Gas concentration measurement device and method of measuring analyte gas concentration in sample gas

Abstract

A gas concentration measurement device 10 comprises a heat-generating resistor 31; a stage 21 supporting the heat-generating resistor 31; a peripheral edge section 24 that is separated from the stage 21 in plan view and surrounds the stage 21; and at least two bridges 22 that extend from a peripheral edge of the stage 21 and are linked to the peripheral edge section 24. The heat-generating resistor 31 overlaps the stage 21 in plan view. The peripheral edge section 24 has a bottom section 41 facing the stage 21 at a lower section thereof. The gas concentration measurement device 10 has a space P demarcated by an upper surface 41a of the bottom section 41 and a lower surface 21b of the stage 21. The peripheral edge section 24 and the stage 21 each have a high thermal insulation section at a location further upward than the heat-generating resistor 31. The gas concentration measurement device 10 measures an analyte gas concentration in a sample gas on the basis of a resistance value of the heat-generating resistor 31.

Description

Gas concentration measuring device and method for measuring the concentration of a target gas in a measured gas

[0001] The present invention relates to a gas concentration measuring device used for measuring the concentration of a target gas in a gas under measurement, and also to a method for measuring the concentration of a target gas in a gas under measurement.

[0002] Various devices for measuring the gas concentration in a measurement gas have been known. One such device is a thermal conduction gas sensor. In a thermal conduction gas sensor, heat from a heating resistor is conducted to the measurement gas, and the gas concentration in the measurement gas is measured by utilizing the heat lost from the heating resistor.

[0003] For example, Patent Document 1 describes a combustible gas detection device equipped with a thermal conduction type gas detection unit.

[0004] Japanese Patent Application Laid-Open No. 2005-156364

[0005] As exemplified by Patent Document 1, various gas sensors have been proposed up to now. However, when starting a gas concentration measurement, these gas sensors sometimes require a long time for the temperature of the gas sensor and the measurement gas present around it to reach a constant value, and this poses a problem in terms of the stability of the gas concentration measurement value at the start of the measurement.

[0006] Therefore, an object of the present invention is to provide a gas concentration measurement device that can improve the stability of gas concentration measurement values ​​at the start of gas concentration measurement.

[0007] The present invention provides a gas concentration measurement device comprising: a heating resistor that generates heat when current is passed through it; a stage that supports the heating resistor; a peripheral portion that is spaced from the stage and surrounds the stage in a planar view; and at least two bridges that extend from the peripheral portion of the stage and are connected to the peripheral portion, wherein the heating resistor overlaps the stage in a planar view; the peripheral portion has a bottom portion below the peripheral portion that faces the stage; the gas concentration measurement device has a space defined by the upper surface of the bottom portion and the lower surface of the stage; the peripheral portion and the stage each have a highly insulating portion located above the heating resistor; and the gas concentration measurement device measures the concentration of a target gas in a measured gas based on the resistance value of the heating resistor.

[0008] The present invention also provides a gas concentration measurement device comprising: a heating resistor that generates heat when current is passed through it; a stage that supports the heating resistor; and a peripheral portion that surrounds the stage in a planar view, wherein the heating resistor overlaps the stage in a planar view, and when the volume of the space in the gas concentration measurement device located above the stage is V1 and the volume of the space located below the stage is V2, the ratio V2 / V1 of V2 to V1 is 0.10 or more and 10 or less, and the gas concentration measurement device measures the concentration of a target gas in a measured gas based on the resistance value of the heating resistor.

[0009] The present invention also provides a gas concentration measurement device comprising: a heating resistor that generates heat when current is passed through it; a stage that supports the heating resistor; a peripheral portion that is spaced from the stage and surrounds the stage in a planar view; and at least two bridges that extend from the peripheral portion of the stage and are connected to the peripheral portion, wherein the heating resistor overlaps the stage in a planar view; and the peripheral portion has a bottom portion facing the stage at a lower part of the peripheral portion and a top surface portion facing the stage at an upper part of the peripheral portion, wherein when the volume of the space located above the stage in the gas concentration measurement device is V1 and the volume of the space located below the stage is V2, the ratio V2 / V1 of V2 to V1 is 0.10 or more and 10 or less, and the gas concentration measurement device measures the concentration of a target gas in a measurement gas based on the resistance value of the heating resistor.

[0010] FIG. 1 is a perspective view schematically showing a preferred embodiment of a gas concentration measurement device of the present invention. FIG. 2 is a plan view of the gas concentration measurement device shown in FIG. 1 as viewed from above. FIG. 3 is a cross-sectional view of the gas concentration measurement device shown in FIG. 1 taken along line III-III. FIG. 4 is a perspective view schematically showing another embodiment of a gas concentration measurement device of the present invention, corresponding to FIG. 1. FIG. 5 is a plan view of the gas concentration measurement device shown in FIG. 4 taken from above, corresponding to FIG. 2. FIG. 6 is a cross-sectional view of the gas concentration measurement device shown in FIG. 4 taken along line VI-VI, corresponding to FIG. 3. FIG. 7 is a perspective view schematically showing yet another embodiment of a gas concentration measurement device of the present invention, corresponding to FIG. 1. FIG. 8 is a plan view of the gas concentration measurement device shown in FIG. 7 taken along line VIII-VIII, viewed from above. FIG. 9 is a cross-sectional view of the gas concentration measurement device shown in FIG. 7 taken along line IX-IX, corresponding to FIG. 3. FIG. 10 is a cross-sectional view of the gas concentration measurement device shown in FIG. 7 taken along line X-X. FIG. 11 is a perspective view schematically showing a preferred method for manufacturing the gas concentration measurement device shown in FIG. 1. FIG. 12 is a perspective view schematically showing a preferred method for manufacturing the gas concentration measurement device shown in FIG. 4, and is a view corresponding to FIG. 11. FIG. 13 is a perspective view schematically showing a preferred method for manufacturing the gas concentration measurement device shown in FIG. 7, and is a view corresponding to FIG. 11. FIG. 14 is a perspective view schematically showing another embodiment of the gas concentration measurement device of the present invention, and is a view corresponding to FIG. 1. FIG. 15 is a plan view of the gas concentration measurement device shown in FIG. 14 as seen from above, and is a view corresponding to FIG. 2. FIG. 16 is a cross-sectional view of the gas concentration measurement device shown in FIG. 14 taken along line XVI-XVI, and is a view corresponding to FIG. 3.

[0011] The present invention will now be described based on preferred embodiments with reference to the drawings. FIGS. 1 to 3 show a preferred embodiment of a gas concentration measurement device according to the present invention. A gas concentration measurement device 10 (hereinafter also referred to as "device 10") according to this embodiment includes a stage 21 and at least two bridges 22 extending from the periphery of the stage 21. The stage 21 and bridges 22 form a bridge structure 20. In the device 10 shown in FIG. 1, the bridge structure 20 includes the stage 21, which is a rectangular plate-like body in plan view, and four bridges 22 extending from each of the four corners of the stage 21. The bridges 22 extend in one direction. The device 10 also includes a peripheral portion 24 spaced from and surrounding the stage 21, and the bridges 22 are connected to the peripheral portion 24. The shape of the stage 21 in plan view is not limited to a rectangular shape.

[0012] In a plan view, the peripheral portion 24 has a hollow rectangular shape defined by a first rectangular portion 26 having four sides and forming an outer contour, and a second rectangular portion 27 having four sides and forming an inner contour. The stage 21 described above is located inside the second rectangular portion 27. The sides of the second rectangular portion 27 in the peripheral portion 24 are non-parallel and non-orthogonal to the sides of the stage 21. Specifically, the stage 21 is disposed inside the second rectangular portion 27 such that the corners of the stage 21 face the sides of the second rectangular portion 27. Each bridge 22 extends from a corner of the stage 21 along the extension of the diagonal of the stage 21. Each bridge 22 extends from a corner of the stage 21 and bends 90 degrees midway, changing its extension direction. The bridge 22 is connected to a wall surface of the peripheral portion 24 located on an extension line of the bending direction, i.e., the second rectangular portion 27 described above.

[0013] As shown in Fig. 3, the stage 21 has a multi-layer structure. Specifically, the stage 21 has a two-layer structure consisting of a first insulating layer 121 and a fourth insulating layer 124 disposed on the first insulating layer 121. However, the layer structure of the stage 21 is not limited to this, and the stage 21 may have, for example, a single-layer structure, a three-layer structure, or a four-layer structure. Note that in Fig. 2, the fourth insulating layer 124 and a second adhesion layer 34 (described later) are omitted from the illustration in order to clearly show the position and shape of the heating resistor 31 (described later).

[0014] As shown in FIG. 3 , the device 10 has a bottom 41 facing the stage 21 below the peripheral edge 24. The bottom 41 forms the lower surface of the device 10 and prevents gas from flowing in and out from the lower surface side of the device 10. In order to more reliably prevent gas from flowing in and out from the lower surface side of the device 10, it is preferable that the bottom 41 does not have any air holes that could serve as a passageway for gas. The device 10 has a space P defined by the upper surface 41 a of the bottom 41 and the lower surface 21 b of the stage 21. The shape of the space P in a cross section taken along the thickness direction of the device 10 may be rectangular, trapezoidal, or dome-shaped.

[0015] The device 10 includes a heating resistor 31 that generates heat when energized. The heating resistor 31 is supported by the stage 21 and overlaps the stage 21 in a plan view. More specifically, in the embodiment shown in FIGS. 1 to 3 , the stage 21 includes the heating resistor 31 within its thickness direction. In this embodiment, the heating resistor 31 is disposed on the first insulating layer 121, and a fourth insulating layer 124 is disposed above and to the sides of the heating resistor 31. The heating resistor 31 is thus surrounded by the first insulating layer 121 and the fourth insulating layer 124, preventing contact with the surrounding gas, thereby improving the durability of the heating resistor 31. The heating resistor 31 extends from the stage 21 to the peripheral edge 24 via the bridge 22 and is connected to two wire bonding pads 32 (hereinafter simply referred to as "pads 32") disposed on the peripheral edge 24. The heating resistor 31 has a shape that extends in one direction on the bridge 22, similar to the bridge 22.

[0016] The heating resistor 31 preferably comprises one or more filaments, and more preferably comprises a series of filaments. In this specification, the term "series of filaments" refers to a single filament or a plurality of filaments having at least both ends in common.

[0017] The heating resistor 31 shown in Figure 2 is composed of a single wire. This wire extends in the stage 21, meandering repeatedly in one direction and then the opposite direction without crossing itself. This shape of the wire can increase the resistance of the heating resistor 31. This allows gas concentration to be measured with lower power consumption.

[0018] An example of an embodiment in which the heating resistor 31 is made up of a plurality of filaments having at least both ends in common is an embodiment (not shown) in which the filaments are arranged so as not to intersect with each other in the stage 21, and the portions of the filaments arranged in the bridges 22 are common (overlapping with each other).

[0019] From the viewpoint of sufficiently increasing the physical strength of the heating resistor 31 and sufficiently increasing the resistance value of the heating resistor 31 to reduce the power consumption of the device 10, the thickness of the heating resistor 31 is preferably 0.01 μm to 100 μm, more preferably 0.02 μm to 75 μm, and even more preferably 0.05 μm to 50 μm. The thicknesses of the heating resistor and the first and second adhesion layers 33 and 34 described below can be measured using a stylus profilometer, an electron microscope, or an optical three-dimensional measuring device.

[0020] When the heating resistor 31 is energized to generate heat, after a predetermined time has passed, the amount of heat generated and the amount of heat absorbed by the surrounding measured gas balance out, and the temperature reaches a steady state. The temperature of the heating resistor 31 at this time depends on the thermal conductivity (heat absorption) of the measured gas. Since the thermal conductivity of the measured gas varies depending on the composition of the gas, the temperature of the heating resistor in the steady state changes depending on the composition of the measured gas. Therefore, the gas concentration in the measured gas can be measured based on the resistance value of the heating resistor 31 at this time.

[0021] As a result of investigations by the present inventors, it was found that by setting the heat capacity of the heating resistor 31 and its surroundings to a predetermined value or less, the amount of temperature change of the heating resistor 31 in response to changes in the concentration of the target gas to be detected can be sufficiently increased, thereby improving the measurement accuracy and measurement sensitivity of the target gas concentration in the measurement gas. In detail, the total heat capacity of the heating resistor 31 and the stage 21 is 8.3×10 －６ J / K or less, and 3.9 × 10 －６ J / K or less is more preferable, and 9.4×10 －７ From the viewpoint of reducing power consumption, the total heat capacity of the heating resistor 31 and the stage 21 is preferably 9.0×10 －１０ J / K or more, and 1.8×10 －９ J / K or more is more preferable, and 3.7×10 －９ 1 to 3 has a bridge structure 20 consisting of a stage 21 containing a heating resistor 31 therein and a bridge 22. By employing a device 10 having such a structure as the gas concentration measurement device of the present invention, the heat capacity of the portion overlapping with the heating resistor 31 in a plan view can be easily controlled to within the above-mentioned range.

[0022] From the viewpoint of controlling the heat capacity of the portion overlapping with the heating resistor 31 in a plan view within the above-mentioned range and from the viewpoint of ensuring sufficient mechanical strength, the area S of the stage 21 in a plan view is set to 3.6×10 ７ μm ２ Preferably, it is 9.0 x 10 or less. ６ μm ２ More preferably, it is 4.0 × 10 or less. ６ μm ２ More preferably, it is 1.0 × 10 or less. ６ μm ２ From the viewpoint of increasing the efficiency of heat transfer with the gas to be measured, S is particularly preferably 1.0×10 ２ μm ２ It is preferable that the ratio is 2.0×10 or more. ２More preferably, it is 4.0 × 10 or more. ２ μm ２ More preferably, it is 1.0 × 10 or more. ３ μm ２ More preferably, it is 1.0 x 10 or more. ４ μm ２ More preferably, it is 1.0 x 10 or more. ５ μm ２ More preferably, it is equal to or greater than this.

[0023] From a similar viewpoint, when the stage 21 is rectangular, the length of one side of the stage 21 is preferably 10 μm or more and 3000 μm or less, more preferably 12.5 μm or more and 2000 μm or less, and even more preferably 20 μm or more and 1000 μm or less, provided that S is within the above-mentioned range.

[0024] In order to ensure a sufficient amount of heat absorption by the gas to be measured and improve the measurement accuracy and sensitivity of the concentration of the gas to be detected, when the total volume of the heating resistor 31 and the stage 21 is V, S / V is set to 0.02 μm －１ It is preferable that the thickness is 0.04 μm or more. －１ More preferably, it is 0.05 μm or more. －１ From the viewpoint of reducing power consumption, S / V is more preferably 10 μm or more. －１ Preferably, it is 7.0 μm or less. －１ More preferably, it is 5.0 μm or less. －１ It is more preferable that:

[0025] As described above, the device 10 has a bottom 41, which prevents gas from flowing in or out from below the device 10, so that the gas (measurement gas) present in the space P located below the stage 21 is less likely to lose heat to gas present outside the device. Therefore, when the device 10 starts measuring the concentration of the target gas, the measurement gas present in the space P is quickly heated. This improves the stability of the gas concentration measurement value at the start of gas concentration measurement in the device 10.

[0026] From the viewpoint of making the above-mentioned effect even more remarkable, it is preferable that the peripheral portion 24 and the stage 21 each have a highly insulating portion located above the heating resistor 31. By providing the highly insulating portion at a position above the stage 21, the heat generated by energizing the heating resistor 31 is less likely to be conducted above the stage 21, so that the measurement gas present in the space P located below the stage 21 is heated more quickly. From the viewpoint described above, the highly insulating portion has a thermal resistance value of 2.0×10 －１２ m ２ K / W or more, and 3.3×10 －１２ m ２ K / W or more is more preferable, and 2.0×10 －１１ m ２ The thermal resistance value can be calculated by dividing the thickness of the highly insulating portion by the thermal conductivity, which will be described later.

[0027] From the same viewpoint, the thermal conductivity of the highly insulating portion is preferably 500 W / (m K) or less, more preferably 300 W / (m K) or less, and even more preferably 50 W / (m K) or less. In this specification, the thermal conductivity can be measured by a method specified by JIS, ASTM, or ISO depending on the material and structure of the object.

[0028] To achieve the thermal conductivity of the highly insulating portion within the above range, for example, the highly insulating portion may be made of a material having the above thermal conductivity, such as ceramics such as silicon dioxide, zirconium oxide, and titanium oxide, or resins such as epoxy resin, acrylic resin, and fluororesin.

[0029] To ensure the above-described effects obtained by providing the high-insulation section, the thickness of the high-insulation section is preferably 0.1 μm or more, more preferably 1 μm or more, and even more preferably 2 μm or more. Furthermore, to adjust the stress generated in the device 10 during manufacturing, the thickness of the high-insulation section is preferably 10 μm or less, more preferably 7.5 μm or less, and even more preferably 5 μm or less.

[0030] In device 10, fourth insulating layer 124 is the high thermal insulation portion. Alternatively, fourth insulating layer 124 may have a multilayer structure made up of multiple layers, some or all of which may be high thermal insulation layers.

[0031] From the viewpoint of quickly heating the measurement gas present in the space P, it is preferable that the first insulating layer 121, which is an insulating layer located below the heating resistor 31, does not have excessively high heat insulation. More specifically, the thermal resistance value of the first insulating layer 121 is 500 m ２ It is preferable that the resistance is 300 m ２ It is more preferable that the value is 50 m ２ It is more preferable that the value is equal to or less than K / W.

[0032] From the same viewpoint, the volume of the space (space P) defined by the upper surface 41 a of the bottom portion 41, the lower surface 21 b of the stage 21 and its imaginary extension surface, and the peripheral portion 24 is 1.6×10 １０ μm ３ Preferably, it is 7.2 × 10 or less. ９ μm ３ More preferably, it is 1.8×10 or less. ９ μm ３ Furthermore, from the viewpoint of reliably forming the space P in an etching step (a step of forming the bridge structure 20) when manufacturing the device 10 by the manufacturing method described later, the volume is preferably 1.0×10 ５ μm ３ It is preferable that the ratio is 3.3×10 or more. ５ μm ３ More preferably, it is 8.0 × 10 or more. ５ μm ３ More preferably, it is equal to or greater than this.

[0033] From the viewpoint of further improving the measurement accuracy and sensitivity of the concentration of the gas to be detected, it is preferable that the resistance value of the heating resistor 31 has a high temperature dependency. ｔis preferably 100 ppm / °C or more, more preferably 500 ppm / °C or more, and even more preferably 1000 ppm / °C or more. ｔ Examples of materials having a resistance to light of 100 ppm / °C or higher include platinum, tungsten, copper, gold, silver, molybdenum, aluminum, and tantalum, as well as alloys thereof. Examples of alloys containing platinum include Pt—Nb, Pt—Rh, and Pt—W. Another example is a cermet made of a platinum group element (platinum, palladium, rhodium, ruthenium, iridium, and osmium) and / or an alloy containing these elements and a metal oxide. Therefore, it is preferable that the heating resistor 31 contains one or more materials selected from the group consisting of these materials. Among these, from the viewpoint of stability in high-temperature environments, it is particularly preferable that the heating resistor 31 contains platinum or an alloy containing platinum.

[0034] From the viewpoint of enhancing the adhesion between the heating resistor 31 and the first insulating layer 121 and the fourth insulating layer 124 and improving the durability of the device 10, it is preferable that a first adhesion layer 33 and a second adhesion layer 34 are disposed in positions that contact the lower and upper surfaces of the heating resistor 31, respectively. When the first adhesion layer 33 and the second adhesion layer 34 are disposed in positions that contact the lower and upper surfaces of the heating resistor 31, the first adhesion layer 33 and the second adhesion layer 34 may also be disposed in positions that contact the lower and upper surfaces of the pad 32. However, if the second adhesion layer 34 is made of a non-conductive material, it is preferable that the second adhesion layer 34 is not disposed on the upper surface of the pad 32. From the viewpoint of sufficiently enhancing the adhesion between the heating resistor 31 and the first insulating layer 121 and the fourth insulating layer 124, the thicknesses of the first adhesion layer 33 and the second adhesion layer 34 are each independently preferably 1 nm or more and 200 nm or less, more preferably 2 nm or more and 150 nm or less, and even more preferably 10 nm or more and 100 nm or less.

[0035] 1 and 3, a portion of the fourth insulating layer 124 disposed on the pad 32 is removed, resulting in the second adhesive layer 34 (or the pad 32 in an embodiment in which the second adhesive layer is not present) being exposed to the outside.

[0036] The peripheral portion 24 preferably includes a substrate 11 and a plurality of insulating layers formed above and below the substrate 11. Specifically, as shown in FIG. 3 , a first insulating layer 121 and a fourth insulating layer 124 are disposed in this order above the substrate 11. A fifth insulating layer 125 is disposed below the substrate 11. However, the layer structure of the peripheral portion 24 is not limited to this. For example, the peripheral portion 24 may include a first insulating layer 121, a second insulating layer (not shown), a third insulating layer (not shown), and a fourth insulating layer 124 disposed in this order above the substrate 11. A fifth insulating layer 125 and a sixth insulating layer (not shown) may be disposed in this order below the substrate.

[0037] The device 10 may or may not have an insulating layer (fifth insulating layer 125) located below the substrate. The presence or absence of the fifth insulating layer 125 allows adjustment of the stress applied to the substrate 11. In the device 10 shown in FIGS. 1 to 3 , the upper surface of the peripheral portion 24 (the surface on the fourth insulating layer 124 side) has a substantially flat shape except for the positions of the pads 32. The lower surface of the peripheral portion 24 (the surface on the fifth insulating layer 125 side) also has a substantially flat shape.

[0038] Next, the materials of each layer described above will be described. Silicon (Si), glass, polyimide resin, etc. can be used as the material of the substrate 11. Among them, it is preferable that the substrate 11 contains silicon (Si). The multiple insulating layers formed on the top and bottom of the substrate 11 preferably contain a silicon (Si) compound from the viewpoints of ease of acquisition, ease of formation, and chemical stability, and silicon dioxide (SiO ２ ) or silicon nitride (SiN ｘ , x is a number of 0.100 or more and 1.667 or less.) ２ It is more preferred that the composition contains:

[0039] From the viewpoint of enhancing adhesion to the third insulating layer 123 and the fourth insulating layer 124, the first adhesion layer 33 and the second adhesion layer 34 preferably contain one or more selected from tantalum (Ta), titanium (Ti), titanium nitride, titanium oxide, titanium oxynitride, tantalum oxide, zirconium, zirconium oxide, yttrium, yttrium oxide, tungsten, tungsten oxide, chromium, chromium oxide, nickel, nickel oxide, and alloys thereof.

[0040] The material of the heating resistor 31 is as already described. The material of the pad 32 can be the same as that of the heating resistor 31. The heating resistor 31 and the pad 32 may be made of different materials or the same material. From the viewpoint of enabling simple manufacturing and reducing manufacturing costs, it is preferable that the heating resistor 31 and the pad 32 be made of the same material.

[0041] Next, a method for measuring the concentration of a target gas in a measurement gas using the device 10 shown in FIGS. 1 to 3 will be described. When measuring the concentration of a target gas in a measurement gas using the device 10, current is applied to the heating resistor 31 to cause it to heat up. The conditions for applying current are not particularly limited, as long as a good linear relationship is established between the concentration of the target gas in the measurement gas and the resistance value of the heating resistor. For example, current application can be performed under constant power conditions, i.e., conditions under which the amount of heat generated by the heating resistor 31 due to current application remains constant even when the concentration of the target gas in the measurement gas changes. Alternatively, current application can be performed under constant voltage conditions, i.e., conditions under which the voltage applied to the heating resistor 31 remains constant even when the concentration of the target gas in the measurement gas changes, or under constant current conditions, i.e., conditions under which the current flowing through the heating resistor 31 remains constant even when the concentration of the target gas in the measurement gas changes. The term "constant power" used here does not require that the power be strictly constant during measurement of the target gas concentration. For example, if the change in power during measurement is 1% or less, more preferably 0.5% or less, the concentration of the target gas can be measured with sufficient accuracy. Therefore, even if a change in power of this magnitude occurs during measurement of the concentration of the target gas, the measurement is considered to have been performed under constant power conditions. This also applies to the "constant voltage" and "constant current" conditions mentioned above.

[0042] Regardless of the conditions under which electricity is applied, the resistance value of the heating resistor 31 changes depending on the temperature of the heating resistor 31, and the concentration of the target gas to be detected can be measured based on that resistance value.

[0043] From the viewpoint of promoting heat absorption by the heating resistor 31 by the measurement gas and further improving the measurement accuracy of the concentration of the target gas, it is preferable to sufficiently increase the temperature of the heating resistor 31 by passing current through it during measurement of the concentration of the target gas. Specifically, when measuring the concentration of the target gas in the measurement gas, it is preferable to pass current through the heating resistor 31 so that the temperature difference between the heating resistor 31 and the measurement gas is preferably 30°C or more, more preferably 60°C or more, and even more preferably 100°C or more. Furthermore, from the viewpoint of suppressing thermal degradation of the heating resistor 31, the temperature difference between the heating resistor 31 and the measurement gas is preferably 800°C or less, more preferably 750°C or less, and even more preferably 700°C or less.

[0044] Examples of target gases in the measurement gas include oxygen gas, nitrogen gas, argon gas, water vapor, hydrogen gas, and carbon dioxide gas. Among these, oxygen gas, water vapor, and carbon dioxide gas are particularly preferred. However, when the target gas is oxygen gas, the temperature change of the heating resistor 31 due to changes in oxygen gas concentration is small due to the relatively low thermal conductivity of oxygen gas. This has led to a problem in conventional thermal conduction gas sensors, which tend to have low accuracy in measuring oxygen gas concentrations. Furthermore, when measuring a target gas containing oxygen gas and nitrogen gas, such as air, the thermal conductivities of oxygen gas and nitrogen gas are similar, making it particularly difficult to measure the oxygen gas concentration with conventional thermal conduction gas sensors. In contrast, as described above, the device 10 sufficiently increases the temperature change of the heating resistor 31 in response to changes in the target gas concentration, allowing the concentration to be measured with high accuracy even when the target gas is oxygen gas. Furthermore, the device 10 allows the oxygen gas concentration to be measured with high accuracy even when the target gas contains oxygen gas and nitrogen gas. In order to make the most of the advantages of the device 10 described above, the total content of oxygen gas and nitrogen gas in the gas to be measured is preferably 0.00001 vol.% or more, more preferably 0.0001 vol.% or more, and even more preferably 0.001 vol.% or more.

[0045] As described above, device 10 can measure the concentration of a target gas in a measurement gas with high accuracy even when it only includes heating resistor 31 as a component sensitive to the target gas. Device 10 can thus be constructed from a relatively small number of components, allowing for easier manufacturing. In this specification, the term "target gas-sensitive component" refers to a component whose properties change in response to the target gas concentration in the measurement gas. When energized, heating resistor 31 changes its resistance value in response to the target gas concentration in the measurement gas, making it a target gas-sensitive component. Another example of a target gas-sensitive component is an electrode unit consisting of a positive electrode, a negative electrode, and an electrolyte disposed between them, where the current flowing through the electrode unit changes in response to the target gas concentration in the measurement gas. Other examples of oxygen-sensitive components include semiconductors such as tin oxide and zinc oxide, and piezoelectric materials such as barium titanate, zirconium titanate, and zinc oxide.

[0046] Next, a gas concentration measurement device 100 (hereinafter also referred to as "device 100") shown in Figures 4 to 6, which is another embodiment of the present invention, will be described. Regarding this embodiment, only differences from the above-described embodiment will be described, and the detailed description of the above-described embodiment will be applied as appropriate to points not specifically described. In Figures 4 to 6, the same components as those in Figures 1 to 3 are designated by the same reference numerals.

[0047] As shown in Figure 6, device 100 does not have a bottom, and the lower part of the device is open to the outside. Furthermore, device 100 has an extension portion 42 above peripheral edge portion 24. As shown in Figures 4 and 5, extension portion 42 has a hollow rectangular shape defined by a third rectangular portion 43 having four sides and forming an outer contour in a plan view, and a fourth rectangular portion 44 having four sides and forming an inner contour. In a plan view, third rectangular portion 43 of extension portion 42 is located inward of first rectangular portion 26 of peripheral edge portion 24. Furthermore, fourth rectangular portion 44 of extension portion 42 coincides with second rectangular portion 27 of peripheral edge portion 24 in a plan view.

[0048] In the device 100, the insulating layers above and below the heating resistor 31 do not necessarily have high thermal insulation properties. In this case, when the heating resistor 31 generates heat due to electrical current, the heat diffuses both above and below the heating resistor 31. If this thermal diffusion causes a difference in temperature between the space A1 located above the stage 21 and the space A2 located below the stage 21, the stability of the measured value of the concentration of the target gas at the start of measurement may be reduced. To prevent this problem from occurring, in the device 100, the volume V1 of the space A1 located above the stage 21 and the volume V2 of the space A2 located below the stage 21 are approximately equal. As a result, the heat capacities of the measurement gas present in the space A1 and the space A2 are approximately equal, making it difficult for a temperature difference to occur between the space A1 and the space A2.

[0049] From the viewpoint of reliably obtaining the above-described effects, the ratio V2 / V1 of the volume V2 of the space A2 to the volume V1 of the space A1 is preferably 0.10 or more and 10.0 or less, more preferably 0.2 or more and 5.0 or less, even more preferably 0.5 or more and 2.0 or less, still more preferably 0.8 or more and 1.25 or less, still more preferably 0.90 or more and 1.1 or less, particularly preferably 0.95 or more and 1.05 or less, and ideally 1.

[0050] 6 , the space A1 is defined by the upper surface 21a of the stage 21, the imaginary extension surface 21c of the upper surface 21a, the extension portion 42, and the imaginary extension surface 42a of the upper surface of the extension portion 42. The space A2 is defined by the lower surface 21b of the stage 21, the imaginary extension surface 21d of the lower surface 21b, the peripheral edge portion 24, and the imaginary extension surface 24b of the lower surface of the peripheral edge portion 24.

[0051] When the thickness of the stage 21 is sufficiently small compared to the thickness of the device 10, V2 / V1 being within the above-mentioned numerical range is equivalent to the ratio V4 / V3 of the volume V3 of the space above the heating resistor 31 to the volume V4 of the space below the heating resistor 31 being within the above-mentioned numerical range of V2 / V1.

[0052] The device 100 has a second insulating layer 122 and a third insulating layer 123 between a first insulating layer 121 and a fourth insulating layer 124. The device 100 also has a sixth insulating layer 126 below a fifth insulating layer 125. The second insulating layer 122 and the sixth insulating layer 126 can be made of, for example, SiNx (where x is a number between 0.100 and 1.667). The third insulating layer 123 can be made of the same material as the first insulating layer 121, for example, SiO ２ The material of the extension 42 can be the same as that of the first insulating layer 121, for example, SiO ２ Alternatively, the extending portion 42 may be made of a resin such as an epoxy resin, an acrylic resin, or a fluororesin.

[0053] Next, a gas concentration measurement device 300 (hereinafter also referred to as "device 300") shown in Figures 14 to 16, which is another embodiment of the present invention, will be described. With regard to this embodiment, only the differences from device 100 shown in Figures 4 to 6 will be described, and the above description of device 100 will apply as appropriate to points not specifically described. In Figures 14 to 16, the same components as in Figures 4 to 6 are assigned the same reference numerals.

[0054] 4 to 6, the device 300 of this embodiment is different from the device 100 shown in FIGS. 4 to 6 in that the first insulating layer 121, the second insulating layer 122, and the third insulating layer 123 are disposed over the entire area in the planar direction of the device 300 (FIG. 16). The fourth insulating layer 124 is also disposed over the entire area in the planar direction of the device 300 except for the portion where the pad 32 is located. Due to this structure, the device 300 of this embodiment does not have the bridge 22 and bridge structure 20 of the device 100 (FIGS. 14 and 15).

[0055] That is, the device 300 has a stage 21 provided with a first insulating layer 121, a second insulating layer 122, a third insulating layer 123, and a fourth insulating layer 124, a peripheral portion 24 surrounding the stage 21, and a heating resistor 31, with the stage 21 and the heating resistor 31 overlapping in a plan view. The stage 21 is rectangular, and the length of one side is preferably 100 μm or more and 4500 μm or less, more preferably 150 μm or more and 3000 μm or less, and even more preferably 200 μm or more and 1500 μm or less. However, the shape of the stage 21 is not limited to a rectangle.

[0056] 16 , in the device 300, the stage 21 is connected to the peripheral portion 24 along the entire periphery thereof. The peripheral portion 24 includes the substrate 11, the fifth insulating layer 125, and the sixth insulating layer 126, and is therefore thicker than the stage 21 that does not include these layers. A portion of the peripheral portion 24 (more specifically, the substrate 11, the fifth insulating layer 125, and the sixth insulating layer 126) extends outward from the lower surface 21b of the stage 21.

[0057] 16 , in this embodiment, the space A1 located above the stage 21 is a space defined by the upper surface 21 a of the stage 21, the extension 42, and an imaginary extension surface 42 a of the upper surface of the extension 42. The space A2 located below the stage 21 is a space defined by the lower surface 21 b of the stage 21, the peripheral edge 24, and an imaginary extension surface 24 b of the lower surface of the peripheral edge 24.

[0058] 14 to 16 , the stage 21 is connected to the peripheral portion 24 along the entire periphery thereof. Alternatively, the stage 21 may have a portion of the periphery that is not connected to the peripheral portion 24. That is, the device 300 may have a connection portion where the periphery of the stage 21 is connected to the peripheral portion, and may also have a separation portion where the peripheral portion 24 is separated from the stage 21. The separation portion allows the measurement gas to move between the upper and lower sides of the stage 21, stabilizing heat exchange between the measurement gas and the heating resistor 31.

[0059] Next, a gas concentration measurement device 200 (hereinafter also referred to as "device 200") shown in Figures 7 to 10 will be described as yet another embodiment of the present invention. Regarding this embodiment, only differences from the device 10 described above will be described, and the detailed description of the previous embodiment will be applied as appropriate to points not specifically described. In Figures 7 to 10, the same components as those in Figures 1 to 3 are designated by the same reference numerals.

[0060] As shown in FIGS. 7 to 10 , the peripheral portion 24 has a top surface 51 at its upper portion. The top surface 51 has a hollowed-out portion at its lower portion, and is U-shaped in cross-sections along the thickness direction of the device 200 ( FIGS. 9 and 10 ). The top surface 51 has a substantially flat upper surface 51a and a lower surface 51b extending perpendicular to the thickness direction. The top surface 51 restricts the flow of gas (measurement gas) present inside the device 200 into and out of the device 200. To allow the measurement gas to flow into the device 200, the top surface 51 has at least one air hole 53 ( FIGS. 7 and 8 ). This air hole 53 may be located on the side or the top of the top surface 51. In FIG. 8, the fourth insulating layer 124 and the second adhesive layer 34 described later are omitted from the illustration in order to clearly show the position and shape of the heating resistor 31 described later.

[0061] 9 and 10 , a bonding layer 54 is disposed on the fourth insulating layer 124, and the top surface 51 is disposed on the bonding layer 54. The bonding layer 54 is provided to bond the fourth insulating layer 124 and the top surface 51 with high strength. However, the device 200 does not need to have the bonding layer 54 as long as the bonding strength between the fourth insulating layer 124 and the top surface 51 can be ensured.

[0062] In the device 200, the insulating layers above and below the heating resistor 31 do not necessarily have high thermal insulation properties. In this case, when the heating resistor 31 generates heat due to electrical current, the heat diffuses both above and below the heating resistor 31. If this thermal diffusion causes a difference in temperature between the space A1 located above the stage 21 and the space A2 located below the stage 21, the stability of the measured value of the concentration of the target gas at the start of measurement may be reduced. To prevent this problem from occurring, in the device 200, the volume V1 of the space A1 located above the stage 21 and the volume V2 of the space A2 located below the stage 21 are approximately equal. As a result, the heat capacities of the measurement gas present in the space A1 and the space A2 are approximately equal, making it difficult for a temperature difference to occur between the space A1 and the space A2. Furthermore, unlike the device 100, the device 200 has a bottom 41 and a top surface 51. This restricts the flow of the gas under measurement, which makes it easier to stabilize the temperature inside the device 200. This makes it possible to further improve the stability of the gas concentration measurement value at the start of gas concentration measurement.

[0063] From the viewpoint of reliably obtaining the above-described effects, the ratio V2 / V1 of the volume V2 of the space A2 to the volume V1 of the space A1 is preferably 0.10 or more and 10.0 or less, more preferably 0.2 or more and 5.0 or less, even more preferably 0.5 or more and 2.0 or less, still more preferably 0.8 or more and 1.25 or less, still more preferably 0.90 or more and 1.1 or less, particularly preferably 0.95 or more and 1.05 or less, and ideally 1.

[0064] 9 and 10 , the space A1 is defined by the upper surface 21 a of the stage 21, an imaginary extension surface 21 c of the upper surface 21 a, and the top surface 51. The space A2 is defined by the lower surface 21 b of the stage 21, an imaginary extension surface 21 d of the lower surface 21 b, and the bottom 41.

[0065] The material of the bonding layer 54 may be any material that can bond the fourth insulating layer 124 and the top surface portion 51. For example, Al２ O ３ , LiNbO ３ , LiTaO ３ , Gd ３ Ga ５ O １２ The top surface 51 may be made of, for example, silicon (Si). Alternatively, the top surface 51 may be made of a resin such as epoxy resin, acrylic resin, or fluororesin.

[0066] Next, a preferred method for producing the gas concentration measuring device of the present invention will be described.

[0067] <Method of Manufacturing Device 10> First, a method of manufacturing the device 10 shown in Figures 1 to 3 will be described. Figures 11(a) to 11(d) show a preferred manufacturing procedure for the device 10 shown in Figures 1 to 3. This manufacturing method includes the following steps in this order: 1. A step of forming an insulating layer on the substrate 11; 2. A step of forming a heating resistor 31 on the insulating layer; 3. A step of forming a fourth insulating layer 124 on the sides and above the heating resistor 31; and 4. A step of forming a bridge structure 20.

[0068] 1. Step of forming an insulating layer on the substrate 11 First, the substrate 11 is thermally oxidized by heating it to 700° C. or higher and 1400° C. or lower in an atmosphere containing oxygen or water vapor, and SiO ２ 11(a)), a first insulating layer 121 and a fifth insulating layer 125 are formed (FIG. 11(a)). Note that the first insulating layer 121 and the fifth insulating layer 125 are omitted from the illustration in FIGS. 11(a) to 11(d).

[0069] 2. Step of Forming the Heating Resistor 31 on the Insulating Layer Prior to forming the heating resistor 31, a first adhesive layer 33 is formed as needed. The first adhesive layer 33 can be formed by patterning using a lift-off method. Specifically, a photoresist layer (not shown) is first provided over the entire first insulating layer 121, and then exposed and developed to form a patterned mask (not shown) having a shape complementary to the shape of the first adhesive layer 33. Next, with the first insulating layer 121 covered with the mask, the first adhesive layer 33 is formed by a thin-film forming method. Examples of thin-film forming methods that can be used include physical vapor deposition (PVD) methods such as evaporation, sputtering, and ion plating, as well as chemical vapor deposition (CVD). However, from the perspective of mass productivity, sputtering is particularly preferred. Finally, the photoresist layer is removed to obtain the first adhesive layer 33 having the desired shape.

[0070] Next, the heating resistor 31 is formed ( FIG. 11( b) ). In this manufacturing method, the heating resistor 31 and the pad 32 are formed simultaneously to simplify the manufacturing process. When forming the heating resistor 31 and the pad 32, it is preferable to first form the heating resistor 31 and the pad 32 over the entire surface of the substrate 11 using any of the thin-film formation methods described above, and then perform patterning. From the viewpoint of mass productivity, it is particularly preferable to use a sputtering method as the thin-film formation method. As the patterning method, it is particularly preferable to use a milling method from the viewpoint of suppressing burrs that occur at the end of the heating resistor 31. Alternatively, a lift-off method can be used instead of the milling method. The method for forming the heating resistor 31 when using the lift-off method is the same as the method for forming the first adhesion layer 33, and therefore a description thereof will be omitted here.

[0071] After forming the heating resistor 31, a second adhesive layer 34 is formed as needed. The second adhesive layer 34 can be formed by the same method as the first adhesive layer 33. Note that the first adhesive layer 33 and the second adhesive layer 34 are not shown in FIG. 4(b).

[0072] 3. Step of forming the fourth insulating layer 124 on the sides and above the heating resistor 31 After forming the heating resistor 31 and, if necessary, the first adhesive layer 33 and the second adhesive layer 34, the fourth insulating layer 124 is formed. The fourth insulating layer 124 is formed on the entire surface of the substrate 11 (FIG. 11(c)). The above-mentioned thin film forming means can be used to form the fourth insulating layer 124. Among them, SiO ２ When forming the fourth insulating layer 124 made of the above, it is preferable to use the PECVD method from the viewpoint of the ability to adjust residual stress and from the viewpoint of mass productivity. By the above steps, a structure 40 including each insulating layer and the heating resistor 31 can be obtained.

[0073] 4. Step of forming bridge structure 20 In this step, the first insulating layer 121 and the fourth insulating layer 124, which are insulating layers located above the substrate 11, and unnecessary portions of the substrate 11 are removed to obtain device 10 ( FIG. 11( d) ). In this step, in parallel with the removal of the unnecessary portions, a portion of the fourth insulating layer 124 formed on pad 32 can be removed to expose pad 32 to the outside.

[0074] The unnecessary portions can be removed by etching methods such as dry etching and wet etching. Dry etching can be reactive ion etching (RIE) using fluorocarbon or halogen gas. Wet etching can be isotropic etching using hydrofluoric acid, nitric acid, sulfuric acid, phosphoric acid, or the like, or anisotropic etching using an alkaline solution such as KOH (potassium hydroxide), TMAH (tetramethylammonium hydroxide), or EDP (ethylenediamine pyrocatechol). Among these, RIE is preferably used to remove the unnecessary portions from the viewpoint of preventing etching of the structure 40.

[0075] <Method of Manufacturing Device 100> Next, a preferred method of manufacturing the device 100 will be described with reference to Figures 12(a) to 12(e). Regarding this manufacturing method, differences from the manufacturing method of the device 10 described above will be described, and for points not specifically described, the detailed explanation of the manufacturing method of the device 10 applies as appropriate. This manufacturing method has the following steps in this order: 1. Step of forming an insulating layer on the substrate 11 2. Step of forming a heating resistor 31 on the insulating layer 3. Step of forming a fourth insulating layer 124 on the sides and above the heating resistor 31 4. Step of forming a bridge structure 20 5. Step of forming an extension 42

[0076] 1. Step of Forming Insulating Layers on Substrate 11 After forming a first insulating layer 121 and a fifth insulating layer 125 on the top and bottom of substrate 11 by thermal oxidation, a second insulating layer 122 and a sixth insulating layer 126 made of SiNx are formed on the surfaces of first insulating layer 121 and fifth insulating layer 125 using the thin film formation method described above. Among these, from the viewpoints of the ability to adjust residual stress and mass productivity, it is preferable to form second insulating layer 122 and sixth insulating layer 126 using PECVD (plasma enhanced chemical vapor deposition) or LP-CVD (low pressure chemical vapor deposition). Note that the first insulating layer 121, second insulating layer 122, third insulating layer 123, fifth insulating layer 125, and sixth insulating layer 126 are not shown in Figures 12(a) to 12(d).

[0077] Next, the third insulating layer 123 is formed on the second insulating layer 122 (FIG. 4A). The third insulating layer 123 is formed on the entire surface of the substrate 11. The above-mentioned thin film forming means can be used to form the third insulating layer 123. Among them, SiO ２ When forming the third insulating layer 123 made of the above, it is preferable to use the PECVD method from the viewpoint of the ability to adjust the residual stress and from the viewpoint of mass productivity.

[0078] 2. Step of forming the heating resistor 31 on the insulating layer This step can be carried out in the same manner as in the manufacturing method of the device 10 (FIG. 12(b)).

[0079] 3. Step of forming the fourth insulating layer 124 on the sides and above the heating resistor 31 This step can be carried out in the same manner as in the manufacturing method of the device 10 (FIG. 12(c)).

[0080] 4. Step of Forming Bridge Structure 20 First, unnecessary portions of the first insulating layer 121, second insulating layer 122, third insulating layer 123, and fourth insulating layer 124, which are insulating layers located above the substrate 11, are removed ( FIG. 12( d) ). As described in the description of the manufacturing method of device 10, in parallel with the removal of the unnecessary portions, portions of the fourth insulating layer 124 formed on the pads 32 can be removed to expose the pads 32 to the outside. Note that by only removing portions of the fourth insulating layer 124 formed on the pads 32 in this step (i.e., not forming the bridge structure 20), it is possible to manufacture device 300 instead of device 100.

[0081] Next, unnecessary portions of the fifth insulating layer 125 and the sixth insulating layer 126, which are insulating layers located below the substrate 11, are removed, and then unnecessary portions of the substrate 11 are removed. The unnecessary portions here refer to portions that do not overlap with the peripheral edge portion 24 in a plan view.

[0082] The method for removing the unnecessary portions can be the same as the method for removing the insulating layer located above the substrate 11. In particular, RIE can be preferably used as a method for removing the unnecessary portions in the insulating layer located below the substrate 11. Also, SF ６ (sulfur hexafluoride) etching process and C ４ F ８ Deep reactive ion etching (DRIE) followed by an alternating passivation process using fluoroalkane gases such as (octafluorocyclobutane) can be preferably used.

[0083] 5. Step of Forming the Extension Portion 42 Finally, the extension portion 42 is formed ( FIG. 12( e) ). First, an extension portion insulating layer (not shown) is formed on the entire surface of the fourth insulating layer 124, for example, in the same manner as the fourth insulating layer 124. Next, unnecessary portions are removed from the extension portion insulating layer using the etching method described above, thereby forming the extension portion 42. Alternatively, the extension portion 42 can be formed by previously preparing a resin molded product having the desired shape of the extension portion 42 and adhering this to the upper surface of the stage 21 with an adhesive.

[0084] Although the method of forming the fourth insulating layer 124 and the extension portion 42 as separate layers has been described above, it is also possible to form the fourth insulating layer 124 and the extension portion 42 as the same layer instead. In this case, in the step "3. Step of forming the fourth insulating layer 124 on the sides and above the heating resistor 31," the fourth insulating layer 124 and the extension portion insulating layer may be formed simultaneously as a single layer, and then the extension portion 42 may be formed by the etching method described above.

[0085] <Method for Manufacturing Device 200> Next, a preferred method for manufacturing the device 200 will be described with reference to Figures 13(a) to 13(f). This manufacturing method includes the following steps in this order: 1. A step of forming an insulating layer on the substrate 11; 2. A step of forming a heating resistor 31 on the insulating layer; 3. A step of forming a fourth insulating layer 124 and a bonding layer 54 on the sides and above the heating resistor 31; 4. A step of forming a bridge structure 20; and 5. A step of forming a top surface portion 51 on the fourth insulating layer 124.

[0086] Of the above steps, the step of forming an insulating layer on the substrate 11 and the step of forming the heating resistor 31 on the insulating layer can be carried out in the same manner as the manufacturing method of the device 10 described above (FIGS. 13(a) and 13(b)).

[0087] 3. Step of forming the fourth insulating layer 124 and the bonding layer 54 on the sides and above the heating resistor 31 First, the fourth insulating layer 124 is formed on the sides and above the heating resistor 31 by the same method as in the device 10. Next, the bonding layer 54 is formed on the fourth insulating layer 124 ( FIG. 13( c) ). When the bonding layer 54 is a metal oxide, it can be formed by the thin film formation method described above, similar to the fourth insulating layer 124.

[0088] 4. Step of forming bridge structure 20 The bridge structure 20 can be formed in the same manner as the manufacturing method of the device 10 described above, but in addition to removing unnecessary portions of the insulating layers (first insulating layer 121 and fourth insulating layer 124) located above the substrate 11, unnecessary portions of the bonding layer 54 are also removed ( FIG. 13( d) ).

[0089] 5. Step of forming the top surface portion 51 on the fourth insulating layer 124 First, the top surface portion 51 to be laminated on the bonding layer 54 is prepared. For example, a Si substrate can be etched to obtain the top surface portion 51 having the desired shape. Next, the top surface portion 51 is laminated on the bonding layer 54, and the top surface portion 51 and the bonding layer 54 are bonded together ( FIG. 13( e) ). The bonding between the top surface portion 51 and the bonding layer 54 can be performed using, for example, a surface activated bonding method or a fusion bonding method. After the top surface portion 51 and the bonding layer 54 are bonded together, air holes 53 are formed by etching, and the device 200 is obtained ( FIG. 13( f) ).

[0090] When manufacturing the device 200 without the bonding layer 54, for example, the following procedure can be used. First, the device 10 without the bonding layer 54 is manufactured by the procedure shown in Figures 11(a) to 11(d). Separately, a resin molded product having the desired shape of the top surface 51 is prepared. The top surface 51 is formed by adhering this resin molded product onto the fourth insulating layer 124 using an adhesive, and the device 200 can be obtained.

[0091] According to the present invention, a gas concentration measurement device is provided that can improve the stability of gas concentration measurements at the start of gas concentration measurement.

Claims

1. A gas concentration measurement device comprising: a heating resistor that generates heat when current is passed through it; a stage that supports the heating resistor; a peripheral portion that is spaced from and surrounds the stage in a planar view; and at least two bridges that extend from the peripheral portion of the stage and are connected to the peripheral portion, wherein the heating resistor overlaps the stage in a planar view; the peripheral portion has a bottom portion below the peripheral portion that faces the stage; the gas concentration measurement device has a space defined by the upper surface of the bottom portion and the lower surface of the stage; the peripheral portion and the stage each have a highly insulating portion located above the heating resistor; and the gas concentration measurement device measures the concentration of a target gas in a measurement gas based on the resistance value of the heating resistor.

2. A gas concentration measurement device comprising: a heating resistor that generates heat when current is applied; a stage that supports the heating resistor; and a peripheral portion that surrounds the stage in a planar view, wherein the heating resistor overlaps the stage in a planar view, and when the volume of the space in the gas concentration measurement device located above the stage is V1 and the volume of the space located below the stage is V2, the ratio V2 / V1 of V2 to V1 is 0.10 or more and 10 or less, and the gas concentration measurement device measures the concentration of a target gas in a measurement gas based on the resistance value of the heating resistor.

3. A gas concentration measurement device as described in claim 2, wherein the peripheral portion is spaced from the stage in a plan view, and further comprising at least two bridges extending from the peripheral portion of the stage and connected to the peripheral portion.

4. The gas concentration measurement device according to claim 2, wherein the stage is connected to the periphery over the entire periphery of the stage.

5. A gas concentration measurement device as described in claim 2, wherein the gas concentration measurement device has a connection portion where the periphery of the stage and the periphery portion are connected, and the gas concentration measurement device has a separation portion where the periphery portion and the stage are separated.

6. A gas concentration measurement device comprising: a heating resistor that generates heat when current is applied; a stage that supports the heating resistor; a peripheral edge that is spaced from and surrounds the stage in a plan view; and at least two bridges that extend from the peripheral edge of the stage and are connected to the peripheral edge, wherein the heating resistor overlaps the stage in a plan view; and the peripheral edge has a bottom that faces the stage at a lower part of the peripheral edge and a top surface that faces the stage at an upper part of the peripheral edge, wherein, when the volume of a space located above the stage in the gas concentration measurement device is V1 and the volume of a space located below the stage is V2, the ratio V2 / V1 of V2 to V1 is 0.10 or more and 10 or less, and the gas concentration measurement device measures the concentration of a target gas in a measurement gas based on the resistance value of the heating resistor.

7. A method for measuring the concentration of a target gas in a measurement gas using the gas concentration measuring device according to any one of claims 1 to 6.

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