Optical gas sensor device

Abstract

The present invention is directed to detecting a desired wavelength.　An optical gas sensor device 100 is provided with a light source 2, optical filters 31, 32, and a light receiving unit 4. The light source 2 emits infrared rays toward a gas G to be detected. The optical filter 31 transmits the infrared rays emitted from the light source 2. The optical filter 32 transmits the infrared rays that have been transmitted through the optical filter 31 and have passed through the gas G to be detected. The light receiving unit 4 detects the infrared rays incident through the optical filter 32 and generates a detection signal. The optical filters 31, 32 have wavelength transmission characteristics different from each other, and transmit a desired wavelength through a combination of the different wavelength transmission characteristics.

Description

Optical gas sensor device

[0001] The present invention relates to an optical gas sensor device.

[0002] Traditionally, continuous monitoring of gas concentrations has been conducted in homes, factories, and businesses from the perspective of managing chemical substances and ensuring worker safety. ２ Non-dispersive infrared absorption (NDIR) gas sensors are known for detecting the concentration of gases such as [list of gases]. NDIR gas sensors utilize the property that many gases absorb specific infrared wavelengths. When infrared light is emitted to the target gas, the sensor detects which wavelengths are absorbed and to what extent, thereby measuring the concentration of the target gas. For example, a gas sensor equipped with an infrared light source and a light receiver detects the concentration of the target gas in the optical path of the light source and light receiver.

[0003] For example, a multi-gas NDIR analyzer is known that has multiple bandpass filters that transmit narrowband infrared light corresponding to the wavelengths of different gases, and detects multiple gases (see Patent Document 1).

[0004] Special Publication No. 2001-503865

[0005] However, the conventional multi-gas NDIR analyzers described above use a bandpass filter with a single wavelength transmission characteristic for each gas, so there is a need to more accurately transmit and detect infrared radiation at a desired wavelength.

[0006] The objective of this invention is to detect a desired wavelength.

[0007] To solve the above problems, the optical gas sensor device of the present invention comprises: a light source that emits infrared rays to a gas to be detected; a first optical filter that transmits the infrared rays emitted from the light source; a second optical filter that transmits infrared rays that have passed through the first optical filter and through the gas to be detected; and a light receiving unit that detects infrared rays incident through the second optical filter and generates a detection signal, wherein the first optical filter and the second optical filter have different wavelength transmission characteristics, and a desired wavelength is transmitted by the combination of these different wavelength transmission characteristics.

[0008] According to the present invention, a desired wavelength can be detected.

[0009] This is a schematic diagram of an optical gas sensor device according to an embodiment of the present invention. This is a perspective view of the optical gas sensor device. This is a partially transmitted perspective view of the optical gas sensor device. This is a perspective view showing the sealing device. This is a perspective view of the light source. This is a diagram showing the transmission spectra of optical filters in the examples and comparative examples. This is a diagram showing the combination of types and composite characteristics of optical filters in the examples, the first modified example, and the second modified example. This is a diagram showing the absorption spectrum of water. This is a diagram showing the absorption spectrum of methane.

[0010] Hereinafter, embodiments and modifications of the present invention will be described in detail with reference to the attached drawings. However, the scope of the invention is not limited to the illustrated examples.

[0011] (Embodiment) An embodiment of the present invention will be described with reference to Figures 1 to 6. First, the schematic configuration of the optical gas sensor device 100 of this embodiment will be described with reference to Figure 1. Figure 1 is a schematic diagram of the optical gas sensor device 100 of this embodiment.

[0012] As shown in Figure 1, the optical gas sensor device 100 of this embodiment is an NDIR type gas sensor. The optical gas sensor device 100 comprises an optical cover 1, a light source 2, optical filters 31 and 32, a light receiving unit 4, a signal processing unit 5, and a switch 81. In the optical gas sensor device 100, the light source 2 emits infrared light. The emitted infrared light is emitted to the gas G of the detection target (measurement target) inside the optical cover 1 via the optical filter 31 and the optical path (path) inside the optical cover 1. The optical filter 31 is a long-pass filter. The long-pass filter cuts out light on the shorter wavelength side than a predetermined cut-on wavelength and transmits light including the absorption wavelength of the gas G on the longer wavelength side.

[0013] The amount of light reaching the light-receiving unit 4 decreases as molecules of the target gas G present in the optical path absorb infrared radiation. The optical gas sensor device 100 detects the infrared radiation partially absorbed by the target gas G via the optical filter 32 to the light-receiving unit 4. The optical filter 32 is a bandpass filter. The bandpass filter transmits light in the wavelength band that includes the absorption wavelength of gas G. With this configuration, the light-receiving unit 4 does not receive unfiltered infrared radiation emitted from sources other than the light source 2, improving the signal-to-noise ratio (SNR) of the sensor.

[0014] The optical gas sensor device 100 processes the detection signal detected by the light receiving unit 4 using the signal processing unit 5 to detect (measure) the concentration of the target gas G and output it. The switch 81 is a switch that turns the light emission of the light source 2 on and off, and is included in the circuit element unit 8, which will be described later. When gas detection is performed, the signal processing unit 5 turns the light source 2 on and off via the switch 81.

[0015] The optical cover 1 has a gas introduction port 11, which serves as a gas inlet and outlet for the gas G to be detected. A contamination filter 12 is attached to the gas introduction port 11. The contamination filter 12 is, for example, a metal mesh filter or a porous resin film, and prevents foreign matter from entering from the outside.

[0016] In this manner, the optical gas sensor device 100 filters the infrared light emitted from the light source 2 to the gas G to be detected by optical filters 31 and 32 and receives it with the light receiving unit 4. Optical filter 31 is located near the light source 2 on the optical path downstream of the light source 2. Optical filter 32 is located near the light receiving unit 4 on the optical path upstream of the light receiving unit 4.

[0017] The optical filter 31 may be configured as a bandpass filter. In this configuration, the optical filter 32 may be configured as a longpass filter.

[0018] In this embodiment, the optical path is designed so that the infrared light received by the light-receiving unit 4 arrives after reflecting off the inner surface of the optical cover 1 from the light source 2. A higher reflectivity on the inner surface of the optical cover 1 is desirable as it increases the efficiency of light (infrared light) utilization. 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 off the inner surface of the optical cover 1, but also an optical path that arrives directly from the light source 2.

[0019] Furthermore, in this embodiment, the light source 2 and the optical filter 31 are packaged as a single component, the sealing device 20, which will be described later. The optical filter 32 and the light receiving unit 4 are packaged as a single component, the sealing device 40, which will be described later.

[0020] The optical gas sensor device 100 is designed to detect alternative fluorocarbon refrigerants, which are used as refrigerants in air conditioners, as the target gas G. Alternative fluorocarbons are synthetic compound (gas) refrigerants used industrially as substitutes for specific chlorofluorocarbons (CFCs). Because CFC refrigerants have a high ozone depletion potential and contribute to the depletion of the Earth's ozone layer, replacement with hydrochlorofluorocarbon (HCFC) refrigerants, which have a lower ozone depletion potential, has begun. Furthermore, in developed countries, there is a shift from HCFC refrigerants to HFC refrigerants (R410A), which have an ozone depletion potential of 0.

[0021] CFC refrigerants, HCFC refrigerants, and HFC refrigerants are known to have high global warming potentials and to be greenhouse gases that cause global warming. For this reason, the replacement of HFC refrigerants (R410A) with HFC refrigerants (R32) with lower global warming potentials is being considered. In this embodiment, for example, R32 as a fluorocarbon refrigerant is detected as the gas G to be detected.

[0022] However, the gas G to be detected is not limited to R32. Other fluorocarbon refrigerants may also be detected, such as R-454C, which has an extremely low Global Warming Potential (GWP). Examples of other fluorocarbon refrigerants include R143a, R152a, R1132, R142b, R1234yf, R1234ze(E), R-444A, R-444B, R-445A, R-446A, R-447A, R-447B, R-451A, R-451B, R-452B, R-454A, R-454B, R-454C, R-455A, R-457A, R-459A, R-459B, R-462A, and R-465A. Furthermore, the gas G to be detected is not limited to fluorocarbon refrigerants, but may also include 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, and the like.

[0023] The optical gas sensor device 100 outputs various status signals based on the gas concentration of the detected gas G to an information processing unit of a 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, fault signals, alarm signals, and monitoring signals (normal signals). A fault signal indicates a fault in the optical gas sensor device 100. An alarm signal indicates that the concentration of the detected gas G exceeds a threshold concentration at which a gas leak is determined to have occurred. A monitoring signal indicates that the concentration of the detected gas G is in a normal state. If the device is an alarm, it will issue various alarms (for example, an alarm for a fault in the optical gas sensor device 100 based on a fault signal, or an alarm for an abnormal concentration of the detected gas G based on an alarm signal) in response to the various signals received from the optical gas sensor device 100. The device may be a device including the optical gas sensor device 100 and an MCU, or it may be a separate device (an external device including an MCU) from the optical gas sensor device 100. The above-mentioned equipment includes room air conditioners, air conditioners for shops and offices, and multi-split air conditioners for buildings.

[0024] Next, the specific configuration of the optical gas sensor device 100 will be described with reference to Figures 2 to 5. Figure 2 is a perspective view of the optical gas sensor device 100. Figure 3 is a partially transmitted perspective view of the optical gas sensor device 100. Figure 4 is a perspective view of the sealing device 20. Figure 5 is a perspective view of the light source 2.

[0025] As shown in Figures 2 and 3, the optical gas sensor device 100 comprises an optical cover 1, sealants 20 and 40, a signal processing unit 5, a substrate 6, a connector 7, and a circuit element unit 8. The sealant 20 has a light source 2 and an optical filter 31. The sealant 40 has an optical filter 32 and a light receiving unit 4. In Figure 2, the x, y, and z axes are shown. These three axes are the same in the other figures. Note that the contamination filter 12 is not shown in Figures 2 and 3.

[0026] The optical cover 1 is mounted on the surface of the substrate 6 in the +z direction and is a cover that covers (encompasses) the sealants 20 and 40. The optical cover 1 has a cavity (space) inside that can accommodate the gas G to be detected, and the gas G to be detected is introduced into and out of the cavity via the gas introduction port 11. The base material of the optical cover 1 is, for example, made of resin.

[0027] As shown in Figure 2, the optical cover 1 has cover portions 110A and 110B. Cover portion 110A is the upper (+z direction) part and is integrated with cover portion 110B by methods such as bonding or heat crimping. Cover portion 110B is the lower (-z direction) part and is integrated with cover portion 110A by methods such as bonding or heat crimping.

[0028] Furthermore, as shown in Figure 3, the optical cover 1 has a light guide section 13, which is a cavity into which the gas G to be detected is introduced. The light guide section 13 is a pipe-shaped optical path, with a circular cross-section perpendicular to the axial direction. Cover section 110A has a half-pipe section. Cover section 110B also has a half-pipe section. The light guide section 13 is formed by the joining of the half-pipe sections of cover sections 110A and 110B. Thus, the optical cover 1 has cover sections 110A and 110B, which are divided by the axial cross-section of the light guide section 13. As shown in Figure 3, the light guide section 13 has a roughly U-shape in three dimensions when viewed from the +z direction (in an xy-plane view).

[0029] The inner surface of the light guide section 13 is covered with an infrared reflective film. In this embodiment, gold is used as the infrared reflective film, but it is not limited to this. Silver or aluminum may also be used as the infrared reflective film. Furthermore, if necessary, a protective film such as silicon oxide or silicon nitride may be formed on the infrared reflective film to prevent corrosion of the metal film of the infrared reflective film. Methods for forming the infrared reflective film and protective film include plating, sputtering, and vacuum deposition. For example, the optical cover 1 may be integrally fabricated from a metal such as aluminum using a metal 3D printer. In any case, it is preferable to have a mirror finish on the inner surface of the light guide section 13 in order to efficiently reflect infrared rays.

[0030] The light guide unit 13 reflects the infrared light emitted from the light source 2 of the sealing device 20 and incident via the optical filter 31 using the infrared reflective film on its inner surface. The light guide unit 13 then emits the reflected infrared light to the light receiving unit 4 via the optical filter 32 of the sealing device 40. In this way, the optical cover 1 plays the role of efficiently guiding the infrared light from the light source 2 to the light receiving unit 4 as an optical path, by reflecting the infrared light emitted from the light source 2 with the infrared reflective film, so that at least a portion of the reflected light reaches the light receiving unit 4 via the optical filter 32.

[0031] In this embodiment, the optical path inside the optical cover 1 is a pipe-shaped light guide section 13 having a circular cross section perpendicular to the axial direction. Thereby, regardless of the diameter and path of the cross-section of the light guide section 13, the reflection angle of infrared rays is kept constant in any direction of the three dimensions (x-axis, y-axis, z-axis), and the infrared rays emitted from the light source 2 are reflected inside the light guide section 13 and can efficiently enter the light receiving section 4. It should be noted that the cross section perpendicular to the axial direction of the optical path of the light guide section 13 of the optical cover 1 may be elliptical or a shape combining a curved line and a straight line.

[0032] In addition, the optical path length of infrared rays 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 guide section 13.

[0033] In addition, regarding the cross-sectional area of the cross-section perpendicular to the axial direction of the light guide section 13, the main portion (a portion other than the inlet section 131 and the outlet section 132 to be described later) is constant in the axial direction. Since the cross-sectional area is constant, the gas concentration per unit volume of the detection target gas G that has entered the light guide section 13 is easily uniformized, and infrared rays pass randomly without passing through a specific path, so it is easy to respond to changes in the gas concentration of the gas G. Fig. 3 shows an optical path propagation state in which a plurality of infrared ray optical paths inside the light guide section 13 are represented by solid arrows. As described above, the infrared optical paths are random inside the light guide section 13.

[0034] In addition, the infrared rays emitted from the light source 2 of the sealing member 20 are incident on the light guide section 13 on the -x direction side through the optical filter 31. The light guide section 13 on the -x direction side extends in the axial direction from the -z direction side to the +z direction side, then bends in an R shape, and extends linearly from the -y direction side to the +y direction side. The end portion on the infrared incident side of the light guide section 13 is defined as the inlet section 131. The light guide section 13 extending toward the +y direction side bends in an R shape, extends in the axial direction from the -x direction side to the +x direction side, and bends in an R shape again.

[0035] Then, the light guide section 13 on the +x direction side extends linearly in the axial direction from the +y direction side to the -y direction side, then bends in an R shape and extends toward the -z direction side. The infrared rays that have passed through the light guide section 13 are emitted to the light receiving section 4 through the optical filter 32 of the sealing member 40. The end portion on the infrared emission side of the light guide section 13 is defined as the outlet section 132.

[0036] The exit portion 132 has a tapered shape in which the cross-sectional area becomes smaller as the axial direction of the light guide portion 13 goes from the +z direction side to the -z direction side. Similarly, the inlet portion 131 has a tapered shape in which the cross-sectional area becomes smaller as the axial direction of the light guide portion 13 goes from the +z direction side to the -z direction side. Therefore, the condensing degree of infrared rays radiated to the light receiving portion 4 through the light guide portion 13 can be increased.

[0037] In addition, the cover portions 110A and 110B each have a hollow portion (not shown) as a space for thinning (coring out). These hollow portions can achieve weight reduction of the optical cover 1 (optical gas sensor device 100).

[0038] Furthermore, the cover portion 110B includes fixing pins 121 and 122. The fixing pins 121 and 122 are convex portions extending in the +z direction, and are butted against recesses (female holes) (not shown) of the cover portion 110A to be integrated by a method such as adhesion or heat caulking. Through the integration achieved by butting the fixing pins against the recesses of the cover portion 110A and integrating by a method such as adhesion or heat caulking, the cover portions 110A and 110B are positioned, fixed, and formed into an integral component.

[0039] As shown in FIG. 2, the cover portion 110A has gas intake ports 111 and 112 as the gas introduction port 11. The gas intake ports 111 and 112 are holes opened in the -z direction from the upper surface of the cover portion 110A. The space around the sealing member 20 is electrically conducted to the light guide portion 13. The space around the sealing member 40 is conducted to the light guide portion 13.

[0040] The gas intake ports 111 and 112 are conducted to the light guide portion 13 via gas introduction ports 133 and 134. The gas taken in from the gas intake ports 111 and 112 once enters the inner space of the optical cover 1, and then is introduced into the light guide portion 13 through the gas introduction ports 133 and 134. Here, the gas introduction ports 133 and 134 are provided at positions where a line connecting the centers of the gas intake ports 111 and 112 and the centers of the gas introduction ports 133 and 134 in a top view forms 45 degrees with respect to the x-axis. It should be noted that the shape, size and position of the gas introduction port 11 (gas intake ports 111, 112) of the optical cover 1 in FIG. 2 are merely examples, and are not limited thereto.

[0041] As shown in Figure 4, the sealing device 20 is mounted on the substrate 6 and seals the light source 2 inside the sealing device 20. The sealing device 20 protects the light source 2 from external environmental factors such as humidity and environmentally harmful gases inside and outside the sealing device 20, i.e., the space enclosed by the cover portions 110A and 110B. Inside the sealing device 20, the light source 2 is mounted by bonding it to the bottom (bottom surface 213) of the space enclosed by the protective cover, for example, the ceramic substrate 21 in this embodiment, using an adhesive portion (not shown), and the optical filter 31 is bonded and sealed to the upper surface of the ceramic substrate 21 with adhesive 33.

[0042] The ceramic substrate 21 is made of, for example, aluminum oxide (alumina) and protects the light source 2 from the sides and bottom. The ceramic substrate 21 is mounted on the bottom of the seal 20 or directly on the substrate 6. The ceramic substrate 21 also has no ventilation holes and the optical filter 31 is mounted on it.

[0043] The ceramic substrate 21 has recesses 211 and 212. Recess 211 is a recess located on the upper surface (+z direction) side, and the planar shape of its opening is approximately rectangular. Recess 212 is a recess located on the lower surface (-z direction) side of recess 211, and the planar shape of its opening is approximately rectangular and smaller than that of recess 211. Recess 212 has a bottom surface 213, and the light source 2 is bonded and mounted on the bottom surface 213. The ceramic substrate 21 electrically connects the terminals of the light source 2 and wire-bonded terminals to the terminals of the substrate 6, for example, by through holes.

[0044] The optical filter 31 is positioned across the entire upper surface of the ceramic substrate 21 so as to cover the opening on the upper surface, and is attached to the ceramic substrate 21 with adhesive 33. The adhesive 33 is an epoxy resin or silicone resin for hermetically sealing the light source 2. The adhesive 33 may also be a glass frit material for sealing the light source 2, or a preform or paste of a metallic material such as AuSn or solder. In the case of a metallic material, it is desirable to apply metallization such as Cr / Pt / Au, Cr / Ni / Au, or Ti / Ni / Au to the bonding area between the ceramic substrate 21 and the optical filter 31 to ensure adhesion.

[0045] As shown in Figure 5, the light source 2 is a MEMS (Micro Electro Mechanical Systems) type light source mounted on the upper surface (the surface in the +z direction) of the bottom surface 213. The light source 2 has a membrane structure M formed on a Si support layer 201. The membrane M is formed such that a planar heater layer 202 covers the membrane M.

[0046] The light source 2, when viewed from the +z direction (in an xy-plane view), has a light source region 230 and electrode pads P1 and P2. The light source region 230 is a region that functions as a light source in a substantially rectangular shape and has electrodes 231 and 232. Electrode 231 extends in the y-axis direction and is located on the +x direction side of the light source region 230. Electrode 231 is electrically connected to electrode pad P1 via wiring. Electrode 232 extends in the y-axis direction and is located at the -x direction end of the light source region 230. Electrode 232 is electrically connected to electrode pad P2 via wiring.

[0047] The light source 2 has a cross-sectional configuration in which, for example, a Si support layer 201, a heater layer support layer, a heater layer 202, electrodes 231, 232, an electrode support layer, and a protective layer (those without a sign are not shown) are stacked in order from the -z direction to the +z direction. The heater layer support layer, electrode support layer, and protective layer are insulating layers that sandwich the heater layer 202 above and below in the z-axis direction.

[0048] The Si support layer 201 is a substrate made of Si and serves as a support layer for the membrane M of the light source 2. The Si support layer 201 has a circular space (cylindrical shape) when viewed from the -z direction. The space is surrounded on all four sides by the outer frame of the Si support layer 201. Therefore, the light source 2 has a circular membrane M on the xy plane perpendicular to the film thickness direction (z-axis direction). The membrane M covers the space from the upper surface (+z direction side) of the outer frame.

[0049] The heater layer support layer has, for example, a silicon oxide film, a silicon nitride film, and a silicon oxide film from the -z direction to the +z direction. The silicon oxide film is silicon dioxide (SiO₂) as an insulator (dielectric). ２It is a thin film composed of ). Furthermore, the membrane M may have a configuration without a silicon oxide film on the -z direction side. The silicon nitride film is silicon nitride (Si ３ N ４ ) which acts as an insulator (dielectric), and is a thin film made of this material. The silicon oxide film is SiO ２ which is a thin film composed of the above. The heater layer 202 is a thin-film heater serving as a light source (metal) layer, which generates heat when energized and heats the membrane M. The heated membrane M emits infrared light having intensity and wavelength dependency that depend on the surface temperature and surface emissivity. The heater layer 202 is configured to be made of, for example, molybdenum disilicide (MoSi ２ ). However, the heater layer 202 is not limited to this, and may also be made of molybdenum (Mo), a compound composed of Mo and Si with a composition ratio different from that of MoSi ２ , tungsten (W), tungsten disilicide (WSi ２ ), a compound composed of W and Si with a composition ratio different from that of WSi ２ , platinum (Pt), titanium (Ti), gold (Au), silver (Ag), nickel chromium (NiCr), nickel (Ni), aluminum (Al), copper (Cu), titanium nitride (TiN), polycrystalline silicon, or other materials. The heater layer 202 is formed in a rectangular shape wider than the outer contour of the circular void portion on the xy plane, so as to equalize the tensile stress in the region of the membrane M.

[0050] Electrodes 231 and 232 are made of metal such as aluminum-silicon alloy (Al-Si), and are arranged to be electrically connected to the heater layer 202. The electrode support layer is made of SiO ２ and supports the electrodes 231 and 232. The protective layer is made of Si ３ N ４ and protects the lower layers including the electrode support layer from external disturbances. The electrodes 231 and 232 are exposed to the +z direction side from the upper surface of the protective layer.

[0051] The membrane M is a film-like portion on the xy plane, consisting of all the layers of the light source 2 except for the Si support layer 201. In other words, the membrane M has, in order from the -z direction to the +z direction, for example, a silicon oxide film, a silicon nitride film, a silicon oxide film, a heater layer 202, an electrode support layer, and a protective layer.

[0052] The heater layer 202 is electrically connected to electrodes 231 and 232. Electrode pads P1 and P2 are electrode pads for wire bonding, with electrode pad P1 electrically connected to electrode 231 and electrode pad P2 electrically connected to electrode 232. Electrode pads P1 and P2 are wire-bonded to the terminals of the wiring pattern on the substrate 6, and the heater layer 202 is energized by the application of voltage.

[0053] Light source 2, as a MEMS-type light source, is small and low-profile, enabling miniaturization of the sensor module. Furthermore, light source 2, as a MEMS-type light source, has features such as long lifespan, low power consumption, and short response time, contributing to low overall power consumption of the sensor module. The short response time of the MEMS-type light source allows for reduced standby time after power-on when performing intermittent operation, thereby lowering average power consumption.

[0054] Furthermore, since light source 2, as a MEMS-type light source, can directly utilize synchrotron radiation from the high-temperature surface, it can also be applied to the detection of gases with absorption bands at high wavelengths. In addition, the infrared radiation-emitting region of light source 2 is precisely patterned as a membrane M on the plane of the Si support layer 201, resulting in very small individual variations in the radiation direction. Therefore, variations in the amount of light received when light source 2 is used to construct a sensor module are reduced, contributing to improved product yield. Moreover, since light source 2 is mass-producible because it is produced in bulk using MEMS technology based on a silicon wafer, it offers excellent mass-production capabilities.

[0055] Furthermore, because the membrane M of the light source 2 is circular in shape on the xy plane and located within the region of the heater layer 202, the thermal stress generated during heating becomes uniform, improving mechanical strength. As a result, damage to the membrane M due to thermal stress during operation is suppressed in the light source 2, contributing to an extended product life.

[0056] The light source 2 is mounted on the bottom surface 213 of the sealant 20 and wire-bonded. The electrode pads P1 and P2 are electrically connected to the terminals of the sealant 20 via wires.

[0057] The optical filter 31 is, for example, a long-pass filter having a silicon substrate as a base material and a multilayer film. The multilayer film is formed on the silicon substrate by coating or the like, and is made of a dielectric material such as ZnS or Ge, which has a lower refractive index than silicon.

[0058] The sealing device 40 has the same structure as the sealing device 20. In other words, the sealing device 40 has a configuration in which the optical filter 31 and light source 2 of the sealing device 20 are replaced with an optical filter 32 and a light receiving unit 4. For this reason, the explanation of the ceramic substrate 21 and other components that serve as a protective cover for the sealing device 40 will be omitted, and the optical filter 32 and light receiving unit 4 will be explained.

[0059] The light-receiving unit 4 is a surface-mount component mounted on the +z side of the bottom surface of the ceramic substrate of the sealing device 40, and detects the amount of incident infrared light and outputs a detection signal as an analog electrical signal. The light-receiving unit 4 is, for example, a MEMS element of a thermopile type optical sensor (infrared sensor) having multiple thermocouples. 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, photovoltaic type infrared sensor, or a thermal type (uncooled type) pyroelectric element type, thermocouple type, bolometer type infrared sensor, etc.

[0060] The optical filter 32 is a bandpass filter that acts as a λ-selective filter, providing light (infrared) of wavelength λ corresponding to the absorption wavelength unique to the gas G being detected, and is positioned to cover the light-receiving surface of the light-receiving unit 4. In this way, the transmission wavelength of the optical filter 32 is designed to match the unique absorption wavelength of the gas G being detected. This suppresses changes in light intensity caused by gases other than the gas G being detected, and improves the signal-to-noise ratio of the detection signal of the light-receiving unit 4.

[0061] The optical filter 32 includes, for example, a silicon substrate as a base material and a dielectric multilayer film, or a multilayer film made of an infrared-transmitting material such as Si, Ge, sulfide, and fluoride. The silicon substrate is a planar silicon substrate. However, the material of the substrate is not limited to silicon, but can also be germanium (Ge), quartz (SiO ２ ), alumina (Al ２ O ３ ), barium fluoride (BaF ２ ), calcium fluoride (CaF ２ ) and the like can be used. A multilayer film is a plurality of layered films provided on both sides of a silicon substrate.

[0062] The signal processing unit 5 is an AFE (Analog Front End)-IC (Integrated Circuit) that is mounted on a planar area other than the optical cover 1 on the +z or -z side surface of the substrate 6 and performs signal processing related to the detection signal of the light receiving unit 4. The signal processing unit 5 amplifies the analog detection signal of the light receiving unit 4 and performs AD (Analog to Digital) conversion, and when the light source 2 is driven intermittently, it 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. The signal processing unit 5 corrects the difference value of the detection values ​​for temperature and individual variations of the optical gas sensor device 100, and generates various status signals from the digital difference value of the detection values. The signal processing unit 5 outputs the digital difference value of the detection values ​​and the status signals.

[0063] The substrate 6 is an FR-4 (Flame Retardant type-4) PCB (Printed Circuit Board) with conductive wiring printed on a board made of glass epoxy resin or the like. The optical cover 1, sealing devices 20 and 40, signal processing unit 5, and circuit element unit 8 are mounted on the +z side of the substrate 6. The +z side of the substrate 6 is approximately parallel to the light-emitting surface of the light source 2, the optical filters 31 and 32, and the light-receiving surface of the light-receiving unit 4.

[0064] Furthermore, a connector (not shown) may be mounted on the circuit board 6. The connector is mounted on a planar area on the +z side surface of the circuit board 6, excluding the optical cover 1 and the signal processing unit 5, and is used to output various digital signals output from the signal processing unit 5 to the information processing unit of a subsequent device. The connector is connected to the information processing unit of the device via a cable with a plug.

[0065] The circuit element section 8 is mounted on the planar area of ​​the substrate 6 on the +z side surface other than the optical cover 1, and consists of circuit elements such as switches 81, amplifiers, chip resistors, and chip capacitors.

[0066] Next, specific examples of the optical filters 31 and 32 will be described with reference to Figure 6. Figure 6 shows the transmission spectra of the optical filters 31 and 32 of the examples and comparative examples.

[0067] Here, the transmission spectrum calculated based on the film configuration determined to obtain the desired characteristics is shown. The transmission spectrum is the transmittance T [%] of the optical filter with respect to the wavelength [μm] of the light source. In the example, optical filter 31 was used as a long-pass filter (LPF) and optical filter 32 as a band-pass filter (BPF). As a comparative example to the example, optical filter 31 was used as an AR (Anti-Reflection) filter and optical filter 32 as a band-pass filter. An AR filter is a filter that transmits infrared light while preventing its reflection.

[0068] The optical filters 31 and 32 in the examples and comparative examples are dielectric multilayer film filters, using Ge and ZnS as the optical films. The substrate material for the optical filters 31 and 32 is single-crystal silicon manufactured by the FZ (Floating Zone) method. For the optical filters 31 and 32, a dielectric multilayer film was deposited on a φ6" (inch) single-crystal silicon wafer, and then the wafer was cut into small pieces of 3.8 × 3.8 × 0.32 [mmt].

[0069] Figure 6 shows the transmission spectrum characteristics of optical filters 31 and 32 of the examples and comparative examples, and the transmission spectrum characteristics of the combined filter of optical filter 31 × optical filter 32 of the examples and comparative examples. The transmission spectrum of the combined filter is the product of the transmittance of optical filter 31 and the transmittance of optical filter 32 at each wavelength. The combined characteristics of the transmission spectrum of optical filter 31 × optical filter 32 represent the spectrum of light reaching the light receiving unit from the light source and determine the definition of the gas G to be detected and the degree of suppression of sensitivity to other gases. Optical filters 31 and 32 use a fluorine-based refrigerant as the gas G to be detected and are designed to transmit light at approximately 9 [μm], which is its absorption wavelength (transmission center wavelength).

[0070] The optical filter 31 of the embodiment transmits light of 5 [μm] or greater, which is the cut-on wavelength. The optical filter 32 of the embodiment transmits light of approximately 9 [μm], which is the detection wavelength (transmission center wavelength), and transmits light of 5 [μm] or less and 11.5 [μm] or greater, which are outside the blocking wavelength band (stop band) excluding the transmission center wavelength. The combined transmission spectrum of the optical filters 31 and 32 of the embodiment has the characteristic of transmitting approximately 9 [μm] and blocking all short wavelength bands where the absorption wavelengths of other gases exist. In this way, the optical filters 31 and 32 of the embodiment perform the functions of blocking and transmission separately.

[0071] The comparative optical filter 31 transmits light at approximately 9 μm and also transmits a large amount of other wavelengths. The comparative optical filter 32 transmits light at approximately 9 μm and also blocks light of shorter wavelengths. The combined transmission spectrum of the comparative optical filters 31 and 32 has similar characteristics to that of the comparative optical filter 32 in terms of the transmission band and cutoff wavelength. Thus, in the comparative optical filters 31 and 32, optical filter 32 performs both the functions of cutoff and transmission.

[0072] Table I shows the design characteristics and dielectric multilayer film configurations of the optical filters 31 and 32 of the examples and comparative examples. Here, the number of layers and total film thickness are the sum of the optical films deposited on the front and back sides of the substrate. The transmission center wavelength of the bandpass filter of the optical filter 32 of the examples and comparative examples was determined to increase the amount of light received, taking into account the angular distribution of light reaching the light receiving section 4 with respect to the light receiving surface.

[0073] In the comparative example optical filters 31 and 32, optical filter 32 has both long-pass and band-pass functions. Thus, when a single optical filter 32 has multiple wavelength transmission characteristics, it requires a large number of layers in the multilayer film, for example, 100 or more. Furthermore, infrared wavelengths are longer than visible light wavelengths, so the thickness of each unit layer constituting the optical filter 32 must also be thick. Therefore, attempting to achieve multiple wavelength transmission characteristics with a single optical film results in a large total film thickness, and the stress on each thin film may cause cracking or warping of the substrate (wafer) at the completion of film deposition, reducing the yield rate of the optical filter 32. Additionally, the comparative example optical filters 31 and 32 have characteristics that make them unsuitable for applications such as motion sensors and non-contact thermometers.

[0074] In contrast, the optical filters 31 and 32 of the embodiment have long-pass wavelength transmission characteristics for optical filter 31 and band-pass wavelength transmission characteristics for optical filter 32. As a result, the number of layers in each of the optical filters 31 and 32 of the embodiment is less than that of the optical filter 32 of the comparative example, and the total film thickness is also smaller. Consequently, in both of the optical filters 31 and 32 of the embodiment, no damage (wafer cracking, warping) occurs at the time of completion of dielectric multilayer film deposition, and the yield rate of the optical gas sensor device 100 (optical filters 31 and 32) is improved. Furthermore, the optical filter 31 of the embodiment has characteristics that allow it to be shared (shared) with other applications such as human presence sensors and non-contact thermometers.

[0075] Next, an optical gas sensor device 100 having the optical filters 31 and 32 of the embodiment shown in Figure 6, and an optical gas sensor device 100 having the optical filters 31 and 32 of the comparative example were prepared. The evaluation results of the relative sensitivity of the optical gas sensor devices 100 of the embodiment and comparative example to various gases are shown in Table II.

[0076] The evaluation involved exposing the optical gas sensor device 100 to a gas specified at a concentration of 10,000 ppm, and measuring the output value of the light-receiving unit 4 at that time (a concentration value adjusted for the target gas G, which is a fluorine-based refrigerant R32). Relative sensitivity was defined as the relative value when R32 is set to 1. The sensitivity characteristics for other gases, such as propane and ethanol, were small for both the example and comparative example optical gas sensor devices 100, indicating good characteristics.

[0077] As described above, according to this embodiment, the optical gas sensor device 100 comprises a light source 2, an optical filter 31 as a first optical filter, an optical filter 32 as a second optical filter, and a light receiving unit 4. The light source 2 emits infrared light to the gas G to be detected. The optical filter 31 transmits the infrared light emitted from the light source 2. The optical filter 32 transmits the infrared light that has passed through the optical filter 31 and through the gas G to be detected. The light receiving unit 4 detects the infrared light incident through the optical filter 32 and generates a detection signal. The optical filters 31 and 32 have different wavelength transmission characteristics, and a desired wavelength is transmitted by the combination of these different wavelength transmission characteristics. The desired wavelength is the absorption wavelength of the gas G to be detected.

[0078] Therefore, by using optical filters 31 and 32, the wavelength of the absorption band of the gas G to be detected can be accurately transmitted and detected as the desired wavelength of the gas G to be detected, based on two different wavelength transmission characteristics, thereby enabling accurate detection of the gas G to be detected. Furthermore, by separating the functions of different wavelength transmission characteristics with optical filters 31 and 32, an increase in the number of layers and total thickness of the dielectric multilayer film can be prevented. Thus, damage to the optical filters 31 and 32 at the time of film deposition completion (wafer cracking, warping) can be prevented, and the yield rate of the optical gas sensor device 100 (optical filters 31 and 32) can be improved.

[0079] Furthermore, optical filter 31 is a long-pass filter, and optical filter 32 is a band-pass filter. Therefore, the absorption wavelength of the gas G to be detected can be set to the transmission band of optical filter 32, and light with wavelengths smaller than the cut-on wavelength of optical filter 31 can be cut off. Thus, the gas G to be detected can be accurately detected, and the sensitivity characteristics of other gases can be reduced. In addition, optical filter 31 (long-pass filter) can be shared with other applications such as motion sensors and non-contact thermometers, so costs can be reduced through mass production effects with other applications.

[0080] Furthermore, the optical gas sensor device 100 includes an optical cover 1 that covers the light source 2, optical filters 31 and 32, and light receiving unit 4, forming an infrared light path from the light source 2 to the light receiving unit 4. Therefore, infrared light can be efficiently guided along the light path of the optical cover 1.

[0081] (Modifications) Referring to Figures 7 to 9, the first and second modifications of the above embodiment will be described. Figure 7 is a diagram showing the combination of types and composite characteristics of the optical filters 31 and 32 of the embodiment, the first modification, and the second modification. Figure 8 is a diagram showing the absorption spectrum of water. Figure 9 is a diagram showing the absorption spectrum of methane.

[0082] As shown in Figure 7, the optical filters 31 and 32 in the above embodiment are of the type of filter, a long-pass filter and a band-pass filter, respectively. The combined filter of the optical filters 31 and 32 in the embodiment has the characteristic of expanding the blocking wavelength band of the band-pass filter. A first and second modification in which the types of filters of optical filters 31 and 32 are used in a different combination than that of the embodiment will be described.

[0083] The optical filters 31 and 32 of the first modified example are, respectively, a long-pass filter and a short-pass filter. The short-pass filter cuts out light on the longer wavelength side of a predetermined cutoff wavelength and transmits light including the absorption wavelength of the gas G on the shorter wavelength side. The combined filter of the optical filters 31 and 32 of the first modified example has the characteristic that the transmission bandwidth between the cut-on wavelength of the long-pass filter and the cutoff wavelength of the short-pass filter can be controlled to the absorption band of the gas G to be detected.

[0084] The optical filters 31 and 32 of the first modified example are effective when detecting the target gas G in the absorption spectrum of a broadband wavelength range. Figure 8 shows the absorption spectrum of the target gas G (H) in relation to the wavelength of light [μm] as the absorption spectrum of the broadband wavelength range. ２ This indicates the transmittance [%] of O at 1000 [ppm-meters]. ２ The absorption spectrum of O shows an absorption band extending from 5.5 to 7 [μm], and the absorption intensity is relatively uniform.

[0085] Returning to Figure 7, the optical filters 31 and 32 in the second modified example are of the type of filter: a notch filter and a bandpass filter, respectively. A notch filter is a type of bandstop filter that attenuates frequencies within a specific band while allowing all other frequencies to pass through without change. The combined filter of the optical filters 31 and 32 in the second modified example has the characteristic of dividing the transmission band by the attenuation band of the notch filter and the transmission band of the bandpass filter.

[0086] The optical filters 31 and 32 of the second modified example are effective when detecting the target gas G whose absorption spectrum has a dip in a specific band and trails to the short and long wavelength sides centered on that specific band. Figure 9 shows the transmittance [%] of the target gas G (100 [ppm-meters] of methane) as an absorption spectrum with a dip in the specific band and trails to the short and long wavelength sides, with respect to the wavelength of light [μm]. The absorption spectrum of methane has a dip in the 3.3 μm band and trails to the short and long wavelength sides centered on that band.

[0087] As described above, according to the first modification, the optical filter 31 is a long-pass filter, and the optical filter 32 is a short-pass filter. Therefore, the absorption band of the gas G to be detected can be controlled within the transmission bandwidth between the cut-on wavelength of the optical filter 31 and the cut-off wavelength of the optical filter 32, and the gas G to be detected can be detected. Furthermore, the optical filter 31 (long-pass filter) can be shared with other applications such as motion sensors and non-contact thermometers, so costs can be reduced through economies of scale with other applications.

[0088] Furthermore, in the second modified configuration, the optical filter 31 is a notch filter, and the optical filter 32 is a bandpass filter. Therefore, the transmission band of the optical filter 32 can be divided by the optical filter 31, and the target gas G can be detected.

[0089] The above description of the embodiment is merely an example of an optical gas sensor device according to the present invention, and is not limited thereto.

[0090] For example, in the above embodiment, the light source 2 and the light receiving unit 4 are sealed with sealing devices 20 and 40, but the configuration is not limited to this. The light source 2 and the light receiving unit 4 may also be surface mounted (COB (Chip On Board) mounted) to the substrate 6 via a plurality of adhesive parts. In this configuration as well, at least one of the light source 2 and the light receiving unit 4 may be sealed on the substrate 6 with a sealing device.

[0091] Alternatively, the light source 2 and the light receiving unit 4 may be surface-mounted onto a small substrate acting as a child substrate via multiple adhesive joints. The small substrate on which the light source 2 or the light receiving unit 4 is mounted is then mounted onto the substrate 6 acting as a parent substrate. In this configuration as well, at least one of the light source 2 and the light receiving unit 4 may be sealed on the small substrate with a sealing device.

[0092] 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.

[0093] As described above, the optical gas sensor device according to the present invention is suitable for detecting gases such as refrigerants.

[0094] 100 Optical gas sensor device G Gas 1 Optical cover 110A, 110B Cover part 11 Gas introduction port 111, 112 Gas intake port 12 Contamination filter 13 Light guide part 131 Inlet part 132 Outlet part 133, 134 Gas introduction port 20, 40 Sealing device M Membrane P1, P2 Electrode pad 21 Ceramic substrate 211, 212 Recess 213 Bottom surface 2 Light source 201 Si support layer 202 Heater layer 230 Light source area part 231, 232 Electrode 31, 32 Optical filter 33 Adhesive 4 Light receiving part 5 Signal processing part 6 Substrate 8 Circuit element part 81 Switch

Claims

1. An optical gas sensor device comprising: a light source that emits infrared radiation to a gas to be detected; a first optical filter that transmits the infrared radiation emitted from the light source; a second optical filter that transmits infrared radiation that has passed through the first optical filter and through the gas to be detected; and a light receiving unit that detects the infrared radiation incident through the second optical filter and generates a detection signal, wherein the first optical filter and the second optical filter have different wavelength transmission characteristics, and a combination of these different wavelength transmission characteristics transmits a desired wavelength.

2. The optical gas sensor device according to claim 1, wherein the desired wavelength is the absorption wavelength of the gas to be detected.

3. The optical gas sensor device according to claim 1, wherein the first optical filter is a long-pass filter and the second optical filter is a band-pass filter.

4. The optical gas sensor device according to claim 1, wherein the first optical filter is a long-pass filter and the second optical filter is a short-pass filter.

5. The optical gas sensor device according to claim 1, wherein the first optical filter is a notch filter and the second optical filter is a bandpass filter.

6. An optical gas sensor device according to any one of claims 1 to 5, comprising an optical cover that covers the light source, the first optical filter, the second optical filter, and the light receiving unit, and forms the optical path of the infrared light from the light source to the light receiving unit.

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