arizona Board Of Regents Method for detection of chemical components
US5939020A (en) * 1993-03-15 1999-08-17 The Arizona Board Of Regents, A Body Corporate Of The State Of Arizona, Acting For And On Behalf Of Arizona State University Chemical switch for detection of chemical components
WO1994029708A1 (en) * 1993-06-03 1994-12-22 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Electrochemical sensor
US5670031A (en) * 1993-06-03 1997-09-23 Fraunhofer-Gesellschaft Zur Angewandten Forschung E.V. Electrochemical sensor
US5985673A (en) * 1994-12-22 1999-11-16 Arizona Baord Of Regents Method for regeneration of a sensor
WO1997013143A1 (en) * 1995-10-06 1997-04-10 The Board Of Trustees Of The University Of Illinois Electrochemical sensors for gas detection
DE19546047C1 (en) * 1995-12-09 1997-02-06 Draegerwerk Ag An electrolyte for an electrochemical measuring cell
FR2795017A1 (en) * 1999-06-21 2000-12-22 Eastman Kodak Co Device for controlling the atmosphere of an ink reservoir applied to the ink-jet
EP1063091A1 (en) * 1999-06-21 2000-12-27 Eastman Kodak Company Atmosphere control device for ink reservoir applied to inkjet printing
US6312118B1 (en) 1999-06-21 2001-11-06 Eastman Kodak Company Atmosphere control device for ink reservoir applied to ink jet printing
EP1590658A2 (en) * 2003-01-16 2005-11-02 Perkinelmer Las, Inc. Electrochemical sensor having improved response time
EP1590658A4 (en) * 2003-01-16 2009-06-03 Perkinelmer Las Inc Electrochemical sensor having improved response time
EP1623218A2 (en) * 2003-05-09 2006-02-08 MST Technology GmbH Electrode comprising material to help stabilize oxide of catalyst for electrochemical sensor
EP1623218A4 (en) * 2003-05-09 2008-08-20 Mst Technology Gmbh Electrode comprising material to help stabilize oxide of catalyst for electrochemical sensor

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