Light source and optical gas sensor device

Abstract

The present invention prolongs the life of a light source.　A light source 2 comprises: an Si support layer 211 that has a space in a central part in plan view; and a membrane M that is continuously provided above the Si support layer 211 and the space, that is fixed to the Si support layer 211 at a peripheral edge part of the space, and that includes a heater layer 213 which has a plurality of electrodes and generates heat by energization between the electrodes to emit infrared rays. The membrane M covers the space, and is layered by including: a silicon nitride film 212B, the heater layer 213, and a protective layer 215 which serve as a tensile stress layer having a tensile stress in a plane direction; and silicon oxide films 212A, 212C and an electrode support layer 214 which serve as a compressive stress layer having a compressive stress in the plane direction. In the membrane M, a ratio of the thickness in a film thickness direction of the tensile stress layer to the total thickness in the film thickness direction of the membrane M above the Si support layer 211 and the space is equal to or greater than a predetermined threshold at which the tensile stress exceeds the compressive stress in the membrane M.

Description

Light source and optical gas sensor device

[0001] The present invention relates to a light source and an optical gas sensor device.

[0002] Conventionally, gas sensors using the non-dispersive infrared absorption method (NDIR) have been known. NDIR gas sensors utilize the property that many gases absorb their own specific infrared wavelengths. When infrared light is emitted to a gas to be detected, the NDIR gas sensor detects which wavelengths are absorbed and to what extent, thereby measuring the concentration of the gas to be detected. For example, the NDIR gas sensor includes an infrared light emitter and an infrared light receiver, and detects the concentration of the gas to be detected located in the optical path between the emitter and the receiver.

[0003] For example, a gas sensor having a MEMS (Micro Electro Mechanical Systems) type light source device as a light-emitting unit is known (see Patent Document 1). The light source device includes a substrate from which a portion has been removed, an electrothermal conversion unit, upper and lower protective layers sandwiching the electrothermal conversion unit, and a radiation unit formed on the upper protective layer. When current is applied to the electrothermal conversion unit, the radiation unit is heated and emits infrared rays. The protective layer in the region from which a portion of the substrate has been removed, the electrothermal conversion unit, and the radiation unit form a membrane structure.

[0004] Japanese Patent Application Laid-Open No. 2022-51217

[0005] However, in the conventional light source device, some layers have tensile stress and some have compressive stress. ２ and Si ３ N ４ has tensile stress. ２ The membrane has compressive stress. The stress applied to the membrane is determined by the internal stress of each layer and the film thickness. Therefore, compressive stress occurs when the electrothermal conversion section generates heat, and mechanical stress caused by deformation of the membrane during operation may shorten the life of the light source device.

[0006] An object of the present invention is to extend the life of a light source.

[0007] In order to solve the above problem, the light source of the present invention comprises: a support layer having a space in the center when viewed in a plane; and a membrane that is provided continuously above the support layer and the space, fixed to the support layer at the periphery of the space, and includes a heater layer that includes a plurality of electrodes and generates heat and emits infrared rays when current is passed between the electrodes; the membrane covers the space and is laminated to include at least one tensile stress layer that has tensile stress in the planar direction and at least one compressive stress layer that has compressive stress in the planar direction; and the ratio of the thickness in the film thickness direction of the tensile stress layer to the total thickness in the film thickness direction of the membrane above the support layer and the space is equal to or greater than a predetermined threshold value at which the tensile stress exceeds the compressive stress in the membrane.

[0008] According to the present invention, the life of the light source can be extended.

[0009] 1 is a schematic diagram of an optical gas sensor device according to a first embodiment of the present invention. FIG. 1 is a perspective view of an optical gas sensor device. FIG. 2 is a partially see-through perspective view of an optical gas sensor device. FIG. 2 is a perspective view of a light source according to the first embodiment. FIG. 3 is a schematic cross-sectional view of a light source according to the first embodiment. FIG. 4 is a top view of a light source according to the first embodiment. FIG. 5 is a diagram showing test time characteristics of light source resistance change for the light source of Example 1 and the light source of Comparative Example 1. FIG. 6 is an external photograph of the light source of Example 1 and the light source of Comparative Example 1 at the time shown in FIG. 7. FIG. 7 is a diagram showing applied voltage characteristics of deformation for the light sources of Examples 2 and 3 of the second embodiment and the light sources of Comparative Examples 2 and 3. FIG. 8 is a diagram showing test time characteristics of light source resistance change for the light source of Example 2 of the second embodiment and the light source of Comparative Example 2. FIG. 9 is an external photograph of the light source of Example 2 and the light source of Comparative Example 2 at the time shown in FIG. 10. FIG. 11 is a diagram showing deformation when 3.3 VDC is applied as a function of the ratio of the tensile stress film thickness to the total membrane thickness for the light sources of Examples 2 and 3 and the light sources of Comparative Examples 2 and 3. FIG. 12 is a schematic cross-sectional view of a light source according to a third embodiment. FIG. 13 is a diagram showing applied voltage characteristics of deformation for the light source of Example 4 of the third embodiment and the light source of Comparative Example 4. 10A and 10B are diagrams showing the displacement X characteristics of the light source in Comparative Example 4. FIG. 10B are diagrams showing the displacement X characteristics of the light source in Example 4. FIG.

[0010] Hereinafter, first to third embodiments of the present invention will be described in detail in order with reference to the accompanying drawings, however, the scope of the invention is not limited to the illustrated examples.

[0011] First Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 8. The light source device of Patent Document 1 includes a substrate with a portion removed, an electrothermal conversion unit, upper and lower protective layers sandwiching the electrothermal conversion unit, and a radiation unit formed on the upper protective layer. When current is applied to the electrothermal conversion unit, the radiation unit is heated and infrared rays are emitted. The protective layer in the region where a portion of the substrate is removed, the electrothermal conversion unit, and the radiation unit form a membrane structure. However, in conventional light source devices, the planar shape of the membrane is rectangular. This causes uneven thermal stress on the plane generated when the electrothermal conversion unit generates heat, which may shorten the life of the light source device. The light source and optical gas sensor device of this embodiment solve this problem.

[0012] First, a schematic configuration of an optical gas sensor device 100 according to the present embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram of the optical gas sensor device 100 according to the present embodiment.

[0013] As shown in FIG. 1 , the optical gas sensor device 100 of this embodiment is an NDIR gas sensor. The optical gas sensor device 100 includes an optical cover 1, a light source 2, an optical filter 3, a light receiving unit 4, a signal processing unit 5, and a switch 81. The optical filter 3 is an optical filter. In the optical gas sensor device 100, the light source 2 radiates (emits or emits) infrared light. The radiated infrared light travels through an optical path (path) within the optical cover 1 and is emitted to a gas G to be detected (measured) within the optical cover 1. An anti-reflection (AR) filter may be disposed between the light source 2 and the optical filter 3. The AR filter is a filter that prevents reflection of infrared light and transmits it. The AR filter is disposed, for example, in a position downstream of the light source 2 on the optical path near the light source 2.

[0014] Molecules of the gas G to be detected that are present in the optical path absorb the infrared light, thereby reducing the amount of light that reaches the light receiving unit 4. In the optical gas sensor device 100, the infrared light that has been partially absorbed by the gas G to be detected is detected by the light receiving unit 4 via the optical filter 3. The optical filter 3 is a filter that transmits infrared light of the absorption wavelength of the gas G from the incident infrared light. With this configuration, the light receiving unit 4 does not receive unfiltered infrared light emitted from sources other than the light source 2, improving the signal-to-noise ratio (SNR) of the sensor.

[0015] The optical gas sensor device 100 processes the detection signal detected by the light receiving unit 4 using the signal processing unit 5, detects (measures) the concentration of the gas G to be detected, and outputs the result. The switch 81 is a switch that turns on / off the light emission of the light source 2, and is included in the circuit element unit 8 described later. When performing gas detection, the signal processing unit 5 turns on / off the light source 2 via the switch 81.

[0016] The optical cover 1 has a gas inlet port 11 as a gas inlet that is an inlet / outlet for the gas G to be detected. A contaminant filter 12 is attached to the gas inlet port 11. The contaminant filter 12 is, for example, a metal mesh filter or a resin porous film, and prevents foreign matter from entering from the outside.

[0017] In this way, in the optical gas sensor device 100, infrared light emitted from the light source 2 toward the gas G to be detected is filtered by the optical filter 3 and received by the light receiving unit 4. The optical filter 3 is disposed in the vicinity of the light receiving unit 4 on the optical path upstream of the light receiving unit 4.

[0018] In this embodiment, the optical path of the infrared light received by the light receiving unit 4 is designed so that it arrives after reflecting from the light source 2 on the inner surface of the optical cover 1. It is desirable that the inner surface of the optical cover 1 have a high reflectivity, as this increases the efficiency of light (infrared) utilization. Note that the optical path of the infrared light received by the light receiving unit 4 may include not only the optical path that arrives after reflecting on the inner surface of the optical cover 1, but also the optical path that arrives directly from the light source 2.

[0019] The optical gas sensor device 100 detects an alternative fluorocarbon refrigerant, which is used as a refrigerant for air conditioners, as the gas G to be detected. Alternative fluorocarbons are synthetic compound (gas) refrigerants used industrially as an alternative to specific chlorofluorocarbons (CFCs). Because CFC refrigerants have a high ozone depletion potential and contribute to the destruction of the Earth's ozone layer, efforts to replace them with hydrochlorofluorocarbon (HCFC) refrigerants, which have a low ozone depletion potential, have begun. In developed countries, there is also a shift from HCFC refrigerants to HFC refrigerants (R410A), which has an ozone depletion potential of zero.

[0020] CFC refrigerants, HCFC refrigerants, and HFC refrigerants have high global warming potentials and are known to cause global warming as greenhouse gases. For this reason, replacement of HFC refrigerant (R410A) with HFC refrigerant (R32), which has a lower global warming potential, is being considered. In this embodiment, for example, R32, a fluorocarbon refrigerant, is detected as the gas G to be detected.

[0021] However, the gas G to be detected is not limited to R32. The gas G to be detected may also be carbon dioxide, carbon monoxide, propane, methane, butane, ammonia, oxygen disulfide, nitrogen dioxide, nitric oxide, ozone, sulfur hexafluoride, difluoromethane, hydrochlorofluorocarbons (HCFCs), other hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), ethylene, etc.

[0022] The optical gas sensor device 100 outputs various status signals based on the detected gas concentration value of the gas G to an information processing unit of the device that performs processing based on the status of the optical gas sensor device 100. The information processing unit is, for example, an MCU (Micro Controller Unit). The status signals are, for example, a fault signal, an alarm signal, and a monitoring signal (normal signal). The fault signal indicates a fault state of the optical gas sensor device 100. The alarm signal indicates that the detected concentration of the gas G is in an abnormal state (alarm state) that requires an alarm. The monitoring signal indicates that the detected concentration of the gas G is in a normal state. If the device is an alarm device, it issues various alarms (e.g., an alarm of a fault of the optical gas sensor device 100 based on a fault signal, an alarm of an abnormality in the detected concentration of the gas G based on an alarm signal) in accordance with the various signals received from the optical gas sensor device 100. The device may include the optical gas sensor device 100 and an MCU, or may be a device separate from the optical gas sensor device 100. The above equipment includes household air conditioners, household water heaters, industrial air conditioners, automotive air conditioners, freezers, refrigeration equipment, refrigerated showcases, air purifiers, household flammable gas leak alarms, household toxic gas alarms, household environmental monitoring equipment, industrial flammable gas leak alarms, industrial toxic gas alarms, industrial gas process monitoring devices, and greenhouse CO2 detectors. ２ CO concentration meter for plant factories ２ Measuring instruments, food packaging CO ２ These include sealing devices and ethylene gas concentration measuring devices for food warehouses.

[0023] Next, a specific device configuration of the optical gas sensor device 100 will be described with reference to Figs. 2 to 6. Fig. 2 is a perspective view of the optical gas sensor device 100. Fig. 3 is a partially see-through perspective view of the optical gas sensor device 100. Fig. 4 is a perspective view of the light source 2 of this embodiment. Fig. 5 is a schematic cross-sectional view of the light source 2 of this embodiment. Fig. 6 is a top view of the light source 2 of this embodiment.

[0024] As shown in Figures 2 and 3, the optical gas sensor device 100 includes an optical cover 1, a light source 2, an optical filter 3, a light receiving unit 4, a signal processing unit 5, a substrate 6, a connector 7, and a circuit element unit 8. Figure 2 also illustrates the x-axis, y-axis, and z-axis. These three axes are the same in the other figures. Note that the contamination filter 12 is not shown in Figures 2 and 3.

[0025] The optical cover 1 is mounted on the +z side surface of the substrate 6, covers (encompasses) the light source 2 and the light receiving unit 4, and forms a hollow portion (space) inside that can contain the gas G to be detected, and the gas G to be detected is introduced into and out of the hollow portion via a gas introduction port 11. The base of the optical cover 1 is made of, for example, resin.

[0026] 2, the optical cover 1 has cover portions 110A and 110B. The cover portion 110A is an upper part (+z direction side) that is butted against the cover portion 110B and integrated with it by a method such as adhesive or thermal caulking. The cover portion 110B is a lower part (-z direction side) that is butted against the cover portion 110A and integrated with it by a method such as adhesive or thermal caulking.

[0027] 3, the optical cover 1 has a light guide portion 13 as a hollow portion into which the gas G to be detected is introduced. The light guide portion 13 is a pipe-shaped optical path, and its cross section perpendicular to the axial direction is circular. The cover portion 110A has a half-pipe portion. The cover portion 110B has a half-pipe portion. The light guide portion 13 is formed by joining the half-pipe portions of the cover portions 110A and 110B. In this way, the optical cover 1 has cover portions 110A and 110B divided by the cross section of the light guide portion 13 in the axial direction. As shown in FIG. 3, the light guide portion 13 has a three-dimensional, approximately U-shape when viewed from the top (the surface in the +z direction).

[0028] The inner surface of the light guide unit 13 is covered with an infrared-reflecting film. In this embodiment, gold is used as the infrared-reflecting film, but this is not limited thereto. Silver or aluminum may also be used as the infrared-reflecting film. Furthermore, if necessary, a protective film such as silicon oxide or silicon nitride may be formed on the infrared-reflecting film to prevent corrosion of the metal film of the infrared-reflecting film. The infrared-reflecting film and the protective film may be formed using a plating method, a sputtering method, a vacuum deposition method, or the like. For example, the optical cover 1 may be integrally formed from a metal such as aluminum using a metal 3D printer. In either case, it is preferable that the inner surface of the light guide unit 13 be mirror-finished to efficiently reflect infrared rays.

[0029] The light guide 13 reflects the infrared rays incident from the light source 2 with an infrared reflective film on its inner surface. The light guide 13 emits the reflected infrared rays to the light receiving unit 4 via the optical filter 3. In this way, the optical cover 1 reflects the infrared rays emitted from the light source 2 with the infrared reflective film, thereby serving as an optical path to efficiently guide the infrared rays from the light source 2 to the light receiving unit 4 so that at least a portion of the reflected light reaches the light receiving unit 4 via the optical filter 3. The optical filter 3 is configured to be disposed on the upper surface on the +z side of the light receiving unit 4. However, this is not limited thereto, and the optical filter 3 may be configured to be provided, for example, at the outlet portion 132 of the end opening of the light guide 13 on the light receiving unit 4 side.

[0030] In this embodiment, by configuring the optical path inside the optical cover 1 as the light guide section 13 in the shape of a pipe with a circular cross section, the reflection angle of the infrared light can be kept constant in any direction in three dimensions (x-axis, y-axis, z-axis) regardless of the diameter or path of the cross section of the light guide section 13, and the infrared light emitted from the light source 2 can be reflected inside the light guide section 13 and efficiently enter the light receiving section 4. Note that the cross section of the light guide section 13 of the optical cover 1 in the axial direction of the optical path may be configured to be elliptical.

[0031] Furthermore, the optical path length of the infrared light from the light source 2 to the light receiving section 4 can be changed relatively easily by changing the diameter of the cross section of the light guiding section 13 .

[0032] 2 and 3, the optical cover 1 is three-dimensionally designed and formed so that a space SP is formed on the substrate 6 on the +y-direction side, where the axial direction of the light guide unit 13 is below a portion of the x-axis direction (-z direction). At least a portion of the signal processing unit 5 and the circuit element unit 8 is disposed in the space SP and mounted on the substrate 6.

[0033] Furthermore, the cross-sectional area of ​​the light guide 13 perpendicular to the axial direction is constant in the axial direction for the main portion (portion other than the entrance portion 131 and the exit portion 132, which are the end openings on the light source 2 side). Because the cross-sectional area is constant, the gas concentration per unit volume of the gas G to be detected that enters the light guide 13 is easily homogenized, and since the infrared rays pass through randomly without following a specific path, the light guide 13 is easily responsive to changes in the gas concentration of the gas G. Figure 3 shows the optical path propagation state, with multiple infrared ray paths within the light guide 13 represented by solid arrows. In this way, the infrared ray paths are random within the light guide 13.

[0034] Furthermore, infrared light emitted from light source 2 is incident on entrance 131 of light-guiding section 13 on the −x direction side. Light-guiding section 13 on the −x direction side extends in an axial direction from the −z direction side to the +z direction side, then curves in an R-shape, and extends linearly from the −y direction side to the +y direction side. The end of light-guiding section 13 on the infrared light incident side is defined as entrance 131. Light-guiding section 13 extending in the +y direction side curves in an R-shape, then extends in an axial direction from the −x direction side to the +x direction side, and then curves in an R-shape again.

[0035] The light guide 13 on the +x-direction side extends linearly from the +y-direction side to the −y-direction side, then curves in an R-shape and extends to the exit 132 on the −z-direction side. The infrared light that has passed through the light guide 13 is emitted to the light receiving unit 4 via the optical filter 3.

[0036] The outlet portion 132 has a tapered shape in which the cross-sectional area becomes smaller as the axial direction of the light-guiding portion 13 moves from the +z direction to the −z direction. Similarly, the inlet portion 131 has a tapered shape in which the cross-sectional area becomes smaller as the axial direction of the light-guiding portion 13 moves from the +z direction to the −z direction. This makes it possible to increase the concentration of infrared light that passes through the light-guiding portion 13 and is radiated to the light-receiving portion 4.

[0037] The cover parts 110A and 110B also have hollow parts (not shown) as spaces for removing material, which can reduce the weight of the optical cover 1 (optical gas sensor device 100).

[0038] The cover part 110B also has a fixing pin (not shown). The fixing pin is a convex part extending in the +z direction, and is fitted into a recess (female hole) (not shown) of the cover part 110A and integrated by a method such as adhesive bonding or thermal caulking. By fitting the fixing pin into the recess of the cover part 110A and integrating it by a method such as adhesive bonding or thermal caulking, the cover parts 110A and 110B are positioned and fixed together as an integrated part.

[0039] As shown in FIG. 2 , the cover 110A has gas inlets 111 and 112 as the gas introduction port 11. The cover 110B has gas inlets (gas introduction holes) 113 and 114 as the gas introduction port 11. The gas inlets 111 and 112 are holes drilled in the −z direction from the top surface of the cover 110A and penetrate to the light guide 13. The gas inlet 113 is a hole drilled from the −y direction side surface of the cover 110B toward the +y direction and penetrates to the space around (beside) the light source 2. The space around the light source 2 is connected to the light guide 13. The gas inlet 114 is a hole drilled from the −y direction side surface of the cover 110B toward the +y direction and penetrates to the space around (beside) the light receiving unit 4. The space around the light receiving unit 4 is connected to the light guide 13.

[0040] Gas inlets 111 and 112 are directly connected to light guide 13 and remove part of the inner surface of light guide 13, resulting in a low efficiency of infrared radiation utilization. In contrast, gas inlet 113 is indirectly connected to light guide 13 via the space around light source 2, resulting in a high efficiency of infrared radiation utilization without damaging (removing) part of the inner surface of light guide 13. Similarly, gas inlet 114 is indirectly connected to light guide 13 via the space around light receiving unit 4, resulting in a high efficiency of infrared radiation utilization without damaging part of the inner surface of light guide 13.

[0041] The shape, size, and position of the gas introduction port 11 (gas intake ports 111, 112, 113, 114) of the optical cover 1 shown in FIG. 2 are merely an example, and are not limited to these.

[0042] 4, the light source 2 is a MEMS type light source mounted on the upper surface (+z side surface) of the substrate 6, and for example, a membrane M having a membrane structure is formed on the Si support layer 211. The light source 2 has an electrode 231 and a pad P1 provided on the +x direction side, and an electrode 232 and a pad P2 provided on the −x direction side.

[0043] 5 is a schematic cross-sectional view of the light source 2, and the actual dimensions are not as shown. As shown in Fig. 5, the light source 2 has a configuration in which, for example, a Si support layer 211, a heater layer support layer 212, a heater layer 213, electrodes 231 and 232, an electrode support layer 214, and a protective layer 215 are stacked in this order from the -z direction side to the +z direction side. The heater layer support layer 212, the electrode support layer 214, and the protective layer 215 are insulating layers that sandwich the heater layer 213 above and below in the z-axis direction.

[0044] The Si support layer 211 is a substrate made of Si, and is an upper support layer for the membrane M of the light source 2. As shown in Figures 5 and 6, the Si support layer 211 has a circular space that is circular when viewed from the -z direction. Therefore, the light source 2 has a membrane M that is circular in shape on the xy plane perpendicular to the film thickness direction (z-axis direction).

[0045] The heater layer support layer 212 has, from the −z direction side to the +z direction side, for example, a silicon oxide film 212A, a silicon nitride film 212B, and a silicon oxide film 212C. The silicon oxide film 212A is made of silicon dioxide (SiO ２ The silicon nitride film 212B is a thin film made of silicon nitride (Si ３ N ４ The silicon oxide film 212C is a thin film made of SiO ２The heater layer 213 is a thin film made of molybdenum disilicide (MoSi). The heater layer 213 is a thin film heater that serves as a light source (metal) layer. The heater layer 213 generates heat when current is applied, and heats the membrane M. The heated membrane M emits infrared rays that have an intensity and wavelength dependency that depend on the surface temperature and surface emissivity. The heater layer 213 is made of, for example, molybdenum disilicide (MoSi ２ However, the heater layer 213 is not limited to this, and may be made of molybdenum (Mo), Mo and silicon (Si), or MoSi ２ Compounds with different composition ratios, tungsten (W), tungsten disilicide (WSi ２ ), consisting of W and Si, WSi ２ The composition may be made of other materials such as compounds with different composition ratios, platinum (Pt), titanium (Ti), gold (Au), silver (Ag), nickel chromium (NiCr), nickel (Ni), aluminum (Al), copper (Cu), titanium nitride (TiN), polycrystalline silicon (Poly-Si), etc.

[0046] The electrodes 231 and 232 are made of a metal such as an aluminum silicon alloy (Al-Si) and are arranged so as to be electrically connected to the heater layer 213. The electrode support layer 214 is made of SiO ２ The protective layer 215 is made of Si ３ N ４ The protective layer 215 is made of a material that protects the lower layers, including the electrode support layer 214, from external disturbances. The electrodes 231 and 232 are exposed on the +z side from the upper surface of the protective layer 215.

[0047] The membrane M is a film-like portion on the xy plane that is made up of each of the multiple layers of the light source 2, excluding the Si support layer 211. That is, the membrane M has, from the −z direction side to the +z direction side, a silicon oxide film 212A, a silicon nitride film 212B, a silicon oxide film 212C, a heater layer 213, an electrode support layer 214, and a protective layer 215, in that order. The membrane M is disposed inside the heater layer 213 in a planar view, and is susceptible to temperature rise due to heat generation from the heater layer 213 and deformation due to thermal stress. Furthermore, in the xy plane of the layered structure of the light source 2, the region corresponding to the Si support layer 211 (region other than the membrane M) experiences little temperature rise due to heat generation from the heater layer 213 and little deformation due to thermal stress.

[0048] The heater layer 213 is electrically connected to the electrodes 231 and 232. The pads P1 and P2 are pads for wire bonding, with the pad P1 electrically connected to the electrode 231 and the pad P2 electrically connected to the electrode 232. The pads P1 and P2 are electrically connected to terminals of a wiring pattern on the substrate 6 by wire bonding, and the heater layer 213 is energized by application of a voltage.

[0049] The light source 2 as a MEMS type light source is small and low-profile, which allows for miniaturization of the sensor module. Furthermore, the light source 2 as a MEMS type light source has features such as a long life, low power consumption, and a short response time, which allows for low power consumption of the entire sensor module. The short response time of the MEMS type light source makes it possible to shorten the standby time after power is turned on when performing intermittent driving, thereby reducing average power consumption.

[0050] Furthermore, since the light source 2 as a MEMS-type light source can directly utilize the light emitted from the surface of the high-temperature part, it can also be applied to the detection of gases with absorption bands at long wavelengths. Furthermore, the infrared emitting region of the light source 2 is patterned with high precision as a membrane M on the flat surface of the Si support layer 211, and individual variations in the direction of radiation are extremely small. Therefore, when a sensor module is constructed using the light source 2, variations in the amount of received light are reduced, contributing to improved product yield. Furthermore, the light source 2 is mass-produced using MEMS technology based on silicon wafers, making it suitable for mass production.

[0051] Furthermore, since the membrane M of the light source 2 has a round shape on the xy plane, the thermal stress generated during heating is uniform, improving the mechanical strength. Therefore, the light source 2 is prevented from being damaged by thermal stress during operation, contributing to an extension of the product life.

[0052] The light source 2 is a surface-mounted component, but is not limited to this and may be housed in a DIP (Dual Inline Package) component (such as a CAN package) or an SMD (Surface Mount Device) component (such as a surface-mounted package made of ceramic, etc.).

[0053] 3, the optical filter 3 is a filter that is provided to cover the light receiving surface of the light receiving unit 4 and transmits light (infrared light) in a wavelength range (band) that corresponds to the absorption wavelength specific to the detection target gas G. In this way, the transmission wavelength of the optical filter 3 is designed to match the absorption wavelength specific to the detection target gas G, thereby suppressing changes in the amount of light caused by gases other than the detection target gas G and improving the signal-to-noise ratio of the detection signal from the light receiving unit 4.

[0054] The optical filter 3 has, for example, a silicon substrate as a substrate, and a dielectric multilayer film or a multilayer film made of an infrared-transmitting material such as Si, germanium (Ge), sulfide, or fluoride. The silicon substrate is a planar silicon substrate. The material of the substrate is not limited to silicon, but may also be germanium (Ge), quartz (SiO ２ ), alumina (Al ２ O ３ ), barium fluoride (BaF ２ ), calcium fluoride (CaF ２ ) or the like can be used. The multilayer film is a film having a plurality of layers formed on both sides of a silicon substrate. The planar shape of the optical filter 3 is rectangular, but is not limited to this and may be other shapes such as circular.

[0055] In this embodiment, the optical filter 3 is, for example, a bandpass filter whose center wavelength of transmittance is shifted by a predetermined amount toward the higher wavelength side from the wavelength showing maximum absorption in the absorption spectrum of the gas G to be detected at normal incidence (θ = 0°). The angle θ is the angle of incidence of infrared light on the optical filter 3 with respect to the central axis of the cross section of the outlet portion 132 of the light guide 13. The center wavelength of transmittance is the center wavelength of two wavelengths corresponding to 50% of the maximum transmittance in the wavelength characteristics of the transmittance of the filter. However, this is not limited thereto, and the optical filter 3 may be configured to use a longpass filter that cuts light on the shorter wavelength side than the wavelength showing maximum absorption in the absorption spectrum of the gas G to be detected and transmits light on the longer wavelength side.

[0056] The light receiving unit 4 is mounted on the +z side surface of the substrate 6 and is a thermopile-type optical sensor (infrared sensor) having multiple thermocouples, which detects the amount of incident infrared light and outputs a detection signal as an analog electrical signal. However, the light receiving unit 4 is not limited to a thermopile-type infrared sensor, and may be a quantum-type (cooled-type) phototube, photoconductive-type, or photovoltaic-type infrared sensor, or a thermal-type (uncooled-type) pyroelectric-type, thermocouple-type, or bolometer-type infrared sensor.

[0057] Furthermore, the light receiving unit 4 is a surface-mounted component, but is not limited to this configuration and may be housed in a DIP component (such as a CAN package) or an SMD component (such as a surface-mounted package made of ceramic, etc.). Furthermore, the light guide 13 can efficiently obtain the amount of light for the light source 2 and the light receiving unit 4 regardless of the orientation of the surface-mounted component, DIP component, etc.

[0058] The signal processing unit 5 is mounted on a flat area other than the optical cover 1 on the +z side surface of the substrate 6, and is an AFE (Analog Front End)-IC (Integrated Circuit) that serves as an electronic component (processor) that performs signal processing on the detection signal of the light receiving unit 4. The signal processing unit 5 amplifies and AD converts the analog detection signal of the light receiving unit 4, and generates a difference value between the detection value when the light source 2 is on and the detection value when the light source 2 is off during intermittent driving of the light source 2, for example. The signal processing unit 5 corrects the difference value of the detection values ​​for temperature and individual variations in the optical gas sensor device 100, and generates various status signals from the difference value of the digital detection values. The signal processing unit 5 outputs the difference value of the digital detection values ​​and status signals.

[0059] The substrate 6 is a PCB (Printed Circuit Board) made of FR-4 (Flame Retardant Type-4) with conductor wiring printed on a plate made of glass epoxy resin or the like. On the +z side of the substrate 6, an optical cover 1, a light source 2, a light receiving unit 4, a signal processing unit 5, a connector 7, and a circuit element unit 8 are mounted. The +z side of the substrate 6 is approximately parallel to the light emitting surface of the light source 2, the optical filter 3, and the light receiving surface of the light receiving unit 4.

[0060] The connector 7 is mounted on a flat area on the +z side of the substrate 6 other than the optical cover 1 and the signal processing unit 5, and is a connector for outputting various digital signals output from the signal processing unit 5 to an information processing unit of a downstream device (e.g., an alarm). The connector 7 is connected to the information processing unit of the device via a cable with a plug.

[0061] The circuit element unit 8 includes circuit elements such as switches such as the switch 81, an amplifier, a chip resistor, a chip capacitor, etc. The switch 81 is configured by an NMOSFET (N-channel Metal-Oxide-Semiconductor Field Effect Transistor), a CMOS (Complementary Metal-Oxide-Semiconductor), or the like.

[0062] 7 and 8, the results of a current test under the same conditions for the light source 2 of Example 1 of the present embodiment and a conventional light source of Comparative Example 1 will be described. Fig. 7 is a diagram showing the test time characteristics of the light source resistance change amount for the light source 2 of Example 1 and the light source of Comparative Example 1. Fig. 8 is a photograph showing the appearance of the light source 2 of Example 1 and the light source of Comparative Example 1 at times T1, T2, and T3 in Fig. 7.

[0063] A 3.3 VDC (Direct Current) was applied to the light source 2 of Example 1 and the light source of Comparative Example 1, and the light source resistance change [Ω] was measured for each test time [h]. The light source resistance change [Ω] is the change [Ω] in the resistance value (light source resistance value [Ω]) of the membrane (heater layer) between two electrodes in the light source. The light source of Comparative Example 1 has a device configuration similar to that of the light source 2 of Example 1, but the shape of the membrane in the xy plane is approximately rectangular. Furthermore, test time = 0 [h] is defined as time T1, test time = 320 [h] is defined as time T2, and test time = 820 [h] is defined as time T3. The light source resistance change [Ω] when the light source resistance value at time T1 is used as the reference was defined as 0 [Ω].

[0064] 7, at time T1 in the initial period of energization, the light source resistance change amount [Ω] is the same between the light source 2 of Example 1 and the light source of Comparative Example 1. As shown in Fig. 8, at time T1, no change is observed between the light source 2 of Example 1 and the light source of Comparative Example 1 on the top surface viewed from the +z direction side.

[0065] After the test time has elapsed, as shown in FIG. 7 , the light source resistance change [Ω] of the light source of Comparative Example 1 drops slightly and then rises significantly until time T2. In contrast, the light source resistance change [Ω] of Light Source 2 of Example 1 drops slightly from time T1 and remains stable until time T2. The phenomenon of the light source resistance change [Ω] dropping around time T1 is caused by the material of the light source. Furthermore, as shown in FIG. 8 , at time T2, no change is observed on the top surface of Light Source 2 of Example 1, but cracks have appeared on the top surface of the light source of Comparative Example 1, as indicated by the arrows.

[0066] Further, after the test time has elapsed, as shown in FIG. 7 , the light source resistance change [Ω] of the light source of Comparative Example 1 rises sharply, reaching a value too large to be measured at time T3. In contrast, the light source resistance change [Ω] of Light Source 2 of Example 1 at time T3 remains stable, with almost no change from the value at time T2. As shown in FIG. 8 , at time T3, damage occurred on the top surface of the light source of Comparative Example 1, as indicated by the arrow. Due to this damage, the electrodes of the light source of Comparative Example 1 were in an open state at time T3. In contrast, no damage was observed on the top surface of Light Source 2 of Example 1 at time T3, and damage to the membrane M was suppressed.

[0067] As described above, according to this embodiment, the light source 2 includes the heater layer 213 that generates heat when current is passed between the electrodes 231 and 232, and the membrane M that is disposed inside the heater layer 213 in a plan view and emits infrared rays when heated. Because the membrane M has a round shape in the xy plane perpendicular to the film thickness direction (z-axis direction), thermal stress generated during heating is alleviated and mechanical strength is improved. Therefore, damage to the membrane M due to thermal stress during operation can be suppressed, and the life of the light source 2 can be extended.

[0068] In particular, when the membrane M has a circular shape, the thermal stress generated during heating becomes uniform, which can further suppress damage to the membrane M due to thermal stress during operation and extend the life of the light source 2. Note that the membrane M may have a round shape other than a circle, such as an ellipse.

[0069] The membrane M has a heater layer support layer 212, an electrode support layer 214, and a protective layer 215. The heater layer support layer 212 supports the heater layer 213. The electrode support layer 214 is formed on the heater layer 213 and supports the electrodes 231 and 232. The protective layer 215 is formed on the electrode support layer 214.

[0070] The optical gas sensor device 100 includes a light source 2, an optical filter 3, a light receiving unit 4, and an optical cover 1. The optical filter 3 transmits infrared light emitted from the light source 2 and transmitted through the gas G to be detected. The light receiving unit 4 detects the infrared light incident thereon through the optical filter 3 and generates a detection signal. The optical cover 1 covers the light source 2, the optical filter 3, and the light receiving unit 4.

[0071] Second Embodiment A second embodiment of the present invention will be described with reference to FIGS. 9 to 12. FIG. 9 is a diagram showing the applied voltage characteristics of the deformation amount for the light source 2 of Examples 2 and 3 of this embodiment and the light source of Comparative Examples 2 and 3. FIG. 10 is a diagram showing the test time characteristics of the light source resistance change amount for the light source 2 of Example 2 of this embodiment and the light source of Comparative Example 2. FIG. 11 is a photograph showing the appearance of the light source 2 of Example 2 and the light source of Comparative Example 2 at times T11 and T12 in FIG. 10. FIG. 12 is a diagram showing the deformation amount when 3.3 VDC is applied as a function of the ratio of the tensile stress film thickness to the total membrane thickness for the light source 2 of Examples 2 and 3 and the light source of Comparative Examples 2 and 3.

[0072] In this embodiment, the optical gas sensor device 100 of the first embodiment is further configured such that the film thickness (length in the z-axis direction) of each layer of the membrane M of the light source 2 is changed. Therefore, the optical gas sensor device 100 of the first embodiment is used as the device configuration of this embodiment. Also, a description of the same parts as those of the optical gas sensor device 100 of the first embodiment will be omitted, and the description will focus mainly on the different parts.

[0073] As shown in FIG. 5, in the optical gas sensor device 100 of this embodiment, the membrane M of the light source 2 is made of MoSi ２ and the heater layer support layer 212, the electrode support layer 214, and the protective layer 215, which are insulating layers. ３ N ４ , SiO ２ and,

[0074] MoSi used in this embodiment ２ and Si ３ N ４ has tensile stress. ２ has compressive stress. The stress applied to the membrane M is determined by the internal stress of each layer and the film thickness. In this embodiment, the stress of the membrane M is set to tensile stress, thereby alleviating the compressive stress that occurs when heat is generated and reducing the mechanical stress caused by deformation during operation. Of the multiple layers of the membrane M, the layer that has tensile stress is referred to as a tensile stress layer, and the layer that has compressive stress is referred to as a compressive stress layer.

[0075] For example, let us consider a light source 2 having a membrane M in which the entire layer is in a tensile stress state, with the thickness configuration of each layer shown in the leftmost column of Table I. The light source 2 having the membrane M with the thickness configuration in the leftmost column of Table I is Example 2 of this embodiment. Similarly, the light source 2 having the membrane M with the thickness configuration in the second column from the left of Table I is Example 3 of this embodiment. Similarly, the light sources having membranes with the thickness configurations in the third and fourth columns from the left of Table I are Comparative Examples 2 and 3, respectively.

[0076] Here, as shown in Table II, the MoSi ２ or Si ３ N ４ The thickness ratio of the tensile stress layer (heater layer 213 + silicon nitride film 212B + protective layer 215) consisting of the above was changed. In Examples 2 and 3, the ratio of the thickness of the tensile stress layer to the total thickness of the membrane M was 0.25 and 0.24, respectively. Similarly, in Comparative Examples 2 and 3, the ratio of the thickness of the tensile stress film to the total thickness of the membrane M was 0.17 and 0.12, respectively. The light sources of Comparative Examples 2 and 3 have the same configuration as the light source 2 except for the film thickness of each layer of the membrane M.

[0077] As shown in FIG. 9 , the deformation amount [μm] in the +z direction of the center position of the xy plane of the membrane M relative to the applied DC voltage [V] was measured for the light source 2 of Examples 2 and 3 and the light sources of Comparative Examples 2 and 3. For the light source of Comparative Example 2, as the applied voltage was increased from 0 [V] to 5 [V], the deformation amount [μm] increased from the deformation amount [μm] at 0 [V], and buckling occurred at approximately 3 [V]. Buckling refers to the phenomenon in which, as the load applied to a structure is gradually increased, the deformation pattern suddenly changes at a certain load, resulting in large deflection. Here, buckling corresponds to a large change from a positive deformation amount [μm] to a negative deformation amount [μm]. For the light source of Comparative Example 3, the deformation amount [μm] increased from the deformation amount [μm] at 0 [V], and buckling occurred at approximately 4 [V].

[0078] In contrast, in the light sources of Examples 2 and 3, even when the applied voltage is increased from 0 V to 5 V, the deformation amount [μm] remains almost unchanged from the deformation amount [μm] at 0 V, and no buckling occurs. Table II includes the deformation amount [μm] and the presence or absence of buckling when the applied voltage is 3.3 VDC for the light source 2 of Examples 2 and 3 and the light sources of Comparative Examples 2 and 3.

[0079] Next, as shown in Fig. 10, a voltage of 3.3 VDC was applied to the light source 2 of Example 2 and the light source of Comparative Example 2, and the change in light source resistance [Ω] versus the test time [h] of voltage application was measured. The change in light source resistance [Ω] is the change in light source resistance value [Ω] when the value at test time = 0 [h] is set as 0 [Ω] as a reference. Test time = 0 [h] is set as time T11, and test time = 3000 [h] is set as time T12.

[0080] 10 , at time T11 before 3.3 VDC is applied to the light source 2 of Example 2 and the light source of Comparative Example 2, the light source resistance change amount is 0 [Ω] in both cases. As shown in FIG. 11 , at time T11, no defects such as deformation occur on the top surface of either the light source 2 of Example 2 or the light source of Comparative Example 2.

[0081] As shown in Fig. 10, after the start of application of 3.3 VDC, as the test time increases, the light source resistance change [Ω] of the light source of Comparative Example 2 drops once and then suddenly rises significantly up to time T12. As shown in Fig. 11, at time T12, the light source of Comparative Example 2 exhibited significant deformation on the upper surface, and in particular, cracks (fissures, fissures) occurred, as indicated by the arrows in the enlarged view.

[0082] In contrast, as shown in Fig. 11, after the start of application of 3.3 VDC, as the test time increases, the light source resistance change [Ω] of the light source 2 of Example 2 decreases once, and then increases gradually and slightly until time T12. As shown in Fig. 11, at time T12, the light source 2 of Example 2 does not experience any significant deformation on the upper surface.

[0083] As shown in FIG. 12 , for the light sources 2 of Examples 2 and 3 and the light sources of Comparative Examples 2 and 3, the deformation amount [μm] in the +z direction at the center position of the xy plane of the membrane M when a voltage of DC 3.3 [V] is applied in FIG. 9 is plotted against the ratio of the tensile stress film thickness to the total thickness of the membrane M. When the ratio of the tensile stress film thickness to the total thickness of the membrane M is less than 0.2, the deformation amount [μm] is large. Furthermore, when this ratio is 0.2, the deformation amount [μm] decreases to approximately 8.5 [μm]. As this ratio increases above 0.2, the deformation amount [μm] also decreases. When this ratio is 0.24 or more, the deformation amount [μm] is also 1 [μm] or less, and the tensile stress exceeds the compressive stress.

[0084] Based on the results shown in Figures 9 to 12, by setting the ratio of the thickness of the tensile stress layer (tensile stress film) to the total thickness of the membrane M to a predetermined threshold value of 0.20 or more, preferably 0.24 or more, deformation and buckling of the membrane M can be suppressed, mechanical stress can be reduced, and the life of the light source 2 can be extended.

[0085] As described above, according to the present embodiment, the light source 2 includes a Si support layer 211 having a space in the center in a planar view, and a membrane M including a heater layer 213 provided continuously above the Si support layer 211 and the space, fixed to the Si support layer 211 around the periphery of the space, and including a plurality of electrodes that generate heat and emit infrared rays when current is applied between the electrodes. The membrane M covers the space and is layered including a silicon nitride film 212B as a tensile stress layer having tensile stress in the planar direction, the heater layer 213, and a protective layer 215, as well as silicon oxide films 212A and 212C as compressive stress layers having compressive stress in the planar direction, and an electrode support layer 214. The ratio of the thickness of the tensile stress layer in the film thickness direction to the total thickness of the membrane M in the film thickness direction above the Si support layer 211 and the space is equal to or greater than a predetermined threshold at which the tensile stress exceeds the compressive stress in the membrane M. This suppresses deformation and buckling of the membrane M, reducing mechanical stress and extending the life of the light source 2.

[0086] The predetermined threshold value is 0.24. Therefore, deformation and buckling of the membrane M can be further suppressed, mechanical stress can be reduced, and the life of the light source 2 can be extended.

[0087] The membrane M comprises a heater layer support layer 212 that supports the heater layer 213, an electrode support layer 214 that is formed on the heater layer 213 and supports the electrodes 231 and 232, and a protective layer 215 that is formed on the electrode support layer 214, and includes at least one tensile stress layer and at least one compressive stress layer. For example, the heater layer 213, the protective layer 215, and the silicon nitride film 212B of the heater layer support layer 212 have tensile stress, while the silicon oxide films 212A and 212C of the heater layer support layer 212 and the electrode support layer 214 have compressive stress. This makes it possible to suppress deformation and buckling of the membrane M, reduce mechanical stress, and extend the life of the light source 2.

[0088] (Third embodiment) A third embodiment of the present invention will be described with reference to Figs. 13 to 16. Fig. 13 is a schematic cross-sectional view of a light source 2a of this embodiment. Fig. 14 is a diagram showing the applied voltage characteristics of the deformation amount of a light source 2a of Example 4 of this embodiment and a light source of Comparative Example 4. Fig. 15 is a diagram showing the displacement Z vs. displacement X characteristics of the light source of Comparative Example 4. Fig. 16 is a diagram showing the displacement Z vs. displacement X characteristics of the light source 2a of Example 4.

[0089] The light source device of Patent Document 1 includes a substrate with a portion removed, upper and lower protective layers, an electrothermal conversion unit sandwiched between the protective layers, and a radiation unit formed on the upper protective layer. When current is applied to the electrothermal conversion unit, the radiation unit is heated and emits infrared rays. The protective layer in the region where a portion of the substrate is removed, the electrothermal conversion unit, and the radiation unit form a membrane (film) structure. However, in the thin-film structure of the light source device of Patent Document 1, depending on the stress distribution in the film thickness direction, warping of the membrane occurs due to thermal stress when heat is generated, which may shorten the lifespan due to mechanical stress.

[0090] In this embodiment, the material, shape, and arrangement of each layer of the membrane M of the light source 2 are further changed in the device configuration of the first embodiment. Therefore, the device configuration of this embodiment is the same as that of the optical gas sensor device 100 of the first embodiment, except that the light source 2 is replaced with the light source 2a shown in Fig. 13. Also, descriptions of the same parts as those of the optical gas sensor device 100 of the first embodiment will be omitted, and the following description will focus mainly on the differences.

[0091] 13 , in the optical gas sensor device 100 of this embodiment, the light source 2a has a configuration in which, from the −z direction side to the +z direction side, a Si support layer 211, a heater layer support layer 212, a heater layer 213, electrodes 231 and 232, an electrode support layer 214, and a protective layer 215 are laminated in this order. However, the membrane Ma of the light source 2a has a configuration in which, from the −z direction side to the +z direction side, a silicon nitride film 212B, a silicon oxide film 212C, the heater layer 213, the electrode support layer 214, and the protective layer 215 are laminated in this order.

[0092] In a thin film structure, stress distribution in the film thickness direction causes warping of the membrane due to thermal stress during heat generation, which raises concerns about reduced lifespan due to mechanical stress. For this reason, in this embodiment, the membrane Ma has a symmetrical structure in the film thickness direction (z-axis direction) with respect to the heater layer 213. That is, in the membrane Ma, layers of the same film type (material) are arranged symmetrically in the film thickness direction for each insulating layer, with the heater layer 213 at the center, and the film thickness (thickness) of each layer is set symmetrically in the film thickness direction.

[0093] More specifically, the membrane Ma has the structure shown in Table III, for example.

[0094] The film type of the silicon oxide film 212C and the electrode support layer 214 adjacent to the heater layer 213 in the +z direction and the −z direction (SiO ２ ) and film thickness (0.8 μm) are set to be the same. Furthermore, the film type (Si ３ N ４ The thickness (0.2 μm) of the membrane is set to be the same as that of the membrane Ma in Table III.

[0095] Next, as shown in Fig. 14, a DC voltage was applied to the light source 2a of Example 4 and the light source of Comparative Example 4, and the deformation amount [µm] in the z-axis direction at the center position of the xy plane of the membrane relative to the applied voltage [V] was measured. The light source of Comparative Example 4 has a configuration similar to that of the light source 2a, but has a structure in which the film type and film thickness of each layer in the membrane are asymmetric in the z-axis direction with the heater layer at the center. Specifically, the light source of Comparative Example 4 is the light source 2 having the film type and film thickness of each layer of Example 2 in Table I.

[0096] 14, as the applied voltage [V] is increased from 0 [V], the deformation amount [μm] of the upper surface of the light source of Comparative Example 4 also increases. In contrast, even when the applied voltage [V] is increased from 0 [V], the deformation amount [μm] of the upper surface of the light source 2a of Example 4 remains almost unchanged.

[0097] As shown in FIG. 15 , for the light source of Comparative Example 4, the displacement Z [μm] in the +z direction of the upper surface was measured relative to the displacement X in the x-axis direction (direction perpendicular to the y-axis direction) at the center position of the membrane in the y-axis direction (the extension direction of the two electrodes in the xy plane). In FIG. 15 , an arbitrary height of the light source was set as the reference (0 μm) for the displacement Z. The driving state of the light source of Comparative Example 4 during measurement was 3.3 VDC driving, in which the applied voltage was 3.3 VDC, and no-load driving, in which no voltage was applied (applied voltage = 0 V). For the light source of Comparative Example 4, the displacement Z [μm] of the membrane portion between the electrodes during no-load driving was almost constant in the x-axis direction. However, for the light source of Comparative Example 4, when driven at 3.3 VDC, the displacement Z [μm] of the membrane portion rose in a dome-like shape along the x-axis direction, resulting in deformation.

[0098] As shown in Figure 16, similar to Figure 15, the displacement Z [µm] relative to the displacement X at the center position of the membrane in the y-axis direction was measured for the light source 2a of Example 4. In Figure 16, an arbitrary height of the light source 2a was also set as the reference (0 [µm]) for the displacement Z. For the light source 2a of Example 4, the displacement Z [µm] of the membrane Ma portion was almost constant in the x-axis direction, even when driven without load and at 3.3 VDC, and no deformation occurred. Since no deformation occurs when driven at 3.3 VDC, deformation due to thermal stress caused by heat generation due to the applied voltage to the heater layer 213 is suppressed, mechanical stress is reduced, and the light source 2a has a longer life.

[0099] As described above, according to this embodiment, the light source 2a includes the heater layer 213 that generates heat when current is applied between the electrodes 231 and 232, and the membrane Ma that emits infrared rays when heated. The membrane Ma has multiple insulating layers stacked together with the heater layer 213. The multiple insulating layers include insulating layers (silicon nitride film 212B, protective layer 215) having tensile stress and insulating layers (silicon oxide film 212C, electrode support layer 214) having compressive stress, which are stacked together with the heater layer 213. Each insulating layer has a structure in which the film type and film thickness are symmetric (axis symmetric) in the film thickness direction (z-axis direction) with respect to the heater layer 213. As a result, no deformation occurs during operation, and deformation due to thermal stress resulting from heat generation due to voltage applied to the heater layer 213 can be suppressed, mechanical stress can be reduced, and the light source 2a can have a longer life.

[0100] The plurality of insulating layers also include a heater layer support layer 212, an electrode support layer 214, and a protective layer 215. The heater layer support layer 212 supports the heater layer 213. The electrode support layer 214 is formed on the heater layer 213 and supports the electrodes 231 and 232. The protective layer 215 is formed on the electrode support layer 214. This can further reduce mechanical stress and extend the life of the light source 2a.

[0101] The description of the first to third embodiments is merely an example of the light source and optical gas sensor device according to the present invention, and the present invention is not limited to these. For example, the configurations of the second and third embodiments may be appropriately combined.

[0102] In the second and third embodiments, the xy plane shape perpendicular to the film thickness direction (z-axis direction) of the membranes M and Ma may be a shape other than a circle, such as a rectangle.

[0103] Furthermore, the detailed configuration and operation of the optical gas sensor device 100 in the above embodiment can also be modified as appropriate without departing from the spirit of the present invention.

[0104] As described above, the light source and the optical gas sensor device according to the present invention are suitable for detecting gases such as refrigerants.

[0105] 100 Optical gas sensor device G Gas 1 Optical cover 110A, 110B Cover portion 11 Gas introduction port 111, 112, 113, 114 Gas intake port 13 Light guide portion 131 Inlet portion 132 Outlet portion 12 Contamination filter SP Space portion 2, 2a Light source 211 Si support layer 212 Heater layer support layer 212A Silicon oxide film 212B Silicon nitride film 212C Silicon oxide film 213 Heater layer 231, 232 Electrode 214 Electrode support layer 215 Protective layer P1, P2 Pad M, Ma Membrane 3 Optical filter 4 Light receiving portion 5 Signal processing portion 6 Substrate 7 Connector 8 Circuit element portion 81 Switch

Claims

1. A light source comprising: a support layer having a space in the center in a planar view; and a membrane provided continuously above the support layer and the space, fixed to the support layer around the periphery of the space, the membrane including a heater layer that includes a plurality of electrodes and generates heat and emits infrared rays when current is passed between the electrodes, the membrane covering the space and comprising a laminate including at least one tensile stress layer having tensile stress in the planar direction and at least one compressive stress layer having compressive stress in the planar direction, the ratio of the thickness in the film thickness direction of the tensile stress layer to the total thickness in the film thickness direction of the membrane above the support layer and the space being equal to or greater than a predetermined threshold at which the tensile stress exceeds the compressive stress in the membrane.

2. The light source of claim 1, wherein the predetermined threshold is 0.

24.

3. The light source described in claim 1, wherein the membrane includes a heater layer support layer that supports the heater layer, an electrode support layer that is formed on the heater layer and that supports the electrodes, and a protective layer that is formed on the electrode support layer, and the heater layer and the protective layer have tensile stress, and the heater layer support layer and the electrode support layer have compressive stress.

4. A light source as described in claim 1, wherein the membrane is composed of an insulating layer having tensile stress and an insulating layer having compressive stress stacked together with the heater layer, and each insulating layer has a stacked structure in which the film type and film thickness are symmetrical in the film thickness direction with the heater layer at the center.

5. The light source according to claim 1, wherein the membrane has a circular shape in a plane perpendicular to the film thickness direction.

6. The light source of claim 5, wherein said round shape is a circle.

7. An optical gas sensor device comprising: a light source according to any one of claims 1 to 6; an optical filter that transmits infrared light emitted from the light source and transmitted through the gas to be detected; a light receiving unit that detects the infrared light incident through the optical filter and generates a detection signal; and an optical cover that covers the light source, the optical filter, and the light receiving unit.

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