WO2018165841A1

WO2018165841A1 - Ultrathin electrochemical gas sensor

Info

Publication number: WO2018165841A1
Application number: PCT/CN2017/076567
Authority: WO
Inventors: Qinghui MU; Ling Liu
Original assignee: Honeywell International Inc.
Priority date: 2017-03-14
Filing date: 2017-03-14
Publication date: 2018-09-20
Also published as: CN110300887A

Abstract

An electrochemical sensor (100) is provided. The electrochemical senor (100) has a substrate (102), a plurality of electrodes (104, 105, 106) disposed on a first surface of the substrate (102), an electrolyte (103) disposed over at least a portion of each electrode of the plurality of electrodes (104, 105, 106), and one or more capillaries (113) disposed through the substrate (102), wherein the one or more capillaries (113) are configured to provide a diffusion pathway for a target gas to pass from an exterior of the sensor to one or more of the plurality of electrodes (104, 105, 106), and wherein the ratio of the length or width of the substrate (102) to the diameter of the one or more capillaries (113) is greater than approximately 30.

Description

ULTRATHIN ELECTROCHEMICAL GAS SENSOR

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Electrochemical sensors traditionally comprise a gas diffusion working (or sensing) electrode, often based on a platinum or graphite/platinum catalyst dispersed on polytetrafluorethylene (PTFE) tape. The target gas is reacted at this electrode while a balancing reaction takes place at the counter electrode. The electrodes are contained within an outer housing which contains a liquid electrolyte, such as sulfuric acid. The gas typically enters the housing through a controlled diffusion access port, which regulates the ingress of target gas into the cell. The gas reacts at the electrode and affects the electrical output of the sensor.

SUMMARY

In an embodiment, an electrochemical sensor may comprise a substrate； a plurality of electrodes disposed on a first surface of the substrate； an electrolyte disposed over at least a portion of each electrode of the plurality of electrodes； and one or more capillaries disposed through the substrate, wherein the one or more capillaries are configured to provide a diffusion pathway for a target gas to pass from an exterior of the housing to one or more of the plurality of electrodes, and wherein the ratio of the length or width of the substrate to the diameter of the one or more capillaries is greater than approximately 30.

In an embodiment, a method of forming an electrochemical sensor may comprise forming one or more capillaries through a substrate, wherein the ratio of the length of the substrate to the diameter of the one or more capillaries is greater than approximately 50； forming a plurality of electrodes on a first surface of the substrate； disposing an electrolyte over at least a portion of each of the plurality of electrodes； and sealing the plurality of electrodes and the electrolyte from an external environment, wherein the one or more capillaries form the only opening between the external environment and the plurality of electrodes.

In an embodiment, an electrochemical sensor may comprise a substrate； a plurality of electrodes disposed on a first surface of the substrate； an electrolyte disposed over at least a portion of each electrode of the plurality of electrodes； and a plurality of capillaries disposed through the substrate, wherein the capillaries are configured to provide a diffusion pathway for a target gas to pass from an exterior of the housing to one or more of the plurality of electrodes, and wherein the ratio of the thickness of the sensor to the diameter of the capillaries is greater than approximately 20.

These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.

FIG. 1 schematically illustrates a cross-sectional view of a sensor according to an embodiment.

FIG. 2 schematically illustrates a sensor on another circuit board according to an embodiment.

FIGS. 3A-3B schematically illustrate close up cross-sectional views of a sensor anda plurality of capillaries according to an embodiment.

FIGS. 4A-4B schematically illustrate top views of a sensor and a plurality of capillaries according to an embodiment.

FIG. 5 schematically illustrates another sensor on a circuit board according to an embodiment.

DETAILED DESCRIPTION

It should be understood at the outset that although illustrative implementations of one or more embodiments are illustrated below, the disclosed systems and methods may be implemented using any number of techniques, whether currently known or not yet in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, but may be modified within the scope of the appended claims along with their full scope of equivalents.

The following brief definition of terms shall apply throughout the application:

The term “comprising” means including but not limited to, and should be interpreted in the manner it is typically used in the patent context；

The phrases “in one embodiment, ” “according to one embodiment, ” and the like generally mean that the particular feature, structure, or characteristic following the phrase may be included in at least one embodiment of the present invention, and may be included in more than one embodiment of thepresent invention (importantly, such phrases do not necessarily refer to the same embodiment) ；

If the specification describes something as “exemplary” or an “example, ” it should be understood that refers to a non-exclusive example；

The terms “about” or “approximately” or the like, when used with a number, may mean that specific number, or alternatively, a range in proximity to the specific number, as understood by persons of skill in the art field； and

If the specification states a component or feature “may, ” “can, ” “could, ” “should, ” “would, ” “preferably, ” “possibly, ” “typically, ” “optionally, ” “for example, ” “often, ” or “might” (or other such language) be included or have a characteristic, that particular component or feature is not required to be included or to have the characteristic. Such component or feature may be optionally included in some embodiments, or it may be excluded.

Embodiments relate to systems and methods for preventing leakage of electrolyte within an electrochemical gas sensor. A typical electrochemical gas sensor comprises a housing, an electrolyte disposed within the housing, and a plurality of electrodes in contact with the electrolyte. Industry trends indicate a desire for decreasing the size of sensor devices. To successfully accomplish the decrease in size, intricate components may be integrated onto one substrate within the electrochemical sensor. The electrodes and electrolyte may be applied (or printed) layer by layer onto the substrate, where the substrate contains capillaries for gas to diffuse through the substrate to the electrode (s) . The outer most layer of the sensor may be a sealing layer, which may also be printed on the top of electrolyte for sealing purposes.

However, a problem may arise with electrolyte leakage from the capillaries in the substrate, particularly at higher ambient humidity. The electrolyte leakage may be caused by damage to the electrode (s) near the capillaries in the substrate. As a result of this leakage, the electrolyte may dry up, causing the sensor to have a decline in sensitivity or even completely lose sensitivity.

Embodiments of the disclosure include systems and methods to prevent electrolyte leakage from the capillaries in the substrate. As an example, the capillary diameter may be reduced, therefore decreasing the surface area of the capillary. When the surface area is decreased, the requirement of electrode strength against deformation at the site of contact between the capillary and the electrode is reduced. Therefore, the risk that the electrode may be damaged at the capillary site is reduced, and the likelihood for electrolyte leakage is removed. Decreasing the diameter of the capillary also decreases the surface of contact between the electrodes and the gas diffusion. To maintain a sufficient amount of gas diffusion to the electrode, when the diameter of the capillaries is decreased, the number of capillaries may be increased.

FIG. 1 schematically illustrates an embodiment of an integrated sensor assembly 100 disposed on a ceramic substrate 102. The sensor element 122 can be implemented on a larger scale to form an integrated sensor assembly 100 on a ceramic substrate along with associated circuitry for operating the sensor. The integrated sensor assembly 100 may use a solid electrolyte 103 and

electrodes

104, 106 on a ceramic substrate 102 to form an integrated sensor, which in some embodiments may not have a housing or other cover associated therewith. The overall integration of the sensing element 122 and the circuitry may provide for an overall small size and low cost as well as a reduced noise in the signal produced by the integrated sensor assembly 100. The reduced noise may be made possible by having shorter connection distances between the components and a reduction or elimination in the use of mechanical contact (e.g., mechanical connection of electrical conductors) . The integrated sensor assembly 100 may also require less power than a sensor 122 that requires separate mechanical connections to the control circuitry. The integrated sensor assembly 100 may be capable of detecting gases or vapors that are susceptible to electrochemical oxidation or reduction atthe sensing electrode, such as carbon monoxide, carbon dioxide, hydrogen sulphide, sulphur dioxide, nitric oxide, nitrogen, nitrogen dioxide, chlorine, hydrogen, hydrogen cyanide, hydrogen chloride, ozone, ethylene oxide, hydrides, and/or oxygen.

The integrated sensor assembly 100 comprises two or more electrodes such as sensing electrode 104 disposed on a substrate 102, counter electrode 106, and a reference electrode (as shown in FIG. 2) , an electrolyte 103, electrical leads 110 in electrical communication with the

electrodes

104, 106, and one or more capillaries 113 disposed through the substrate 102. As noted herein, the use of a reference electrode is optional and the reference electrode may not be present in some embodiments. In addition, more than three electrodes may be present in some embodiments. An encapsulant 112 may be disposed over the electrolyte 103 to seal the electrolyte and

electrodes

104, 106 from the ambient atmosphere so that the only fluid communication between the

electrodes

104, 106 and the ambient environment is through the capillaries 113. Other circuitry can also be disposed on the substrate 102 as described in more detail herein.

The substrate 102 serves to support and retain the sensing element 122. In the embodiment shown in FIG. 1, the substrate may function as a printed circuit board or other support for various circuitry. As a result, the substrate 102 may comprise an electrically insulating material. In some embodiments, the substrate 102 can comprise a ceramic such as alumina or silica, though other ceramic substrates can also be used. The use of a ceramic material may allow semiconductor manufacturing techniques to be used to produce the integrated sensor assembly 100.

The

electrodes

104, 106 may comprise materials capable of being deposited by such processes as thermal deposition, sputtering, chemical vapor deposition, etching, electrodeposition, or the like. For example, the

electrodes

104, 105, 106 may comprise materials capable of being electrodeposited and etched to form the individual electrodes.

The

electrodes

104, 105, 106 generally allow for various reactions to take place to allow a current or potential to develop in response to the presence of a target gas. The resulting signal may then allow for the concentration of the target gas to be determined. The electrodes can comprise a reactive material suitable for carrying out a desired reaction. For example, the sensing electrode 104 and/or the counter electrode 106 can be formed of one or more metals or metal oxides such as copper, silver, gold, nickel, palladium, platinum, ruthenium, iridium, tungsten, carbon, combinations thereof, alloys thereof, and/or oxides thereof. The reference electrode 105 can comprise any of the materials listed for the sensing electrode 104 and/or the counter electrode 106 and/or salts thereof, though the reference electrode 105 may generally be inert to the materials in the electrolyte in order to provide a reference potential for the sensor. For example, the reference electrode can contain a noble metal such as platinum and gold or a high conductivity metal/salt combination such as Ag/AgCl.

In some embodiments, one or more of the

electrodes

104, 105, 106 can comprise a porous, gas permeable membrane. In this embodiment, the electrode (e.g., the sensing electrode 104) , may be placed over the aperture or capillary 113. The gas diffusing through the capillary 113 may then contact and diffuse through the permeable membrane to react with the electrolyte at the opposite surface of the electrode. Such an electrode can be formed of any of the materials described herein. In addition to any of the materials for forming the electrode, various hydrophobic components such as PTFE can be combined with the electrode material and/or used as a backing layer (e.g., as a tape or support) for the electrode on the substrate 102. For example, sensing electrode 104 can comprise a catalyst such as platinum or carbon, supported on a PTFE membrane. In some embodiments, such as toxic gas sensors, the counter electrode 106 may comprise a catalyst mounted on a PTFE backing tape, in the same manner as the gas sensing electrode 104.

In some embodiments, the electrodes can comprise hydrophobic materials. Various coating such as PTFE coatings can be used to provide a hydrophobic surface while maintaining a degree of porosity for gas diffusion of the target gas. In some embodiments, the electrode material can be formed to exhibit hydrophobicity or superhydrophobicity. Various materials and preparation techniques are disclosed in U.S. 8,142,625 to Pratt, which is incorporated herein in its entirety, can be used to prepare a hydrophobic electrode or electrodes. In an embodiment, the electrode material can be formed using a template material to form a patterned surface for the electrode, where the pattern may impart hydrophobic properties to the electrode. The patterning material can include any suitable material that can be removed once the electrode is formed. In an embodiment, nanosized polymer spheres (e.g., nanosized latex spheres—which are commercially available) can be arranged on a suitable sacrificial substrate (e.g., a metal such as copper) . The electrode metal can then be electroplated around the assembled spheres to produce a suitable hydrophobic surface. The resulting electrode surface may also have porosity for gas diffusibility. Plating bath additives may be added as appropriate. Alternatively, other templating techniques such as self-assembled surfactant molecules can be used. The templating material can then be subsequently removed, for example by dissolution, heat, or the like. The resulting electrode material can then be used for one or more of the

electrode

104, 105, 106 while exhibiting hydrophobic properties.

The size of the

electrodes

104, 106 may utilize various deposition techniques such as screen printing, thick film deposition, ink printing, and the like. In some embodiments, the electrodes may be formed using a single deposition layer of an electrode material followed by etching to form the final electrode structure. The resulting structure can include a co-planar arrangement of the

electrodes

104, 106 on the substrate 102.

The

electrodes

104, 105, 106 may be at least partially covered by or in contact with the electrolyte 103. Electrical contact can be made with an external contact electrical lead 110 through one or more electrical conductors such as wires 109. The wires 109 can comprise foils, wires, or deposited materials on the substrate 102. The electrical conductors may comprise noble metals (e.g., platinum) , such as by being formed from noble metals or coated with noble metals if the conductors are in contact with the electrolyte. In some embodiments, the electrical conductors may not be formed from noble metals if the electrical conductors are not in contact with the electrolyte 103. In some embodiments, the leads 110 may not pass through the electrolyte 103 as shown in FIG. 1, but could be connected to exposed regions of the

electrodes

104, 105, 106 outside the electrolyte 103 and/or through the use of via holes or multiple layers to the same or opposite face of the substrate to avoid contact between the electrolyte 103 and the leads 110, as described in more detail with respect to FIG. 6. Any of the configurations of the leads described with respect to FIG. 6 can also be adapted for use with the sensor 100. The external contact leads 110 may be electrically coupled to control circuitry such as a potentiostat and/or detection circuitry external to the sensing assembly 122 and/or housing 101.

The electrolyte 103 may comprise any material capable of providing an electrically conductive pathway between the

electrodes

104, 105, 106. The electrolyte 103 may be non-reactive with the substrate 102 material. If the electrolyte 103 and the substrate 102 can react, an insulting, non-reactive layer may be placed over the substrate prior to disposition of the

electrodes

104, 105, 106 and the electrolyte 103. The electrolyte 103 can comprise a liquid electrolyte, a gelled electrolyte, a solid electrolyte, or the like. In some embodiments, the electrolyte 103 can be contained in or retained by a porous or absorbent material.

In an embodiment, the electrolyte 103 can comprise any aqueous electrolyte 103 such as a solution of a salt, an acid, and/or a base depending on the target gas of interest. In an embodiment, the electrolyte can comprise a hygroscopic acid such as sulfuric acid for use in an oxygen sensor. For example, the electrolyte 103 can comprise sulfuric acid having a molar concentration between about 3 M to about 10 M. Since sulfuric acid is hygroscopic, the concentration can vary from about 10 to about 70 wt％ (1 to 11.5 molar) over a relative humidity (RH) range of the environment of about 3 to about 95％. As another example, the electrolyte can include a lithium chloride salt having about 30％to about 60％LiCl by weight, with the balance being an aqueous solution. Other target gases may use the same or electrolyte compositions.

In addition to aqueous based electrolytes, ionic liquid electrolytes can also be used to detect certain gases. The ionic liquids may have a greater viscosity than a corresponding aqueous electrolyte. In any of the electrolytes, a viscosifier may be added to provide an increased viscosity, which may aid in retaining the electrolyte in contact with the electrolytes. In some embodiments, the electrolyte can be present in the form of a gel or a semi-solid.

In an embodiment, the electrolyte can comprise a solid electrolyte. Solid electrolytes can include electrolytes adsorbed or absorbed into a solid structure such as a solid porous material and/or materials that allow protonic and or electronic conduction as formed. In an embodiment, the solid electrolyte can be a protonic conductive electrolyte membrane. The solid electrolyte can be a perfluorinated ion-exchange polymer such as Nafion or a protonic conductive polymer such as poly (ethylene glycol) , poly (ethylene oxide) , poly (propylene carbonate) . Nafion is a hydrated copolymer of polytretafluoroethylene and polysulfonyl fluoride vinyl ether containing pendant sulfuric acid groups. When used, a Nafion membrane can optionally be treated with an acid such as H3PO4, sulfuric acid, or the like, which improves the moisture retention characteristics of Nafion and the conductivity of hydrogen ions through the Nafion membrane. The sensing, counter and reference electrodes can be hot-pressed onto the Nafion membrane to provide a high conductivity between the electrodes and the solid electrolyte.

In some embodiments, the solid electrolyte 103 can comprise a polymer matrix as the porous material and a charge carrying component within the polymer matrix. The charge carrying component can comprise a molecule that is smaller than the polymer matrix and is dispersed therein. The polymer itself can be nonconducting, and the polymer matrix can be non-ionic and/or non-ionizable, which may provide greater freedom of design for the acid host and allow the removal of the proton to be rendered more facile to improve the conductivity of the system. The use of the terms non-ionic and/or non-ionizable refers to the use of the solid electrolyte under normal operating conditions.

The polymer of the solid electrolyte system can be a homopolymer of vinylidene fluoride (PVdF) or copolymer of vinylidene fluoride with fluorinated co-monomers, for instance a copolymer of vinylidene fluoride and hexafluoropropylene (HFP) , trifluoroethylene (VF3) or chlorotrifluoroethylene (CTFE) . The charge carrying component can comprise a fluorinated organic proton conductor dispersed in the polymer matrix. The fluorinated organic proton conductor can impart conductivity and is chosen to be chemically compatible with the polymer matrix to provide a high degree of solubility of the fluorinated organic proton conductor in the polymer. In an embodiment, the organic proton conductor can comprise a fluorinated sulphonic acid, or a fluorinated-sulphonamide. In some embodiments, the fluorinated organic proton conductor may be one or more of the following: heptadecafluorooctane sulphonic acid (Hepta) , bis-trifluoromethane sulphonimide (Bis) , N- (2, 6-diethylphenyl) -1, 1, 1-trifluoromethane sulphonamide, N-benzyltrifluoromethane sulphonamide, N, N-cyclohexane-1, 2-diylbis (1, 1, 1-trifluoromethanesulphonamide) and perfluoro (2-ethoxyethane) sulphonic acid and N-ethylperfluorooctylsulphonamide. A variety of additive can also be included in the polymer matrix. Additional details of the solid electrolyte are provided in U.S. Patent Application Publication No. 2004/0026246 to Chapples et al. and filed on July 27, 2001, which is incorporatedherein by reference in its entirety.

The solid electrolyte 103 can also comprise one or more solid electrolyte 103 materials. For example, ifthe gas to be detected is CO2 and/or humidity, the solid electrolyte 103 may be lanthanum oxide, La2O3. The solid electrolyte can be a layer of La2O3 or a layer of material (such as silica, for example) doped with La2O3, as desired. Other solid electrolyte materials can include, but are not limited to, a yttria stabilized zirconia (YSZ) , K2CO3, Na1+xZr2SixP3-xO12, β-Al2O3 (Na2O. 11Al2O3) , Li3PO4, LISICON (Li2+2xZn1-xGeO4) , lithium phosphorous oxynitride, Li2CO3—MgO, Li2SO4, Li4SiO4, Li14ZnGe4O16, γ-Li3.6Ge0.6V0.4O4, Li3N, Li-β-alumina Li1-xTi2-xMx (PO4) 3 where (M＝Al, Sc, Y or La) , LGPS (Li2GeP2S12) and LixLa (2-x) /3TiO3. The solid electrodes 103 can be disposed on the substrate 102 using a metal mask or directly at a desired portion through a deposition process such as thermal deposition, sputtering, screen printing, a sol-gel process, chemical vapor deposition, atomic layer deposition, inkjet printing, or the like.

The capillary 113 can be disposed through the substrate 102 to provide fluid communication between an ambient gas and one or more of the

electrodes

104, 106 and the electrolyte 103. The capillary 113 can have a diameter selected to provide a desired diffusion rate through the substrate to one or more of the

electrodes

104, 106 and/or the electrolyte 103. The capillary 113 can have a diameter greater than about 0.5 micrometers (μm) , greater than about 1 μm, greater than about 5 μm, greater than about 10 μm, greater than about 20 μm, greater than about 40 μm, greater than about 50 μm, greater than about 60 μm, greater than about 70 μm, or greater than about 80 μm. In some embodiments, the diameter of the capillary 113 may be less than about 200 μm, less than about 150 μm, less than about 100 μm, less than about 80 μm, or less than about 60 μm. In some embodiments, the diameter of the capillary 113 can be in a range extending from any of the lower capillary diameters to any of the upper capillary diameters. The capillary 113 can be formed through the substrate 102 using any known techniques including chemical etching, drilling (e.g., mechanical drilling, laser drilling, etc. ) , or any other suitable techniques.

The capillaries 113 can be formed through the substrate 102 to align with one or more of the

electrodes

104, 106. In an embodiment, the capillaries 13 can provide a diffusional pathway to the sensing electrode 104. The sensing electrode 104 can extend across the opening of the capillaries 113 or the sensing electrode 104 may have an opening to provide a path for a target gas to pass through the capillary and contact the electrolyte 103. In some embodiments, a plurality of capillaries may be present through the substrate 102.

The encapsulant 112 can be placed over the components of the sensing assembly 122 to seal the sensing assembly 122 from the environment. The encapsulant 112 can be placed over the

electrodes

104, 106 and the electrolyte 103. In some embodiments, an optional hydration layer can be included between the electrolyte 103 and the encapsulant 112 The encapsulant 112 may extend a distance around the

electrodes

104, 106 and the electrolyte 103 sufficient to provide a seal over the components with the substrate 102. The capillary 113 may then be the only port for communication of a target gas to the

electrodes

104, 106 and the electrolyte 103.

The encapsulant 112 may comprise any material suitable for bonding to the substrate and retaining the electrolyte 103 in position on the substrate 102. The encapsulant 112 may comprise a polymeric material (e.g., epoxies, resins, thermoset polymers, thermal polymers, etc. ) or a solder, and/or silicone rubber or other polymeric materials can also be used as the encapsulant 112.

In some embodiments, the encapsulant 112 can comprise a parylene layer, a silicon layer, or any combination thereof. Examples of parylene, i.e., poly (para-xylylene) , can include “Parylene N” or its substituted derivatives such as, “Parylene C, ” and “Parylene D. ” The Parylene "C" coating is para-xylyene with a chlorine atom substituted into its structure. The "C" variant of para-xylene is applied using a chemical vapor deposition (CVD) process, which may not require a "line-of-sight" for the coating at a pressure of 0.1 torr. There are numerous other parylene derivatives that may be suitable including Parylene AM, AF, SF, HT, X, E, VT, CF and more.

Other hydrophobic, chemically resistant coatings may also be useful as an encapsulant 112 in any of the embodiments described herein. In general, any materials that perform as a good barrier for inorganic and organic solvents, strong acids, caustic solutions, gases, and water vapor may be used. When the sensor is used to detect oxygen in an oxygen pump configuration, the encapsulant 112 may also allow for sufficient diffusion of oxygen to allow the oxygen to escape the sensor when generated at the counter electrode. If oxygen cannot escape in an oxygen sensor, for example if a completely hermetic barrier is used, then the reference potential can drift and/or the counter electrode 106 may change its mechanism to hydrogen evolution rather than oxygen reduction in order to pass the required sensor current. Neither of these effects is desirable. Suitable barrier materials for an oxygen sensor can comprise those with a high ratio of oxygen to water transport, for example fluorinated polymers (e.g., PTFE, etc. ) or polymers such as polypropylene, polyethylene etc. In cases where the electrolyte contains a hygroscopic material such as strong sulfuric acid as a humidification material, unless this can be isolated from the barrier material then the latter also needs to be chemically stable in the presence of the high acid concentrations that can exist under very dry conditions.

Other features of the encapsulant 112 can include demonstrating electrical isolation with high tension strain and low dielectric constant, being micropore and pin-hole free, exhibiting thermal and mechanical stability, having very low permeability to gases, and demonstrating high electrical impedance. The encapsulant 112 can be deposited over a layer of silicone. The encapsulant 112 can be on the outer surface of the silicone layer that directly covers the electrolyte, including a solid electrolyte or electrolytes. The encapsulant 112 can have a suitable thickness, and in some embodiments, the encapsulant112 can have a thickness of about one to about fifty micrometers. In another embodiment, the encapsulant 112 can comprises a thickness of less than about ten micrometers.

The encapsulant 112 may comprise a flexible or compliant material such as silicone rubber and/or parylene to accommodate any volumetric changes in the electrolyte 103. The solid electrolytes 103 can absorb moisture and/or lose moisture depending on the humidity of the ambient environment. The thickness of the encapsulant 112 may depend on the composition of the encapsulant 112 and the acceptable fluid loss through the encapsulant 112. The encapsulant layer 112 can be thick enough so that the diffusion rate of one or more components of the electrolyte 103 is below an acceptable threshold.

As shown in FIG. 1, the use of the ceramic substrate 102 may allow for standard fabrication techniques to be used to form one or more of the components, as described in more detail below. In some embodiments, the leads 110 can be formed on either surface of the substrate 102, through one or more vias or holes. As shown, the lead 110 coupled to the counter electrode 106 may be formed between the counter electrode 106 and a first surface of the substrate 102. The lead 110 can then pass through a via to a second surface of the substrate 102 before connecting to various components. As shown in FIG. 1, the lead 110 may pass through a second via to contact the control circuit 504. Such a configuration may prevent the lead 110 from being in direct contact with the electrolyte 103, which may be beneficial in some embodiments. Such a configuration may also allow the encapsulant 112 to directly contact the substrate 102 around the

electrodes

104, 106, which may help reduce the amount of moisture escaping the sensor assembly 122, which can occur at a leak point around any connections passing through the encapsulant 112 and/or between the encapsulant 112 and the substrate 102.

FIG. 2 illustrates a top plan view of the integrated sensor assembly 100 comprising the substrate 102 having the sensor assembly 122 disposed thereon in addition to the various circuitry such as a control circuit 504, one or more additional sensors or meters 506, a potentiostat 502, operating and control circuitry 504 including for example, processor 510 and/or memory 512, communication circuitry 508, and the like. The various circuitry and components can be the same or similar as the components described below in FIG. 5. In this embodiment, the substrate 102 is common to the various components. Additional vias or through-holes can be formed in the substrate as needed to provide electrical connections through the substrate as part of the circuit board. Solder and other components can be used as part of the formation process for the board as well as a connection means for coupling external circuitry to the substrate.

In some embodiments, more than one sensor assembly 122 can be disposed on a single substrate 102. For example, a plurality of individual sensor assemblies 122, each designed to detect the same or different target gases can be formed on a single substrate 102. The plurality of sensor assemblies 122 can use the same circuitry, such as the same control circuitry, or alternatively, individual circuitry may be provided for each sensor assembly.

Any suitable manufacturing processes can be used to form the integrated sensor assembly 100. Referring to FIGS. 1 and 2, a manufacturing process for producing the sensor assembly 100 can begin be providing a substrate 102. The capillary or capillaries 113 can be formed through the substrate. If more than one sensing assembly 122 is used with the integrated sensor assembly 100, then the corresponding capillaries may be formed an initial process in the appropriate locations on the substrate 102. Any via holes or other holes through the substrate 102 can also be formed in the substrate 102.

In the next step, any printed circuit board tracks such as the leads, electrical connections between components, interface leads, PCB tracks, edge connectors, via holes, and the like can then be formed on the substrate 102. Additional components including resistors, capacitors, and the like can be fabricated directly on the substrate using semiconductor fabrication techniques or processes. Such processes can use a mask process, screen printing, etching, electrodeposition, or any other suitable process to form the printed circuit board tracks. In some embodiments, thick film screen printing can be used to form the various components on the substrate 102. Once the appropriate components are formed, any external components can be coupled to the substrate using solder, wirebonding, or other printed circuit board connection techniques. Since these processes usually involve the application of heat and use of chemicals that could contaminate the sensor materials (e.g., the electrodes, electrolyte, the encapsulant, etc. ) , the various portions of the integrated sensor assembly 100 may be formed prior to forming the sensing assembly or assemblies 122.

Once the portions of the board have been formed, the electrodes can be deposited using film deposition, screen printing, ink printing, or any of the other techniques described herein. The electrolyte can then be formulated and applied over the electrodes. As a final step, the encapsulant can be applied over the sensing assemblies 122 to seal the

electrodes

104, 105, 106 and the electrolyte 103. If a hydration layer is present, it can be applied over the electrolyte prior to deposition of the encapsulant. A curing step can be carried out if need to cure the encapsulant or any other components. The sensing assembly or assemblies 122 and the integrated sensor assembly 100 may then be ready for use. The integrated sensor assembly 100 can be incorporated into a larger package or device or used as a stand-alone component.

While described as being fabricated in a certain order, the fabrication process can take place in a different order or using different fabrication techniques. For example, any external components that are coupled to the board can be coupled to the board after the sensor assembly 122 is formed (e.g., prior to or while incorporating the integrated sensor assembly 100 into a larger electronic assembly, etc. ) .

Electrochemical sensors may be assembled and compressed and/or heated to attach the layers of components of the sensor 122. Typical electrochemical sensors may experience electrolyte leakage into and through the capillaries 113 in the substrate 102 to other areas of the sensor 100, which may be in part caused by the pressure exerted on the substrate 102 during assembly of the sensor 122. For example, the pressure may cause damage to the electrode 104, allowing the electrolyte 103 to enter the capillary 113. Additionally, if the electrolyte 103 leaks via the capillary 113, the electrolyte 103 may be depleted and dry out, causing the sensor 122 to no longer function.

Referring now to FIG. 3A, gas diffusion 300 may occur via the capillaries 113 to the electrode (s) 108, as described above. In some embodiments, the thickness 302 of the sensor 122 may be between approximately 0.8 to 2 millimeters (mm) . In some embodiments, the thickness 302 of the sensor 122 may be greater than approximately 0.5 mm.

The electrode 104 shown in FIG. 3A may be similar to other electrodes within the sensor 122. The area of the electrode 104 in contact with the capillary 113 may be exposed to gas diffusion 130, wherein the gas diffusion 130 may also occur within the electrode 104 itself. During assembly of the sensor, the contact point between the capillary 113 and the electrode 104 may create a high stress point due to the compression applied to the electrode 104 and/or substrate 102. As described above, the electrode 104 may be damaged or broken near the contact point with the capillary 113, allowing electrolyte 103 to leak into the capillary 113.

Referring to FIG. 3B, in an embodiments of the disclosure, the diameter of the capillaries 113 may be decreased to reduce the stress on the electrode 104 at the contact point between the electrode 104 and the capillary 113. However, when the diameter of the capillary 113 is decreased, the surface area of exposure of the electrode 104 to the gas diffusion 130 is subsequently decreased. Therefore, the number of capillaries 113 may be increased to compensate for the decrease in capillary diameter (as shown in FIG. 3B) . The diameter and amount of capillaries 113 may be adjusted to tune the sensor sensitivity.

By decreasing the diameter and increasing the amount of the capillaries 113, the velocity of gas diffusion 300 into sensor can be controlled, which will allow for control of the sensitivity of the sensor. Additionally, the diffusion points located at the contact points between the capillaries 113 and the electrode 104 are better distributed on the electrode 104 than those shown in FIG. 3A, which improve the utilization of the catalyst activity. The decrease in diameter of the capillaries 113 may improve the support provided to the electrode 104 by the substrate 102, thereby preventing damage to the electrode 104 and electrolyte 103 leakage via the capillaries 113. As an example, the substrate 102 may be modified by decreasing the diameter of the capillaries 113 from approximately 150 μm to less than approximately 30 μm.

Referring now to FIGS. 4A and 4B, a top view is shown of the sensors 122 shown in FIGS. 3A and 3B. The capillaries 113 are shown below the

electrodes

104, 106. As described above in FIGS. 3A and 3B, the diameter 404 of the capillaries 113 shown in FIG. 4A may be decreased to a smaller diameter 404, as shown in FIG. 4B. The number and pattern of the capillaries 113 shown in FIGS. 4A and 4B are examples, where any number or pattern of capillaries may be used depending on the size of the capillaries 113, the size of the sensor 122, and the expected usage of the sensor 122.

In some embodiments, the ratio of the length 402 of one side of the substrate 102 (or the length of the overall sensor 122) to the diameter 404 of one of the capillaries 113 (or length 402/diameter404) may be greater than approximately 30. The ratio of the length 402 of one side of the substrate 102 to the diameter 404 of one of the capillaries may be greater than approximately 50. The ratio of the length402 of one side of the substrate 102 to the diameter 404 of one of the capillaries may be greater than approximately 100. The ratio of the length 402 of one side of the substrate 102 to the diameter 404 of one of the capillaries may be between approximately 50 and approximately 400.

In some embodiments, the ratio of the thickness 302 (shown in FIGS. 3A-3B) of the sensor 122 to the diameter 404 of one of the capillaries 113 (or thickness 302/diameter 404) may be greater than approximately 20. The ratio of the thickness 302 of the sensor 122 to the diameter 404 of one of the capillaries 113 may be greater than approximately 50. The ratio of the thickness 302 of the sensor 122 to the diameter 404 of one of the capillaries 113 may be greater than approximately 60. The ratio of the thickness 302 of the sensor 122 to the diameter 404 of one of the capillaries 113 may be between approximately 20 and approximately 80.

FIG. 5 illustrates the sensor 100 in the context of a larger circuit. The circuit can include a circuit board 501 can comprise a separate component from the sensor, a portion of the housing, or in some embodiments, an extension of the substrate such that the sensor 100 is formed on a single substrate that the other components are also disposed on. In this embodiment, the leads 110 may extend through a wall of the housing, and contact various external circuitry such as various sensing circuitry 506 (e.g. sensors, meters, etc. ) , a potentiostat 502, operating and control circuitry 504, communication circuitry 508, and the like. The sensor and meters can comprise additional sensors such as temperature and/or pressure sensors, which may allow for compensation of the sensor 100 outputs such that the compensation measurements are taken at or near the sensor 100 itself. Further, the location of the sensing circuitry 506 at or near the sensor 100 may allow smaller currents to be detected without intervening resistance, current loss, or electrical noise in longer electrical conductors. The control circuitry 504 may comprise a processor 510 and a memory 512 for performing various calculations and control functions, which can be performed in software or hardware. The communication circuitry 508 may allow the overall sensor results or readings to be communicated to an external source, and can include both wired communications using for example contacts on the board, or wireless communications using a transceiver operating under a variety of communication protocols (e.g., WiFi, Bluetooth, etc. ) . In some embodiments, the sensor 100 can be a separate component that is electrically coupled to external operating circuitry.

In a first embodiment, an electrochemical sensor may comprise a substrate； a plurality of electrodes disposed on a first surface of the substrate； an electrolyte disposed over at least a portion of each electrode of the plurality of electrodes； and one or more capillaries disposed through the substrate, wherein the one or more capillaries are configured to provide a diffusion pathway for a target gas to pass from an exterior of the housing to one or more of the plurality of electrodes, and wherein the ratio of the length or width of the substrate to the diameter of the one or more capillaries is greater than approximately 30.

A second embodiment can include the electrochemical sensor of the first embodiment, wherein the one or more capillaries comprises a plurality of capillaries disposed through the substrate.

A third embodiment can include the electrochemical sensor of the first or second embodiments, wherein the substrate has a length or width between about 10μm to about 10 mm. A fourth embodiment can include the electrochemical sensor of any of the first to third embodiments, wherein the capillary has a diameter between about 0.5μm and about 30μm.

A fifth embodiment can include the electrochemical sensor of any of the first to fourth embodiments, wherein the sensor has a thickness between approximately 0.2 mm and about 2 mm.

A sixth embodiment can include the electrochemical sensor of any of the first to fifth embodiments, wherein the ratio of the length or width of the substrate to the diameter of the one or more capillaries is greater than approximately 50.

A seventh embodiment can include the electrochemical sensor of any of the first to sixth embodiments, wherein the ratio of the length of the substrate to the diameter of the one or more capillaries is greater than approximately 100.

An eighth embodiment can include the electrochemical sensor of any of the first to seventh embodiments, wherein the ratio of the thickness of the sensor to the diameter of the one or more capillaries is greater than approximately 20.

A ninth embodiment can include the electrochemical sensor of any of the first to eighth embodiments, further comprising an encapsulant applied over the electrolyte, wherein the one or more capillaries are the only fluid communication pathway between an external environment and the plurality of electrodes.

A tenth embodiment can include the electrochemical sensor of any of the first to ninth embodiments, wherein at least one capillary of the one or more capillaries comprises an opening on the first surface of the substrate, and wherein the opening is surrounded by a sensing electrode of the plurality of electrodes.

In a eleventh embodiment, a method of forming an electrochemical sensor may comprise forming one or more capillaries through a substrate, wherein the ratio of the length of the substrate to the diameter of the one or more capillaries is greater than approximately 50； forming a plurality of electrodes on a first surface of the substrate； disposing an electrolyte over at least a portion of each of the plurality of electrodes； and sealing the plurality of electrodes and the electrolyte from an external environment, wherein the one or more capillaries form the only opening between the external environment and the plurality of electrodes.

A twelfth embodiment can include the method of the eleventh embodiment, wherein sealing the plurality of electrodes and the electrolyte from the external environment comprises applying an encapsulant over the plurality of electrodes.

A thirteenth embodiment can include the method of the eleventh or twelfth embodiments, wherein forming one or more capillaries comprises forming a plurality of capillaries in a pattern through the substrate.

A fourteenth embodiment can include the method of any of the eleventh to thirteenth embodiment, wherein forming the plurality of electrodes comprises forming at least one electrode adjacent to an opening of at least one of the one or more capillaries on the first surface, wherein the at least one electrode is disposed about the opening of the at least one of the one or more capillaries.

A fifteenth embodiment can include the method of the fourteenth embodiment, wherein disposing the electrolyte over at least the portion of the plurality of electrodes comprises disposing the electrolyte on the at least one electrode over the opening.

In a sixteenth embodiment, an electrochemical sensor may comprise a substrate； a plurality of electrodes disposed on a first surface of the substrate； an electrolyte disposed over at least a portion of each electrode of the plurality of electrodes； and a plurality of capillaries disposed through the substrate, wherein the capillaries are configured to provide a diffusion pathway for a target gas to pass from an exterior of the housing to one or more of the plurality of electrodes, and wherein the ratio of the thickness of the sensor to the diameter of the capillaries is greater than approximately 20.

A seventeenth embodiment can include the electrochemical sensor of the sixteenth embodiment, wherein at least one capillary of the plurality of capillaries comprises an opening on the first surface of the substrate, and wherein the opening is surrounded by a sensing electrode of the plurality of electrodes.

An eighteenth embodiment can include the electrochemical sensor of the sixteenth or seventeenth embodiments, wherein at least one capillary of the plurality of capillaries comprises an opening on the first surface of the substrate, and wherein the opening is surrounded by a counter electrode of the plurality of electrodes.

A nineteenth embodiment can include the electrochemical sensor of any of the sixteenth to eighteenth embodiments, wherein the substrate comprises silicon, silicon nitride, silicon oxide, a doped silicon, or any combination thereof.

A twentieth embodiment can include the electrochemical sensor of any of the sixteenth to nineteenth embodiments, wherein the ratio of the length or width of the substrate to the diameter of the one or more capillaries is greater than approximately 30.

While various embodiments in accordance with the principles disclosed herein have been shown and described above, modifications thereof may be made by one skilled in the art without departing from the spirit and the teachings of the disclosure. The embodiments described herein are representative only and are not intended to be limiting. Many variations, combinations, and modifications are possible and are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment (s) are also within the scope of the disclosure. Accordingly, the scope of protection is not limited by the description set out above, but is defined by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment (s) of the present invention (s) . Furthermore, any advantages and features described above may relate to specific embodiments, but shall not limit the application of such issued claims to processes and structures accomplishing any or all of the above advantages or having any or all of the above features.

Additionally, the section headings used herein are provided for consistency with the suggestions under 37 C.F.R. 1.77 or to otherwise provide organizational cues. These headings shall not limit or characterize the invention (s) set out in any claims that may issue from this disclosure. Specifically and by way of example, although the headings might refer to a “Field, ” the claims should not be limited by the language chosen under this heading to describe the so-called field. Further, a description of a technology in the “Background” is not to be construed as an admission that certain technology is prior art to any invention (s) in this disclosure. Neither is the “Summary” to be considered as a limiting characterization of the invention (s) set forth in issued claims. Furthermore, any reference in this disclosure to “invention” in the singular should not be used to argue that there is only a single point of novelty in this disclosure. Multiple inventions may be set forth according to the limitations of the multiple claims issuing from this disclosure, and such claims accordingly define the invention (s) , and their equivalents, that are protected thereby. In all instances, the scope of the claims shall be considered on their own merits in light of this disclosure, but should not be constrained by the headings set forth herein.

Use of broader terms such as “comprises, ” “includes, ” and “having” should be understood to provide support for narrower terms such as “consisting of, ” “consisting essentially of, ” and “comprised substantially of. ” Use of the terms “optionally, ” “may, ” “might, ” “possibly, ” and the like with respect to any element of an embodiment means that the element is not required, or alternatively, the element is required, both alternatives being within the scope of the embodiment (s) . Also, references to examples are merely provided for illustrative purposes, and are not intended to be exclusive.

While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted or not implemented.

Also, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component, whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.

Claims

An electrochemical sensor (100) comprising:

a substrate (102) ；

a plurality of electrodes (104, 105, 106) disposed on a first surface of the substrate (102) ；

an electrolyte (103) disposed over at least a portion of each electrode of the plurality of electrodes (104, 105, 106) ； and

one or more capillaries (113) disposed through the substrate (102) , wherein the one or more capillaries (113) are configured to provide a diffusion pathway for a target gas to pass from an exterior of the sensor to one or more of the plurality of electrodes (104, 105, 106) , and wherein the ratio of the length or width of the substrate (102) to the diameter of the one or more capillaries (113) is greater than approximately 30.
The electrochemical sensor (100) of claim 1, wherein the one or more capillaries (113) comprises a plurality of capillaries (113) disposed through the substrate (102) .
The electrochemical sensor (100) of claim 1, wherein the substrate (102) has a length or width between about 10μm to about 10 mm.
The electrochemical sensor (100) of claim 1, wherein the one or more capillaries (113) have a diameter between about 0.5μm and about 30μm.
The electrochemical sensor (100) of claim 1, wherein the sensor (100) has a thickness between approximately 0.2 mm and about 2 mm.
The electrochemical sensor (100) of claim 1, wherein the ratio of the length or width of the substrate (102) to the diameter of the one or more capillaries (113) is greater than approximately 50.
The electrochemical sensor (100) of claim 1, wherein the ratio of the length of the substrate (102) to the diameter of the one or more capillaries (113) is greater than approximately 100.
The electrochemical sensor (100) of claim 1, wherein the ratio of the thickness of the sensor (100) to the diameter of the one or more capillaries (113) is greater than approximately 20.
The electrochemical sensor (100) of claim 1, further comprising an encapsulant (112) applied over the electrolyte (103) , wherein the one or more capillaries (113) are the only fluid communication pathway between an external environment and the plurality of electrodes (104, 105, 106) .
The electrochemical sensor (100) of claim 1, wherein at least one capillary of the one or more capillaries (113) comprises an opening on the first surface of the substrate (102) , and wherein the opening is surrounded by a sensing electrode (104) of the plurality of electrodes.
A method of forming an electrochemical sensor, the method comprising:

forming one or more capillaries through a substrate, wherein the ratio of the length of the substrate to the diameter of the one or more capillaries is greater than approximately 50；

forming a plurality of electrodes on a first surface of the substrate；

disposing an electrolyte over at least a portion of each of the plurality of electrodes； and

sealing the plurality of electrodes and the electrolyte from an external environment, wherein the one or more capillaries form the only opening between the external environment and the plurality of electrodes.
The method of claim 11, wherein sealing the plurality of electrodes and the electrolyte from the external environment comprises applying an encapsulant over the plurality of electrodes.
The method of claim 11, wherein forming one or more capillaries comprises forming a plurality of capillaries in a pattern through the substrate.
The method of claim 11, wherein forming the plurality of electrodes comprises forming at least one electrode adjacent to an opening of at least one of the one or more capillaries on the first surface, wherein the at least one electrode is disposed about the opening of the at least one of the one or more capillaries.
The method of claim 14, wherein disposing the electrolyte over at least the portion of the plurality of electrodes comprises disposing the electrolyte on the at least one electrode over the opening.