Gas concentration measuring device and method for measuring concentration of gas to be detected in gas to be measured

Abstract

This gas concentration measuring device includes: a heating resistor that generates heat by energization; and a stage that supports the heating resistor. The heating resistor overlaps the stage in plan view. An area S of the stage in plan view is 3.6×107 μm2 or less. When a total volume of the heating resistor and the stage is V, S / V is from 0.0010 μm-1 to 0010 μm-1. The gas concentration measuring device measures, on the basis of a resistance value of the heating resistor, the concentration of a gas to be detected in a gas to be measured.

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 measurement gas, and also to a method for measuring the concentration of a target gas in a measurement gas.

[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, but these gas sensors have room for improvement in terms of ease of manufacturing.

[0006] Therefore, an object of the present invention is to provide a gas concentration measurement device that can be easily manufactured.

[0007] The present invention provides a heat generating resistor that generates heat when energized, and a stage that supports the heat generating resistor, wherein the heat generating resistor overlaps the stage in a plan view, and an area S of the stage in a plan view is 3.6×10 ７ μm ２ When the total volume of the heating resistor and the stage is V, S / V is 0.0010 μm or less. －１ 10 μm or more －１ The present invention provides a gas concentration measuring device that measures the concentration of a target gas in a measurement gas based on the resistance value of the heating resistor, as follows:

[0008] The present invention also provides a method for measuring the concentration of a target gas in a measurement gas using the gas concentration measuring device.

[0009] 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 showing the position and shape of a heating resistor in the gas concentration measurement device shown in FIG. 1. FIG. 3-1 is a cross-sectional view of the gas concentration measurement device shown in FIG. 1 taken along line III-III. FIG. 3-2 is a cross-sectional view of the gas concentration measurement device shown in FIG. 1 taken along line IV-IV. FIG. 3-3 is a cross-sectional view showing another embodiment of a gas concentration measurement device of the present invention, corresponding to FIG. 3-2. FIG. 3-4 is a cross-sectional view showing another embodiment of a gas concentration measurement device of the present invention, corresponding to FIG. 3-2. FIG. 4 is a perspective view schematically showing a preferred method for manufacturing the gas concentration measurement device shown in FIG. 1. FIG. 5 is a perspective view schematically showing another embodiment of a gas concentration measurement device of the present invention. FIG. 6 is a plan view of the stage of the gas concentration measurement device shown in FIG. 5, viewed from the back. FIG. 7 is a cross-sectional view of the gas concentration measurement device shown in FIG. 5 taken along line VII-VII. FIG. 8 is a cross-sectional view of a gas concentration measurement device of Comparative Example 1, corresponding to FIG. 7. FIG. 9 is a perspective view schematically illustrating another embodiment of a gas concentration measurement device of the present invention, and is a view equivalent to FIG. 1 . FIG. 10 is a plan view illustrating the position and shape of the heating resistor in the gas concentration measurement device shown in FIG. 9 , and is a view equivalent to FIG. 2 . FIG. 11 is a cross-sectional view of the gas concentration measurement device shown in FIG. 9 taken along line XI-XI, and is a view equivalent to FIG. 3-1 . FIG. 12 is a perspective view schematically illustrating another embodiment of a gas concentration measurement device of the present invention, and is a view equivalent to FIG. 1 . FIG. 13 is a plan view illustrating the position and shape of the heating resistor in the gas concentration measurement device shown in FIG. 12, and is a view equivalent to FIG. 2 . FIG. 14 is a cross-sectional view of the gas concentration measurement device shown in FIG. 12 taken along line XIV-XIV, and is a view equivalent to FIG. 3-1 . FIG. 15 is a graph showing the relationship between measurement time and the rate of resistance change of the heating resistor when the gas concentration measurement devices of Examples 1 to 3 are energized at a constant power of 80 mW. FIG. 16 is a graph showing the relationship between the oxygen gas concentration of the measurement gas and the resistance change rate of the heating resistor when the gas concentration measuring devices of Examples 1 to 3 are energized at a constant power of 80 mW.17 is a graph showing the relationship between measurement time and the rate of resistance change of the heating resistor when current is applied to the gas concentration measurement devices of Examples 2, 4, and 6 in a mixed gas flow of argon and nitrogen. FIG. 18 is a graph showing the relationship between measurement time and the rate of resistance change of the heating resistor when current is applied to the gas concentration measurement devices of Examples 2, 4, and 6 in a mixed gas flow of helium and nitrogen. FIG. 19 is a graph showing the relationship between measurement time and the rate of resistance change of the heating resistor when current is applied to the gas concentration measurement devices of Examples 2, 4, and 6 in a mixed gas flow of hydrogen and nitrogen. FIG. 20 is a graph showing the relationship between measurement time and the rate of resistance change of the heating resistor when current is applied to the gas concentration measurement device of Example 4 in a mixed gas atmosphere of water vapor and nitrogen. FIG. 21 is a graph showing the relationship between the argon gas concentration of the measured gas and the rate of resistance change of the heating resistor when current is applied to the gas concentration measurement devices of Examples 2, 4, and 6 in a mixed gas flow of argon and nitrogen. Fig. 22 is a graph showing the relationship between the helium gas concentration of the measurement gas and the resistance change rate of the heating resistor when current is applied to the gas concentration measurement devices of Examples 2, 4, and 6 in a mixed gas flow of helium and nitrogen. Fig. 23 is a graph showing the relationship between the hydrogen gas concentration of the measurement gas and the resistance change rate of the heating resistor when current is applied to the gas concentration measurement devices of Examples 2, 4, and 6 in a mixed gas flow of hydrogen and nitrogen. Fig. 24 is a graph showing the relationship between the relative humidity of the measurement gas and the resistance change rate of the heating resistor when current is applied to the gas concentration measurement device of Example 4 in a mixed gas atmosphere of water vapor and nitrogen.

[0010] The present invention will now be described based on preferred embodiments with reference to the drawings. FIGS. 1, 2, 3-1, and 3-2 show a preferred embodiment of a gas concentration measurement device of the present invention. A gas concentration measurement device 10 (hereinafter also referred to as "device 10") of this embodiment includes a stage 21 and one or more bridges 22 extending from the periphery of the stage 21, forming 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 a plan view, and four bridges 22 extending from the periphery of the stage 21. The bridges 22 extend from the four corners of the stage 21. The device 10 also has a peripheral portion 24 that is connected to the bridges 22 and surrounds the stage 21. Note that the shape of the stage 21 in a plan view is not limited to a rectangular shape.

[0011] As shown in FIG. 3-1 , the stage 21 has a multi-layer structure. Specifically, the stage 21 has a four-layer structure consisting of a first insulating layer 121, a second insulating layer 122 disposed on the first insulating layer 121, a third insulating layer 123 disposed on the second insulating layer 122, and a fourth insulating layer 124 disposed on the third insulating layer 123. However, the layer structure of the stage 21 is not limited to this; for example, the stage 21 may have a single-layer structure, a two-layer structure, or a three-layer structure. In the device 10 shown in FIG. 2 , the fourth insulating layer 124 and a 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).

[0012] The device 10 has a heating resistor 31 that generates heat when current is applied. 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, 2, 3-1, and 3-2, the stage 21 includes the heating resistor 31 inside in its thickness direction. In this embodiment, the heating resistor 31 is disposed on a third insulating layer 123, and a fourth insulating layer 124 is disposed above and to the side of the heating resistor 31. In this way, the heating resistor 31 is surrounded by the third insulating layer 123 and the fourth insulating layer 124, preventing contact with the surrounding gas, thereby improving the durability of the heating resistor 31.

[0013] 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 multiple filaments having at least two common ends. The series of filaments arranged inside the thickness direction of the stage 21 forms the heating resistor 31 inside the thickness direction of the stage 21. The series of filaments also extends to the two bridges 22, 22 and the peripheral portion 24, forming two wirings 312, 312. In other words, the series of filaments comprises the heating resistor 31 arranged inside the thickness direction of the stage 21 and the wiring 312 extending to the bridges 22 and the peripheral portion 24. To enable the formation of the two wirings 312, 312, it is preferable that two or more bridges 22 extend from the peripheral portion of the stage 21. Furthermore, from the viewpoint of more stably supporting the stage 21, it is preferable that three or more, and more preferably four or more, bridges 22 extend from the periphery of the stage 21. The heating resistor 31 is connected to two wires 312, 312, and is further connected via the two wires 312, 312 to two wire bonding pads 32, 32 (hereinafter simply referred to as "pads 32") arranged on the periphery 24. The wires 312 have a shape that extends in one direction on the bridges 22.

[0014] 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.

[0015] 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).

[0016] 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.

[0017] When the heating resistor 31 is made of one or more wires, the resistance value of the wiring 312 at the portion overlapping the bridge 22 in a plan view is R Ｂ and the resistance value of the heating resistor 31 is R Ｓ When this is done, R Ｂ R against Ｓ The ratio R Ｓ / R Ｂ is preferably within a predetermined numerical range. Ｓ / R Ｂ is preferably 0.01 or more, more preferably 0.1 or more, and even more preferably 1 or more. Ｓ / R ＢBy setting R to 0.01 or more, heat radiation from the wiring 312 at the portion overlapping with the bridge 22 in plan view is reduced, and therefore the accuracy and sensitivity in measuring the concentration of the gas to be detected can be improved. Ｓ / R Ｂ is preferably 10,000 or less, more preferably 1,000 or less, and even more preferably 100 or less. Ｓ / R Ｂ By setting R to 10,000 or less, the wiring 312 and the heating resistor 31 can be appropriately designed, and the device 10 can be easily formed. Ｓ / R Ｂ In order to set the value within the above-mentioned range, for example, the width or thickness of the filament on the stage 21 and the bridge 22 may be adjusted appropriately.

[0018] When the heating resistor 31 is energized to generate heat, the amount of heat generated eventually balances with the amount of heat absorbed by the surrounding measured gas, and a steady state is reached. 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.

[0019] 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 sensitivity of the target gas concentration in the measurement gas. In particular, the total heat capacity of the heating resistor 31 and the stage 21 is 3.2×10 －２ J / K or less, and 2.2 × 10 －２ J / K or less is more preferable, and 1.5×10 －２ J / K or less is more preferable, and 1.0 × 10 －３ J / K or less is more preferable, and 1.0×10 －４ It is even more preferable that the value is 4.0×10 －５From the viewpoint of reducing power consumption, the total heat capacity of the heating resistor 31 and the stage 21 is preferably 1.0×10 －１０ J / K or more, and 1.0 × 10 －９ J / K or more is more preferable, and 2.0 × 10 －９ It is more preferable that the ratio is 1.0×10 －８ J / K or more is more preferable, and 1.0 × 10 －７ It is particularly preferable that the heat capacity is J / K or more. As already explained, the device 10 shown in Figures 1, 2, 3-1 and 3-2 has a bridge structure 20 consisting of a stage 21 containing a heating resistor 31 therein and a bridge 22. By employing the device 10 having such a structure as the gas concentration measurement device of the present invention, the total heat capacity of the heating resistor 31 and the stage 21 can be easily controlled within the above-mentioned range.

[0020] From the viewpoint of controlling the total heat capacity of the heating resistor 31 and the stage 21 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 3.0 × 10 or less. ７ μm ２ More preferably, it is 2.5 × 10 or less. ７ μm ２ More preferably, it is 9.0 × 10 or less. ６ μm ２ More preferably, it is 4.0 x 10 or less. ６ μm ２ It is particularly preferable that S is 100 μm or less from the viewpoint of increasing the efficiency of heat transfer with the gas to be measured. ２ It is preferable that the thickness is 200 μm or more. ２ More preferably, it is 400 μm or more. ２ More preferably, it is 2.5×10 or more. ３ μm ２ More preferably, it is 1.5×10 or more. ４ μm ２ More preferably, it is equal to or greater than this.

[0021] 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 2500 μm or less, and even more preferably 20 μm or more and 2000 μm or less, provided that S is within the above-mentioned range.

[0022] 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 0.0010 μm －１ It is preferable that the thickness is 0.00125 μm or more. －１ More preferably, it is 0.0016 μm or more. －１ More preferably, it is 0.010 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 More preferably, it is 3.0 μm or less. －１ More preferably, it is 1.0 μm or less. －１ It is particularly preferred that:

[0023] 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. ｔ is preferably 100 ppm / °C or more, more preferably 500 ppm / °C or more, and even more preferably 1000 ppm / °C or more. ｔExamples 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.

[0024] From the viewpoint of increasing the adhesion between the heating resistor 31 and the third insulating layer 123 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. 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, it is preferable that the first adhesion layer 33 and the second adhesion layer 34 are also disposed in positions that contact the lower and upper surfaces of the wiring 312 and the pad 32. From the viewpoint of sufficiently increasing the adhesion between the heating resistor 31 and the third insulating layer 123 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.

[0025] 1 and 3A, a portion of the fourth insulating layer 124 disposed on the pad 32 is removed, resulting in the second adhesive layer 34 (or a portion of the pad 32 in an embodiment in which the second adhesive layer is not present) being exposed to the outside.

[0026] As described above, the device 10 has a peripheral portion 24 surrounding the stage 21. The peripheral portion 24 is preferably spaced apart from the stage 21, and the two are preferably connected via a bridge 22. The peripheral portion 24 preferably includes a substrate 11 and a plurality of insulating layers formed above and below the substrate 11. In detail, as shown in FIG. 3-1 , a first insulating layer 121, a second insulating layer 122, a third insulating layer 123, and a fourth insulating layer 124 are disposed in this order above the substrate 11. In addition, a fifth insulating layer 125 and a sixth insulating layer 126 are disposed in this order below the substrate 11.

[0027] The device 10 may or may not have a fifth insulating layer 125 and a sixth insulating layer 126. The presence or absence of the fifth insulating layer 125 and the sixth insulating layer 126 makes it possible to adjust the stress applied to the substrate 11. In the device 10, 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. In addition, the lower surface of the peripheral portion 24 (the surface on the sixth insulating layer 126 side) also has a substantially flat shape.

[0028] As shown in FIG. 3-2, in the device 10 of this embodiment, the stage 21 and the bridge 22 have the same thickness and are both smaller than the thickness of the peripheral edge 24. However, the relationship in thickness between the stage 21, the bridge 22, and the peripheral edge 24 is not limited to this. For example, as shown in FIG. 3-3, the stage 21, the bridge 22, and the peripheral edge 24 may all have the same thickness. Furthermore, as shown in FIG. 3-4, the bridge 22 and the peripheral edge 24 may have the same thickness, and the stage 21 may be smaller than the bridge 22 and the peripheral edge 24.

[0029] Next, the materials of each layer described above will be described. The substrate 11 preferably contains silicon (Si). The insulating layers formed above and below the substrate 11 preferably contain a silicon (Si) compound from the viewpoints of ease of availability, ease of formation, and chemical stability. ２ ) and silicon nitride (SiN ｘ, x is a number equal to or greater than 0.100 and equal to or less than 1.667. More specifically, the first insulating layer 121, the third insulating layer 123, the fourth insulating layer 124, and the fifth insulating layer 125 preferably contain SiO ２ The second insulating layer 122 and the sixth insulating layer 126 are made of SiN ｘ It is preferable that it consists of:

[0030] 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.

[0031] 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.

[0032] FIG. 5 shows a device 10 according to another embodiment of the present invention. FIG. 6 shows a plan view of the stage 21 (described in detail below) constituting the device 10 according to the embodiment shown in FIG. 5, viewed from the rear side. FIG. 7 shows a cross-sectional view of the device 10 according to the embodiment shown in FIG. 5, taken along line VII-VII. The following description of this embodiment will mainly focus on the differences from the embodiments shown in FIGS. 1, 2, 3-1, and 3-2. For points not specifically described in this embodiment, the description of the embodiments shown in FIGS. 1, 2, 3-1, and 3-2 applies as appropriate.

[0033] The device 10 of this embodiment includes a terminal block 50 and a plurality of pillar-shaped members 51 penetrating the terminal block 50 in its thickness direction. A terminal 52 for wire bonding is provided on the top surface of each pillar-shaped member 51. The device 10 also includes a stage 21 and a plurality of bridges 22 extending from the periphery of the stage 21. The stage 21 is fixed to the terminals 52 via the plurality of bridges 22. Specifically, as shown in FIG. 5 , the stage 21 and the bridges 22 (hereinafter also referred to as "first supports 35") are joined at two joints 37 on the top surface of the stage 21. As shown in FIG. 6 , the stage 21 and the bridges 22 (hereinafter also referred to as "second supports 36") are also joined at two joints 37 on the back surface of the stage 21. As shown in FIG. 5 , the bridges 22 in this embodiment have a wire shape.

[0034] As shown in FIGS. 6 and 7 , a heating resistor 31 and two pads 32 are formed on one surface of the stage 21. In other words, the stage 21 supports the heating resistor 31 and the pad 32. The aforementioned joint 37 is provided on the pad 32, and the pad 32 and the second support 36 are joined at the joint 37. If a conductor is used as the material of the second support 36, the heating resistor 31 is electrically connected to the columnar member 51 via the second support 36. Therefore, electricity can be applied to the heating resistor 31 by connecting the columnar member 51 to a power source. For this purpose, the second support 36 preferably contains, for example, platinum. In contrast, in this embodiment, the first support 35 is used solely for supporting the stage 21. Therefore, the material of the first support 35 is not limited to a conductor. In this embodiment, the heating resistor 31 is composed of a single wire, which does not extend to the bridge 22.

[0035] The stage 21 may have a single-layer structure or a multi-layer structure, but preferably has a single-layer structure from the viewpoint of easier manufacturing. Examples of materials for the stage 21 include silicon, alumina, glass, forsterite, polyimide, polyamide, polycarbonate, polyamideimide, polyacetal, polyphenylene ether, polybutylene terephthalate, fluororesin, epoxy resin, and phenolic resin.

[0036] From the viewpoint of ensuring sufficient physical strength and reducing the heat capacity of the stage 21, the thickness of the stage 21 is preferably 0.5 μm or more and 2000 μm or less, more preferably 1.0 μm or more and 1000 μm or less, and even more preferably 1.5 μm or more and 500 μm or less.

[0037] From the viewpoint of increasing the physical strength of the first support 35 and the second support 36 and suppressing heat dissipation from the heating resistor, the wire diameters of the first support 35 and the second support 36 are each independently preferably 1.0 μm or more and 100 μm or less, more preferably 5.0 μm or more and 80 μm or less, and even more preferably 10 μm or more and 50 μm or less.

[0038] The terminal block 50 is preferably made of an insulating material, and the columnar members 51 and the terminals 52 are preferably made of conductive materials. The columnar members 51 and the terminals 52 may be made of the same material or different materials.

[0039] Figures 9 to 11 show a device 10 according to yet another embodiment of the present invention. The following description of this embodiment will focus mainly on the differences from the embodiment shown in Figures 1, 2, 3-1, and 3-2. For points not specifically described in this embodiment, the descriptions of the embodiment shown in Figures 1, 2, 3-1, and 3-2 apply as appropriate. Figures 9 to 11 correspond to Figures 1, 2, and 3-1, respectively.

[0040] 1, 2, 3-1, and 3-2, the device 10 of this embodiment has a first insulating layer 121, a second insulating layer 122, and a third insulating layer 123 disposed over the entire area in the planar direction of the device 10 (FIG. 11). The fourth insulating layer 124 is also disposed over the entire area in the planar direction of the device 10 except for the area where the pad 32 is located. Due to this structure, the device 10 of this embodiment does not have a bridge 22 or a bridge structure 20 (FIGS. 9 and 10).

[0041] That is, the device 10 includes a diaphragm 23 having a first insulating layer 121, a second insulating layer 122, a third insulating layer 123, and a fourth insulating layer 124, a peripheral edge 24 surrounding the diaphragm 23, and a heating resistor 31 provided at a position somewhere in the thickness direction of the diaphragm 23. The diaphragm 23 is made of a thin film, and its thickness can be the same as the thickness of the stage 21 described above. The diaphragm 23 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 diaphragm 23 is not limited to a rectangle.

[0042] 9 and 10 , the device 10 of this embodiment has a heating resistor 31 and two wires 312, 312 connecting the heating resistor 31 and a pad 32. Each end of the heating resistor 31 is connected to each end of the two wires 312, 312, respectively, to form a single linear body as a whole. In this embodiment, if the heating resistor 31 and the wires 312, 312 are made of the same material, the portion of the linear body that is densely packed due to meandering or the like is defined as the heating resistor 31, and the portion extending outward from the heating resistor 31 is defined as the wire 312. The heating resistor 31 is located approximately in the center of the diaphragm 23.

[0043] 10 , in this embodiment, when the figure obtained by connecting the outer edges of the heating resistors 31 in a plan view of the device 10 is defined as K, the portion that overlaps with the figure K in a plan view (excluding the heating resistors 31) is defined as the stage 21 of the device 10. In FIG. 10 , the figure K is indicated by a dashed line and has a rectangular shape. Therefore, in this embodiment, the above-mentioned "area S of the stage 21 in a plan view" is synonymous with the "area of ​​the figure K." Furthermore, in this embodiment, the above-mentioned "total volume V of the heating resistors 31 and the stage 21" is synonymous with the "volume of the portion that overlaps with the figure K in a plan view."

[0044] Figures 12 to 14 show a device 10 according to yet another embodiment of the present invention. The following description of this embodiment will focus mainly on the differences from the embodiment shown in Figures 1, 2, 3-1, and 3-2. For points not specifically described in this embodiment, the descriptions of the embodiment shown in Figures 1, 2, 3-1, and 3-2 apply as appropriate. Figures 12 to 14 correspond to Figures 1, 2, and 3-1, respectively.

[0045] The device 10 of 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. The bridges 22 extend in one direction. The device 10 also has a peripheral portion 24 that is spaced apart from the stage 21 and surrounds it, and the bridges 22 are connected to the peripheral portion 24. 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 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. More specifically, the stage 21 is disposed inside the second rectangular portion 27 in a positional relationship such that each corner of the stage 21 faces each side of the second rectangular portion 27. Each bridge 22 extends from a corner of the stage 21 along the extension direction of a diagonal of the stage 21. Furthermore, each bridge 22 extends from a corner of the stage 21 and is bent 90 degrees midway, changing its extension direction, and is connected to the wall surface of the peripheral portion 24 located on the extension line of the bending direction, i.e., the above-mentioned second rectangular portion 27.

[0046] 13, the peripheral portion 24 surrounding the stage 21 has a pair of first portions 24a, 24a that extend in the same direction and face each other at a distance, and a pair of second portions 24b, 24b that extend in a direction perpendicular to the extension direction of the first portions 24a, 24a and face each other at a distance. Each end of the first portions 24a, 24a is connected to each end of the second portions 24b, 24b.

[0047] 12 to 14 , the device 10 has a portion (hereinafter also referred to as a "partition wall 25") that extends inward from the wall of the peripheral edge portion 24 toward the stage 21. The partition wall 25 is disposed in the space between adjacent bridges 22, 22 in a plan view so as to separate the bridges 22, 22. As shown in FIG. 14 , like the peripheral edge portion 24, the partition wall 25 has a first insulating layer 121, a second insulating layer 122, a third insulating layer 123, a fourth insulating layer 124, a substrate 11, a fifth insulating layer 125, and a sixth insulating layer 126 along its thickness direction, and extends from the top end to the bottom end of the device 10.

[0048] In a plan view, the partition wall 25 has a shape defined by four sides: a wall surface (second rectangular portion 27) of the peripheral portion 24; a pair of parallel protruding sides 28 extending from the wall surface toward the stage 21; and a connecting side 29 connecting the tips of the protruding sides. The pair of protruding sides 28 are perpendicular to the wall surface of the peripheral portion 24. The lengths of the pair of protruding sides 28 are different from each other. As a result, the connecting side 29 is non-parallel to the peripheral portion 24. The connecting side 29 faces one side of the stage 21, which is a quadrangle. The connecting side 29 and the opposite side of the stage 21 are parallel to each other and spaced apart. Of the pair of protruding sides 28, the longer protruding side 28a is parallel to and spaced apart from the side adjacent to the side from which the protruding side 28a protrudes, among the four sides constituting the second rectangular portion 27. On the other hand, of the pair of protruding sides 28, 28, the protruding side 28b having a shorter length is spaced apart from and parallel to the bridge 22 extending from the corner of the stage 21. Having such a shape in a plan view of the partition wall 25 is advantageous in that it allows for effective control of V', which will be described later, while ensuring an appropriate distance between the stage 21 and the bridge 22.

[0049] From the viewpoint of suppressing heat conduction from the bridge 22 to the partition wall 25, when the device 10 has the partition wall 25, the minimum distance between the bridge 22 and the partition wall 25 is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. Furthermore, from the viewpoint of reliably forming the partition wall 25 and efficiently controlling V′ (described later), when the device 10 has the partition wall 25, the minimum distance between the bridge 22 and the partition wall 25 is preferably 1500 μm or less, more preferably 400 μm or less, even more preferably 300 μm or less, and particularly preferably 200 μm or less. The “minimum distance between the bridge 22 and the partition wall 25” refers to the smallest distance between any point on the bridge 22 and any point on the partition wall 25.

[0050] From the viewpoint of suppressing heat conduction from the stage 21 to the partition wall 25, when the device 10 has the partition wall 25, the minimum distance between the stage 21 and the partition wall 25 is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. Furthermore, from the viewpoint of reliably forming the partition wall 25 and efficiently controlling V (described later), when the device 10 has the partition wall 25, the minimum distance between the stage 21 and the partition wall 25 is preferably 1500 μm or less, more preferably 400 μm or less, even more preferably 300 μm or less, and particularly preferably 200 μm or less. The "minimum distance between the stage 21 and the partition wall 25" refers to the smallest distance between any point on the stage 21 and any point on the partition wall 25.

[0051] In device 10, from the viewpoint of improving the measurement sensitivity and accuracy of the concentration of the gas to be detected, it is preferable that there be a predetermined relationship between the volume of the space within device 10 and the area of ​​device 10 in a planar view. In detail, when the total volume of space A1 located below stage 21 and space A2 between stage 21 and peripheral portion 24 in device 10 is V' and the area of ​​stage 21 in a planar view is S, the value of V' / S is 10 or more and 2.0 × 10 or less. ９By setting V' / S within this range, heat transfer from the underside of the stage 21 can be suppressed, which can improve the sensitivity and accuracy of measuring the concentration of the target gas. To make this effect even more pronounced, the value of V' / S is preferably 10 or more and 1.6 × 10 or less. ６ More preferably, it is 50 or more and 7.3 × 10 or less. ５ More preferably, it is 1.0 × 10 or less. ２ 1.8 x 10 ５ More preferably, it is 5.0 x 10 or less. ２ Above 1.0 x 10 ４ It is particularly preferred that:

[0052] 14, space A1 is a space surrounded by the stage 21, an extension P1 of the lower surface of the stage 21, the peripheral edge 24, the partition wall 25, and an extension P2 of the lower surface of the peripheral edge 24. Space A2 is a space surrounded by the stage 21, an extension P1 of the lower surface of the stage 21, the peripheral edge 24, the partition wall 25, and an extension P3 of the upper surface of the stage 21. It is preferable that all of the extension planes P1 to P3 extend horizontally.

[0053] In order to set V' / S within the above-mentioned numerical range, for example, V' may be appropriately adjusted. Adjustment of V' can be performed, for example, by appropriately setting the size of the partition wall 25. Alternatively, the distance d1 between the pair of opposing first portions 24a, 24a and the distance d2 between the pair of opposing second portions 24b, 24b may be appropriately set. In detail, d1 and d2 are each independently 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.

[0054] From the viewpoint of shortening the time required to reach a steady state where the heat generated by the heating resistor 31 and the heat absorbed by the surrounding gas to be measured are balanced, V' is set to 1.8×10 １１ It is preferable that the ratio is 1.6×10 or more. １０ μm ３It is more preferable that the value is 7.2×10 or less. ９ μm ３ More preferably, it is 1.8 × 10 or less. ９ μm ３ It is even more preferred that:

[0055] In a plan view, the minimum width of the bridge 22 is preferably 5 μm or more, more preferably 7.5 μm or more, even more preferably 10 μm or more, even more preferably 20 μm or more, and particularly preferably 30 μm or more. By setting the minimum width of the bridge 22 to 5 μm or more, the physical strength of the bridge 22 can be sufficiently ensured. The above effect can be obtained. Furthermore, the minimum width of the bridge 22 is preferably 1500 μm or less, more preferably 450 μm or less, even more preferably 300 μm or less, and even more preferably 200 μm or less. By setting the minimum width of the bridge 22 to 450 μm or less, heat conduction from the stage 21 to the bridge 22 can be further suppressed. The "minimum width of the bridge 22" refers to the width at the position where the width of the bridge 22 (the length perpendicular to the longitudinal direction of the bridge 22) is minimum in a plan view of the device 10.

[0056] The above discussion regarding V' / S, V' and the minimum width of bridge 22 also applies to embodiments without septum 25 (eg, device 10 shown in FIG. 1 and device 10 shown in FIG. 9).

[0057] From the viewpoint of improving the measurement accuracy and sensitivity of the concentration of the target gas in the measurement gas, the total heat capacity of the heating resistor 31 and the stage 21 in the device 10 shown in FIGS. 12 to 14 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 in the device 10 shown in FIGS. －１０ J / K or more, and 1.8×10－９ J / K or more is more preferable, and 3.7×10 －９ It is more preferably J / K or more.

[0058] From the viewpoint of controlling the total heat capacity of the heating resistor 31 and the stage 21 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 in the device 10 shown in FIGS. 12 to 14 is 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 More preferably, it is 4.9×10 or less. ５ μm ２ From the viewpoint of increasing the efficiency of heat transfer with the gas to be measured, it is particularly preferable that the area S of the stage 21 in a plan view in the device 10 shown in FIGS. ２ μm ２ It is preferable that the ratio is 2.0×10 or more. ２ More 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.

[0059] From the viewpoint of ensuring a sufficient amount of heat absorption by the gas to be measured and improving the measurement accuracy and sensitivity of the concentration of the gas to be detected, the above-mentioned S / V in the device 10 shown in FIGS. 12 to 14 is 0.020 μm －１ It is preferable that the thickness is 0.040 μm or more. －１ More preferably, it is 0.050 μm or more. －１From the viewpoint of reducing power consumption, the above-mentioned S / V in the device 10 shown in FIGS. －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:

[0060] Next, a method for measuring the concentration of a target gas in a measurement gas using the device 10 will be described. The measurement gas includes the target gas and a remainder consisting of other gases. The remainder may include only one type of gas, or may include two or more types of gases. When the remainder includes two or more types of gases, it is preferable that the proportion of each gas included in the remainder be constant during measurement of the target gas, from the viewpoint of improving the measurement accuracy of the target gas concentration. However, when the remainder includes two or more types of gases with similar thermal conductivities (for example, when it includes nitrogen gas and oxygen gas), the proportion of each gas component included in the remainder does not necessarily have to be constant.

[0061] 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 can be applied 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 can be applied 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" as used herein does not require that the power be strictly constant during measurement of the target gas concentration. For example, a change in power of 1% or less, more preferably 0.5% or less, during measurement can enable the target gas concentration to be measured with sufficient accuracy. Therefore, even if a power change of this magnitude occurs during measurement of the concentration of a 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.

[0062] 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.

[0063] 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.

[0064] Examples of gases to be detected in the measurement gas include, but are not limited to, oxygen gas, nitrogen gas, argon gas, helium gas, water vapor, hydrogen gas, and carbon dioxide gas. Measurement is possible if there is a difference in thermal conductivity between the target gas and other gases contained in the measurement gas. Preferred target gases are oxygen gas, argon gas, helium gas, water vapor, or carbon dioxide gas, with oxygen gas, water vapor, or carbon dioxide gas being 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 concentration. Furthermore, when measuring a 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 oxygen gas concentration with high accuracy using conventional thermal conduction gas sensors. In contrast, in the device 10, the temperature change of the heating resistor 31 in response to changes in the concentration of the target gas is sufficiently increased as described above, so that the concentration can be measured with high accuracy even when the target gas is oxygen gas. Furthermore, the device 10 can measure the oxygen gas concentration with high accuracy even when the target gas contains oxygen gas and nitrogen gas. To utilize the advantages of the device 10 described above, the total content of oxygen gas and nitrogen gas in the target gas is preferably 0.00001 vol.% or more, more preferably 0.0001 vol.% or more, and even more preferably 0.001 vol.% or more. Note that water vapor also has a thermal conductivity similar to that of oxygen gas and nitrogen gas. Therefore, the device 10 is also excellent in that it can measure humidity in a target gas (e.g., air) containing oxygen gas and / or nitrogen gas with high accuracy.

[0065] 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.

[0066] Next, a preferred method for manufacturing the gas concentration measurement device of the present invention will be described using the method for manufacturing the device 10 shown in Figures 1, 2, 3-1, and 3-2 as an example. Figures 4(a) to 4(e) show a preferred manufacturing procedure for the device 10 shown in Figures 1, 2, 3-1, and 3-2. 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.

[0067] 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 Next, a second insulating layer 122 and a sixth insulating layer 126 made of SiNx are formed on the surfaces of the first insulating layer 121 and the fifth insulating layer 125 using a thin film forming method described later.

[0068] As a thin film formation method, physical vapor deposition (PVD) methods such as evaporation, sputtering, and ion plating, and chemical vapor deposition (CVD) methods can be used. Among them, from the viewpoint of the ability to adjust residual stress and mass productivity, it is preferable to form the second insulating layer 122 and the 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, the second insulating layer 122, the third insulating layer 123, the fifth insulating layer 125, and the sixth insulating layer 126 are not shown in Figures 4(a) to 4(e).

[0069] 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.

[0070] 2. Step of Forming Heating Resistor 31 on 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 surface of the third insulating layer 123, and then exposed and developed to form a patterned mask (not shown) having a shape complementary to that of the first adhesive layer 33. Next, with the third insulating layer 123 covered with the mask, the first adhesive layer 33 is formed by a thin-film forming method. From the viewpoint of mass productivity, a sputtering method is particularly preferable as the thin-film forming method. Finally, the photoresist layer is removed to obtain the first adhesive layer 33 having the desired shape.

[0071] Next, the heating resistor 31 is formed ( FIG. 4B ). In this manufacturing method, to simplify the manufacturing process, the heating resistor 31, the wiring 312, and the pad 32 are formed simultaneously. When forming the heating resistor 31, the wiring 312, and the pad 32, it is preferable to first form the heating resistor 31, the wiring 312, 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 generated 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 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.

[0072] 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).

[0073] 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 over the entire surface of the substrate 11 ( FIG. 4( c) ). The fourth insulating layer 124 can be formed by the same method as the third insulating layer 123. Through the above steps, a structure 40 including each insulating layer and the heating resistor 31 can be obtained.

[0074] 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. 4( d) ). The unnecessary portions here refer to portions of the target device 10 ( FIG. 1 ) that do not overlap with the bridge structure 20 or the peripheral portion 24 in a planar view. In this step, in parallel with the removal of the unnecessary portions, a portion of the fourth insulating layer 124 formed on the pad 32 can be removed to expose the pad 32 to the outside. At this time, if necessary, a portion of the second adhesive layer 34 may be removed in addition to a portion of the fourth insulating layer 124.

[0075] 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.

[0076] 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 ( FIG. 4( e) ). The unnecessary portions here refer to portions that do not overlap with the peripheral edge portion 24 in a plan view.

[0077] 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 ８Deep reactive ion etching (DRIE) followed by an alternating passivation process using fluoroalkane gases such as (octafluorocyclobutane) can be preferably used.

[0078] 9 instead of the device 10 shown in Fig. 1, it is only necessary to avoid removing unnecessary portions in the "step of forming the bridge structure 20" shown in Fig. 4(d). In this case, as in Fig. 4(d), it is preferable to remove a portion of the fourth insulating layer 124 formed on the pad 32 and, if necessary, a portion of the second adhesion layer 34 to expose the pad 32 to the outside.

[0079] When manufacturing the device 10 shown in FIG. 12 instead of the device 10 shown in FIG. 1, unnecessary portions may be removed in the "process for forming the bridge structure 20" shown in FIG. 4(d) so that the partition wall 25 shown in FIG. 12 is formed.

[0080] Although the gas concentration measuring device of the present invention has been described above based on the preferred embodiment, the present invention is not limited to such an embodiment.

[0081] The above-described embodiments of the present invention encompass the following technical concepts: [1] A gas concentration measurement device comprising a heating resistor that generates heat when energized and a stage that supports the heating resistor, the heating resistor overlapping the stage in a plan view, and measuring 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 energized and a stage that supports the heating resistor; －１０ J / K or above 3.2×10 －２[1] The gas concentration measurement device according to [1], wherein the resistance of the gas to be detected is 100 kJ / K or less. [3] The gas concentration measurement device according to [1] or [2], further comprising one or more bridges extending from the periphery of the stage to form a bridge structure. [4] The gas concentration measurement device according to any one of [1] to [3], wherein the gas to be detected is oxygen gas, argon gas, helium gas, water vapor, or carbon dioxide gas. [5] The gas concentration measurement device according to any one of [1] to [4], wherein the gas to be detected is oxygen gas. [6] The gas concentration measurement device according to [3], wherein the heating resistor is made of a series of filaments, and the series of filaments is made of a single filament or a plurality of filaments having at least both ends in common, and at least two of the bridges extend from the periphery of the stage, and the series of filaments extends to each of the two bridges. [7] The area S of the stage in a plan view is 3.6×10 ７ μm ２ [8] The gas concentration measurement device according to [3] or [6], wherein when the total volume of the heating resistor and the stage is V and the area of ​​the stage in a plan view is S, S / V is 0.0010 μm or less. －１ 10 μm or more －１ [9] The gas concentration measurement device according to any one of [1] to [8], wherein the temperature coefficient of resistance αt at 25°C of the heating resistor is 100 ppm / °C or more.

[10] The gas concentration measurement device according to any one of [1] to [9], wherein the heating resistor includes platinum or an alloy containing platinum.

[11] The gas concentration measurement device according to any one of [1] to

[10] , wherein the heating resistor is the only member sensitive to the gas to be detected.

[0082]

[12] A device further comprising a peripheral edge portion spaced apart from the stage and surrounding the stage in a plan view, and at least two bridges extending from the peripheral edge of the stage and connected to the peripheral edge portion, wherein when V' is the total volume of a space located below the stage and a space between the stage and the peripheral edge portion, and S is the area of ​​the stage in a plan view, the value of V' / S is 10 μm or more and 2.0 × 10 ９

[13] The gas concentration measurement device according to any one of [1] to

[12] , wherein the heating resistor is connected to wiring extending to the bridge and the peripheral edge portion.

[14] The heating resistor is made of one or more filaments, and the resistance value R of the wiring in a portion overlapping with the bridge in a plan view is Ｂ The resistance value R of the heating resistor Ｓ R is the ratio of Ｓ / R Ｂ

[15] The gas concentration measurement device according to

[13] , wherein the value of V′ is 2.5×10 ４ μm ３ 1.8 x 10 １１ μm ３ the area S is 1.0×10 ２ μm ２ 3.6 x 10 ７ μm ２

[16] The gas concentration measurement device according to any one of

[12] to

[15] , wherein the stage is rectangular in plan view, the bridges extend from the four corners of the stage, and a partition wall is disposed in the space between adjacent bridges in plan view to separate the bridges, and the minimum distance between the bridge and the partition wall is 5 μm or more and 1500 μm or less in plan view.

[17] The gas concentration measurement device according to

[16] , wherein the minimum width of the bridge is 5 μm or more and 1500 μm or less in plan view.

[18] The gas concentration measurement device according to

[16] or

[17] , wherein the minimum distance between the stage and the partition wall is 5 μm or more and 1500 μm or less in plan view.

[19] The gas concentration measurement device according to any one of

[12] to

[15] , wherein the stage is rectangular in plan view, the bridges extend from the four corners of the stage, and a partition wall is disposed in the space between adjacent bridges in plan view to separate the bridges, and the minimum distance between the bridge and the partition wall is 5 μm or more and 1500 μm or less in plan view.

[19] The gas concentration measurement device according to any one of

[12] to

[15] , wherein the minimum width of the bridge is 5 μm or more and 1500 μm or less in plan view.

[20] The gas concentration measurement device according to ７ μm ２ When the total volume of the heating resistor and the stage is V, S / V is 0.0010 μm or less. －１ 10 μm or more －１

[20] A gas concentration measurement device according to any one of [1] to

[18] , which measures the concentration of oxygen gas in a measurement gas based on the resistance value of the heating resistor.

[21] The measurement method according to

[20] , which measures the concentration of a target gas in a measurement gas using the gas concentration measurement device according to any one of [1] to

[19] .

[22] The measurement method according to

[20] , which measures the concentration of a target gas in the measurement gas by passing current through the heating resistor, with the temperature difference between the heating resistor and the measurement gas being 30°C or more.

[23] The measurement method according to

[20] or

[21] , wherein the measurement gas contains oxygen gas and nitrogen gas.

[23] A gas concentration measurement device comprising: a heating resistor that generates heat when energized; a stage that supports the heating resistor; a peripheral edge that is spaced from the stage 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 when V' is the total volume of a space in the gas concentration measurement device that is located below the stage and a space between the stage and the peripheral edge, and S is the area of ​​the stage in a plan view, the value of V' / S is 10 μm or more and 2.0 × 10 ９

[24] A gas concentration measuring device comprising: a heating resistor that generates heat when energized; and a stage that supports the heating resistor, wherein the heating resistor overlaps with the stage in a plan view; and an area S of the stage in a plan view of 3.6×10 ７ μm ２ When the total volume of the heating resistor and the stage is V, S / V is 0.0010 μm or less. －１ 10 μm or more －１ a gas concentration measuring device for measuring a concentration of a target gas in a measurement gas based on a resistance value of the heating resistor, the device comprising:

[0083] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0084] Example 1 In this example, a device 10 shown in FIG. 1 was manufactured.

[0085] <Formation of insulating layer> A silicon substrate 11 having a crystal orientation of <100> and a thickness of 500 μm was prepared. The substrate 11 was thermally oxidized to form SiO ２ The first insulating layer 121 and the fifth insulating layer 125 were formed using the LP-CVD method. The thickness of the first insulating layer 121 and the fifth insulating layer 125 was 600 nm. ｘ The second insulating layer 122 and the sixth insulating layer 126 were formed using the PECVD method. The thickness of the second insulating layer 122 and the sixth insulating layer 126 was 200 nm. ２ A third insulating layer 123 made of the following was formed on the second insulating layer 122. The thickness of the third insulating layer 123 was 1000 nm.

[0086] <Formation of Heating Resistor 31> According to the method described above, the first adhesive layer 33, the heating resistor 31 and pad 32, and the second adhesive layer 34 were formed in this order on the third insulating layer 123 using a sputtering method. The first adhesive layer 33 and the second adhesive layer 34 were patterned using a lift-off method, and the heating resistor 31 and the pad 32 were patterned using a milling method. A target material made of platinum was used as the sputtering target material when forming the heating resistor 31 and the pad 32. A target material made of tantalum was used when forming the first adhesive layer 33 and the second adhesive layer 34. The thickness of the heating resistor 31 was 0.3 μm, and the thickness of the first adhesive layer 33 and the second adhesive layer 34 was 0.02 μm.

[0087] <Formation of fourth insulating layer 124> A SiO 2 film is formed on the third insulating layer 123 by the same method as for the third insulating layer 123. ２ The fourth insulating layer 124 was formed to a thickness of 4000 nm. The thickness of each layer was calculated based on the film formation speed and film formation time.

[0088] <Formation of bridge structure 20> Using RIE, unnecessary portions were removed from the first insulating layer 121, the second insulating layer 122, the third insulating layer 123, and the fourth insulating layer 124, which are insulating layers located above the substrate 11. Next, unnecessary portions were removed from the fifth insulating layer 125 and the sixth insulating layer 126, which are insulating layers located below the substrate 11. The unnecessary portions of the fifth insulating layer 125 and the sixth insulating layer 126 were removed by RIE, thereby obtaining a gas concentration measurement device. To remove the unnecessary portions of the substrate 11, SF ６ and an etching process using C ４ F ８ The etch was performed by DRIE followed by an alternating passivation process with .

[0089] [Example 2] In this example, the gas concentration measuring device shown in Figs. 5 to 7 was manufactured. First, a stage 21 made of silicon with a crystal orientation of <100> and a thickness of 290 µm was prepared. On one surface of this stage 21, a heating resistor 31 and a pad 32 with a thickness of 0.3 µm were formed by sputtering. As the target material for the sputtering method, a 2-inch target material made of platinum and a Y ２ O ３ A 2-inch target material consisting of ZnO and ZnO was used. The film was formed by a co-sputtering method in which power is supplied to the two targets simultaneously. The platinum was formed by a DC sputtering method, and the Y ２ O ３ The RF sputtering method was used for the heating resistor 31. The sputtering was performed using argon gas, with the flow rate of the argon gas set to 50 sccm and the pressure of the argon gas set to 4 Pa. The power was set to 90 W and 200 W, respectively, and the sputtering was performed at room temperature. ２ O ３ and 75% by volume of platinum.

[0090] Platinum paste was applied to two pads 32 and two other pads on the opposite side of the substrate, and then fired at 700°C for 1 hour in air to form joints 37. Next, a 50 μm diameter Pt wire (bridge 22) was bonded to each platinum paste by resistance welding. The other end of the Pt wire was then bonded to a terminal 52 by resistance welding, thereby fixing the stage 21 to the terminal 52 via the bridge 22, and a gas concentration measurement device was obtained.

[0091] Example 3 A gas concentration measurement device was manufactured in the same manner as in Example 2, except that a 0.26 mm thick alumina substrate was used as the stage 21, and that a 13 μm thick heating resistor 31 and pad 32 were formed on one surface of the substrate using Pt paste by screen printing.

[0092] Example 4 The device 10 shown in FIG. 1 was manufactured in the same manner as in Example 1 except that the substrate 11 had a thickness of 300 μm and the fourth insulating layer 124 had a thickness of 1000 nm.

[0093] Example 5: A substrate 11 having a thickness of 300 μm was used, the fourth insulating layer 124 had a thickness of 1000 nm, and in the <Formation of bridge structure 20>, only the fourth insulating layer 124 located above the pad 32 was removed to expose the pad 32 to the outside. No bridge structure 20 was formed. Except for the above points, the device 10 shown in FIGS. 9 to 11 was manufactured in the same manner as in Example 1, without the bridge 22.

[0094] 1 was manufactured in the same manner as in Example 4, except that the positions and sizes of the unnecessary portions to be removed in <Formation of bridge structure 20> were changed. The stage 21 and bridge 22 in the device 10 of Example 6 were similar in shape to the stage 21 and bridge 22 in the device 10 of Example 4 in plan view, and when the sizes in plan view were compared, the former were 0.3 times larger than the latter.

[0095] Comparative Example 1 A gas concentration measuring device shown in Fig. 8 was manufactured. In Example 3, after the heating resistor 31 was formed on one surface of the stage 21, an electrode 61a made of platinum and a perovskite-type La ０．６ Sr ０．４ Co ０．２ Fe ０．８ O ３－δ A cell including a solid electrolyte 62 made of lanthanum silicate and disposed between composite oxide electrodes 61b was bonded to one surface of the stage 21 using Pt paste. Next, a sealing material 63 made of glass was applied in an air atmosphere to seal the electrode 61a, which of the two electrodes 61a, 61b is located closer to the stage 21. A gas concentration measurement device was obtained in the same manner as in Example 3 except for this. The gas concentration measurement device of Comparative Example 1 can measure the oxygen concentration based on the concentration electromotive force generated between the two electrodes 61a, 61b, and the heating resistor 31 is used to heat the solid electrolyte 62.

[0096] [Evaluation] <Measurement of S, V, and Heat Capacity> In Examples 1 and 4 to 6, the thicknesses of the layers constituting the stage 21 and the heating resistor 31 were calculated from the film formation rates of the layers and the heating resistor 31 calculated in advance. In Examples 2 and 3, the thicknesses of the stage 21 and the heating resistor 31 were measured using a vernier caliper. Dimensions other than the thickness of the stage 21 and the heating resistor 31 were measured using a microscope (VHX-8000 manufactured by Keyence Corporation) or a vernier caliper. Based on the dimensions measured as described above, as well as the specific heat and density of the materials constituting each layer, the area S of the stage 21 in a plan view, and the total volume V and total heat capacity of the heating resistor 31 and the stage 21 were calculated. These results are shown in Table 1.

[0097] <Measurement of oxygen gas concentration response> The oxygen gas concentration response of the heating resistor 31 was measured when current was applied to the heating resistor. The measurement was carried out using the gas concentration measurement devices of Examples 1 to 5 under the following conditions: Current application conditions: constant power drive at atmospheric pressure with an applied voltage of 40 mW, 50 mW, 80 mW, 700 mW, or 1300 mW Gas flow rate: 100 sccm Measured gas: mixed gas of oxygen gas and nitrogen gas Room temperature (temperature of measured gas): 25°C The oxygen gas concentrations in the measured gas were as follows: 140 to 240 seconds after the start of measurement: 100 volume % 240 to 340 seconds after the start of measurement: 80 volume % 340 to 440 seconds after the start of measurement: 60 volume % 440 to 540 seconds after the start of measurement: 40 volume % 540 to 640 seconds after the start of measurement: 21 volume % 640 to 740 seconds after the start of measurement: 10 volume % 740 to 800 seconds after the start of measurement: 21 volume % The resistance change rate of the heating resistor 31 when electricity is applied to the heating resistor 31 under a constant power condition of 80 mW is shown in Figure 15. The resistance change rate is a value (ppm) based on the resistance value of the heating resistor 31 when the oxygen concentration in the measured gas is 21 volume %, and is calculated based on the following formula. In the formula, R ｘ represents the resistance value at an oxygen concentration of x volume %, and R ２１ represents the resistance value at an oxygen concentration of 21% by volume. ｘ -R ２１ ) / R ２１ x10 ６ Table 2 also shows the temperature of the heating resistor 31 and the temperature difference from room temperature (temperature of the gas to be measured) during current application under each constant power condition. The temperature of the heating resistor 31 was measured in an environment with an oxygen concentration of 21% using a radiation thermometer (FLIR T640, CLOSE-UP LENS). The emissivity was measured at 0.66 for Example 1, 0.63 for Example 2, 0.88 for Example 3 and Comparative Example 1, and 0.70 for Examples 4 and 5. In Tables 1 and 2, "-" indicates that the value was not measured.

[0098] <Calculation of Sensitivity> The resistance change rate (ppm) of the heating resistor 31 obtained in the <Measurement of Oxygen Gas Concentration Response> above was plotted against the oxygen concentration (%) of the measured gas. Next, a regression line was obtained by the least squares method, and the slope of the regression line was calculated as the sensitivity. The results are shown in Table 2. Also, Fig. 16 is a graph showing the relationship between the resistance change rate of the heating resistor 31 and the oxygen concentration when electricity is applied to the heating resistor 31 at a constant power condition of 80 mW.

[0099] <Evaluation of Response Speed> In the gas concentration measurement devices of Example 3 and Comparative Example 1, the oxygen gas concentration was changed from 60% to 90%, and the time it took for the sensor output to respond from 10% to 90% was compared as the response speed (sec). The sensor output of Example 3 is the resistance value of the heating resistor, and the sensor output of Comparative Example 1 is the electromotive force value generated between the two electrodes. The current was applied under a constant power condition of 1300 mW. The flow rate of Comparative Example 1 was 50 sccm. All other conditions were the same as those in <Measurement of Oxygen Gas Concentration Response> above. The results are shown in Table 2.

[0100] <Temperature coefficient of resistance α of heating resistor t Measurement of the rate of change in resistance (R) of the heating resistor 31 when heated to 500°C using a hot / cold stage (manufactured by INSTEC) with the resistance of the heating resistor 31 at 25°C as the reference when the oxygen concentration in the gas to be measured is 21% by volume. ５００ -R ２５ ) / R ２５ / (500-25) x 10 ６ (ppm / ℃) (wherein, R ５００ represents the resistance value at 500°C, and R ２５ The resistance value at the reference temperature of 25° C. was measured. The results are shown in Table 1.

[0101]

[0102]

[0103] As shown in Figure 13 and Table 2, the oxygen gas concentration in the measurement gas and the resistance value of the heating resistor 31 showed a good linear relationship. Therefore, it can be seen that the gas concentration measurement device of the present invention can measure the oxygen gas concentration with high accuracy even when the measurement gas contains oxygen gas and nitrogen gas, despite being easily manufactured. In contrast, the gas concentration measurement device of Comparative Example 1 had room for improvement in that its manufacturing process was complicated.

[0104] <Measurement of hydrogen gas, helium gas, argon gas, and water vapor concentration response> Using hydrogen gas, helium gas, argon gas, or water vapor as the target gas, the target gas concentration response was measured in the same manner as for oxygen gas. The measurements were performed using the gas concentration measurement devices of Examples 2, 4, and 6 under the following conditions: - Power supply conditions: Atmospheric pressure, constant power drive with an applied voltage of 30 mW - Gas flow rate: 200 sccm - Measured gas: Mixed gas of target gas and nitrogen gas - Room temperature (temperature of measured gas): 25°C The target gas concentrations in the measured gas were as follows. [When the gas to be detected is hydrogen gas] ・0 to 180 seconds after the start of measurement: 0 volume % ・180 to 360 seconds after the start of measurement: 2 volume % ・360 to 540 seconds after the start of measurement: 3 volume % ・540 to 720 seconds after the start of measurement: 4 volume % ・720 to 900 seconds after the start of measurement: 0 volume % [When the gas to be detected is helium gas or argon gas] ・0 to 180 seconds after the start of measurement: 0 volume % ・180 to 360 seconds after the start of measurement: 5 volume % ・360 to 540 seconds after the start of measurement: 10 volume % ・540 to 720 seconds after the start of measurement: 20 volume % ・720 to 900 seconds after the start of measurement: 50 volume % ・900 to 1080 seconds after the start of measurement: 100 volume % - 1080 to 1260 seconds after the start of measurement: 0 vol% [When the gas to be detected is water vapor] Instead of performing measurements under a flow of the gas to be detected, the thermo-humidistat chamber housing the gas concentration measurement device was filled with the gas to be detected at 25°C, and the relative humidity inside the thermo-humidistat chamber was then changed as follows: - 0 to 4 hours after the start of measurement: 10% RH - 4 to 7 hours after the start of measurement: 20% RH - 710 hours after the start of measurement: 40% RH - 10 to 13 hours after the start of measurement: 60% RH - 13 to 16 hours after the start of measurement: 80% RH - 16 to 19 hours after the start of measurement: 60% RH

[0105] 17 to 20 show the resistance change rate of the heating resistor 31 for each gas to be detected when current is applied to the heating resistor 31 under the above conditions. The resistance change rate is a value (ppm) based on the resistance value of the heating resistor 31 when the concentration of the gas to be detected in the measurement gas is 0% by volume (10% RH when the gas to be detected is water vapor), and is calculated using the following formula: In the formula, R ｘrepresents the resistance value at a target gas concentration of x volume % (x% RH when the target gas is water vapor), and R ０ represents the resistance value at a detection target gas concentration of 0% by volume (10% RH when the detection target gas is water vapor). Resistance change rate = (R ｘ -R ０ ) / R ０ x10 ６

[0106] <Calculation of Sensitivity> The resistance change rate (ppm) of the heating resistor 31 obtained in the above <Measurement of Hydrogen Gas, Helium Gas, Argon Gas, and Water Vapor Concentration Response> was plotted against the target gas concentration (%) in the measurement gas. Next, a regression line was obtained using the least squares method, and the slope of the regression line was calculated as the sensitivity. The calculated sensitivities are shown in Table 3. Graphs showing the relationship between the resistance change rate of the heating resistor 31 and the target gas concentration when current is applied to the heating resistor 31 under the above-mentioned conditions are shown in Figures 21 to 24 for each target gas. In Table 3, "-" indicates that the measurement was not performed.

[0107]

[0108] As shown in Table 3, it is clear that the concentration of the target gas can be measured with high sensitivity even when hydrogen gas, helium gas, argon gas, or water vapor is used as the target gas.

[0109] [Examples 7 to 16] In Examples 7 to 16, the devices 10 shown in Figures 12 to 14 were manufactured. The distances d1 and d2 (d1 = d2 in all Examples) and R Ｓ / R Ｂ The minimum width of the bridge 22, the minimum distance between the bridge 22 and the partition wall 25, S, V', and V' / S are shown in Table 4. The minimum distance between the stage 21 and the partition wall 25 is the same as the minimum distance between the bridge 22 and the partition wall 25. The devices 10 of Examples 7 and 10 to 16 did not have a partition wall 25.

[0110] <Formation of insulating layer> A substrate 11 made of silicon with a crystal orientation of <100> and a thickness of 300 μm was prepared. The substrate 11 was thermally oxidized to form SiO ２ The first insulating layer 121 and the fifth insulating layer 125 were formed using the LP-CVD method. The thickness of the first insulating layer 121 and the fifth insulating layer 125 was 600 nm. ｘ The second insulating layer 122 and the sixth insulating layer 126 were formed using the PECVD method. The thickness of the second insulating layer 122 and the sixth insulating layer 126 was 200 nm. ２ A third insulating layer 123 made of the following was formed on the second insulating layer 122. The thickness of the third insulating layer 123 was 1000 nm.

[0111] <Formation of Heating Resistor 31> According to the method described above, the first adhesive layer 33, the heating resistor 31 and pad 32, and the second adhesive layer 34 were formed in this order on the third insulating layer 123 using a sputtering method. The first adhesive layer 33 and the second adhesive layer 34 were patterned using a lift-off method, and the heating resistor 31 and the pad 32 were patterned using a milling method. When forming the heating resistor 31 and the pad 32, a target material made of platinum was used as the sputtering target material. When forming the first adhesive layer 33 and the second adhesive layer 34, sputtering was performed using a target material made of tantalum. The thickness of the heating resistor 31 was 0.20 μm, and the thickness of the first adhesive layer 33 and the second adhesive layer 34 was 0.020 μm.

[0112] <Formation of fourth insulating layer 124> A SiO 2 film is formed on the third insulating layer 123 by the same method as for the third insulating layer 123. ２ The fourth insulating layer 124 was formed to a thickness of 1000 nm. The thickness of each layer was calculated based on the film formation rate and film formation time.

[0113] <Formation of bridge structure 20> Using RIE, unnecessary portions were removed from the first insulating layer 121, the second insulating layer 122, the third insulating layer 123, and the fourth insulating layer 124, which are insulating layers located above the substrate 11. Next, unnecessary portions were removed from the fifth insulating layer 125 and the sixth insulating layer 126, which are insulating layers located below the substrate 11. The unnecessary portions of the fifth insulating layer 125 and the sixth insulating layer 126 were removed by RIE, thereby obtaining a gas concentration measurement device. To remove the unnecessary portions of the substrate 11, SF ６ and an etching process using C ４ F ８ The etch was performed by DRIE followed by an alternating passivation process with .

[0114] [Evaluation] <Measurement of oxygen gas concentration response> The oxygen gas concentration response of the heating resistor 31 was measured when current was applied to the heating resistor. The measurement was carried out under the following conditions. Current application conditions: constant power drive at atmospheric pressure with an applied voltage of 50 mW Gas flow rate: 300 sccm Measured gas: mixed gas of oxygen gas and nitrogen gas Room temperature (temperature of measured gas): 25°C The oxygen gas concentration in the measured gas was as follows: 180 to 360 seconds after the start of measurement: 100% by volume 360 ​​to 540 seconds after the start of measurement: 80% by volume 540 to 720 seconds after the start of measurement: 60% by volume 720 to 900 seconds after the start of measurement: 40% by volume 900 to 1080 seconds after the start of measurement: 21% by volume 1080 to 1260 seconds after the start of measurement: 10% by volume 1260 to 1440 seconds after the start of measurement: 21% by volume The resistance change rate is a value (ppm) based on the resistance value of the heating resistor 31 when the oxygen concentration in the gas to be measured is 21% by volume, and is calculated based on the following formula. In the formula, R ｘ represents the resistance value at an oxygen concentration of x volume %, and R ２１ represents the resistance value at an oxygen concentration of 21% by volume. ｘ -R ２１ ) / R ２１ x10 ６

[0115] <Calculation of Sensitivity> The resistance change rate (ppm) of the heating resistor 31 obtained in the above <Measurement of Oxygen Gas Concentration Response> was plotted against the oxygen concentration (%) of the measured gas. Next, a regression line was obtained by the least squares method, and the slope of the regression line was calculated as the sensitivity. The results are shown in Table 4.

[0116]

[0117] As shown in Table 4, the gas concentration measurement devices of the examples in which V' / S was within the predetermined range showed excellent measurement sensitivity. Ｓ / R Ｂ The larger the value of , the higher the sensitivity. Also, the smaller the stage area S, the higher the sensitivity tends to be.

[0118] According to the present invention, a gas concentration measurement device that can be easily manufactured is provided.

Claims

1. A heat generating resistor that generates heat when current is applied and a stage that supports the heat generating resistor, the heat generating resistor overlaps the stage in a plan view, and the area S of the stage in a plan view is 3.6×10 ７ μm ２ When the total volume of the heating resistor and the stage is V, S / V is 0.0010 μm or less. －１ 10 μm or more －１ a gas concentration measuring device for measuring a concentration of a target gas in a measurement gas based on a resistance value of the heating resistor, 2. The total heat capacity of the heating resistor and the stage is 1.0 x 10 －１０ J / K or above 3.2×10 －２ The gas concentration measurement device according to claim 1 , wherein the resistance is equal to or less than J / K.

3. The gas concentration measurement device of claim 1, further comprising one or more bridges extending from a periphery of said stage to form a bridge structure.

4. The gas concentration measuring device according to claim 1, wherein the gas to be detected is oxygen gas, argon gas, helium gas, water vapor or carbon dioxide gas.

5. The gas concentration measuring device according to claim 1, wherein the gas to be detected is oxygen gas.

6. A gas concentration measurement device as described in claim 3, wherein the heating resistor is made of a series of wires, the series of wires being made of a single wire or a plurality of wires having at least both ends in common, at least two of the bridges extend from the periphery of the stage, and the series of wires extends to each of the two bridges.

7. The temperature coefficient of resistance α of the heating resistor at 25°C ｔ The gas concentration measuring device according to claim 1 , wherein the temperature coefficient of thermal expansion is 100 ppm / ° C. or more.

8. The gas concentration measurement device according to claim 1, wherein the heating resistor comprises platinum or an alloy containing platinum.

9. A gas concentration measuring device according to claim 1, comprising only said heating resistor as a member sensitive to the gas to be detected.

10. A device further comprising a peripheral portion that is spaced apart from the stage and surrounds the stage in a plan view, and at least two bridges that extend from the peripheral portion of the stage and are connected to the peripheral portion, wherein when the total volume of the space located below the stage and the space between the stage and the peripheral portion is V', the value of V' / S is 10 μm or more and 2.0×10 ９ The gas concentration measuring device according to claim 1 , wherein the particle size is equal to or smaller than 1 μm.

11. The gas concentration measurement device according to claim 10, wherein the heating resistor is connected to wiring extending to the bridge and the peripheral portion.

12. The heating resistor is made of one or more wires, and the resistance value R of the wiring at the portion overlapping with the bridge in a plan view Ｂ The resistance value R of the heating resistor Ｓ R is the ratio of Ｓ / R Ｂ The gas concentration measurement device according to claim 11 , wherein the value of is 0.01 or more and 10,000 or less.

13. The total volume V' is 2.5 x 10 ４ μm ３ That's 1.8 x 10 １１ μm ３ The area S is 1.0×10 ２ μm ２ The gas concentration measuring device according to claim 10 .

14. A gas concentration measurement device as described in claim 10, wherein the stage is rectangular in a planar view, the bridges extend from each of the four corners of the stage, a partition wall is disposed in the space between adjacent bridges in a planar view to separate the bridges, and the minimum distance between the bridge and the partition wall in a planar view is 5 μm or more and 1500 μm or less.

15. The gas concentration measurement device according to claim 14, wherein the minimum width of the bridge in a plan view is 5 μm or more and 1500 μm or less.

16. The gas concentration measuring device according to claim 14, wherein the minimum distance between the stage and the partition wall in a plan view is 5 μm or more and 1500 μm or less.

17. 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 16.

18. The measurement method according to claim 17, wherein the concentration of the target gas in the measured gas is measured in a state where a temperature difference between the heating resistor and the measured gas is set to 30° C. or more by passing a current through the heating resistor.

19. The measurement method according to claim 17, wherein the gas to be measured contains oxygen gas and nitrogen gas.

20. A gas concentration measurement device comprising: a heating resistor that generates heat when electricity is applied; a stage that supports the heating resistor; a peripheral portion that is spaced from the stage in a plan view and surrounds the stage; 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 plan view; and when V' is the total volume of a space in the gas concentration measurement device that is located below the stage and a space between the stage and the peripheral portion, and S is the area of ​​the stage in a plan view, the value of V' / S is 10 μm or more and 2.0×10 ９ a resistance value of the heating resistor being equal to or less than 1 μm, and measuring a concentration of a target gas in a measurement gas based on the resistance value of the heating resistor.

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