Gas concentration measurement device and method for measurement of concentration of target gas in gas to be measured

Abstract

To provide an oxygen gas concentration measurement device that can be easily manufactured.SOLUTION: An oxygen gas concentration measurement device 10 has a heat element 31 that generates heat when electrically energized, and a stage 21 that supports the heat element 31. The heat element 31 is aligned with the stage 21 in a planar view. The oxygen gas concentration measurement device 10 measures the oxygen gas concentration in gas to be measured based on the resistance value of the heat element 31. It is preferable that the total heat capacity of the heat element 31 and the stage 21 is 1×10-10 J / K or more and 3.2×10-2 J / K or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a gas concentration measurement device used for measuring the concentration of a gas to be detected in a gas to be measured. The present invention also relates to a method for measuring the concentration of a gas to be detected in a gas to be measured.

Background Art

[0002] Conventionally, various devices for measuring the gas concentration in a gas to be measured are known. One such device is a thermal conductivity gas sensor. In a thermal conductivity gas sensor, heat from a heating resistor is conducted to the gas to be measured, and the gas concentration in the gas to be measured is measured by utilizing the heat lost from the heating resistor.

[0003] For example, Patent Document 1 describes a combustible gas detection device including a thermal conductivity gas detection unit.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] As exemplified in Patent Document 1, various gas sensors have been proposed so far, but these gas sensors have room for improvement in terms of manufacturing simplicity.

[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 has a heating resistor that generates heat by energization and a stage that supports the heating resistor, the heating resistor overlaps the stage in a plan view, and provides a gas concentration measurement device that measures the concentration of a gas to be detected in a gas to be measured based on the resistance value of the heating resistor.

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

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described with reference to the drawings based on its preferred embodiments. Figures 1 to 3 show a preferred embodiment of the gas concentration measurement device of the present invention. The gas concentration measurement device 10 (hereinafter also referred to as "device 10") of this embodiment includes a stage 21 and one or a plurality of bridges 22 extending from the periphery of the stage 21, forming a bridge structure 20. In the device 10 shown in Figure 1, the bridge structure 20 has a stage 21 in the form of a rectangular plate in 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 connected to the bridges 22 and surrounding the stage 21. Note that the shape of the stage 21 in plan view is not limited to a rectangle.

[0011] As shown in Figure 3, the stage 21 has a multilayer structure. Specifically, the stage 21 has a four-layer structure composed 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, and for example, the stage 21 may have a single-layer structure, a two-layer structure, or a three-layer structure. In addition, in the device 10 shown in Figure 2, the illustration of the fourth insulating layer 124 and the second adhesion layer 34 described later is omitted in order to clearly show the position and shape of the heating resistor 31 described later.

[0012] Device 10 has a heating resistor 31 that generates heat when energized. The heating resistor 31 is supported by the stage 21 and overlaps the stage 21 in plan view. More specifically, in the embodiment shown in FIGS. 1 to 3, the stage 21 includes the heating resistor 31 inside in its thickness direction. In the present embodiment, the heating resistor 31 is disposed on the third insulating layer 123, and the fourth insulating layer 124 is disposed above and laterally thereof. In this way, since the heating resistor 31 is surrounded by the third insulating layer 123 and the fourth insulating layer 124 and contact with the surrounding gas is prevented, the durability of the heating resistor 31 can be improved.

[0013] The heating resistor 31 preferably consists of a series of linear bodies. In this specification, the "series of linear bodies" refers to a single linear body or a plurality of linear bodies at least both ends of which are common. The series of linear bodies disposed in the stage 21 form the heating resistor 31 in the stage 21. The series of linear bodies also extend to the two bridges 22, 22 and the peripheral portion 24 and form the two wirings 312, 312. That is, the series of linear bodies consists of the heating resistor 31 disposed in the stage 21 and the wirings 312 extending to the bridges 22 and the peripheral portion 24. In order to form such two wirings 312, 312, it is preferable that two or more bridges 22 extend from the periphery of the stage 21. Further, from the viewpoint of supporting the stage 21 more stably, it is preferable that three or more, more preferably four or more bridges 22 extend from the periphery of the stage 21. The heating resistor 31 is connected to two wire bonding pads 32, 32 (hereinafter also simply referred to as "pad 32") disposed on the peripheral portion 24 via the two wirings 312, 312.

[0014] The heating resistor 31 shown in Fig. 2 is composed of a single strip. This strip extends in a repeated serpentine pattern in one direction and the opposite direction without crossing within the stage 21. By having such a shape, the resistance value of the heating resistor 31 can be increased. As a result, it becomes possible to measure the gas concentration with lower power consumption.

[0015] As an example of an embodiment in which the heating resistor 31 is composed of a plurality of strips with at least both ends being common, an embodiment (not shown) can be cited in which the plurality of strips are arranged so as not to intersect each other within the stage 21, and the portions arranged in the bridge 22 of the plurality of strips are common (overlap 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 or more and 100 μm or less, more preferably 0.02 μm or more and 75 μm or less, and even more preferably 0.05 μm or more and 50 μm or less. The thicknesses of the heating resistor and the first adhesion layer 33 and the second adhesion layer 34 described later can be measured by a stylus profilometer, an electron microscope, or an optical three-dimensional measuring instrument.

[0017] When an electric current is passed through the heating resistor 31 to generate heat, after a predetermined time has elapsed, the amount of heat generated and the amount of heat absorbed by the surrounding gas to be measured balance out and reach a steady state. The temperature of the heating resistor 31 at this time depends on the thermal conductivity (heat absorption property) of the gas to be measured. Since the thermal conductivity of the gas to be measured changes depending on the composition of the gas, the temperature of the heating resistor in the steady state changes according to the composition of the gas to be measured. Therefore, based on the resistance value of the heating resistor 31 at this time, the gas concentration in the gas to be measured can be measured.

[0018] As a result of the inventors' studies, 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 corresponding to the change in the concentration of the gas to be detected can be sufficiently increased. Therefore, it has been found that the measurement accuracy and sensitivity of the concentration of the gas to be detected in the gas to be measured can be improved. Specifically, the total heat capacity of the heating resistor 31 and the stage 21 is preferably 3.2×10 -2 J / K or less, more preferably 2.2×10 -2 J / K or less, and even more preferably 1.5×10 -2 J / K or less. Also, from 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, more preferably 1.0×10 -9 J / K or more, and even more preferably 2.0×10 -9 J / K or more. As described above, the device 10 shown in FIGS. 1 to 3 includes a bridge structure 20 including a stage 21 that contains a heating resistor 31 inside and a bridge 22. By adopting the device 10 having such a structure as the gas concentration measurement device of the present invention, the heat capacity of the portion overlapping the heating resistor 31 in plan view can be easily controlled within the above range.

[0019] From the viewpoint of controlling the heat capacity of the portion overlapping the heating resistor 31 in plan view within the above range and ensuring sufficient mechanical strength, the area S of the stage 21 in plan view is preferably 3.6×10 7 μm 2 or less, more preferably 3.0×10 7 μm 2 or less, and even more preferably 2.5×10 7 μm 2 or less. Also, from the viewpoint of enhancing the efficiency of heat transfer with the gas to be measured, S is preferably 100μm 2 or more, more preferably 200μm 2 or more, and even more preferably 400μm 2 or more.

[0020] From the same perspective, when the stage 21 is rectangular, on the condition that S is within the above-mentioned range, 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 still more preferably 20 μm or more and 2000 μm or less.

[0021] From the perspective of sufficiently ensuring the heat absorption amount by the gas to be measured and improving the measurement accuracy and sensitivity of the gas concentration to be detected, when the total volume of the heating resistor 31 and the stage 21 is V, S / V is 0.0010 μm -1 or more is preferable, 0.00125 μm -1 or more is more preferable, 0.0016 μm -1 or more is still more preferable. Also, from the perspective of reducing power consumption, S / V is preferably 10 μm -1 or less, more preferably 7.0 μm -1 or less, and still more preferably 5.0 μm -1 or less.

[0022] From the perspective of further enhancing the measurement accuracy and sensitivity of the gas concentration to be detected, it is preferable that the heating resistor 31 has a high temperature dependence of its resistance value. Specifically, the resistance temperature coefficient α t at 25°C of the heating resistor 31 is preferably 100 ppm / °C or more, more preferably 500 ppm / °C or more, and still more preferably 1000 ppm / °C or more. The resistance temperature coefficient α at 25°C tExamples of materials having a coefficient of resistance temperature of 100 ppm / °C or more 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, Pt-W, etc. As another example, cermets of platinum group elements (platinum, palladium, rhodium, ruthenium, iridium, and osmium) and / or alloys containing these and metal oxides can be mentioned. Therefore, it is preferable that the heating resistor 31 contains one or more selected from the group consisting of these materials. Among them, from the viewpoint of stability in a high-temperature environment, it is particularly preferable that the heating resistor 31 contains platinum or an alloy containing platinum.

[0023] From the viewpoint of enhancing the adhesion between the heating resistor 31, 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 respectively disposed at positions in contact with the lower surface and the upper surface of the heating resistor 31. When the first adhesion layer 33 and the second adhesion layer 34 are disposed at positions in contact with the lower surface and the upper surface of the heating resistor 31, it is preferable that the first adhesion layer 33 and the second adhesion layer 34 are also disposed at positions in contact with the lower surface and the upper surface of the wiring 312 and the pad 32. From the viewpoint of sufficiently enhancing the adhesion between the heating resistor 31, 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 still more preferably 10 nm or more and 100 nm or less.

[0024] As shown in FIGS. 1 and 3, a part of the fourth insulating layer 124 disposed on the pad 32 is removed. Due to this, a part of the second adhesion layer 34 (in an embodiment where the second adhesion layer does not exist, a part of the pad 32) is exposed to the outside.

[0025] As described above, the device 10 has a peripheral portion 24 surrounding the stage 21. The peripheral portion 24 is preferably separated from the stage 21 and the two are connected via a bridge 22. The peripheral portion 24 preferably includes the substrate 11 and a plurality of insulating layers formed above and below the substrate 11. Specifically, as shown in FIG. 3, a first insulating layer 121, a second insulating layer 122, a third insulating layer 123, and a fourth insulating layer 124 are arranged in this order above the substrate 11. Also, a fifth insulating layer 125 and a sixth insulating layer 126 are arranged in this order below the substrate 11.

[0026] The device 10 may or may not have the fifth insulating layer 125 and the sixth insulating layer 126. The stress applied to the substrate 11 can be adjusted depending on the presence or absence of the fifth insulating layer 125 and the sixth insulating layer 126.

[0027] Next, the materials of each layer described above will be described. The substrate 11 preferably contains silicon (Si). The plurality of insulating layers formed above and below the substrate 11 preferably contain a silicon (Si) compound from the viewpoints of easy availability, easy formation, and chemical stability, and silicon dioxide (SiO 2 ) and silicon nitride (SiN x , where x is a number from 0.100 to 1.667). More preferably, the first insulating layer 121, the third insulating layer 123, the fourth insulating layer 124, and the fifth insulating layer 125 are made of SiO 2 , and the second insulating layer 122 and the sixth insulating layer 126 are preferably made of SiN x .

[0028] 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 from the viewpoint of enhancing the adhesion to the third insulating layer 123 and the fourth insulating layer 124.

[0029] The material of the heating resistor 31 is as described above. As the material of the pad 32, the material described above for the heating resistor 31 can be used. 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 suppressing manufacturing costs, it is preferable that the heating resistor 31 and the pad 32 are made of the same material.

[0030] FIG. 5 shows a device 10 according to another embodiment of the present invention. FIG. 6 shows a plan view of a stage 21 (details will be described later) constituting the device 10 of the embodiment shown in FIG. 5 as viewed from the back side. Further, FIG. 7 shows a cross-sectional view of the device 10 of the embodiment shown in FIG. 5 cut along line VII-VII. Hereinafter, this embodiment will be mainly described with differences from the embodiments shown in FIGS. 1 to 3. For points not particularly described in this embodiment, the descriptions of the embodiments shown in FIGS. 1 to 3 are appropriately applied.

[0031] The device 10 of this embodiment has a terminal block 50 and a plurality of columnar members 51 penetrating the terminal block 50 in its thickness direction. Terminals 52 for wire bonding are installed on the upper surfaces of the respective columnar members 51. The device 10 has a stage 21 and a plurality of bridges 22 extending from the periphery of the stage 21. The stage 21 is fixed to the terminal 52 via the plurality of bridges 22. Specifically, as shown in FIG. 5, on the upper surface of the stage 21, the stage 21 and the bridge 22 (hereinafter also referred to as the "first support 35") are joined at the joining portions 37 provided at two locations. Also, as shown in FIG. 6, on the back surface of the stage 21, the stage 21 and the bridge 22 (hereinafter also referred to as the "second support 36") are joined at the joining portions 37 provided at two locations. As shown in FIG. 5, the bridge 22 in this embodiment has the shape of a wire.

[0032] 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 pads 32. On the pad 32, the above-described joint portion 37 is provided, and the pad 32 and the second support 36 are joined at the joint portion 37. When 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, by connecting the columnar member 51 to a power source, the heating resistor 31 can be energized. For this purpose, the second support 36 preferably contains, for example, platinum. On the other hand, in the present embodiment, the first support 35 is used solely for the purpose of supporting the stage 21. Therefore, the material of the first support 35 is not limited to a conductor. The heating resistor 31 of the present embodiment is formed of a single strip, and the strip does not extend to the bridge 22.

[0033] The stage 21 may have a single-layer structure or a multilayer structure, but from the viewpoint of making the manufacturing simpler, it preferably has a single-layer structure. Examples of the material of the stage 21 include silicon, alumina, glass, forsterite, polyimide, polyamide, polycarbonate, polyamideimide, polyacetal, polyphenylene ether, polybutylene terephthalate, fluororesin, epoxy resin, phenol resin, and the like.

[0034] From the viewpoints 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 still more preferably 1.5 μm or more and 500 μm or less.

[0035] From the viewpoints of enhancing 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 still more preferably 10 μm or more and 50 μm or less.

[0036] The terminal block 50 preferably consists of an insulator, and the columnar member 51 and the terminal 52 preferably consist of a conductor. The columnar member 51 and the terminal 52 may be made of the same material or different materials.

[0037] Next, a method for measuring the concentration of the gas to be detected in the gas to be measured using the device 10 shown in FIGS. 1 to 3 or the device 10 shown in FIGS. 5 to 7 will be described. When measuring the concentration of the gas to be detected in the gas to be measured using the device 10, an electric current is passed through the heating resistor 31 to cause the heating resistor 31 to generate heat. The energization conditions are not particularly limited as long as a good linear relationship is established between the concentration of the gas to be detected in the gas to be measured and the resistance value of the heating resistor. For example, the energization can be carried out under constant power conditions, that is, even when the concentration of the gas to be detected in the gas to be measured changes, the amount of heat generated from the heating resistor 31 due to the energization is constant. Alternatively, the energization can be carried out under constant voltage conditions, that is, even when the concentration of the gas to be detected in the gas to be measured changes, the voltage applied to the heating resistor 31 is constant, or under constant current conditions, that is, even when the concentration of the gas to be detected in the gas to be measured changes, the current flowing through the heating resistor 31 is constant. The "constant power" mentioned here does not require the power to be strictly constant during the measurement of the concentration of the gas to be detected. For example, if the change in power during the measurement is 1% or less, more preferably 0.5% or less, the concentration of the gas to be detected can be measured with sufficient accuracy. Therefore, even if such a power change occurs during the measurement of the concentration of the gas to be detected, the measurement is regarded as having been carried out under constant power conditions. This also applies to the "constant voltage" and "constant current" described above.

[0038] Regardless of the energization conditions, since the resistance value of the heating resistor 31 changes depending on the temperature of the heating resistor 31, the concentration of the gas to be detected can be measured based on the resistance value.

[0039] From the viewpoint of promoting heat absorption from the heating resistor 31 by the gas to be measured and further improving the measurement accuracy of the concentration of the gas to be detected, it is preferable to sufficiently increase the temperature of the heating resistor 31 by energization during the measurement of the concentration of the gas to be detected. Specifically, when measuring the concentration of the gas to be detected in the gas to be measured, by energizing the heating resistor 31, the temperature difference between the heating resistor 31 and the gas to be measured is preferably 30°C or more, more preferably 60°C or more, and still more preferably 100°C or more. Also, from the viewpoint of suppressing deterioration of the heating resistor 31 due to heat, the temperature difference between the heating resistor 31 and the gas to be measured is preferably 800°C or less, more preferably 750°C or less, and still more preferably 700°C or less.

[0040] Examples of the gas to be detected in the gas to be measured include oxygen gas, nitrogen gas, argon gas, water vapor, hydrogen gas, carbon dioxide gas, and the like. Among them, particularly preferred gases to be detected are oxygen gas, water vapor, or carbon dioxide gas. By the way, when the gas to be detected is oxygen gas, since the oxygen gas has a relatively low thermal conductivity, the temperature change of the heating resistor 31 accompanying the change in the oxygen gas concentration becomes small. Due to this, there has been a problem that the measurement accuracy of the oxygen gas concentration tends to be low in a conventional thermal conductivity type gas sensor. Further, when measuring a gas to be measured containing oxygen gas and nitrogen gas such as air, since the thermal conductivities of oxygen gas and nitrogen gas are close, it has been particularly difficult to measure the oxygen gas concentration with high accuracy using a conventional thermal conductivity type gas sensor. On the other hand, in the device 10, since the amount of temperature change of the heating resistor 31 corresponding to the change in the concentration of the gas to be detected is sufficiently increased as described above, even when the gas to be detected is oxygen gas, its concentration can be measured with high precision. Further, according to the device 10, even when the gas to be measured contains oxygen gas and nitrogen gas, the oxygen gas concentration can be measured with high precision. From the viewpoint of taking advantage of the above-described advantages of the device 10, the total content of oxygen gas and nitrogen gas in the gas to be measured is preferably 0.00001% by volume or more, more preferably 0.0001% by volume or more, and still more preferably 0.001% by volume or more.

[0041] As described above, in the device 10, even if it has only the heating resistor 31 as a member having gas-to-be-detected sensitivity, it is possible to measure the concentration of the gas to be detected in the gas to be measured with high precision. Thus, since the device 10 can be composed of a relatively small number of members, it can be manufactured more simply. In this specification, the "member having gas-to-be-detected sensitivity" refers to a member whose properties change according to the concentration of the gas to be detected in the gas to be measured. When the heating resistor 31 is energized, its resistance value changes according to the concentration of the gas to be detected in the gas to be measured, so it corresponds to a member having gas-to-be-detected sensitivity. As another example of a member having gas-to-be-detected sensitivity, there can be mentioned an electrode part composed of a positive electrode, a negative electrode, and an electrolyte disposed therebetween, and the value of the current flowing through the electrode part changes according to the concentration of the gas to be detected in the gas to be measured. Examples of members having oxygen gas sensitivity also include semiconductors such as tin oxide and zinc oxide, and piezoelectric bodies such as barium titanate, zirconium titanate, and zinc oxide.

[0042] Next, regarding a preferred manufacturing method of the gas concentration measurement device of the present invention, the manufacturing method of the device 10 shown in FIGS. 1 to 3 will be described by taking it as an example. FIGS. 4(a) to (e) show preferred manufacturing procedures of the device 10 shown in FIGS. 1 to 3. This manufacturing method has the following steps in this order. 1. Step of forming an insulating layer on the substrate 11 2. Step of forming the heating resistor 31 on the insulating layer 3. Step of forming the fourth insulating layer 124 on the side and above the heating resistor 31 4. Step of forming the bridge structure 20

[0043] 1. Step of forming an insulating layer on the substrate 11 First, in an atmosphere containing oxygen or water vapor, the substrate 11 is thermally oxidized by heating it to 700 °C or higher and 1400 °C or lower, and the first insulating layer 121 and the fifth insulating layer 125 made of SiO 2 are formed on the surface of the substrate 11. Next, using the thin film forming means described later, the second insulating layer 122 and the sixth insulating layer 126 made of SiNx are formed on the surfaces of the first insulating layer 121 and the fifth insulating layer 125.

[0044] As the thin film forming means, physical vapor deposition (PVD) methods such as evaporation method, sputtering method, and ion plating method, and chemical vapor deposition (CVD) methods can be used. Among them, from the viewpoints of being able to adjust the residual stress and mass productivity, it is preferable to form the second insulating layer 122 and the sixth insulating layer 126 using the PECVD (plasma chemical vapor deposition) method or the LP-CVD (low pressure chemical vapor deposition) method. In FIGS. 4(a) to (e), the illustrations of 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 omitted.

[0045] Next, the third insulating layer 123 is formed on the second insulating layer 122 (FIG. 4(a)). The third insulating layer 123 is formed on the entire surface on the substrate 11. For the formation of the third insulating layer 123, the thin film forming means described above can be used. Among them, SiO 2When forming the third insulating layer 123 consisting of [PECVD method], it is preferable to use the PECVD method from the viewpoints of adjusting residual stress and mass productivity.

[0046] 2. Step of forming the heating resistor 31 on the insulating layer Prior to the formation of the heating resistor 31, a first adhesion layer 33 is formed as necessary. The first adhesion layer 33 can be formed by patterning using the lift-off method. Specifically, first, a layer (not shown) made of photoresist is provided over the entire area of the third insulating layer 123, and then exposure and development are performed to pattern a mask (not shown) having a complementary shape to the shape of the first adhesion layer 33. Next, the first adhesion layer 33 is formed by a thin film forming means while the third insulating layer 123 is covered with the mask. From the viewpoint of mass productivity, it is particularly preferable to use the sputtering method as the thin film forming means. Finally, the layer made of photoresist is removed to obtain the first adhesion layer 33 having a desired shape.

[0047] Next, the heating resistor 31 is formed (Fig. 4(b)). In this manufacturing method, in order 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, first, the heating resistor 31, the wiring 312, and the pad 32 are formed over the entire surface of the substrate 11 using any of the above-described thin film forming means, and then patterning is performed. From the viewpoint of mass productivity, it is particularly preferable to use the sputtering method as the thin film forming means. As the patterning method, from the viewpoint of suppressing burrs generated at the ends of the heating resistor 31, it is particularly preferable to use the milling method. Also, instead of the milling method, the lift-off method can be used. The method of forming the heating resistor 31 when using the lift-off method is the same as the method of forming the first adhesion layer 33, and thus the description here is omitted.

[0048] After forming the heating resistor 31, a second adhesion layer 34 is formed as necessary. The second adhesion layer 34 can be formed by the same method as the first adhesion layer 33. In addition, in FIG. 4(b), the illustration of the first adhesion layer 33 and the second adhesion layer 34 is omitted.

[0049] 3. Step of forming a fourth insulating layer 124 on the side and above of the heating resistor 31 After forming the heating resistor 31 and, if necessary, the first adhesion layer 33 and the second adhesion layer 34, the fourth insulating layer 124 is formed. The fourth insulating layer 124 is formed on the entire surface on the substrate 11 (FIG. 4(c)). The fourth insulating layer 124 can be formed by the same method as the third insulating layer 123. By the above steps, a structure 40 including each insulating layer and the heating resistor 31 can be obtained.

[0050] 4. Step of forming the bridge structure 20 First, unnecessary portions in 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, are removed (FIG. 4(d)). The unnecessary portions here refer to portions that do not overlap with the bridge structure 20 or the peripheral portion 24 in a plan view in the target device 10 (FIG. 1). In this step, in parallel with the removal of the unnecessary portions, a part of the fourth insulating layer 124 formed on the pad 32 can be removed to expose the pad 32 to the outside.

[0051] The removal of the unnecessary portions can be performed by an etching method such as a dry etching method and a wet etching method. As the dry etching method, reactive ion etching (RIE) using a fluorocarbon or a halogen gas can be used. As the wet etching method, isotropic etching using hydrofluoric acid, nitric acid, sulfuric acid, phosphoric acid, etc., or anisotropic etching using an alkaline solution such as KOH (potassium hydroxide), TMAH (tetramethylammonium hydroxide), EDP (ethylenediamine pyrocatechol), etc. can be used. Among them, from the viewpoint of preventing the etching of the structure 40, RIE can be preferably used for removing the unnecessary portions.

[0052] Next, unnecessary portions in the fifth insulating layer 125 and the sixth insulating layer 126, which are insulating layers positioned below the substrate 11, are removed, and then unnecessary portions in the substrate 11 are removed (FIG. 4(e)). The unnecessary portions referred to here mean portions that do not overlap with the peripheral portion 24 in plan view.

[0053] The method of removing the unnecessary portions can be the same as the method of removing the insulating layer positioned above the substrate 11. In particular, as a method of removing unnecessary portions in the insulating layer positioned below the substrate 11, RIE can be preferably used. As a method of removing unnecessary portions in the substrate 11, SF 6 (sulfur hexafluoride) is used for an etching process, and C 4 F 8 (octafluorocyclobutane) and other fluoroalkane-based gases are used for a passivation process alternately, and deep reactive ion etching (DRIE) can be preferably used.

[0054] As described above, the gas concentration measuring device of the present invention has been described based on its preferred embodiments, but the present invention is not limited to such embodiments. For example, the gas concentration measuring device of the present invention may not have a structure including the bridge structure 20.

[0055] The above embodiments of the present invention include the following technical ideas. 〔1〕 A gas concentration measuring device having a heating resistor that generates heat by energization and a stage that supports the heating resistor, wherein the heating resistor overlaps the stage in plan view, and the concentration of the gas to be detected in the gas to be measured is measured based on the resistance value of the heating resistor. 〔2〕 The gas concentration measuring device according to 〔1〕, wherein the total heat capacity of the heating resistor and the stage is 1.0×10 -10 J / K or more and 3.2×10 -2 J / K or less. 〔3〕 The gas concentration measurement device according to 〔1〕 or 〔2〕, further comprising one or a plurality of bridges extending from the periphery of the stage, and forming 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, 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 heating resistor is composed of a series of linear bodies, The series of linear bodies is composed of one linear body or a plurality of linear bodies having at least common ends, At least two of the bridges extend from the periphery of the stage, The gas concentration measurement device according to 〔3〕, wherein the series of linear bodies extends to each of the two bridges. 〔7〕 The gas concentration measurement device according to 〔3〕 or 〔6〕, wherein the area S in the plan view of the stage is 3.6×10 7 μm 2 or less. 〔8〕 When the total volume of the heating resistor and the stage is V, and the area in the plan view of the stage is S, S / V is 0.0010 μm -1 or more and 10 μm -1 or less. The gas concentration measurement device according to any one of 〔3〕, 〔6〕 and 〔7〕. 〔9〕 The gas concentration measurement device according to any one of 〔1〕 to 〔8〕, wherein the temperature coefficient of resistance αt of the heating resistor at 25 °C is 100 ppm / °C or more. 〔10〕 The gas concentration measurement device according to any one of 〔1〕 to 〔9〕, wherein the heating resistor contains platinum or an alloy containing platinum. 〔11〕 The gas concentration measurement device according to any one of 〔1〕 to 〔10〕, having only the heating resistor as a member having detectant gas sensitivity. A method for measuring the concentration of a target gas to be detected in a gas to be measured, using the gas concentration measuring device according to any one of [1] to

[11] . 〔13〕 The measuring method according to

[12] , wherein the concentration of the target gas to be detected in the gas to be measured is measured in a state where the temperature difference between the heating resistor and the gas to be measured is 30 ° C or more by energizing the heating resistor. 〔14〕 The measuring method according to

[12] or

[13] , wherein the gas to be measured contains oxygen gas and nitrogen gas.

Example

[0056] Hereinafter, the present invention will be described in more detail by way of examples. However, the scope of the present invention is not limited to such examples.

[0057] 〔Example 1〕 In this example, the device 10 shown in FIGS. 1 to 3 was manufactured.

[0058] <Formation of insulating layer> A substrate 11 made of silicon with a crystal orientation <100> and a thickness of 500 μm was prepared. This substrate 11 was thermally oxidized to form a first insulating layer 121 and a fifth insulating layer 125 made of SiO 2 . The thicknesses of the first insulating layer 121 and the fifth insulating layer 125 were each 600 nm. Next, a second insulating layer 122 and a sixth insulating layer 126 made of SiN x were formed by using the LP-CVD method. The thicknesses of the second insulating layer 122 and the sixth insulating layer 126 were each 200 nm. Further, a third insulating layer 123 made of SiO 2 was formed on the second insulating layer 122 by using the PECVD method. The thickness of the third insulating layer 123 was 1000 nm.

[0059] <Formation of heating resistor 31> According to the above method, using the sputtering method, the first adhesion layer 33, the heating resistor 31, the pad 32, and the second adhesion layer 34 were formed on the third insulating layer 123 in this order. The lift-off method was used for patterning the first adhesion layer 33 and the second adhesion layer 34, and the milling method was used for patterning the heating resistor 31 and the pad 32. When forming the heating resistor 31 and the pad 32, a target material made of platinum was used as the sputtering target material. The film formation of the heating resistor 31 and the pad 32 was performed using the sputtering method. When forming the first adhesion layer 33 and the second adhesion layer 34, sputtering was performed using a target material made of tantalum. The thickness of the heating resistor 31 was 0.3 μm, and the thicknesses of the first adhesion layer 33 and the second adhesion layer 34 were 0.02 μm.

[0060] <Formation of the fourth insulating layer 124> In the same manner as the third insulating layer 123, a fourth insulating layer 124 made of SiO 2 was formed on the third insulating layer 123. The thickness of the fourth insulating layer 124 was 4000 nm. The thicknesses of the above-mentioned respective layers were calculated based on the film formation rate and the film formation time.

[0061] <Formation of the bridge structure 20> Using RIE, unnecessary portions in 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, were removed. Next, unnecessary portions in the fifth insulating layer 125 and the sixth insulating layer 126, which are insulating layers located below the substrate 11, were removed. The removal of the unnecessary portions in the fifth insulating layer 125 and the sixth insulating layer 126 was performed by RIE to obtain a gas concentration measurement device. For the removal of the unnecessary portions on the substrate 11, an etching process using SF 6 and a passivation process using C 4 F 8 were alternately performed by DRIE.

[0062] 〔Example 2〕 In this example, a gas concentration measurement device shown in FIGS. 5 to 7 was manufactured. First, a stage 21 made of silicon with a crystal orientation <100> and a thickness of 290 μm was prepared. On one surface of this stage 21, a heating resistor 31 and pads 32 each with a thickness of 0.3 μm were formed by sputtering. As the target materials for the sputtering method, a 2-inch sized target material made of platinum and a 2-inch sized target material made of Y 2 O 3 were used. Film formation was performed using a co-sputtering method in which power was supplied to the two targets simultaneously. For platinum, the DC sputtering method was used, and for Y 2 O 3 , the RF sputtering method was used. Sputtering was performed using argon gas. The flow rate of the argon gas was 50 sccm, and the pressure of the argon gas was 4 Pa. The powers were 90 W and 200 W respectively, and sputtering was performed at room temperature. The heating resistor 31 contained 25% by volume of Y 2 O 3 and 75% by volume of platinum.

[0063] After applying platinum paste to two pads 32 and two locations on the surface opposite to the pads 32, and then baking at 700 °C for 1 hour in the atmosphere, a joint portion 37 was formed. Next, a Pt wire (bridge 22) with a wire diameter of 50 μm was bonded to each platinum paste by resistance welding. By bonding the other end of the Pt wire to the terminal 52 by resistance welding, the stage 21 was fixed to the terminal 52 via the bridge 22, and a gas concentration measurement device was obtained.

[0064] 〔Example 3〕 A gas concentration measurement device was manufactured in the same manner as in Example 2, except that a substrate made of alumina with a thickness of 0.26 mm was used as the stage 21, and a heating resistor 31 and pads 32 each with a thickness of 13 μm were formed on one surface of the substrate using Pt paste by screen printing.

[0065] 〔Comparative Example 1〕 The gas concentration measurement device shown in Fig. 8 was manufactured. In Example 3, after forming the heating resistor 31 on one surface of the stage 21, on the other 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 composed of a solid electrolyte 62 made of lanthanum silicate, which is disposed between the composite oxide electrodes 61b, was adhered to one surface of the stage 21 using a Pt paste. Next, in an air atmosphere, a sealing material 63 made of glass was applied to seal the electrode 61a located closer to the stage 21 among the two electrodes 61a and 61b. Otherwise, in the same manner as in Example 3, a gas concentration measurement device was obtained. The gas concentration measurement device of Comparative Example 1 can measure the oxygen concentration based on the concentration difference electromotive force generated between the two electrodes 61a and 61b, and the heating resistor 31 is used to heat the solid electrolyte 62.

[0066] 〔Evaluation〕 <Measurement of S, V, and Heat Capacity> In Example 1, the thicknesses of each layer constituting the stage 21 and the heating resistor 31 were calculated from the film formation rates of each layer 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 calipers. Dimensions other than the thicknesses of the stage 21 and the heating resistor 31 were measured using a microscope (VHX-8000 manufactured by Keyence Corporation) or calipers. Based on the dimensions measured as described above, and the specific heat and density of the materials constituting each layer, the area S in the plan view of the stage 21, 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.

[0067] <Measurement of Oxygen Gas Concentration Responsiveness> The oxygen gas concentration responsiveness of the heating resistor 31 when an electric current was passed through the heating resistor was measured. The measurement was performed under the following conditions. · Power supply conditions: Constant power drive at an applied voltage that results in 40 mW, 80 mW, 700 mW, or 1300 mW under atmospheric pressure · Gas flow rate: 100 sccm · Gas to be measured: Mixed gas of oxygen gas and nitrogen gas · Room temperature (temperature of the gas to be measured): 25°C The oxygen gas concentration in the gas to be measured was as follows. · 140 to 240 seconds after the start of measurement: 100% by volume · 240 to 340 seconds after the start of measurement: 80% by volume · 340 to 440 seconds after the start of measurement: 60% by volume · 440 to 540 seconds after the start of measurement: 40% by volume · 540 to 640 seconds after the start of measurement: 21% by volume · 640 to 740 seconds after the start of measurement: 10% by volume · 740 to 800 seconds after the start of measurement: 21% by volume Fig. 9 shows the resistance change rate of the heating resistor 31 when an electric current was passed through the heating resistor 31 under the constant power condition of 80 mW. 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% by volume, and R 21 represents the resistance value at an oxygen concentration of 21% by volume. Resistance change rate = (R x - R 21 ) / R 21 × 10 6 Also, Table 2 shows the temperature difference between the temperature of the heating resistor 31 and the room temperature (temperature of the gas to be measured) during energization 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 as 0.66 for Example 1, 0.63 for Example 2, and 0.88 for Example 3 and Comparative Example 1. Note that in Table 2, "-" indicates non-measurement.

[0068] <Calculation of sensitivity> The resistance change rate (ppm) of the heating resistor 31 obtained in the <Measurement of Oxygen Gas Concentration Responsiveness> was plotted against the oxygen concentration (%) of the gas to be measured. Subsequently, 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. 10 shows a graph representing the relationship between the resistance change rate of the heating resistor 31 and the oxygen concentration when the heating resistor 31 was energized under the constant power condition of 80 mW.

[0069] <Evaluation of Response Speed> In the gas concentration measurement devices of Example 3 and Comparative Example 1, after changing the oxygen gas concentration from 60% to 90%, the time taken for the response from 10% to 90% of the sensor output 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 energization condition was a constant voltage condition of 1300 mW. The flow rate of Comparative Example 3 was 50 sccm. Other conditions were the same as those in the <Measurement of Oxygen Gas Concentration Responsiveness>. The results are shown in Table 2.

[0070] <Measurement of the Resistance Temperature Coefficient α of the Heating Resistor t of Using a hot - cold stage (manufactured by INSTEC), with reference to the resistance value of the heating resistor 31 when the oxygen concentration in the gas to be measured was 21 vol% and at 25°C, the change rate of the resistance value of the heating resistor (R 500 -R 25 ) / R 25 / (500 - 25)×10 6 (ppm / °C) (wherein R 500 represents the resistance value at 500°C, and R 25 represents the resistance value at the reference temperature of 25°C.) was measured. The results are shown in Table 1.

[0071]

Table 1

[0072]

Table 2

[0073] As shown in FIG. 10 and Table 2, a good linear relationship was shown between the oxygen gas concentration in the gas to be measured and the resistance value of the heating resistor 31. Therefore, it can be understood that the gas concentration measuring device of the present invention can measure the oxygen gas concentration with high accuracy even when the gas to be measured contains oxygen gas and nitrogen gas, although it can be easily manufactured. On the other hand, the gas concentration measuring device of Comparative Example 1 had room for improvement in that its manufacturing process became complicated.

Industrial Applicability

[0074] According to the present invention, there is provided a gas concentration measuring device that can be easily manufactured.

Claims

1. The heater includes a heating resistor that generates heat when an electric current is applied thereto, and a stage that supports the heating resistor; the heating resistor overlaps with the stage in a plan view, 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.

2. The total heat capacity of the heating resistor and the stage is 1.0×10 －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. 10. The gas concentration measurement device of claim 1, further comprising one or more bridges extending from a periphery of the stage to form a bridge structure.

4. 2. The gas concentration measuring device according to claim 1, wherein the detection target gas is oxygen gas, water vapor or carbon dioxide gas.

5. 2. The gas concentration measuring device according to claim 1, wherein the detection target gas is oxygen gas.

6. The heating resistor is made of a series of wires, The series of filaments may be a single filament or a plurality of filaments having at least both ends in common, At least two of the bridges extend from a periphery of the stage; The gas concentration measurement device according to claim 3 , wherein the series of wires extend to each of the two bridges.

7. The area S of the stage in a plan view is 3.6×10 ７ μm ２ 4. The gas concentration measuring device according to claim 3, wherein:

8. The total volume of the heating resistor and the stage is V, When the area of ​​the stage in a plan view is S, S / V is 0.0010 μm －１ 10 μm or more －１ 4. The gas concentration measuring device according to claim 3, wherein:

9. The resistance temperature coefficient 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.

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

11. 2. The gas concentration measuring device according to claim 1, wherein the heating resistor is the only member sensitive to the target gas.

12. A method for measuring a concentration of a target gas in a measurement gas, using the gas concentration measuring device according to claim 1 .

13. 13. The method according to claim 12, further comprising the step of: measuring the concentration of the target gas in the measurement gas by passing a current through the heating resistor so that a temperature difference between the heating resistor and the measurement gas is set to 30° C. or more.

14. 13. The measurement method according to claim 12, wherein the measurement gas contains oxygen gas and nitrogen gas.

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