Gas sensor and gas sensor device

Abstract

To provide a gas sensor and a gas sensor device that can accurately detect target gas.SOLUTION: A gas sensor 10 comprises: at least one electrode pair 70 having a pair of electrodes (a first electrode 71 and a second electrode 72) arranged apart from each other; a sensitive film 60 that electrically connects the pair of electrodes (the first electrode 71 and the second electrode 72); and a heat generator 40 that heats the sensitive film 60. The sensitive film 60 includes a mixture of an oxide semiconductor and a solid electrolyte body having an activation temperature higher than that of the oxide semiconductor. The electrodes (the first electrode 71 and the second electrode 72) are in direct contact with the mixture.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas sensor and a gas sensor device. [Background technology]

[0002] The gas detection device of Patent Document 1 includes a metal oxide semiconductor gas sensor, a heating unit that heats the metal oxide semiconductor gas sensor to an operating temperature, and a signal voltage application means that measures the resistance value of the metal oxide semiconductor gas sensor. This gas detection device is configured to change the gas sensitivity by changing the signal voltage using the signal voltage application means. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-283943 Summary of the Invention [Problem to be solved by the invention]

[0004] In the gas detection device of Patent Document 1, it is expected that the sensitivity will change due to oxygen adsorbed to the metal oxide semiconductor gas sensor during operation. Therefore, even if the voltage applied to the metal oxide semiconductor gas sensor is adjusted, there is a concern that the sensitivity will not be stable. Therefore, a configuration that can detect the target gas with high accuracy is required.

[0005] The present disclosure provides a gas sensor and a gas sensor device that can detect a target gas with high accuracy. [Means for solving the problem]

[0006] The gas sensor of the present disclosure comprises: At least one electrode pair having a pair of electrodes spaced apart from each other; a sensitive membrane electrically connecting the pair of electrodes; a heat generating unit that heats the sensitive film; A gas sensor comprising: the sensitive film contains a mixture of an oxide semiconductor and a solid electrolyte having an activation temperature higher than that of the oxide semiconductor, The electrode and the mixture are in direct contact with each other or are electrically connected via a mixed conductor having electronic and ionic conductivity. [Effects of the Invention]

[0007] The technology according to the present disclosure can detect target gases with high accuracy. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a side cross-sectional view schematically showing a gas sensor according to a first embodiment. [Figure 2] FIG. 2 is a partially enlarged view of the gas sensor of FIG. [Figure 3] FIG. 3 is a plan view schematically showing a first electrode and a second electrode formed on an insulating layer. [Figure 4] FIG. 4 is a schematic diagram illustrating a part of the gas sensor. [Figure 5] FIG. 5(A) is an explanatory diagram illustrating the depletion layer of the oxide semiconductor before the gas sensor is exposed to the target gas, and FIG. 5(B) is an explanatory diagram illustrating the depletion layer of the oxide semiconductor after the gas sensor is exposed to the target gas. [Figure 6] FIG. 6 is a process diagram illustrating the manufacturing process of the gas sensor. [Figure 7] FIG. 7 is a process diagram illustrating the manufacturing process of the gas sensor following FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] In the following, embodiments of the present disclosure are listed and illustrated. [1] At least one electrode pair having a pair of electrodes spaced apart from each other; a sensitive membrane electrically connecting the pair of electrodes; a heat generating unit that heats the sensitive film; A gas sensor comprising: the sensitive film contains a mixture of an oxide semiconductor and a solid electrolyte having an activation temperature higher than that of the oxide semiconductor, The electrode and the mixture are in direct contact with each other or are electrically connected to each other via a mixed conductor having electronic conductivity and ionic conductivity. Gas sensor.

[0010] According to this configuration, since the sensitive film contains a mixture of an oxide semiconductor and a solid electrolyte, the concentration of the target gas can be detected by the concentration detection function of the oxide semiconductor (resistance change due to the concentration of the target gas), and ions adsorbed to the sensitive film can be removed by the ion migration function of the solid electrolyte. In particular, since the activation temperature of the oxide semiconductor and the activation temperature of the solid electrolyte are different, the concentration detection function of the oxide semiconductor and the ion migration function of the solid electrolyte can be selectively used by appropriate temperature adjustment. Therefore, the gas sensor can accurately detect the target gas while preventing sensitivity degradation by removing ions adsorbed to the sensitive film.

[0011] [2] The gas sensor according to [1], wherein the volume ratio of the oxide semiconductor to the solid electrolyte in the mixture is 3:7-7:3.

[0012] This configuration makes it possible to form a mixture that can fully obtain the properties of both the oxide semiconductor and the solid electrolyte.

[0013] [3] The gas sensor according to [1] or [2]; a voltage application unit that applies a voltage between the pair of electrodes; a control unit that controls a heating operation of the heat generating unit and a voltage application operation of the voltage application unit, The control unit a first control that heats the sensitive film by the heating unit to a first temperature at which electrons or holes are conducted in the oxide semiconductor, applies a voltage between the pair of electrodes by the voltage application unit, and detects the concentration of the target gas based on a current flowing between the pair of electrodes or a resistance value between the pair of electrodes; and a second control is performed in which the heat generating unit heats the sensitive membrane to a second temperature that is higher than the first temperature and at which ions are conducted in the solid electrolyte body, and the voltage applying unit applies a voltage between the pair of electrodes. Gas sensor device.

[0014] This configuration allows the concentration of the target gas to be measured at a relatively low desired temperature during gas detection without needlessly raising the temperature, while enabling accurate ion removal control (refresh control) at a relatively high temperature where ions adsorbed on the sensitive film (more specifically, the oxide semiconductor) are likely to migrate.

[0015] [4] The control unit In the first control, the voltage application unit applies a voltage of a first voltage value between the pair of electrodes, In the second control, the voltage application unit applies a second voltage greater than the first voltage value between the pair of electrodes. The gas sensor device according to [3].

[0016] According to this configuration, it is possible to more effectively move ions during removal control (refresh control) of ions adsorbed on the sensitive film (more specifically, oxide semiconductor).

[0017] First Embodiment 1-1.Gas sensor configuration A first embodiment of the present invention will be described below with reference to Figures 1 to 7. A gas sensor 10 of the first embodiment shown in Figure 1 is an example of a gas sensor of the present disclosure. In the following description, for convenience of explanation, the up-down direction shown in Figures 1 and 2 is defined as the up-down direction, but it does not have to coincide with the up-down direction in the actual arrangement of the gas sensor 10.

[0018] The gas sensor 10 includes a substrate 20, insulating layers 31, 32, 33, 34, and 35, a heat generating portion 40, an electrode portion 50, and a sensitive membrane 60. The electrode portion 50 includes one or more electrode pairs 70 each having a first electrode 71 and a second electrode 72. The electrode portion 50 may include four or more electrode pairs 70, or may include 100 or more electrode pairs 70.

[0019] 3 illustrates an electrode unit 50 provided with one electrode pair 70. As shown in FIG. 3, in the electrode pair 70, a first electrode 71 and a second electrode 72 are spaced apart. The first electrode 71 and the second electrode 72 face each other in a direction parallel to the upper surface of the substrate 20.

[0020] The substrate 20 is made of, for example, a silicon wafer. The material of the substrate 20 is not particularly limited, but may be a semiconductor such as silicon. If a ceramic substrate such as sapphire, zirconia, or alumina is used for the substrate 20, the formation of the insulating layers 31, 32, 33, and 34 described below can be omitted. The planar shape of the substrate 20 is not particularly limited, and may be, for example, rectangular or circular. The size of the substrate 20 is not particularly limited, and may be a rectangular substrate with a side length of 0.1 mm to 10 mm, or a circular substrate with a similar area. The thickness of the substrate 20 is not particularly limited, and may be, for example, 400 μm to 500 μm.

[0021] The substrate 20 may have a space 21 formed by cutting out a portion of itself. The space 21 may be, for example, a hollow that opens to both the front and back surfaces of the substrate 20 and penetrates the substrate 20, or a recess that opens to only one of the front and back surfaces of the substrate 20. The shape of the opening 22 of the space 21 and the cross-sectional shape of the interior of the space 21 are not particularly limited, but are usually simple shapes such as rectangular or circular. The size of the space 21 is not particularly limited, and when the space 21 is hollow, it is preferable that the opening area of ​​one of the openings on the front and back surfaces of the substrate 20 is larger. This opening area is not particularly limited, but it is preferable that the larger opening area is 0.01 mm 2 -4mm 2 It is preferable to set the thickness to 0.25 mm. 2 -2mm 2 When the space 21 is a recess, the opening area can be set to the same range as that of a cavity.

[0022] The electrode unit 50, which will be described later, is insulated from the substrate 20 by insulating layers 31, 32, 33, 34, and 35 provided on the substrate 20. The insulating layers 31, 32, 33, 34, and 35 may be formed on the entire surface of the substrate 20 or on only a portion of the substrate 20. The insulating layers 31, 33, and 35 are laminated on one surface (upper surface) of the substrate 20. The substrate 20 is provided with a space 21. When the substrate 20 has the space 21, the insulating layers 31, 33, and 35 cover an opening 22 in the space 21 and are supported by the substrate 20. The insulating layers 31, 33, and 35 may be formed to cover the entire surface of the opening 22, or may be formed to cover only a portion of the opening 22 as long as they can be supported by the substrate 20. The insulating layers 32 and 34 are laminated on the other surface (lower surface) of the substrate 20. The insulating layers 31, 32, 33, 34, and 35 are not particularly limited in material as long as they have sufficient insulating properties. For example, examples of the material for the insulating layers 31, 32, 33, 34, and 35 include SiO2, Si3N4, and SiO x N y(x and y are arbitrary values) and other silicon compounds. The shapes and thicknesses of the insulating layers 31, 32, 33, 34, and 35 are not particularly limited. A single insulating layer may be provided instead of the insulating layers 31, 33, and 35. By forming a silicon oxide film on the substrate 20, leakage current between the electrodes of the electrode pair 70 can be suppressed.

[0023] The gas sensor 10 is provided with a plurality of heat generating elements 40. The heat generating elements 40 are provided on the insulating layer 33 and covered with the insulating layer 35. Leads (not shown) for supplying power from an external circuit are connected to the heat generating elements 40 via heat generating element contacts (not shown). Contact pads (not shown) are provided on the surfaces of the heat generating element contacts. The heat generating elements 40 generate heat when a voltage is applied. This causes the temperature of the sensitive film 60 to rise and become activated, enabling measurement of the gas concentration. The positions of the heat generating elements 40 are not particularly limited as long as they are inside the insulating layers 31, 33, and 35. However, if a space 21 is formed in the substrate 20, the heat generating elements 40 are preferably provided at positions corresponding to the space 21. By providing the heat generating elements 40 at positions corresponding to the space 21, heat dissipation from the heat generating elements 40 to the substrate 20 can be suppressed. Furthermore, heat can be efficiently transferred to the sensitive film 60, allowing for more accurate control of the temperature of the sensitive film 60. The position corresponding to the space 21 means that at least a portion of the heat generating portion 40 overlaps with the space 21 in the thickness direction of the substrate 20, and it is more preferable that the entire heat generating portion 40 overlaps with the space 21. The heat generating portion 40 is conductive, and its material is not particularly limited. For example, platinum, a platinum alloy, a nickel alloy, a chromium alloy, a nickel chromium alloy, or the like can be used for the heat generating portion 40. Among these, it is preferable to use platinum or a nickel chromium alloy for the heat generating portion 40, as these have a large temperature coefficient of resistance and are unlikely to change in resistance value or temperature coefficient of resistance even with long-term repeated use.

[0024] The electrode section 50 (one or more electrode pairs 70) is provided on the surface of the insulating layer 35. The first electrode 71 and the second electrode 72 are formed of one or more types of metal. Examples of metals that may be used to form the first electrode 71 and the second electrode 72 include gold (Au) and platinum (Pt). The first electrode 71 and the second electrode 72 have a two-layer structure, for example, consisting of a lower electrode and an upper electrode. For example, the lower electrode is made of titanium (Ti) and the upper electrode is made of platinum (Pt).

[0025] Lead portions (not shown) for supplying power from an external circuit are connected via electrode contact portions (not shown) to the first electrode 71 and the second electrode 72. Contact pads (not shown) are provided on the surfaces of the electrode contact portions.

[0026] The sensitive film 60 is provided on the upper surface of the first electrode 71, the upper surface of the second electrode 72, and the upper surface of the insulating layer 35. The sensitive film 60 is disposed between the first electrode 71 and the second electrode 72 in the electrode pair 70. The sensitive film 60 is in contact with the first electrode 71 and the second electrode 72. The sensitive film 60 electrically connects the first electrode 71 and the second electrode 72.

[0027] The sensitive film 60 contains a mixture of an oxide semiconductor (see oxide semiconductor 61 in FIG. 4) and a solid electrolyte (see solid electrolyte 62 in FIG. 4). The oxide semiconductor is preferably an n-type semiconductor from the viewpoint of not causing oxygen ion conduction. The oxide semiconductor is preferably SnO2, ZnO, In2O3, Fe2O3, ITO (tin-doped indium), or WO3 from the viewpoint of being less likely to adsorb oxygen.

[0028] The solid electrolyte body preferably does not have the characteristics of an oxide semiconductor (the characteristic that the resistance value does not change due to the adsorption of the target gas). The solid electrolyte body preferably contains stabilized zirconia and / or partially stabilized zirconia. The stabilized zirconia is preferably yttria-stabilized zirconia (YSZ).

[0029] The activation temperature of the solid electrolyte body is higher than the activation temperature of the oxide semiconductor. The activation temperature of the solid electrolyte body is the temperature at which electrons or holes conduct in the solid electrolyte body or higher. In other words, the activation temperature of the solid electrolyte body is the temperature at which electrons or holes begin to conduct in the solid electrolyte body when the temperature is increased. The activation temperature of the solid electrolyte body is, for example, 450°C. The activation temperature of the oxide semiconductor is the temperature at which ions (e.g., oxide ions) begin to conduct in the oxide semiconductor or higher. In other words, the activation temperature of the oxide semiconductor is the temperature at which ions (e.g., oxide ions) begin to conduct in the oxide semiconductor when the temperature is increased. The activation temperature of the oxide semiconductor is, for example, 150°C.

[0030] The volume ratio of the oxide semiconductor to the solid electrolyte body in the mixture is preferably 3:7-7:3, more preferably 4:6-6:4, and even more preferably 5:5. By setting the volume ratio in the mixture within this range, it is possible to fully obtain the characteristics of both the oxide semiconductor and the solid electrolyte body in the sensitive membrane 60. The volume ratio of the oxide semiconductor to the solid electrolyte body in the mixture can be determined, for example, from the ratio of the area occupied by the oxide semiconductor to the area occupied by the solid electrolyte body, as observed in a cross-sectional SEM image of the sensitive membrane 60.

[0031] At least some of the oxide semiconductor particles that make up the sensitive film 60 are electrically bonded (bonded) to each other. The electrical bonding between the particles allows electrons to flow between the particles (a state in which current can flow between the particles). The electrical bonding between the particles that make up the sensitive film 60 reduces the contact resistance between the particles, facilitating the movement of electrons in the depletion layer. In addition, at least some of the electrically coupled oxide semiconductor particles are also electrically connected to the first electrode 71 and the second electrode 72. This facilitates the movement of electrons between the first electrode 71 and the second electrode 72 via the sensitive film 60.

[0032] At least some of the particles in the solid electrolyte body that constitutes the sensitive membrane 60 are electrically coupled (bonded) to each other. This electrical coupling between the particles allows ions (e.g., oxide ions) to flow between the particles. Furthermore, at least some of the electrically coupled particles in the solid electrolyte body are also electrically connected to the first electrode 71 and the second electrode 72. This facilitates the movement of ions (e.g., oxide ions) between the first electrode 71 and the second electrode 72 via the sensitive membrane 60.

[0033] 1-2.Configuration of the gas sensor device 4 is an example of the gas sensor device of the present disclosure. The gas sensor device 100 includes a gas sensor 10, a voltage application unit 80, a control unit 90, and a resistance detection unit 92.

[0034] The voltage application unit 80 applies a voltage between the first electrode 71 side and the second electrode 72 side of the electrode unit 50. The voltage application unit 80 has, for example, a power supply 81 and a switch 82. The switch 82 is provided between the power supply 81 and the electrode unit 50, and is turned on and off under the control of the control unit 90. The voltage application unit 80 may have, for example, a voltage control circuit (such as a constant voltage circuit) that applies a voltage to the electrode unit 50 based on the power supplied from the power supply.

[0035] The control unit 90 controls the operation of the gas sensor device 100. The control unit 90 is mainly configured with a microcomputer and includes, for example, a CPU, a ROM, and a RAM. The control unit 90 controls detection of the concentration of the target gas based on the current flowing between the first electrode 71 and the second electrode 72 or the resistance value between the first electrode 71 and the second electrode 72. For example, as shown in FIG. 4 , a resistance detection unit 92 is electrically connected to the first electrode 71 and the second electrode 72 and is also electrically connected to a power source 81 and a switch 82. The control unit 90 may acquire the resistance value between the first electrode 71 and the second electrode 72 detected by the resistance detection unit 92, or may calculate the resistance value between the first electrode 71 and the second electrode 72 based on the current flowing between the first electrode 71 and the second electrode 72 detected by the resistance detection unit 92. The control unit 90 outputs, for example, the gas concentration detected using the first electrode 71 and the second electrode 72 as an electrical signal. The control unit 90 may include an amplifier or the like for amplifying the electrical signal. Furthermore, the control unit 90 controls the heating operation of the heat generating unit 40 and the voltage application operation of the voltage application unit 80 .

[0036] The gas sensor 10 is, for example, a resistance measurement type or an impedance measurement type. The target gas (detection gas) of the gas sensor 10 is, for example, flammable. The target gas changes the resistance of the gas sensor 10. The target gas is, for example, ketones (acetone, etc.), alcohols (ethanol, etc.), carbon monoxide, nitrogen oxides (NO, NO), aldehydes (acetaldehyde, etc.), sulfide gases (hydrogen sulfide, etc.), VOC gases (toluene, etc.), etc.

[0037] 5 is a diagram illustrating the gas concentration dependence of the current flowing through the sensitive film 60 in the gas sensor 10 of the first embodiment. The gas concentration dependence of the current flowing through the sensitive film 60 is based on the change in the concentration of oxygen vacancies in the sensitive film 60 (specifically, the oxide semiconductor) due to the gas (acetone is shown as an example in FIG. 5). FIG. 5 shows the case where SnO2 is used as the oxide semiconductor. As shown in the change from FIG. 5(A) to FIG. 5(B), when the gas sensor 10 is exposed to the target gas under a low oxygen partial pressure, the width of the depletion layer in the oxide semiconductor decreases from L1 to L2 under the low oxygen partial pressure, facilitating electron movement, which is thought to result in a decrease in resistance.

[0038] 1-3. Control of gas sensor device The control of the gas sensor device 100 will be described. The control unit 90 performs a first control and a second control. In the first control, the heating unit 40 heats the sensitive film 60 to a first temperature, which is a temperature at which electrons or holes are conducted in the oxide semiconductor, and the voltage application unit 80 applies a voltage between the first electrode 71 and the second electrode 72. The concentration of the target gas is detected based on the current flowing between the first electrode 71 and the second electrode 72 or the resistance value between the first electrode 71 and the second electrode 72. The first temperature is, for example, a temperature equal to or higher than the activation temperature of the oxide semiconductor and lower than the activation temperature of the solid electrolyte body. The first temperature is, for example, 150°C to 400°C.

[0039] In the first control, the voltage application unit 80 applies a voltage of a first voltage value between the first electrode 71 and the second electrode 72. The first voltage is, for example, 0.5V to 3V.

[0040] The second control is a control in which the heating unit 40 heats the sensitive film 60 to a second temperature, which is higher than the first temperature and at which ions are conducted in the solid electrolyte body, and the voltage application unit 80 applies a voltage between the first electrode 71 and the second electrode 72. The second temperature is, for example, a temperature equal to or higher than the activation temperature of the solid electrolyte body. The second temperature is, for example, 450°C to 800°C. As a result, as shown in FIG. 4, ions (e.g., oxide ions) adsorbed to the sensitive film 60 (more specifically, the oxide semiconductor) during gas detection or the like move between the first electrode 71 and the second electrode 72 and are gasified and removed by an electrode (e.g., an electrode on the higher potential side).

[0041] In the second control, the voltage application unit 80 applies a second voltage greater than the first voltage between the first electrode 71 and the second electrode 72. The second voltage is, for example, 1V-4V.

[0042] Through the above control, the gas sensor device 100 can measure the concentration of the target gas at a relatively low desired temperature (first temperature) during gas detection without unnecessarily raising the temperature. On the other hand, the gas sensor device 100 can accurately perform ion removal control (refresh control) at a relatively high temperature (second temperature) where ion migration is likely to occur. Furthermore, the gas sensor device 100 can more effectively migrate ions by applying a relatively high voltage (second voltage) during ion removal control (refresh control).

[0043] 1-4. Gas sensor manufacturing method A method for manufacturing the gas sensor 10 embodying the present invention will be described with reference to FIGS. The method for manufacturing the gas sensor 10 includes a step of forming the electrode portion 50 on the substrate 20 by lift-off, and a step of forming the sensitive film 60 in the gap portion of the electrode portion 50.

[0044] First, insulating layers 31, 33, and 35 and a heating element 40 are formed on a cleaned substrate 20 (silicon wafer). The cleaned substrate 20 is placed in a heat treatment furnace, and a silicon oxide film (see FIG. 6A) that will become insulating layer 31 (first insulating layer) is formed over the entire surface of the substrate 20 by thermal oxidation. Note that FIGS. 6A-6C and 7A-7D only show the top surface of the substrate 20, and the description of the formation of insulating layers 32 and 34 is omitted. Next, as shown in FIG. 6A, a silicon nitride film is formed on insulating layer 31 by plasma CVD using, for example, SiH4 and NH3 as source gases, to form insulating layer 33 (lower insulating layer). Thereafter, as shown in FIG. 6B, a heating element 40 is formed on the surface of insulating layer 33 by, for example, sputtering. For example, the heating element 40 is composed of a Ti layer and a Pt layer thereon. Next, the resist is patterned by photolithography, and the pattern of the heat generating portion 40 is formed by etching.

[0045] The method for forming the heat generating portion 40 is not particularly limited. For example, components that will become the heat generating portion 40 are deposited on the surface of the insulating layer 33, and then unnecessary portions are removed by various etching methods similar to those exemplified in the method for forming the space portion 21. Next, as shown in FIG. 6(C), an insulating layer 35, such as a silicon nitride film, is formed on the surface to form the insulating layer 35 (upper insulating layer). In this way, insulating layers 33 and 35 (second insulating layers) and the heat generating portion 40 disposed inside the insulating layers 33 and 35 (second insulating layers) are formed. Note that the insulating layers 31, 32, 33, 34, and 35 can also be formed by depositing components that will become the insulating layers 31, 32, 33, 34, and 35 on the surface of the substrate 20, or by laminating a pre-formed insulating layer onto the surface of the substrate.

[0046] Next, as shown in FIG. 7(A), a photoresist composition is applied onto the insulating layer 35 by spin coating and dried to form a resist film 37. Note that in FIGS. 7(A) to 7(D), the configuration below the insulating layer 35 and the heating portion 40 is not shown. The resist film 37 is formed to a thickness of, for example, 20 nm to 40 nm. The resist film 37 is formed from a photoresist composition for electron beam exposure. A mask pattern is created by exposing the resist film 37 by electron beam lithography and developing it.

[0047] Next, as shown in FIG. 7B, a metal film 70A is formed to cover substantially the entire surfaces of the insulating layer 35 and the resist film 37. The metal film 70A is made of gold (Au) or platinum (Pt). The thickness of the metal film 70A is preferably 5 nm to 20 nm, e.g., 15 nm. The metal film 70A is formed, for example, by electron beam evaporation. The mask pattern is peeled off, and the metal film 70A overlapping the mask pattern is simultaneously removed. This results in the formation of the electrode section 50 (electrode pair 70) in which the metal film 70A is laminated, as shown in FIG. 7C. The width of the first electrode 71 and the second electrode 72 is formed to be, for example, 15 nm. The electrode pair 70 may be formed by electron beam lithography, or alternatively, by nanoimprint lithography, in which a pattern is transferred to a resist by stamping a mold (metal die) as a master. After the electrodes are formed, annealing (e.g., heat treatment at 360°C) may be performed in a vacuum.

[0048] As shown in FIG. 1, when a space 21 is provided in the substrate 20, it can be formed, for example, by removing a part of the substrate 20 by etching. In this case, the etching method is not particularly limited, and a wet etching method or a dry etching method may be used. Furthermore, the etching method may be anisotropic etching or isotropic etching. When a cavity is formed in the substrate 20, a wet etching method using an anisotropic etching solution is preferable.

[0049] 7(D), the sensitive film 60 is formed on the upper surface of the first electrode 71, the upper surface of the second electrode 72, and the upper surface of the insulating layer 35. The sensitive film 60 is preferably formed by physical vapor deposition (PVD) or chemical vapor deposition (CVD). An example of physical vapor deposition (PVD) is sputtering. The sensitive film 60 is simultaneously formed by co-sputtering using an RF sputtering device, for example, using a tin oxide (SnO) target for sputtering and an 8YSZ (stabilized zirconia with yttria solid solution, 8 mol% Y2O3-92 mol% ZrO2) target.

[0050] The sensitive film 60 may be subjected to a heat treatment after deposition. This causes the particles contained in the sensitive film 60 to bond together, forming a dense sensitive film 60. The heat treatment at this time uses a heater (heat generating unit 40) installed in the gas sensor, and changes the temperature by passing electricity through it. This facilitates bonding between the particles that make up the sensitive film 60, reduces the contact resistance between the particles, and facilitates the movement of electrons in the depletion layer. In this manner, the gas sensor 10 is manufactured.

[0051] 2. Effects of the First Embodiment The gas sensor 10 of the first embodiment includes at least one electrode pair 70 having a pair of electrodes (a first electrode 71 and a second electrode 72) spaced apart from each other, a sensitive membrane 60 electrically connecting the pair of electrodes (the first electrode 71 and the second electrode 72), and a heat generating unit 40 for heating the sensitive membrane 60. The sensitive membrane 60 includes a mixture of an oxide semiconductor and a solid electrolyte having an activation temperature higher than that of the oxide semiconductor. The electrodes (the first electrode 71 and the second electrode 72) and the mixture are in direct contact with each other. According to this configuration, the sensitive film 60 contains a mixture of an oxide semiconductor and a solid electrolyte, so that the concentration of the target gas can be detected by the concentration detection function of the oxide semiconductor (resistance change due to the concentration of the target gas), and ions adsorbed to the sensitive film 60 can be removed by the ion migration function of the solid electrolyte. In particular, because the activation temperature of the oxide semiconductor and the activation temperature of the solid electrolyte are different, the concentration detection function of the oxide semiconductor and the ion migration function of the solid electrolyte can be selectively used by appropriate temperature adjustment. Therefore, the gas sensor 10 can accurately detect the target gas while preventing sensitivity degradation by removing ions adsorbed to the sensitive film 60.

[0052] In the gas sensor 10 of the first embodiment, the volume ratio of the oxide semiconductor to the solid electrolyte body in the mixture is 3:7-7:3. This configuration makes it possible to form a mixture that can fully obtain the properties of both the oxide semiconductor and the solid electrolyte.

[0053] The gas sensor device 100 of the first embodiment includes a gas sensor 10, a voltage application unit 80 that applies a voltage between a pair of electrodes (a first electrode 71 and a second electrode 72), and a control unit 90 that controls the heating operation of the heat generation unit 40 and the voltage application operation by the voltage application unit 80. The control unit 90 performs a first control in which the heating unit 40 heats the sensitive film 60 to a first temperature, which is a temperature at which electrons or holes conduct in the oxide semiconductor, and the voltage application unit 80 applies a voltage between a pair of electrodes (first electrode 71, second electrode 72), and detects the concentration of the target gas based on the current flowing between the pair of electrodes (first electrode 71, second electrode 72) or the resistance value between the pair of electrodes (first electrode 71, second electrode 72); and a second control in which the heating unit 40 heats the sensitive film 60 to a second temperature, which is higher than the first temperature and is a temperature at which ions conduct in the solid electrolyte body, and the voltage application unit 80 applies a voltage between the pair of electrodes (first electrode 71, second electrode 72). This configuration allows the concentration of the target gas to be measured at a relatively low desired temperature during gas detection without needlessly raising the temperature, while also enabling accurate control (refresh control) of removal of ions adsorbed on the sensitive film 60 (more specifically, the oxide semiconductor) at a relatively high temperature where ion migration is likely to occur.

[0054] In the gas sensor device 100 of the first embodiment, the control unit 90, in the first control, causes the voltage application unit 80 to apply a voltage of a first voltage value between a pair of electrodes (first electrode 71, second electrode 72), and in the second control, causes the voltage application unit to apply a voltage of a second voltage value greater than the first voltage value between the pair of electrodes (first electrode 71, second electrode 72). According to this configuration, ions can be moved more effectively during removal control (refresh control) of ions adsorbed on the sensitive film 60 (more specifically, oxide semiconductor).

[0055] <Other embodiments> The present invention is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments are also included within the technical scope of the present invention. Furthermore, the various features of the above-mentioned embodiments and the embodiments to be described later may be combined in any manner as long as they are not contradictory.

[0056] In the first embodiment, the sensitive membrane 60 is in direct contact with the first electrode 71 and the second electrode 72. However, they may be electrically connected via a mixed conductor having both electronic and oxide ion conductivity. That is, the mixed conductor may be in contact with the sensitive membrane 60 and the first electrode 71, or may be in contact with the sensitive membrane 60 and the second electrode 72. The mixed conductor conducts (permeates) electrons and ions (e.g., oxide ions). The mixed conductor may be n-type, which conducts electrons, or p-type, which conducts holes. For example, when the oxide semiconductor contained in the mixture is n-type, the mixed conductor is preferably n-type, and when the oxide semiconductor contained in the mixture is p-type, the mixed conductor is preferably p-type.

[0057] In the first embodiment, gold (Au), platinum (Pt), and titanium (Ti) are exemplified as materials for the first electrode 71 and the second electrode 72, but materials with high catalytic activity such as palladium (Pd), ruthenium (Ru), rhodium (Rh), and iridium (Ir) may also be used. Furthermore, although a two-layer structure of titanium (Ti) and platinum (Pt) is exemplified as the first electrode 71 and the second electrode 72, a two-layer structure of tantalum (Ta) and platinum (Pt) may also be used, and a noble metal or a transition metal such as iron (Fe) may also be used instead of platinum (Pt).

[0058] In the first embodiment, the sensitive film 60 may contain a sensitizer, which is, for example, a noble metal such as platinum (Pt), gold (Au), or palladium (Pd).

[0059] In the first embodiment, the heat generating portion 40 and the electrode portion 50 are formed on the insulating layer 33 and the insulating layer 35, respectively, but they may also be formed on an insulating film such as a silicon oxide (SiO2) film or an alumina (Al2O3) film.

[0060] In the first embodiment, the solid electrolyte body may be any material that does not change resistance, such as GDC (gadolinium-doped ceria) or SDC (samarium-doped ceria).

[0061] It should be noted that the embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is not limited to the embodiments disclosed herein, but is intended to include all modifications within the scope indicated by the claims or the scope equivalent to the claims. [Explanation of symbols]

[0062] 10: Gas sensor 20: PCB 21: Space part 22: Opening 31, 32, 33, 34, 35: Insulating layer 37: Resist film 40: Heat generating part 50: Electrode section 60: Sensitive membrane 70: Electrode pair 70A: Metal film 71: 1st electrode 72: 2nd electrode 80: Voltage application section 81: Power supply 82: Switch 90: Control section 92: Resistance detection section 100: Gas sensor device

Claims

1. At least one electrode pair having a pair of electrodes spaced apart from each other; a sensitive membrane electrically connecting the pair of electrodes; a heat generating unit that heats the sensitive film; A gas sensor comprising: the sensitive film contains a mixture of an oxide semiconductor and a solid electrolyte having an activation temperature higher than that of the oxide semiconductor, The electrode and the mixture are in direct contact with each other or are electrically connected to each other via a mixed conductor having electronic conductivity and ionic conductivity. Gas sensor.

2. a volume ratio of the oxide semiconductor to the solid electrolyte in the mixture of 3:7 to 7:3; 2. The gas sensor according to claim 1.

3. The gas sensor according to claim 1 or 2; a voltage application unit that applies a voltage between the pair of electrodes; a control unit that controls a heating operation of the heat generating unit and a voltage application operation of the voltage application unit, The control unit a first control that heats the sensitive film by the heating unit to a first temperature at which electrons or holes are conducted in the oxide semiconductor, applies a voltage between the pair of electrodes by the voltage application unit, and detects the concentration of the target gas based on a current flowing between the pair of electrodes or a resistance value between the pair of electrodes; and a second control is performed in which the heat generating unit heats the sensitive membrane to a second temperature that is higher than the first temperature and at which ions are conducted in the solid electrolyte body, and the voltage applying unit applies a voltage between the pair of electrodes. Gas sensor device.

4. The control unit In the first control, the voltage application unit applies a voltage of a first voltage value between the pair of electrodes, In the second control, the voltage application unit applies a second voltage greater than the first voltage value between the pair of electrodes.

4. The gas sensor device according to claim 3.

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