Gas sensing element and manufacturing method thereof

Abstract

A gas sensing element for a gas sensor and a method of manufacturing the same are disclosed. The gas sensing element includes a substrate having a metal oxide semiconductor formed of a first metal. Further, the gas sensing element includes a gas sensing surface disposed on the substrate. The gas sensing surface includes a metal oxide semiconductor formed of a first metal and at least one dopant having at least one of a second metal and at least one compound. Further, the gas sensing element includes at least one inert conductive element disposed between the substrate and the gas sensing surface. The at least one inert conductive element is adapted to maintain a predetermined minimum conductivity of the gas sensing element.

Description

Technical Field

[0001] The present disclosure relates to gas sensors, and more particularly, to gas sensing elements and methods of making the same. Background Art

[0002] Gas sensors have been used in various applications such as process monitoring and control and safety monitoring. Typically, gas sensors are used to detect the presence of gaseous compounds in an environment. Such gaseous compounds may also be flammable or explosive in nature. Gas sensors have also been used for leak detection where such gaseous compounds are used or manufactured. Typically, gas sensors such as MOS sensors rely on the interaction between gaseous compounds such as hydrogen sulfide or hydrocarbons and adsorbed oxygen on the metal oxide semiconductor surface of such sensors.

[0003] With the long-term use of such gas sensors, it is important to be able to determine when the sensor becomes ineffective and loses its ability to detect gaseous compounds. Typically, the conductivity of a sensor changes based on the presence of gaseous compounds in its surroundings. For example, in the presence of gaseous compounds, the conductivity of the sensor can be significantly higher than the conductivity of the sensor in the absence of gaseous compounds. There is a considerable difference between the conductivity of the sensor in the absence of gaseous compounds and in the presence of gaseous compounds. In the absence of gaseous compounds, the conductivity of the sensor is quite low, so it becomes difficult to determine the integrity of such a sensor. Therefore, it is desirable to design the sensor in such a way that the integrity of such a sensor can be accurately determined regardless of the presence or absence of gaseous compounds. Summary of the invention

[0004] This summary is provided to introduce a selection of concepts in a simplified format that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention nor to be used to determine the scope of the invention.

[0005] In one or more embodiments of the present disclosure, a gas sensing element for a gas sensor is disclosed. The gas sensing element includes a substrate having a metal oxide semiconductor formed of a first metal. In addition, the gas sensing element includes a gas sensing surface disposed on the substrate. The gas sensing surface includes a metal oxide semiconductor formed of a first metal and at least one dopant, the at least one dopant having at least one of a second metal and at least one compound. In addition, the gas sensing element includes at least one inert conductive element disposed between the substrate and the gas sensing surface. The at least one inert conductive element is adapted to maintain a predetermined minimum conductivity of the gas sensing element.

[0006] In one or more embodiments of the present disclosure, the predetermined minimum conductivity is adjustable corresponding to the series resistance of the gas sensor, and is adjustable in at least one range of 1E-5mS to 1E-3mS, 1E-4mS to 1E-2mS, 1E-3mS to 1E-1mS, and 1E-2mS to 1mS.

[0007] In one or more embodiments of the present disclosure, the at least one inert conductive element is adapted to maintain a predetermined minimum conductivity of the gas sensing element based on the conductivity of the at least one inert conductive element, and wherein the conductivity of the at least one inert conductive element varies based on at least one of: a geometric pattern of material deposition of the at least one inert conductive element, a thickness of the material deposition of the at least one inert conductive element, a width of the material deposition of the at least one inert conductive element, a thickness of a substrate beneath the at least one inert conductive element, and an overlap area between an electrode of the gas sensor, the substrate, and the material deposition of the at least one inert conductive element.

[0008] In one or more embodiments of the present disclosure, the electrical conductivity of the at least one inert conductive element is higher in the presence of gas than in the absence of gas, wherein the electrical conductivity of the at least one inert conductive element is constant in the absence of gas.

[0009] In one or more embodiments of the present disclosure, the electrical conductivity of the at least one inert conductive element is proportional to the thickness of the material deposition of the at least one inert conductive element.

[0010] In one or more embodiments of the present disclosure, the at least one inert conductive element is embodied as a non-continuous film having an average thickness in the range of 0.1 nm to 9 nm.

[0011] In one or more embodiments of the present disclosure, the at least one inert conductive element is embodied as a continuous film having an average thickness in the range of 5 nm to 15 nm.

[0012] In one or more embodiments of the present disclosure, the at least one inert conductive element is embodied as a continuous film having an average thickness in the range of 20 nm to 50 nm.

[0013] In one or more embodiments of the present disclosure, the at least one inert conductive element has a serpentine pattern.

[0014] In one or more embodiments of the present disclosure, the at least one inert conductive element has an island pattern.

[0015] In one or more embodiments of the present disclosure, the at least one inert conductive element has a planar geometry.

[0016] In one or more embodiments of the present disclosure, the at least one inert conductive element has a double helix pattern.

[0017] In one or more embodiments of the present disclosure, the at least one inert conductive element is formed of a non-reactive conductive material.

[0018] In one or more embodiments of the present disclosure, the first metal includes aluminum, bismuth, cadmium, cerium, chromium, cobalt, copper, iron, gallium, indium, molybdenum, niobium, tantalum, tin, titanium, tungsten, vanadium or zinc.

[0019] In one or more embodiments of the present disclosure, the first metal includes aluminum, bismuth, cadmium, cerium, chromium, cobalt, copper, iron, gallium, indium, molybdenum, niobium, tantalum, tin, titanium, tungsten, vanadium or zinc, and the second metal includes one or more Group 5 to Group 11 transition metals.

[0020] In one or more embodiments of the present disclosure, the at least one inert conductive element is adapted to maintain a predetermined minimum conductivity of the gas sensing element to assess the operational integrity of the gas sensing surface in at least one of the absence and presence of a gas to be tested.

[0021] In one or more embodiments of the present disclosure, the gas is embodied as one of hydrogen and hydrogen sulfide.

[0022] In one or more embodiments of the present disclosure, a gas sensor is disclosed. The gas sensor includes a substrate and a gas sensing element disposed on the substrate. The gas sensing element includes a substrate, the substrate including a metal oxide semiconductor formed of a first metal. In addition, the gas sensing element includes a gas sensing surface disposed on the substrate. The gas sensing surface includes a metal oxide semiconductor formed of a first metal and a dopant having a second metal. The gas sensing element includes at least one inert conductive element disposed between the substrate and the gas sensing surface. The at least one inert conductive element is suitable for maintaining a predetermined minimum conductivity of the gas sensing element. In addition, the gas sensor includes a plurality of electrodes connected to the gas sensing element and a circuit. The circuit is suitable for measuring at least one of a voltage across the gas sensing element, a resistance associated with the gas sensing element and at least one conductive element, an impedance, a current, and a conductance.

[0023] In one or more embodiments of the present disclosure, a method of manufacturing a gas sensing element is disclosed. The method includes providing a substrate including a metal oxide semiconductor formed of a first metal. In addition, the method includes providing a gas sensing surface having the metal oxide semiconductor on the substrate. The metal oxide semiconductor is formed of a first metal and at least one dopant, the at least one dopant having at least one of a second metal and at least one compound. The method includes providing at least one inert conductive element between the substrate and the gas sensing surface. The at least one inert conductive element is adapted to maintain a predetermined minimum conductivity of the gas sensing element.

[0024] In order to further illustrate the advantages and features of these methods, systems and equipment / devices, a more specific description of these methods, systems and equipment / devices will be presented by reference to their specific embodiments shown in the accompanying drawings. It is to be appreciated that these drawings only depict typical embodiments of the present disclosure and are therefore not to be considered as limiting the scope thereof. The present disclosure will be described and explained using the accompanying drawings with additional specificity and detail. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] These and other features, aspects and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings, in which like characters represent like parts throughout the drawings, and in which:

[0026] Figure 1 A schematic diagram illustrating a gas sensor having a gas sensing element according to one or more embodiments of the present disclosure;

[0027] Figure 2 A schematic diagram illustrating a gas sensing element according to one or more embodiments of the present disclosure;

[0028] Figure 3a-3d illustrating different types of inert conductive elements of a gas sensing element according to various embodiments of the present disclosure; and

[0029] Figure 4 The diagram depicts a flow chart of a method of manufacturing a gas sensing element according to one or more embodiments of the present disclosure.

[0030] Furthermore, those skilled in the art will appreciate that the elements in the drawings are shown for simplicity and may not necessarily be drawn to scale. For example, a flow chart illustrates a method in terms of the most salient steps involved to help promote understanding of various aspects of the present disclosure. Furthermore, with respect to the construction of an apparatus, one or more components of the apparatus may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details relevant to understanding the embodiments of the present disclosure, so as not to bury the drawings in details that would be readily apparent to those skilled in the art having the benefit of the description herein. DETAILED DESCRIPTION

[0031] To promote an understanding of the principles of the present disclosure, reference will now be made to various embodiments and specific language will be used to describe these embodiments. It will be understood, however, that no limitation of the scope of the present disclosure is intended thereby, and such changes and further modifications in the illustrated systems and devices, and such further applications of the principles of the present disclosure as illustrated therein are deemed to be what would normally occur to one skilled in the art to which the present disclosure relates.

[0032] Those skilled in the art will understand that the foregoing general description and the following detailed description are illustrative of the present disclosure and are not intended to limit the present disclosure.

[0033] References throughout this specification to "aspect," "another aspect," or similar language mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrases "in an embodiment," "in another embodiment," "some embodiments," "one or more embodiments," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0034] The terms "include", "comprises" or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process or method that includes a series of steps does not include only those steps, but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or subsystems or elements or structures or components beginning with "includes ... a" do not exclude the presence of other devices or other subsystems or other elements or other structures or other components or additional devices or additional subsystems or additional elements or additional structures or additional components without more constraints.

[0035] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0036] Typically, gas sensors such as MOS sensors rely on the interaction between gaseous compounds such as hydrogen sulfide or hydrocarbons and adsorbed oxygen on the metal oxide semiconductor surface of such sensors. The conductivity of such gas sensors varies based on the presence of gaseous compounds (such as reducing gases) near the sensing surface of the gas sensor. Although in the absence of gaseous compounds, the conductivity of the gas sensor is quite low, and therefore it is often difficult to determine whether such gas sensors are operational or whether their operational integrity is compromised.

[0037] The present disclosure provides a gas sensor with a gas sensing element having an inert conductive element to maintain a predetermined minimum conductivity of the gas sensing element. In particular, the inert conductive element maintains a measurable level of the predetermined minimum conductivity of the gas sensing element even in the absence of a gaseous compound. In the absence of a gaseous compound, a change in the predetermined minimum conductivity indicates that the integrity of a gas sensing surface of the gas sensing element has been compromised due to a rupture or peeling of such surface from the gas sensing element. Thus, the implementation of the inert conductive element facilitates the evaluation of the operational integrity of the gas sensing surface in the absence and presence of at least one of a gas to be tested.

[0038] Figure 1 A schematic diagram of a gas sensor 100 having a gas sensing element 102 according to one or more embodiments of the present disclosure is illustrated. In one or more embodiments, the gas sensor 100 may be embodied as a metal oxide semiconductor (MOS) sensor without departing from the scope of the present disclosure. In the illustrated embodiment, the gas sensor 100 may be, but is not limited to, a substrate 104, a gas sensing element 102, a plurality of electrodes 106, and a circuit 108.

[0039] refer to Figure 1 , the gas sensing element 102 may be disposed on a substrate 104. In one or more embodiments, the gas sensing element 102 may include, but is not limited to, a substrate 110, a gas sensing surface 112, and at least one inert conductive element 114. The substrate 110 may include a metal oxide semiconductor formed of a first metal. In one or more embodiments, the first metal may include, but is not limited to, aluminum, bismuth, cadmium, cerium, chromium, cobalt, copper, iron, gallium, indium, molybdenum, niobium, tantalum, tin, titanium, tungsten, vanadium, or zinc. In one or more embodiments, the term 'first metal' may also refer to a metal mixture without departing from the scope of the present disclosure.

[0040] The metal oxide semiconductor of the substrate 110 may be embodied as, but not limited to, aluminum (III) oxide, bismuth (III) oxide, cadmium oxide, cerium (IV) oxide, chromium (III) oxide, cobalt (III) oxide, copper (II) oxide, iron (III) oxide, gallium (III) oxide, indium (III) oxide, molybdenum (VI) oxide, niobium (V) oxide, nickel (II) oxide, tantalum (V) oxide, tin (IV) oxide, titanium (IV) oxide, tungsten (VI) oxide, vanadium (V) oxide, zinc (II) oxide, and mixtures thereof. Mixed metal oxides (e.g., SnO2-CuO or other mixed oxides of the above metal oxides) may also be used to form the metal oxide semiconductor of the substrate 110.

[0041] Figure 2 A schematic diagram of a gas sensing element 102 is shown according to one or more embodiments of the present disclosure. Figure 1and Figure 2 In the illustrated embodiment, the gas sensing surface 112 of the gas sensing element 102 may be disposed on the substrate 110. In one or more embodiments, the gas sensing surface 112 may be deposited on the substrate 110 using electron beam deposition, ion beam deposition, or thermal deposition techniques such as sputtering, physical vapor deposition, chemical vapor deposition, or thermal spraying without departing from the scope of the present disclosure.

[0042] The gas sensing surface 112 may include, but is not limited to, a metal oxide semiconductor. In the absence of a gas, the metal oxide semiconductor absorbs atmospheric oxygen at the gas sensing surface 112, and this absorbed oxygen captures free electrons from the metal oxide semiconductor, resulting in a measurable level of substrate resistance of the semiconductor being at a relatively high level. When the gas sensing surface 112 is exposed to a gas, such a gas interacts with the adsorbed oxygen, causing the gas sensing surface 112 to release free electrons back to the metal oxide semiconductor at the gas sensing surface 112, resulting in a measurable decrease in resistance that can be correlated to a measured level of the gas. In particular, a change in the measurable level of resistance or conductivity associated with the metal oxide semiconductor at the gas sensing surface 112 indicates a level of gas sensed by the gas sensor 100. In one or more embodiments, the gas may be embodied as one of hydrogen and hydrogen sulfide without departing from the scope of the present disclosure.

[0043] In one or more embodiments, the metal oxide semiconductor of the gas sensing surface 112 can be formed of a first metal and at least one dopant. Without departing from the scope of the present disclosure, the at least one dopant can be interchangeably referred to as a metal dopant. The metal dopant can be used to enhance the responsiveness of the metal oxide semiconductor to the gas being sensed (also referred to as a target gas, such as hydrogen sulfide and hydrogen), and allow the target gas to be distinguished from other gases that may also produce a change in a measurable level of resistance or conductivity at the gas sensing surface 112.

[0044] At least one dopant may include, but is not limited to, at least one of a second metal and at least one compound such as silver sulfide. The second metal may be different from the first metal. The second metal may include, but is not limited to, one or more transition metals from Groups 5 to 11. Examples of transition metal dopants include copper, silver, gold, iron, ruthenium, nickel, platinum, palladium, or vanadium. Although any of the above materials may exhibit changes in resistance or conductivity in response to exposure to various test gases, some materials for specific applications have been more widely used than others. For example, copper-doped tin oxide may be used for hydrogen sulfide sensing elements, while platinum and palladium doping is typically used for sensing hydrogen or hydrocarbons. Such combinations and other combinations are included in this disclosure.

[0045] Various other materials may be included in the metal oxide semiconductor of the gas sensing surface 112, including but not limited to noble metals (e.g., silver, gold). Dopants, metal oxide semiconductors, other materials, and combinations thereof are disclosed in Kaur, M., Aswal, DK, and Yakhmi, JV, "Chemiresistor Gas Sensors: Materials, Mechanisms and Fabrication," Chapter 2, Science and Technology of Chemiresistor Gas Sensors, Ed. Aswal, DK and Gupta, SK Nova Scientific Publishers, New York, 2007, and Bochenkov, VE and Sergeev, GB, "Sensitivity, Selectivity, and Stability of Gas-Sensitive Metal-Oxide Nanostructures," Chapter 2, Metal Oxide Nanostructures and Their Applications, American Science Press, California, 2010.

[0046] It should be understood that the metal oxide semiconductor may be doped with different dopants that are selected based on the target gas to be detected by the gas sensing element 102. Furthermore, in alternative embodiments, the metal oxide semiconductor of the gas sensing surface 112 may be formed without any dopants based on the target gas to be detected by the gas sensing element 102. Therefore, it should be understood that the metal oxide semiconductor of the gas sensing surface 112 may be a doped or undoped semiconductor based on the target gas for which such gas sensing element 112 is to be deployed without departing from the scope of the present disclosure.

[0047] As explained previously, in the absence of a test gas, the conductivity level of the gas sensing surface 112 may be quite low relative to the conductivity level of the gas sensing surface 112 in the presence of a test gas. Due to such a significant difference between the conductivity levels, it may be difficult to determine whether the gas sensing surface 112 is operational, especially when such a gas sensing surface 112 does not interact with any of the test gas. Therefore, in order to increase the overall conductivity of the gas sensing surface 112, at least one inert conductive element 114 may be disposed between the substrate 110 and the gas sensing surface 112 of the gas sensor 100.

[0048] The at least one inert conductive element 114 can be adapted to maintain a desired conductivity that is measurable in the absence of a test gas, and thus, even in the absence of a test gas, it becomes easier to determine whether the gas sensing surface 112 is operational. In particular, due to the implementation of the at least one inert conductive element 114, the operational integrity of the gas sensing surface 112 can be tested in at least one of the absence and presence of a gas. The structural and operational details of the at least one inert conductive element 114 are explained in detail in subsequent sections of the present disclosure.

[0049] The gas sensing element 102 may include at least one inert conductive element 114. In one or more embodiments, the at least one inert conductive element 114 may be interchangeably referred to as the inert conductive element 114 without departing from the scope of the present disclosure. As previously mentioned, the inert conductive element 114 may be disposed between the substrate 110 and the gas sensing surface 112. In one or more embodiments, the inert conductive element 114 may be deposited between the substrate 110 and the gas sensing surface 112 using electron beam deposition, ion beam deposition, or thermal deposition techniques such as sputtering, physical vapor deposition, chemical vapor deposition, or thermal spraying without departing from the scope of the present disclosure.

[0050] In one or more embodiments, the inert conductive element 114 can be formed of a non-reactive conductive material. In an example, the non-reactive conductive material can be embodied as a noble metal without departing from the scope of the present disclosure. In such an example, the non-reactive conductive material can be embodied as gold (Au). However, this should not be construed as limiting, and the non-reactive conductive material can be embodied as any other material, such as a non-noble metal, TiN, an oxide, graphene, and an alloy of two or more metals without departing from the scope of the present disclosure.

[0051] An inert conductive element 114 may be provided to increase the overall conductivity of the gas sensing surface 112 and reduce the magnitude of fluctuations / variations in the overall conductivity in the absence or presence of a test gas. This enables accurate detection of the integrity of the gas sensing element 102 and thereby allows effective detection of whether the gas sensor 100 has become operationally ineffective.

[0052] In one or more embodiments, the inert conductive element 114 may be adapted to maintain a predetermined minimum conductivity of the gas sensing element 102. In one or more embodiments, the term "predetermined minimum conductivity" refers to the conductivity of the gas sensing element 102 in the absence of a test gas. The predetermined minimum conductivity may be adjustable for a series resistance of the gas sensor 100 and be in at least one of a range of 1E-5mS to 1E-3mS, 1E-4mS to 1E-2mS, 1E-3mS to 1E-1mS, and 1E-2mS to 1mS. In one or more embodiments, the predetermined minimum conductivity may be adjustable for a series resistance of the gas sensor 100 such that sufficient current flow to the gas sensing element 102 of the gas sensor 100 is maintained.

[0053] The inert conductive element 114 may be adapted to maintain a predetermined minimum conductivity of the gas sensing element 102 based on the conductivity of the inert conductive element 114. The conductivity of the inert conductive element 114 may be higher in the presence of a test gas than in the absence of a test gas. In the absence of a gas, the conductivity of the inert conductive element 114 may be constant.

[0054] The inert conductive element 114 may be adapted to maintain a predetermined minimum conductivity of the gas sensing element 102 to assess the operational integrity of the gas sensing surface 112 in at least one of the absence and presence of a gas to be tested. As previously explained, the conductivity of the inert conductive element 114 may remain constant in the absence of a gas, and thus, the predetermined minimum conductivity of the gas sensing element 102 may also remain constant in the absence of a gas. If a change in the predetermined minimum conductivity of the gas sensing element 102 is measured in the absence of a gas, it may be determined that the operational integrity of the gas sensing surface 112 is compromised. For example, if the conductivity of the gas sensing surface 112 decreases below the predetermined minimum conductivity, it may be determined that the operational integrity of the gas sensing surface 112 is compromised.

[0055] For example, the inert conductive element 114 may be disposed between the gas sensing surface 112 and the substrate 110 in such a manner that when the gas sensing surface 112 is cracked and peeled off, then the inert conductive element 114 may also be damaged. This causes a change in the conductivity of the inert conductive element 114 and thereby affects the conductivity of the gas sensing surface 112. Such a change in conductivity indicates that the operational integrity of the gas sensing element 102 is compromised due to the cracking and peeling of the gas sensing surface 112. Therefore, the implementation of the inert conductive element 114 significantly simplifies the testing of the operational integrity of the gas sensing surface 112 of the gas sensing element 102.

[0056] In one or more embodiments, the conductivity of the inert conductive element 114 may vary based on the thickness 't' of the material deposition of the inert conductive element 114. In one or more embodiments, the inert conductive element 114 may be deposited as a line of material such as gold (Au) having a thickness 't' between the gas sensing surface 112 and the substrate 110. In another embodiment, the inert conductive element 114 may be deposited as a film of material such as gold (Au) having a thickness 't' between the gas sensing surface 112 and the substrate 110. The conductivity of the inert conductive element 114 may be proportional to the thickness 't' of the material deposition of the inert conductive element 114. For example, the conductivity of the inert conductive element 114 may be increased by increasing the thickness 't' of the material deposition of the inert conductive element 114, and thereby increasing the predetermined minimum conductivity of the gas sensing element 102.

[0057] In one or more embodiments, the inert conductive element 114 may be embodied as a non-continuous film having an average thickness in the range of 0.1 nm to 9 nm. In another embodiment, the inert conductive element 114 may be embodied as a continuous film having an average thickness in the range of 5 nm to 15 nm. In yet another embodiment, the inert conductive element 114 may be embodied as a continuous film having an average thickness in the range of 20 nm to 50 nm.

[0058] Furthermore, in one or more embodiments, the conductivity of the inert conductive element 114 may vary based on the width 'w' of the material deposition of the inert conductive element 114. The conductivity of the inert conductive element 114 may be proportional to the width 'w' of the material deposition of the inert conductive element 114. For example, the conductivity of the inert conductive element 114 may be increased by increasing the width 'w' of the material deposition of the inert conductive element 114, and thereby increasing the predetermined minimum conductivity of the gas sensing element 102.

[0059] In one or more embodiments, the inert conductive element 114 may be deposited as a line of material such as gold (Au) having a width 'w' between the gas sensing surface 112 and the substrate 110. In another embodiment, the inert conductive element 114 may be deposited as a film of material such as gold (Au) having a width 'w' between the gas sensing surface 112 and the substrate 110. In one or more embodiments, the film of the inert conductive element 114 may provide a higher conductivity than a line of the inert conductive element 114.

[0060] In one example, the width of the material deposition of the inert conductive element 114 can be in the range of 1-10 microns. In another example, the width of the material deposition can be in the range of 20-50 microns. However, the foregoing examples of widths should not be construed as limiting, and the material can be deposited at different widths based on various factors, such as the type of deposition technique, operating parameters associated with the deposition technique, and the size of the gas sensing element 102 to be deployed in the gas sensor 100, without departing from the scope of the present disclosure.

[0061] In one or more embodiments, the conductivity of the at least one inert conductive element 114 may vary based on the conductivity and thickness of the substrate 110 beneath the at least one inert conductive element 114 .

[0062] In one or more embodiments, the conductivity of the inert conductive element 114 may vary based on the overlap area between the electrodes (such as the plurality of electrodes 106) of the gas sensor 100, the substrate 110, and the material deposition of the inert conductive element 114. The term "overlap area" may refer to the area of ​​at least a portion of the inert conductive element 114 that coincides with the plurality of electrodes 106 and the substrate 110 of the gas sensor 100. In one or more embodiments, the conductivity of the inert conductive element 114 may be increased by increasing the overlap area between the inert conductive element 114, the substrate 110, and the plurality of electrodes 106.

[0063] In addition, in one or more embodiments, the conductivity of the inert conductive element 114 can vary based on the geometric pattern in which the material of the inert conductive element 114 is deposited. The term "geometric pattern" can refer to the geometric shape in which the material of the inert conductive element 114 is deposited between the gas sensing surface 112 and the substrate 110. As previously explained, the material can be deposited in the form of a line extending from one electrical contact of the gas sensor 100 to another electrical contact. The line of material, such as a noble metal, can be deposited in a manner that defines a specific geometric pattern to obtain the desired conductivity of the inert conductive element 114. In one or more embodiments, the length of the line of material deposited to define a specific geometric pattern may also result in a change in the conductivity of the inert conductive element 114. For example, if the length of the line of material deposited to define a first geometric pattern is greater than the length of the line of material deposited to define a second geometric pattern, the conductivity of the first geometric pattern is higher than the conductivity of the second geometric pattern.

[0064] Figure 3a-3d Different types of inert conductive elements 114 of the gas sensing element 102 are shown according to various embodiments of the present disclosure. Figure 3a In one or more embodiments, the inert conductive element 114 may have a serpentine pattern. Figure 3bIn another embodiment, the inert conductive element 114 may have an island pattern. Figure 3c In yet another embodiment, the inert conductive element 114 may have a double helix pattern. In another embodiment, the inert conductive element 114 may have a planar geometric shape. In various examples, the planar geometric shape may include, but is not limited to, a rectangular shape, a circular shape, a square shape, a triangular shape, a polygonal shape, without departing from the scope of the present disclosure. In the illustrated embodiment, reference is made to Figure 3d , the inert conductive element 114 may have a rectangular shape.

[0065] It should be understood by those skilled in the art that the geometry of the inert conductive element 114 should not be construed as limited to the shapes explained in the present disclosure, and the material of the inert conductive element 114 may be deposited in different shapes to obtain the desired conductivity of the inert conductive element 114 without departing from the scope of the present disclosure.

[0066] Furthermore, the gas sensing element 102 described above may be incorporated into the gas sensor 100, such as Figure 1 As schematically depicted in Figure 1 As shown in , the gas sensor 100 includes a gas sensing element 102 having a substrate 110, a gas sensing surface 112, and an inert conductive element 114, the gas sensing element 102 integrating parallel electrodes or interdigitated electrodes, such as a plurality of electrodes 106. In the illustrated embodiment, the plurality of electrodes 106 may be depicted below the gas sensing element 102, but may also be disposed above or on the gas sensing element 102.

[0067] In one or more embodiments, the plurality of electrodes 106 may be connected to the gas sensing element 102 and the circuit 108. The circuit 108 may be adapted to measure at least one of a voltage across the gas sensing element 102, a resistance, an impedance, a current, and a conductance associated with the gas sensing element 102 and the inert conductive element 114. Figure 1 , the plurality of electrodes 106 may be externally connected to the gas sensing element 102 via a circuit 108 including a signal processor 116. The signal processor 116 may be a voltmeter or an ammeter, but in different embodiments includes a constant potential circuit, a voltage divider circuit, a bridge circuit, a microprocessor, an electronic control unit (ECU), or a similar electronic device with integrated voltage and / or ampere measurement capabilities, and may apply a bias voltage between the plurality of electrodes 106. Figure 1 Other gas sensor components, including but not limited to housing, mounting hardware, gas flow conduits, and fluid chambers are not shown, but may be incorporated into gas sensor 100 by one skilled in the art.

[0068] Figure 4The diagram depicts a flow chart of a method 400 of manufacturing a gas sensing element 102 according to one or more embodiments of the present disclosure. At step 402, the method 400 includes providing a substrate 110 including a metal oxide semiconductor formed of a first metal. In one or more embodiments, the substrate 110 may be deposited on the substrate 104 of the gas sensor 100 by performing a thermal deposition technique such as sputtering, physical vapor deposition, chemical vapor deposition, or thermal spraying.

[0069] At step 404, the method 400 includes disposing a gas sensing surface 112 having a metal oxide semiconductor on the substrate 110. The metal oxide semiconductor is formed of a first metal and at least one dopant, the at least one dopant having at least one of a second metal and at least one compound. In one or more embodiments, the gas sensing surface 112 can be deposited on the substrate 110 of the gas sensor 100 by performing a thermal deposition technique such as sputtering, physical vapor deposition, chemical vapor deposition, or thermal spraying.

[0070] At step 404, method 400 includes disposing an inert conductive element 114 between substrate 110 and gas sensing surface 112. Inert conductive element 114 may be adapted to maintain a predetermined minimum conductivity of gas sensing element 102. Inert conductive element 114 may be adapted to maintain the predetermined minimum conductivity of gas sensing element 102 based on the conductivity of inert conductive element 114. As previously explained, the conductivity of inert conductive element 114 may vary based on at least the thickness, geometric pattern, width, and overlap area of ​​material deposition of inert conductive element 114 between substrate 110 and gas sensing surface 112.

[0071] Although shown and described in a particular order Figure 4 However, according to various embodiments of the present disclosure, the steps may appear in a variation of this order. In addition, for the sake of brevity, Figure 1 -3 The descriptions related to Figure 4 The details of each step will not be discussed in detail again here.

[0072] As will be gathered, the present disclosure provides a gas sensing element 102 and a method 400 of manufacturing the gas sensing element 102. As previously explained, the inert conductive element 114 can maintain a predetermined minimum conductivity of the gas sensing element 102 to assess the operational integrity of the gas sensing surface 112 of the gas sensing element 102. The predetermined minimum conductivity can be varied by varying at least one of the thickness, width, geometric pattern, and overlap area of ​​the material deposition of the inert conductive element 114. This significantly provides greater flexibility in designing gas sensing elements such as 102 with different minimum conductivities for different applications and requirements.

[0073] Furthermore, due to the implementation of the inert conductive element 114, the integrity of the gas sensing surface 112 can be efficiently and effectively tested even in the absence of a test gas. In particular, the gas sensing element 102 having the inert conductive element 114 has a higher conductivity in the absence of a test gas than a conventional gas sensing element, and thus makes it easier to determine whether the gas sensing element 102 is operable.

[0074] In addition, since the inert conductive element 114 is implemented to increase conductivity, reactive sputtering can be used in an oxygen-containing atmosphere to deposit metal oxides from readily available high-purity metal targets, which is in contrast to sputtering thin films from doped ceramic metal oxide targets. Compared to doped ceramic metal oxide targets, metal targets tend to have better heat transfer capabilities and are easier and cheaper to obtain. Therefore, the implementation of the inert conductive element 114 can eliminate the need for doped metal oxides to increase conductivity. In conventional gas sensing elements, the amount of dopant can be controlled to change conductivity. However, the amount of dopant may be difficult to control. The exact amount of dopant can vary from one sputtering system to another, and it can even vary from one metal oxide sputtering target to another metal oxide sputtering target. Therefore, the gas sensing element 102 and method 400 of the present disclosure are efficient, durable, flexible to implement, cost-effective and convenient.

[0075] Although specific language has been used to describe the subject matter, any limitations resulting therefrom are not intended. As will be apparent to those skilled in the art, various modifications in operation may be made to the method to realize the inventive concept as taught herein. The accompanying drawings and the foregoing description provide examples of embodiments. Those skilled in the art will appreciate that one or more of the elements described may be well combined into a single functional element. Alternatively, some elements may be divided into a plurality of functional elements. Elements from one embodiment may be added to another embodiment.

Claims

1. A gas sensing element for a gas sensor, the gas sensing element comprising: a substrate comprising a metal oxide semiconductor formed of a first metal; a gas sensing surface disposed on the substrate and comprising: a metal oxide semiconductor formed from the first metal and at least one dopant having at least one of a second metal and at least one compound, and at least one inert conductive element disposed between the substrate and the gas sensing surface, Wherein the at least one inert conductive element is adapted to maintain a predetermined minimum conductivity of the gas sensing element.

2. The gas sensing element according to claim 1, wherein: The predetermined minimum conductivity is adjustable corresponding to a series resistance of the gas sensor and is adjustable in at least one of the ranges of 1E-5mS to 1E-3mS, 1E-4mS to 1E-2mS, 1E-3mS to 1E-1mS, and 1E-2 to 1mS.

3. The gas sensing element according to any one of claims 1 or 2, wherein: The at least one inert conductive element is adapted to maintain the predetermined minimum conductivity of the gas sensing element based on conductivity of the at least one inert conductive element, and wherein the conductivity of the at least one inert conductive element varies based on at least one of: a geometric pattern of deposition of material of said at least one inert conductive element, the thickness of the material deposition of the at least one inert conductive element, the width of the material deposition of the at least one inert conductive element, the thickness of the substrate beneath the at least one inert conductive element, and The overlap area between the material deposition of the electrode of the gas sensor, the substrate and the at least one inert conductive element.

4. The gas sensing element according to any one of claims 1 to 3, wherein: The electrical conductivity of the at least one inert conductive element is higher in the presence of the gas than in the absence of the gas, wherein the electrical conductivity of the at least one inert conductive element is constant in the absence of the gas.

5. The gas sensing element according to any one of claims 3 or 4, wherein: The electrical conductivity of the at least one inert conductive element is proportional to the thickness of the material deposition of the at least one inert conductive element.

6. The gas sensing element according to any one of claims 3 or 5, wherein: The at least one inert conductive element is embodied as a non-continuous film having an average thickness in the range of 0.1 nm to 9 nm.

7. The gas sensing element according to any one of claims 3 or 5, wherein: The at least one inert conductive element is embodied as a continuous film having an average thickness in the range of 5 nm to 15 nm.

8. The gas sensing element according to any one of claims 3 or 5, wherein: The at least one inert conductive element is embodied as a continuous film having an average thickness in the range of 20 nm to 50 nm.

9. The gas sensing element according to any one of claims 3 or 5, wherein: The at least one inert conductive element has a serpentine pattern.

10. A gas sensing element according to any one of the preceding claims, wherein: The at least one inert conductive element has an island pattern.

11. A gas sensing element according to any one of the preceding claims, wherein: The at least one inert conducting element has a planar geometry.

12. A gas sensing element according to any one of the preceding claims, wherein: The at least one inert conductive element has a double helical pattern.

13. A gas sensing element according to any one of the preceding claims, wherein: The at least one inert conductive element is formed from a non-reactive conductive material.

14. The gas sensing element according to claim 1, wherein: The first metal includes aluminum, bismuth, cadmium, cerium, chromium, cobalt, copper, iron, gallium, indium, molybdenum, niobium, tantalum, tin, titanium, tungsten, vanadium or zinc.

15. The gas sensing element according to claim 1, wherein: The first metal includes aluminum, bismuth, cadmium, cerium, chromium, cobalt, copper, iron, gallium, indium, molybdenum, niobium, tantalum, tin, titanium, tungsten, vanadium or zinc, and The second metal includes one or more Group 5 to Group 11 transition metals.

16. A gas sensing element according to any one of the preceding claims, wherein: The at least one inert conductive element is adapted to maintain the predetermined minimum conductivity of the gas sensing element to assess the operational integrity of the gas sensing surface in at least one of the absence and presence of a gas to be tested.

17. A gas sensing element according to any one of the preceding claims, wherein: The gas is embodied as one of hydrogen and hydrogen sulfide.

18. A gas sensor comprising: substrate; A gas sensing element is disposed on the substrate and includes: a substrate including a metal oxide semiconductor formed of a first metal; A gas sensing surface disposed on the substrate and comprising: a metal oxide semiconductor formed from the first metal and at least one dopant having at least one of a second metal and at least one compound, and at least one inert conductive element disposed between the substrate and the gas sensing surface, wherein the at least one inert conductive element is adapted to maintain a predetermined minimum conductivity of the gas sensing element, and A plurality of electrodes connected to the gas sensing element and circuitry, wherein the circuitry is adapted to measure at least one of a voltage across the gas sensing element, a resistance, an impedance, a current, and a conductance associated with the gas sensing element and the at least one conductive element.

19. A method for manufacturing a gas sensing element according to any one of claims 1 to 17, the method comprising: providing a substrate including a metal oxide semiconductor formed of a first metal; disposing a gas sensing surface having a metal oxide semiconductor on the substrate, wherein the metal oxide semiconductor is formed of the first metal and at least one dopant having at least one of a second metal and at least one compound; as well as disposing at least one inert conductive element between the substrate and the gas sensing surface, Wherein the at least one inert conductive element is adapted to maintain a predetermined minimum conductivity of the gas sensing element.

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