Light source driving device and optical gas sensor device

Abstract

To prevent deterioration and mechanical destruction of a membrane in a light source by suppressing electromigration in the light source.SOLUTION: A light-source driving device 80A includes a light source 2, a power source 800, and an NMOSFET 801, 802, 803, and 804 as a switching element. The light source 2 has a heater layer containing metal, and emits infrared rays based on a power supply voltage applied to the heater layer. The power supply 800 outputs a voltage V as the power supply voltage to the light source 2. The NMOSFET 801 to 804 switches a path of current flowing from the power source 800 to the light sources 2 and alternately drives a direction of the current flowing to the light sources 2.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[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 the 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, a gas sensor equipped with an infrared light emitter and receiver detects the concentration of the target gas located in the optical path between the emitter and receiver.

[0003] For example, a MEMS (Micro Electro Mechanical Systems) type light source is known as a light-emitting element. The light source is a chip-shaped infrared light source based on a silicon substrate with an etched backside film. The light source generates infrared light by heating a resistor in a film state (membrane structure) floating above the substrate. In the light source, continuous operation causes the membrane resistor to heat up to several hundred degrees when emitting light, resulting in electromigration as a failure mode. Electromigration is a phenomenon in which current flowing through metal wiring collides with metal atoms and transports them. In the light source, areas where metal atoms are reduced cause wire breakage. Adjacent wiring to areas where metal atoms have accumulated causes a short circuit. This causes abnormal appearance of the light source surface. Electromigration eventually induces mechanical destruction of the membrane, significantly affecting the product reliability of the light source.

[0004] For this reason, an optical gas sensor device is known that includes a light source having a structure that is resistant to electromigration (see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2023-149364 Summary of the Invention [Problem to be solved by the invention]

[0006] There is a demand for preventing electromigration not by the structure of the light source (design of material composition, shape, stress, etc.), but by the method of driving the light source. A light source driving device 80C as a conventional light source driving circuit will be described with reference to Figs. 13 and 14. Fig. 13 is a circuit diagram showing the conventional light source driving device 80C. Fig. 14 is a timing chart showing the signals of light source driving device 80C.

[0007] As shown in FIG. 13, the light-source driving device 80C includes a light source 2C, a power supply 820, and an NMOSFET (N-type Metal-Oxide-Semiconductor Field-Effect Transistor) 821. The light source 2C is a MEMS-type light source. The power supply 820 is a constant-voltage power supply that outputs a constant voltage V as a power supply voltage. The NMOSFET 821 is a switching element that turns on and off a path between its drain and source in accordance with a gate voltage input to its gate. A drive signal Vgs is input to the gate of the NMOSFET 821. The drain of the NMOSFET 821 is electrically connected to the anode of the power supply 820 via the light source 2C. The source of the NMOSFET 821 is electrically connected to the cathode of the power supply 820 and to the ground GND. The NMOSFET 821 includes a diode 821a.

[0008] As shown in FIG. 14, the drive signal Vgs is an intermittent pulse whose voltage is high (H) and low (L). The light-source drive device 80C has one current path mode. The voltage v0 applied to the light source 2 and the path of the current i0 flowing through the light source 2 are indicated by dashed lines in FIG. 13. The voltage v shown in FIG. 14 is the potential difference between the potential of the electrode 231 and the potential of the electrode 232, which serves as a reference, in the light source 2C. The current i shown in FIG. 14 is the current value of the current flowing from the electrode 231 to the electrode 232 in the light source 2C. The voltage v and the current i have waveforms synchronized with the on (high) state of the drive signal Vgs. In this way, the light-source drive device 80C has a circuit configuration that unipolarly drives the light source 2. However, the current i0 is a current (electron) flow that is unidirectional, which causes an imbalance in the flow of electrons in the light source 2. As a result, electromigration occurs at biased positions in the membrane, reflecting the bias in the flow of electrons in one direction, which may cause abnormalities in appearance (voids, protrusions).

[0009] An object of the present invention is to suppress electromigration in a light source and prevent deterioration and mechanical destruction of the membrane in the light source. [Means for solving the problem]

[0010] In order to solve the above problems, the light source driving device of the present invention comprises: a light source having a heater layer containing a metal and emitting infrared rays based on a power supply voltage applied to the heater layer; a light source that emits infrared rays based on a power supply voltage applied to the light source; a power supply that outputs a power supply voltage; The light source includes a switching element that switches the path of the current flowing from the power supply to the light source, and alternately drives the direction of the current flowing to the light source. [Effects of the Invention]

[0011] According to the present invention, it is possible to improve the reliability of the light source by suppressing electromigration in the light source and preventing deterioration and mechanical destruction of the membrane in the light source. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic view of an optical gas sensor device according to a first embodiment of the present invention. [Figure 2] FIG. 1 is a perspective view of an optical gas sensor device. [Figure 3] FIG. 2 is a partially transparent perspective view of the optical gas sensor device. [Figure 4] FIG. [Figure 5] FIG. 2 is a cross-sectional schematic view of a light source. [Figure 6] FIG. [Figure 7] 1 is a circuit diagram showing a light source driving device according to a first embodiment. [Figure 8] 4 is a timing chart showing each signal of the light source driving device of the first embodiment. [Figure 9] 4 is a photograph showing the top surface of a light source driven by the light source driving device of the first embodiment. [Figure 10] 10 is a photograph showing the top surface of a light source driven by a conventional light source driving device. [Figure 11] FIG. 10 is a circuit diagram showing a light source driving device according to a second embodiment. [Figure 12] 10 is a timing chart showing each signal of the light source driving device of the second embodiment. [Figure 13] FIG. 1 is a circuit diagram showing a conventional light source driving device. [Figure 14] 10 is a timing chart showing signals of a conventional light source driving device. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, first and second 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.

[0014] (First embodiment) A first embodiment of the present invention will be described with reference to Figures 1 to 8. First, a schematic configuration of an 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.

[0015] 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. 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 gas G, which is a detection target (measurement target) within the optical cover 1. An AR (Anti-Reflection) 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.

[0016] 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.

[0017] 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 a switching element of a light source driving device 80A, which will be described later. When gas detection is performed, the signal processing unit 5 controls the switch 81 to turn on / off the light emission of the light source 2.

[0018] 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.

[0019] In this way, the optical gas sensor device 100 filters the infrared light emitted from the light source 2 to the gas G to be detected by the optical filter 3 and receives the filtered infrared light with 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.

[0020] 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 light) 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.

[0021] The optical gas sensor device 100 detects an alternative fluorocarbon refrigerant, which is 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). CFC refrigerants have a high ozone depletion potential and are a cause of destruction of the Earth's ozone layer, so replacement with hydrochlorofluorocarbon (HCFC) refrigerants, which have a low ozone depletion potential, has begun. In developed countries, there is also a shift from HCFC refrigerants to HFC refrigerants (R410A), which has an ozone depletion potential of zero.

[0022] CFC refrigerants, HCFC refrigerants, and HFC refrigerants are known to have high global warming potentials and 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.

[0023] 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.

[0024] The optical gas sensor device 100 outputs various status signals based on the detected gas concentration value of 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 gas G is in an abnormal state (alarm state) that requires an alarm. The monitoring signal indicates that the detected concentration of gas G is in a normal state. If the device is an alarm device, it issues various alarms (for example, 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 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, CO2 concentration measuring devices for greenhouse horticulture, CO2 measuring devices for plant factories, CO2 sealing devices for food packaging, and ethylene gas concentration measuring devices for food warehouses.

[0025] 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. Fig. 5 is a schematic cross-sectional view of the light source 2. Fig. 6 is a top view of the light source 2.

[0026] 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.

[0027] 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.

[0028] 2, the optical cover 1 has cover portions 110A and 110B. The cover portion 110A is an upper part (on the +z side) that is butted against and integrated with the cover portion 110B by a method such as adhesive bonding or thermal caulking. The cover portion 110B is a lower part (on the -z side) that is butted against and integrated with the cover portion 110A.

[0029] As shown in FIG. 3, the optical cover 1 has a light guide section 13 as a hollow section into which the gas G to be detected is introduced. The light guide section 13 is a pipe-shaped optical path, and its cross section perpendicular to the axial direction is circular. The cover section 110A has a half-pipe section. The cover section 110B has a half-pipe section. The half-pipe sections of the cover sections 110A and 110B are joined together to form the light guide section 13. In this way, the optical cover 1 has cover sections 110A and 110B divided by the cross section of the light guide section 13 in the axial direction. As shown in FIG. 3, the light guide section 13 has a three-dimensional, approximately U-shape when viewed from the top (the surface in the +z direction).

[0030] 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 the material 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 by plating, sputtering, vacuum deposition, or the like. Note that, 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.

[0031] 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 efficiently guiding the infrared rays from the light source 2 to the light receiving unit 4 as an optical path 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 of the +z side of the light receiving unit 4. However, the present invention is not limited to this, and the optical filter 3 may be configured to be disposed, for example, at the outlet portion 132 of the end opening of the light guide 13 on the light receiving unit 4 side.

[0032] In this embodiment, the light path inside the optical cover 1 is formed as a pipe-shaped light guide 13 with a circular cross section, so that the reflection angle of the infrared light is 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 13, and the infrared light emitted from the light source 2 is reflected inside the light guide 13 and can efficiently enter the light receiving unit 4. Note that the cross section of the light path axial direction of the light guide 13 of the optical cover 1 may be configured to be elliptical.

[0033] 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 .

[0034] 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, below a portion of the x-axis direction (-z direction) where the axial direction of the light guide section 13 is located. At least a portion of the signal processing section 5 and the circuit element section 8 is disposed in the space SP and mounted on the substrate 6.

[0035] Furthermore, the cross-sectional area of ​​the cross section perpendicular to the axial direction of light guide 13 is constant in the axial direction for the main portion (portion other than inlet portion 131, which is the end opening on the light source 2 side, and outlet portion 132). Because the cross-sectional area is constant, the gas concentration per unit volume of the gas G to be detected that enters light guide 13 is easily homogenized, and because infrared rays pass through randomly without following a specific path, it is easy to respond to changes in the gas concentration of gas G. Figure 3 shows the optical path propagation state of multiple infrared light ray paths within light guide 13, represented by solid arrows. In this way, the infrared light ray paths are random within light guide 13.

[0036] Furthermore, infrared light emitted from light source 2 is incident on inlet portion 131 of light guiding portion 13 on the -x direction side. Light guiding portion 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 portion 13 on the infrared light incident side is defined as inlet portion 131. Light guiding portion 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.

[0037] Light-guiding section 13 on the +x-direction side extends linearly from the +y-direction side to the −y-direction side, then bends in an R-shape and extends to exit section 132 on the −z-direction side. The infrared light that has passed through light-guiding section 13 is emitted to light-receiving section 4 via optical filter 3.

[0038] Outlet portion 132 has a tapered shape in which the cross-sectional area becomes smaller as the axial direction of light-guiding portion 13 moves from the +z direction to the -z direction. Similarly, inlet portion 131 has a tapered shape in which the cross-sectional area becomes smaller as the axial direction of 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 light-guiding portion 13 and is radiated to light-receiving portion 4.

[0039] The cover parts 110A and 110B also have hollow parts (not shown) as spaces for removing weight (removing weight). These hollow parts make it possible to reduce the weight of the optical cover 1 (optical gas sensor device 100).

[0040] The cover part 110B also has a fixing pin (not shown). The fixing pin is a protrusion 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.

[0041] 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 that are opened 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 that is opened from the −y direction side surface of the cover 110B to the +y direction and penetrates to the space around (beside) the light source 2. The space around the light source 2 is in communication with the light guide 13. The gas inlet 114 is a hole that is opened from the −y direction side surface of the cover 110B to the +y direction and penetrates to the space around (beside) the light receiving unit 4. The space around the light receiving unit 4 is in communication with the light guide 13.

[0042] Gas inlets 111 and 112 are directly connected to light guiding section 13 and remove part of the inner surface of light guiding section 13, resulting in a low efficiency of infrared radiation utilization. In contrast, gas inlet 113 is indirectly connected to light guiding section 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 guiding section 13. Similarly, gas inlet 114 is indirectly connected to light guiding section 13 via the space around light receiving section 4, resulting in a high efficiency of infrared radiation utilization without damaging part of the inner surface of light guiding section 13.

[0043] 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.

[0044] 4, the light source 2 is a MEMS 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.

[0045] Fig. 5 is a schematic cross-sectional view of light source 2, and the actual dimensions are not as shown. As shown in Fig. 5, light source 2 has a configuration in which, for example, Si support layer 211, heater layer support layer 212, heater layer 213, electrodes 231 and 232, electrode support layer 214, and protective layer 215 are laminated in this order from the -z direction side to the +z direction side. Heater layer support layer 212, electrode support layer 214, and protective layer 215 are insulating layers that sandwich heater layer 213 above and below in the z-axis direction.

[0046] 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 FIGS. 5 and 6, the Si support layer 211 has a circular space when viewed from the -z direction. Therefore, the light source 2 has a circular membrane M on the xy plane perpendicular to the film thickness direction (z-axis direction). However, the shape of the membrane M on the xy plane is not limited to a circle, and may be a round shape such as an oval, a rectangle, or the like.

[0047] 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 a thin film made of silicon dioxide (SiO2) as an insulator (dielectric). The silicon nitride film 212B is a thin film made of silicon nitride (Si3N4) as an insulator (dielectric). The silicon oxide film 212C is a thin film made of SiO2. The heater layer 213 is a thin film heater serving as a light source (metal) layer. The heater layer 213 generates heat when current is applied, heating the membrane M. The heated membrane M emits infrared rays whose intensity and wavelength dependency depend on the surface temperature and surface emissivity. The heater layer 213 is made of, for example, MoSi2. However, without being limited thereto, the heater layer 213 may be composed of other materials such as Mo, a compound of Mo and Si having a different composition ratio from MoSi2, W, tungsten disilicide (WSi2), a compound of W and Si having a different composition ratio from WSi2, Pt, Ti, Au, Ag, NiCr, Ni, Al, Cu, TiN, Polysilicon, etc. The shape of the heater layer 213 on the xy plane is rectangular.

[0048] The electrodes 231 and 232 are made of a metal such as AlSi and are arranged so as to be electrically connected to the heater layer 213. The electrode support layer 214 is made of SiO and supports the electrodes 231 and 232. The protective layer 215 is made of SiN and 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.

[0049] The membrane M is a film-like portion on the xy plane that is made up of all of the layers of the light source 2 except for 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 temperature of the membrane M increases due to heat generation from the heater layer 213, and the membrane M is prone to 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 increase due to heat generation from the heater layer 213 and little deformation due to thermal stress.

[0050] The heater layer 213 is electrically connected to the electrodes 231 and 232. The pad P1 is a pad for wire bonding and is electrically connected to the electrode 231. The pad P2 is a pad for wire bonding and is electrically connected to the electrode 232. The pads P1 and P2 are wire-bonded to terminals of a wiring pattern on the substrate 6, and the heater layer 213 is energized by application of a voltage by a light source driving device 80A, which will be described later.

[0051] The light source 2 as a MEMS-type light source is small and low-profile, allowing for miniaturization of the sensor module. In addition, the light source 2 as a MEMS-type light source has features such as a long life, low power consumption, and short response time, allowing 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.

[0052] Furthermore, as a MEMS-type light source, light source 2 can directly utilize the light emitted from the surface of the high-temperature part, making it possible to apply it to the detection of gases with absorption bands at long wavelengths. Furthermore, the infrared emitting area of ​​light source 2 is patterned with high precision as membrane M on the flat surface of Si support layer 211, and there is very little individual variation in the radiation direction. This reduces variation in the amount of light received when a sensor module is constructed using light source 2, contributing to improved product yield. Furthermore, light source 2 is easily mass-produced using MEMS technology based on silicon wafers.

[0053] Furthermore, when the membrane M of the light source 2 is round on the xy plane, the thermal stress generated during heating is uniform, improving the mechanical strength of the light source 2. This reduces damage to the membrane M due to thermal stress during operation, contributing to extending the product life.

[0054] The light source 2 is a surface-mounted component, but is not limited to this and may be a DIP (Dual Inline Package) component (such as a CAN package).

[0055] 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 gas G to be detected. In this way, the transmission wavelength of the optical filter 3 is designed to match the absorption wavelength specific to the gas G to be detected, thereby suppressing changes in the amount of light caused by gases other than the gas G to be detected and improving the signal-to-noise ratio of the detection signal from the light receiving unit 4.

[0056] The optical filter 3 includes, 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, Ge, sulfide, or fluoride. The silicon substrate is a planar silicon substrate. The material of the substrate is not limited to silicon, and Ge (germanium), quartz, alumina, BaF2 (barium fluoride), CaF2 (calcium fluoride), etc. can also be used. The multilayer film is a film with multiple layers provided on both sides of the silicon substrate. The planar shape of the optical filter 3 is rectangular, but is not limited thereto and may be other shapes such as circular.

[0057] In this embodiment, the optical filter 3 is, for example, a bandpass filter whose central 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 132 of the light guide 13. The central wavelength of transmittance is the central 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.

[0058] 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.

[0059] Furthermore, the light receiving unit 4 is a surface-mounted component, but is not limited to this configuration and may be a DIP component (such as a CAN package). 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 component, such as a surface-mounted component or a DIP component.

[0060] Next, the configuration and operation of light source driving device 80A of this embodiment will be described with reference to Figures 7 to 10. Figure 7 is a circuit diagram showing light source driving device 80A of this embodiment. Figure 8 is a timing chart showing each signal of light source driving device 80A. Figure 9 is a photograph showing the top surface of light source 2 driven by light source driving device 80A. Figure 10 is a photograph showing the top surface of light source 2C driven by conventional light source driving device 80C.

[0061] The optical gas sensor device 100 includes a light source driving device 80A including a light source 2, a signal processing unit 5, and a part of the circuit element unit 8. As shown in FIG. 7, the light source driving device 80A includes a light source 2, a power supply 800, NMOSFETs 801, 802, 803, and 804, and a signal processing unit 5 (not shown in FIG. 7). The NMOSFETs 801, 802, 803, and 804 function as switching elements, respectively, as first, second, third, and fourth transistors. The signal processing unit 5 functions as a control unit.

[0062] The power supply 800 is a constant-voltage power supply that outputs a constant voltage V as a power supply voltage. NMOSFETs 801 to 804 are switching elements that function as a switch 81 and turn on and off a path between their drains and sources in response to a gate voltage input to their gates. A drive signal VgsH1 is input to the gate of the NMOSFET 801 from the signal processing unit 5. The drain of the NMOSFET 801 is electrically connected to the anode of the power supply 800. The source of the NMOSFET 801 is electrically connected to the drain of the NMOSFET 802 and the electrode 231 of the light source 2. The electrodes 231 and 232 of the light source 2 in the figure are merely an example and may be reversed. The resistance between the electrodes 231 and 232 of the light source 2 is defined as a resistor R5.

[0063] A drive signal VgsL1 is input to the gate of the NMOSFET 802 from the signal processing unit 5. The drain of the NMOSFET 802 is electrically connected to the source of the NMOSFET 801 and the electrode 231 of the light source 2. The source of the NMOSFET 802 is electrically connected to the cathode of the power supply 800 and the ground GND.

[0064] A drive signal VgsH2 is input to the gate of the NMOSFET 803 from the signal processing unit 5. The drain of the NMOSFET 803 is electrically connected to the anode of the power supply 800 and the drain of the NMOSFET 801. The source of the NMOSFET 803 is electrically connected to the drain of the NMOSFET 804 and the electrode 232 of the light source 2.

[0065] A drive signal VgsL2 is input to the gate of the NMOSFET 804 from the signal processing unit 5. The drain of the NMOSFET 804 is electrically connected to the source of the NMOSFET 803 and the electrode 232 of the light source 2. The source of the NMOSFET 804 is electrically connected to the source of the NMOSFET 802, the cathode of the power supply 800, and the ground GND.

[0066] The NMOSFET 801 has a diode 801a. The diode 801a is a parasitic diode configured in parallel between the drain and source of the NMOSFET 801. Similarly, the NMOSFET 802 has a diode 802a. The NMOSFET 803 has a diode 803a. The NMOSFET 804 has a diode 804a.

[0067] In this way, the NMOSFETs 801 to 804 are connected to the power supply 800 and the light source 2 in a full-bridge configuration.

[0068] As shown in FIG. 8, the drive signals VgsH1 and VgsL2 are intermittent pulses whose voltages alternate between high H (ON) and low L (OFF). The drive signals VgsL1 and VgsH2 are intermittent pulses whose voltages alternate between high H and low L. The drive signals VgsL1 and VgsH2 are ON during the low L periods between the high H periods of the drive signals VgsH1 and VgsL2. The current path of the light source drive device 80A has two modes. In the first mode, the drive signals VgsH1 and VgsL2 are ON and the drive signals VgsL1 and VgsH2 are OFF. In the first mode, the voltage v0 applied to the light source 2 and the path of the current i0 flowing through the light source 2 are shown by dashed lines in FIG. 7. In the second mode, the drive signals VgsH1 and VgsL2 are OFF and the drive signals VgsL1 and VgsH2 are ON. In the second mode, the voltage v0 applied to the light source 2 and the path of the current i0 flowing through the light source 2 are shown by dashed lines in FIG.

[0069] 8 is the potential difference between the potential of electrode 231 and the potential of electrode 232, which serves as a reference, in light source 2. Voltage v has a waveform that alternates between a +V period synchronized with the on-state of drive signals VgsH1 and VgsL2 and a -V period synchronized with the on-state of drive signals VgsL1 and VgsH2. Current i shown in FIG. 8 is the current value of a current that flows in the direction from electrode 231 to electrode 232 in light source 2. Current i has a waveform that alternates between a +V / R5 period synchronized with the on-state of drive signals VgsH1 and VgsL2 and a -V / R5 period synchronized with the on-state of drive signals VgsL1 and VgsH2.

[0070] In this way, the light source driving device 80A has a circuit configuration that bipolarly drives the light source 2. The direction of the current (electrons) flow of the current i0 alternates, which provides an electromigration suppression effect.

[0071] FIG. 9 shows a photograph of the top surface of the membrane M of light source 2 driven for a predetermined drive time by light-source driving device 80A. As shown in FIG. 9, no abnormalities in appearance due to electromigration occurred. FIG. 10 shows a photograph of the top surface of the membrane of light source 2C driven for a predetermined drive time by conventional light-source driving device 80C. Light source 2C has the same structure as light source 2. Electrodes (electrodes 231 and 232 in light source 2) are arranged outside the frame on both the left and right sides of the photographs in FIGS. 9 and 10. The predetermined drive times in FIGS. 9 and 10 are the same.

[0072] As shown by the arrows, light source 2C in FIG. 10 has an appearance defect (void, protrusion) due to electromigration on the left side of the photograph. The appearance defect on the left side is due to the current i0 flowing through light source 2C being unidirectional. Note that if light source 2 in FIG. 9 continues to be driven after a predetermined drive time, an appearance defect may occur. However, the time until an appearance defect occurs in light source 2 in FIG. 9 is significantly longer than the predetermined drive time for light source 2C in FIG. 10. Here, because the current i0 flowing through light source 2 is bidirectional, the appearance defect occurring in light source 2 appears on both the left and right sides of the photograph in FIG. 9.

[0073] As described above, according to this embodiment, light-source driving device 80A includes light source 2, power supply 800, and NMOSFETs 801-804. Light source 2 has heater layer 213 containing metal, and emits infrared rays based on a power supply voltage applied to heater layer 213. Power supply 800 outputs voltage V as the power supply voltage. NMOSFETs 801-804 switch the path of current flowing from power supply 800 to light source 2, thereby alternately driving the direction of current flowing through light source 2. Light-source driving device 80A also includes signal processing unit 5 that controls NMOSFETs 801-804.

[0074] Therefore, the direction of the current flowing through the light source 2 is alternately driven, thereby preventing bias in the current in the light source 2 and suppressing electromigration, and preventing deterioration and mechanical destruction of the membrane M in the light source 2, thereby improving the reliability of the light source 2.

[0075] NMOSFETs 801 to 804 are connected to a power supply 800 and a light source 2 in a full-bridge configuration. When both NMOSFETs 801 and 804 are turned on, they are driven to pass a current from the power supply 800 to the light source 2 via a first-mode current path. When both NMOSFETs 802 and 803 are turned on, they are driven to pass a current from the power supply 800 to the light source 2 via a second-mode current path that is opposite in direction to the first-mode current path. The NMOSFETs 801 and 804 and the NMOSFETs 802 and 803 are alternately turned on. This allows the power supply voltages (+V, -V) of the power supply 800 to be applied directly to the light source 2.

[0076] The optical gas sensor device 100 includes a light source driving device 80A, 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 passing through the gas to be detected. The light receiving unit 4 detects the infrared light incident 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. Therefore, in the optical gas sensor device 100, electromigration in the light source 2 can be prevented.

[0077] (Second embodiment) A second embodiment of the present invention will be described with reference to Figures 11 and 12. Figure 11 is a circuit diagram showing a light source driving device 80B of this embodiment. Figure 12 is a timing chart showing each signal of light source driving device 80B.

[0078] In the first embodiment, the light source driving device 80A is configured to include four NMOSFETs. In this embodiment, the light source driving device is configured to include two NMOSFETs.

[0079] The device configuration of this embodiment is the same as that of the first embodiment, and uses the optical gas sensor device 100. However, in the optical gas sensor device 100, the light source driving device 80A is replaced with a light source driving device 80B, which will be described later.

[0080] Next, the configuration and operation of a light-source driving device 80B of this embodiment will be described with reference to Figures 11 and 12. As shown in Figure 11, the light-source driving device 80B includes a light source 2, a power supply 800, NMOSFETs 801 and 802, capacitors 805 and 806, and a signal processing unit 5 (not shown in Figure 11). The NMOSFETs 801 and 802 function as switching elements (first and second transistors, respectively).

[0081] A drive signal VgsH is input to the gate of the NMOSFET 801 from the signal processing unit 5. The drain of the NMOSFET 801 is electrically connected to the anode of the power supply 800 and a capacitor 805. The source of the NMOSFET 801 is electrically connected to the drain of the NMOSFET 802 and the electrode 231 of the light source 2.

[0082] A drive signal VgsL is input to the gate of the NMOSFET 802 from the signal processing unit 5. The drain of the NMOSFET 803 is electrically connected to the source of the NMOSFET 801 and the electrode 231 of the light source 2. The source of the NMOSFET 802 is electrically connected to the cathode of the power supply 800, the ground GND, and a capacitor 806.

[0083] The capacitors 805 and 806 are capacitors for dividing the voltage V of the power supply 800. The capacitors 805 and 806 are connected in series and in parallel to the power supply 800. A node between the capacitors 805 and 806 is connected to the electrode 232 of the light source 2. The capacitors 805 and 806 have the same capacitance so as to equally divide the voltage V (V / 2). The capacitors 805 and 806 may be replaced with two resistors having the same resistance value.

[0084] As shown in FIG. 12, the drive signal VgsH is an intermittent pulse whose voltage alternates between high H (ON) and low L (OFF). The drive signal VgsL is an intermittent pulse whose voltage alternates between high H and low L. The drive signal VgsL is ON during the period between the high H periods of the drive signal VgsH. The current path of the light source drive device 80B operates in two modes. The first mode is a mode in which the drive signal VgsH is ON and the drive signal VgsL is OFF. In the first mode, the voltage v0 applied to the light source 2 and the path of the current i0 flowing through the light source 2 are shown by dashed lines in FIG. 11. In the second mode, the drive signal VgsH is OFF and the drive signal VgsL is ON. In the second mode, the voltage v0 applied to the light source 2 and the path of the current i0 flowing through the light source 2 are shown by dashed lines in FIG. 11.

[0085] 12 is the potential difference between the potential of electrode 231 and the potential of electrode 232, which serves as a reference, in light source 2. Voltage v has a waveform that alternates between a +V / 2 period synchronized with the on-state of drive signal VgsH and a -V / 2 period synchronized with the on-state of drive signal VgsL. Current i shown in FIG. 12 is the current value of a current that flows in the direction from electrode 231 to electrode 232 in light source 2. Current i has a waveform that alternates between a +V / 2R5 period synchronized with the on-state of drive signal VgsH and a -V / 2R5 period synchronized with the on-state of drive signal VgsL.

[0086] In this way, the light source driving device 80C has a circuit configuration that bipolarly drives the light source 2. The direction of the current (electrons) flow of the current i0 alternates, which provides an electromigration suppression effect.

[0087] As described above, according to this embodiment, the light source driving device 80B includes the light source 2, the power supply 800, and NMOSFETs 801 and 802. The NMOSFETs 801 and 802 are connected to the power supply 800 and the light source 2 in a half-bridge configuration. When the NMOSFET 801 is turned on, it drives the device so that a current flows from the power supply 800 to the light source 2 via a first mode current path. When the NMOSFET 802 is turned on, it drives the device so that a current flows from the power supply 800 to the light source 2 via a second mode current path that is opposite to the first mode current path. The NMOSFETs 801 and 802 are alternately turned on. This allows the number of NMOSFETs to be reduced compared to the light source driving device 80A, simplifying the device configuration.

[0088] Furthermore, light source driving device 80B includes capacitors 805 and 806. Capacitors 805 and 806 are provided in parallel with power supply 800 and divide power supply voltage V. Capacitors 805 and 806 apply the divided power supply voltage to light source 2. Therefore, the divided power supply voltage (+V / 2, −V / 2) of power supply 800 can be applied to light source 2.

[0089] The above-described embodiments are merely examples of the light source driving device and the optical gas sensor device according to the present invention, and the present invention is not limited to these.

[0090] 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. [Explanation of symbols]

[0091] 100 Optical gas sensor device G Gas 1 Optical cover 110A, 110B cover 11 Gas inlet port 111,112,113,114 Gas intake 13 Light guide section 131 Entrance 132 Exit section 12 Contamination filter SP space part 2,2C 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 electrodes 214 Electrode support layer 215 Protective layer P1, P2 pads M,Ma membrane 3 Optical Filters 4 Light receiving section 5. Signal Processing Section 6 PCB 7 Connectors 8 Circuit element section 80A, 80B, 80C Light source driving device 81 Switch 800,820 Power supply 801,802,803,804,821 NMOSFET 801a, 802a, 803a, 804a, 821a diodes 805,806 capacitors

Claims

1. a light source having a heater layer containing a metal and emitting infrared rays based on a power supply voltage applied to the heater layer; a power supply that outputs a power supply voltage to the light source; a switching element that switches a path of a current flowing from the power supply to the light source, thereby alternately driving the direction of the current flowing to the light source.

2. The light source driving device according to claim 1 , further comprising a control unit that controls the switching element.

3. the switching element includes first to fourth transistors, the first to fourth transistors are connected to the power supply and the light source in a full-bridge configuration; the first and fourth transistors are driven to flow a current from the power supply to the light source through a first current path by being turned on in common; the second and third transistors are driven by being turned on in common to cause a current to flow from the power source to the light source through a second current path in a direction opposite to the first current path; 2. The light source driving device according to claim 1, wherein the first and fourth transistors and the second and third transistors are alternately turned on.

4. the switching element includes first and second transistors; the first and second transistors are connected to the power supply and the light source in a half-bridge configuration; When the first transistor is turned on, it drives the first transistor to pass a current from the power supply to the light source through a first current path; When the second transistor is turned on, it drives the second transistor to pass a current from the power supply to the light source through a second current path in a direction opposite to the first current path; The light source driving device according to claim 1 , wherein the first transistor and the second transistor are alternately turned on.

5. a first voltage dividing element and a second voltage dividing element provided in parallel with the power supply and dividing the power supply voltage; 5. The light source driving device according to claim 4, wherein the first and second transistors apply the divided power supply voltage to the light source.

6. The light source driving device according to any one of claims 1 to 5, 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 infrared rays incident through the optical filter and generates a detection signal; an optical cover that covers the light source, the optical filter, and the light receiving portion.

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