JP2010008371A - Flammable gas sensor - Google Patents

Abstract

The present invention provides a technology capable of realizing a combustible gas sensor that is lightweight and compact and has explosion-proof properties.
A combustible gas sensor GS1 includes a sensor chip 1, a stem 2 on which the sensor chip 1 is mounted, an upper part and a side part, and a metal cap in which the lowermost part of the side part is welded to the outer periphery of the stem 2. 6, and the sensor chip 1 is surrounded by the stem 2 and the metal cap 6. A hole 8 having a diameter of 0.5 to 3 mm, for example, is formed in the upper portion of the metal cap 6, and the hole 8 is covered inside the metal cap 6. For example, the hole diameter is 1 to 4 μm and the thickness is 0. A waterproof and moisture-permeable material 9 of 3 to 1 mm is caulked by the heat insulating material 10.
[Selection] Figure 1

Description

  The present invention relates to a combustible gas sensor, and more particularly to a technique that is effective when applied to a gas sensor mounting structure for detecting hydrogen gas.

  For example, the mounting structure of a gas sensor that detects a flammable gas (for example, hydrogen gas or methane gas) that may explode is the Industrial Safety Institute Technical Guidelines, Factory Electrical Equipment Explosion Protection Guidelines (Gas Steam Explosion Protection 2006), and Industrial Safety It is described in Research Institute, pp138-143 (Non-patent Document 1). The gas sensor mounting structure according to this standard is certified as a flameproof structure. The explosion-proof structure is a structure that ensures that the explosive gas existing in the space outside the gas sensor does not ignite or explode if a gas explosion occurs in the space inside the gas sensor.

  As an example of a gas sensor for detecting hydrogen gas, a Si-MOSFET (Metal Oxide Semiconductor Field Effect Transistor) type hydrogen gas sensor using Pd as a gate proposed by Lundstroem et al. In 1975 (Non-patent Document 2) ) After that, although various devices have been added to the gate structure, the operation temperature of the Si-MOSFET type hydrogen gas sensor is, for example, about 100 to 150 ° C., and the operation of the contact combustion type sensor or the metal oxide semiconductor sensor The temperature is lower than 300 to 500 ° C.

  Further, in Japanese Patent No. 2848818 (Patent Document 1), an extension gate of a gate electrode is formed across a source / drain electrode, and locally by a microheater disposed by recessing a silicon substrate under the extension gate. A Si-MOSFET type hydrogen gas sensor is disclosed that transports hydrogen to the interface of the gate insulating film by heating, dissociating the hydrogen gas with an extension gate, and diffusing the gate electrode.

In addition, for the practical application of fuel cell automobiles and household fuel cells, the 2007 NEDO 2006 results report symposium, July 12 (3rd) poster presentation abstracts, p84 (Non-patent Document 3) includes a semiconductor chip. An Si-MOSFET type hydrogen gas sensor including a sensor chip on which a heater, a sensor element, and a pn junction diode for measuring temperature are mounted is described.
Japanese Patent No. 2848818 Industrial Safety Institute Technical Guidelines, Factory Electrical Equipment Explosion Protection Guidelines (Gas Steam Explosion Protection 2006), published by National Institute for Industrial Safety, pp138-143 I. Lundstroem Sensors and Actuators, B1 (1990), pp 15-20 2007NEDO FY2006 Results Report Symposium, July 12th (3rd) Poster Presentation Abstract, p84

  In general, the size of many sensor parts for detecting flammable gas is about several millimeters and the weight is about 50 mg. However, if the above-mentioned explosion-proof construction is adopted, the outer capacity is about 650 mL (outer dimension: about 70 (W)). × 150 (H) × 110 (D) mm, not including mounting brackets), and the weight is as heavy as about 900g. This limits the installation location of the gas sensor with the explosion-proof construction and improves the workability during actual installation. Also gets worse. Therefore, in the case of flammable gas, there is a problem that a gas sensor having a pressure-proof explosion-proof structure cannot always be installed at a location where gas leakage is likely to occur even though the location where gas leakage occurs can be predicted in advance. . Since flammable gases, especially hydrogen gas, that may explode, diffuse very quickly, if you do not place a gas sensor in a place where there is a risk of leakage, you may miss it if it is an open space. May explode before reacts.

  In a strict sense, it is not an explosion-proof area, but gas leaks with explosion-proof performance can be used in places where there is a risk of explosion, such as gas stations or semiconductor factories that frequently use hydrogen gas as a carrier gas. It is desired to install in a place where there is a high possibility of occurrence. However, even in places where there is a risk of such an explosion, as described above, there are restrictions on the installation location of the gas sensor with the explosion-proof construction, so the gas sensor with the explosion-proof construction is used in a place where there is a risk of gas leakage. Can not always be installed. In addition, there is a problem that the workability of replacement of the gas sensor due to new installation or life guarantee is also poor.

  Therefore, for example, when a gas sensor is installed at the generation source of the combustible gas, only the sensor portion may be installed without adopting the above-described flameproof structure. However, since the explosion-proof structure is not adopted, the explosion-proof property cannot be guaranteed.

  Further, according to the above-mentioned explosion-proof guideline, when sintered metal is used for the flame arrester portion which is the most core of explosion-proof explosion-proof structure, the maximum nominal filtration diameter is 70 to 120 μm, and the minimum thickness is 2 It is determined to be ~ 4 mm. In addition, when a sintered wire mesh is used for the frame arrester part, the minimum number of 100 mesh wire meshes is 4-8, the maximum nominal filtration diameter of the different mesh 5-layer sintered wire mesh is 100 μm, and the minimum number of thicknesses. Is decided to be one. In addition, a strength standard is provided so as to withstand external impacts, and a gas sensor is usually provided with an iron protective cover. As described above, since a special structure is required to realize the explosion-proof structure, the manufacturing price of the gas sensor having the pressure-proof structure tends to be very high.

  In addition to explosion-proof, many gas sensors that detect flammable gases protect the gas sensor from disturbances caused by outside air (for example, gases such as moisture, salt, NOx, or dust) in order to guarantee the reliability of the gas sensor. Implementation is also essential.

  By the way, in the Si-MOSFET type hydrogen gas sensor that detects the hydrogen gas described above, it is possible to give the sensor chip an explosion-proof property by reducing the power consumption of the sensor chip while maintaining an operating temperature of about 100 to 150 ° C. it can. In fact, if the power consumption of the Si-MOSFET type hydrogen gas sensor is 25 mW or less, the operating conditions of a rated voltage of 1.2 V or less and a rated current of 0.1 A or less can be realized, it is legally not necessary to provide an explosion-proof structure for the sensor chip. Is also accepted.

  However, in general, the power consumption of the sensor chip of the combustible gas sensor is often about several hundreds mW. For example, in a sensor with an operating temperature of 300 to 500 ° C. called a contact combustion type, even in a “μ-CS sensor” in which the size of the sensor chip is as small as about 200 μm, the power consumption is about 70 mW, and the power consumption is further reduced. It is not easy to do. Further, in the gas sensor disclosed in Japanese Patent Application No. 2008-156427 (filed 2008.6.616) of Usagawa et al., The power consumption when operating at about 100 to 150 ° C. is about 100 to 150 mW, and the consumption The power was 25 mW or less, the rated voltage was 1.2 V or less, and the rated current was 0.1 A or less. Furthermore, the Si-MOSFET type hydrogen gas sensor described in Patent Document 1 described above also has a problem that the response speed is slow because the temperature of the gate electrode in the vicinity of the gate insulating film does not increase and the diffusion distance is long.

  The objective of this invention is providing the technique which can implement | achieve the combustible gas sensor which is lightweight and small and has explosion-proof property.

  Another object of the present invention is to provide a technology capable of realizing a Si-MOSFET type hydrogen gas sensor having a power consumption of 25 mW or less, a rated voltage of 1.2 V or less, and a rated current of 0.1 A or less without impairing gas sensor characteristics. It is to provide.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in this application, an embodiment of a representative one will be briefly described as follows.

  In this embodiment, a sensor chip, a stem on which the sensor chip is mounted, a heat insulating material inserted between the sensor chip and the stem, and a metal cap in which the lowermost portion of the side portion is welded to the outer periphery of the stem. A combustible gas sensor including a sensor chip surrounded by a stem and a metal cap. A hole is formed in the upper part of the metal cap, and a waterproof and moisture-permeable material covering the hole is caulked inside the metal cap by a heat insulating material. The hole diameter of the waterproof and moisture-permeable material is 1 to 4 μm, and the thickness is 0.3 to 1 mm.

  Moreover, this embodiment is a combustible gas sensor including a sensor chip, a stem on which the sensor chip is mounted, and a heat insulating material inserted between the sensor chip and the stem. In the sensor chip, a sensor field effect transistor, a reference field effect transistor, a heater wiring, and a pn junction diode are formed. The gap between the catalyst metal gate and the source electrode of the sensor field effect transistor and the catalyst metal gate and drain are formed. The distance between the electrode and the electrode is increased, the heater wiring is formed here, and the thickness of the substrate in the area where the catalytic metal gate and the heater wiring are formed is the same as that of the area where the catalytic metal gate and the heater wiring are not formed. Processed thinner than the thickness of the substrate. The thickness of the substrate in the region where the catalyst metal gate and the heater wiring are formed is 0.1 to 20 μm.

  Among the inventions disclosed in the present application, effects obtained by one embodiment of a representative one will be briefly described as follows.

  A combustible gas sensor that is lightweight and compact and has explosion-proof properties can be realized. In addition, a Si-MOSFET type hydrogen gas sensor having a power consumption of 25 mW or less, a rated voltage of 1.2 V or less, and a rated current of 0.1 A or less can be realized without impairing gas sensor characteristics.

  In the following embodiments, when necessary for the sake of convenience, the description will be divided into a plurality of sections or embodiments. However, unless otherwise specified, they are not irrelevant to each other, and one is the other. There are some or all of the modifications, details, supplementary explanations, and the like.

  Further, in the following embodiments, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), especially when clearly indicated and when clearly limited to a specific number in principle, etc. Except, it is not limited to the specific number, and may be more or less than the specific number. Further, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily indispensable unless otherwise specified and apparently essential in principle. Needless to say. Similarly, in the following embodiments, when referring to the shapes, positional relationships, etc. of the components, etc., the shapes are substantially the same unless otherwise specified, or otherwise apparent in principle. And the like are included. The same applies to the above numerical values and ranges.

Further, in the drawings used in the following embodiments, hatching may be added to make the drawings easy to see even if they are plan views. In the following embodiments, a MISFET (Metal Insulator Semiconductor Field Effect Transistor) representing a field effect transistor is abbreviated as MIS, a p-channel type MISFET is abbreviated as a p-channel MIS, and an n-channel type MISFET is an n-channel. Abbreviated as MIS. A MOSFET (Metal Oxide Semiconductor FET) is a field effect transistor having a structure in which a gate insulating film is a silicon oxide (SiO ₂ or the like) film, and is included in the subordinate concept of the MIS. In the following embodiments, the term “wafer” is mainly a Si (Silicon) single crystal wafer. However, not only that, but also an SOI (Silicon On Insulator) wafer and an integrated circuit are formed thereon. Insulating film substrate or the like. The shape includes not only a circle or a substantially circle but also a square, a rectangle and the like.

  In all the drawings for explaining the following embodiments, components having the same function are denoted by the same reference numerals in principle, and repeated description thereof is omitted. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  In the embodiment of the present invention, a Si-MOSFET type hydrogen gas sensor will be described as an example of a combustible gas sensor, but it goes without saying that it can be applied to another type of gas sensor.

(Embodiment 1)
A basic configuration of a combustible gas sensor having a simple explosion-proof structure according to the first embodiment will be described with reference to FIG. 1A, 1B, and 1C are a cross-sectional view, a bottom view, and a perspective view of parts for caulking a waterproof and moisture-permeable material, respectively, of a combustible gas sensor.

  As shown in FIGS. 1A and 1B, the combustible gas sensor GS <b> 1 uses the sensor chip 1, and the sensor chip 1 is disposed on the stem 2 via the heat insulating material 3. The sensor chip 1 is attached to the upper surface of the heat insulating material 3. The stem 2 penetrates the stem 2, and the front surface (the surface side on which the sensor chip 1 and the heat insulating material 3 are disposed) and the back surface (the opposite side to the surface on which the sensor chip 1 and the heat insulating material 3 are disposed). And a plurality of lead terminals (here, twelve are illustrated) 4 are provided, and the lead terminals 4 are fixed to the stem 2 by a glass material 2 a provided on the outer periphery of the lead terminals 4. ing. A plurality of electrode pads formed on the main surface of the sensor chip 1 and a plurality of lead terminals 4 connected to the stem 2 are connected by wires 5, respectively.

  Further, the sensor chip 1, the heat insulating material 3, and the plurality of wires 5 are covered with a cylindrical metal cap 6, and the lowermost portion (the brim portion 6 a) of the side of the metal cap 6 is welded to the periphery of the stem 2. Are joined by. Since the sensor chip 1 detects hydrogen gas in the outside air, a hole 8 for introducing outside air into the metal cap 6 is formed in the metal cap 6 at substantially the center of the upper portion of the metal cap 6. . Further, a waterproof and moisture permeable material 9 is installed inside the metal cap 6 in contact with the upper portion of the metal cap 6, and the waterproof and moisture permeable material 9 is caulked by a cylindrical heat insulating material 10 shown in FIG. It has been. In the first embodiment, the hole 8 is provided in the upper part of the metal cap 6. However, the present invention is not limited to this. For example, the hole 8 may be formed in the side part of the metal cap 6.

The waterproof and moisture-permeable material 9 is a porous film that can directly take in and out ambient air (for example, air) and gas, for example. This waterproof and moisture-permeable material 9 has an effect of dust resistance or chemical resistance in addition to water resistance, and also has an explosion-proof function. As a typical waterproof and moisture-permeable material 9, for example, Gore-Tex (registered trademark) produced by combining a film obtained by stretching polytetrafluoroethylene, which is a typical fluororesin, and a polyurethane polymer is available. The waterproof and moisture permeable material 9 has a feature of allowing water vapor to pass but not allowing water (both waterproof and moisture permeable). For example, the Gore-Tex has 1.4 billion fine holes per 1 cm ² . .

  Next, the explosion-proof property of the waterproof and moisture-permeable material according to the first embodiment will be described with reference to FIG. FIG. 2 is an auxiliary diagram for explaining the explosion-proof property of the waterproof and moisture-permeable material. FIGS. 2 (a), (b) and (c) are the flame strength and film of the waterproof and moisture-permeable material and the sintered metal plate, respectively. It is the graph which shows the relationship with thickness, the schematic diagram explaining the internal state of a waterproof moisture-permeable material, and the schematic diagram explaining the internal state of a metal sintered compact board.

  The operating temperature of the sensor chip 1 provided in the combustible gas sensor GS1 described above is, for example, 100 to 150 ° C. The mounting structure of the combustible gas sensor GS1 is not changed even if hydrogen gas explodes inside the metal cap 6. It is necessary to ignite the hydrogen gas existing outside the flank so that it does not explode. According to the theory of gas explosion, if a gas-fired flame propagates through the gas and is cooled when it passes through the wall and then dies in the wall, there will be no external flammable explosion. If it doesn't pass, an external flammable explosion will occur. Factors that govern this phenomenon include wall hole particle size, wall hole density, thermal conductivity of the materials that make up the wall, and the area of the wall that is exposed to flame propagation. Then, since the explosion energy inside the mounting becomes large, it is necessary to consider the volume inside the mounting where the gas is confined.

  Therefore, in the first embodiment, if the volume inside the mounting (inside the metal cap 6) is constant, the metal cap 6 that is a wall forming the mounting space and the waterproof and moisture-permeable material 9 made of a porous film are covered. The pressure is mainly a problem, and in particular, the pressure on the waterproof and moisture-permeable material 9 that is located in the hole 8 provided in the metal cap 6 and has a lower strength than the metal cap 6 is a problem.

  Then, the explosion-proof test of the porous film made of the same material as the waterproof and moisture-permeable material 9 used in the combustible gas sensor GS1 was performed. FIG. 2A shows the relationship between the flame strength and the film thickness that passes through the waterproof and moisture-permeable material (the same material as the waterproof and moisture-permeable material 9 used in the combustible gas sensor GS1). For comparison, the relationship between the flame strength passing through the sintered metal plate and the film thickness is also shown in FIG. As shown in FIG. 2B, the internal state of the waterproof and moisture-permeable material 9 is composed of polytetrafluoroethylene 11 and a gap 12, and the hole diameter of the gap 12 is, for example, 1 to 4 μm. Further, as shown in FIG. 2C, the internal state of the metal sintered body plate is composed of the metal sintered body 13 and the gap 14, and the hole diameter of the gap 14 is, for example, about 100 μm.

  As shown to Fig.2 (a), as for the waterproof moisture-permeable raw material and a metal sintered compact board, the flame strength to pass through attenuates as the film thickness becomes thick. However, the attenuation of the flame strength that passes through is different between the waterproof and moisture permeable material and the sintered metal plate, and when compared with the same film thickness (same volume and same exposed area), the waterproof permeability is small. It can be seen that the wet strength of the wet material is smaller than that of the sintered metal plate having a large hole diameter. Therefore, even if there is a difference in the thermal conductivity of the material, it is considered that the explosion-proof effect of the porous membrane is improved by reducing the hole diameter of the gap.

  In the first embodiment, the hole 8 formed in the upper part of the metal cap 6 is covered with the waterproof and moisture permeable material 9, but a porous film having a hole diameter of 1 to 4 μm is formed on the waterproof and moisture permeable material 9. By using it, the flame kernel can be extinguished. In addition, explosion may occur continuously inside the mounting, and in this case, the waterproof and moisture-permeable material 9 may melt due to the heat generation effect. However, by constantly monitoring the temperature of the sensor chip 1 or the resistance of the heater wiring, an explosion can be detected immediately inside the mounting.

  Next, a specific structure of the combustible gas sensor having a simple explosion-proof structure according to the first embodiment will be described with reference to FIGS. 3 is an optical micrograph of an example of a sensor chip provided in the combustible gas sensor, FIG. 4 is a top view of the heat insulating material to which the sensor chip is attached, and FIG. 5 is an optical micrograph of the heat insulating material to which the sensor chip is attached. FIG. 6 is a cross-sectional view of a main part of the combustible gas sensor. The sensor chip shown in FIG. 3 is an example of a sensor chip investigated by the present inventors, and the configuration and wiring of each element are not limited to this.

  As illustrated in FIG. 3, the sensor chip 1 includes a sensor n-channel MIS 16, a reference n-channel MIS 17, a heater 18 using metal wiring, a pn junction diode 19 for measuring chip temperature, and a plurality of sensors on a silicon substrate 15. The electrode pads 20 are arranged. The sensor n-channel MIS 16 and the reference n-channel MIS 17 have substantially the same structure. The gate length of the catalytic metal gate of the sensor n-channel MIS 16 and the reference n-channel MIS 17 is, for example, 20 μm, and the gate width is, for example, 300 μm.

  The catalytic metal gate, the source region, and the drain region of the sensor n-channel MIS 16 are connected to the electrode pad 20 via the wiring 21 respectively. Similarly, the catalytic metal gate, the source region, and the drain region of the reference n-channel MIS 17 are connected to the electrode pad 20 through the wiring 21 respectively. Further, both ends of the heater 18 are connected to the electrode pad 20 via the wiring 21, respectively, and the p region and the n region of the pn junction diode 19 are connected to the electrode pad 20 via the wiring 21, respectively.

  As shown in FIGS. 4 to 6, the sensor chip 1 is bonded to the upper surface of a heat insulating material 3 obtained by processing a PEEK material (polyether, ether, ketone material) into a cylindrical shape having a height of 3 to 5 mm. 3 is bonded to the upper surface of the stem 2 (for example, TO 5-12 pin). The stem 2 is made of, for example, Auvar-plated Kovar (an alloy in which Fe and Ni and Co are blended), and the pedestal inner diameter thereof is, for example, 7.6φ. The thickness of the sensor chip 1 is, for example, 200 to 500 μm, and the chip size is, for example, 2 mm × 2 mm. The metal cap 6 is made of, for example, Kovar plated with Au. The height of the metal cap 6 is, for example, 15 mm, and the diameter of the hole 8 formed in the upper portion of the metal cap 6 is, for example, 0.5 to 1.5 mm. The hole diameter of the waterproof and moisture permeable material 9 is 1 to 4 μm, and the thickness thereof is, for example, 0.3 to 1 mm. The thickness of the heat insulating material 10 is 3 mm, for example, and is caulked inside the metal cap 6. The metal cap 6 and the stem 2 are welded by a resistance welding method at the lowermost portion (the brim portion 6a) of the side portion of the metal cap 6.

  In the outer peripheral region of the heat insulating material 3, twelve lead terminals 4 provided through the stem 2 are arranged. Of the plurality of electrode pads 20 provided on the sensor chip 1, the electrode pad 20 electrically connected to the catalytic metal gate, the source region and the drain region of the sensor n-channel MIS 16 via the wirings 21, and the reference n An electrode pad 20 electrically connected to the catalytic metal gate, the source region and the drain region of the channel MIS 17 via the wiring 21; and an electrode pad 20 electrically connected to both ends of the heater 18 via the wiring 21; The electrode pads 20 electrically connected to the p region and the n region of the pn junction diode 19 via the wirings 21 are connected to the lead terminals 4 using the wires 5, respectively. The wire 5 is, for example, an Al wire or an Au wire. In order to facilitate bonding of the wire 5, the lead terminal 4 is formed so as to penetrate through the heat insulating material 3 and lower than the upper surface of the heat insulating material 3 to which the sensor chip 1 is attached. In addition, one lead terminal 4 is provided for grounding the sensor chip 1, thereby stabilizing the electrical characteristics of the sensor chip 1. Here, illustration of wiring electrically connected to a well layer, a substrate, and the like is omitted.

  Next, the explosion-proof performance of the combustible gas sensor according to the first embodiment will be described. Hereinafter, hydrogen explosion experiments conducted by the present inventors and the results thereof will be described with reference to FIGS. 7 is a cross-sectional view of a main part of a container used in a hydrogen explosion-proof experiment, FIG. 8 is a cross-sectional view of a main part of a sample for an explosive experiment having the same mounting structure as the combustible gas sensor according to Embodiment 1, and It is principal part sectional drawing of the sample for an explosive experiment which the inventors formed for the comparison.

  In the hydrogen explosion experiment, an approximately 50 mL copper container 35 shown in FIG. 7 was used. The container 35 is equipped with a nichrome wire (not shown) that can be heated to a hydrogen ignition temperature of 560 ° C. or higher. The upper part of the container 35 is covered with a film 36 made of, for example, polyvinylidene chloride, and the container 35 and the film 36 are bonded using a clay 37. Whether or not the explosion experiment sample will explode by installing an explosion experiment sample (for example, the explosion experiment sample S1 shown in the figure) inside the container 35 and applying a voltage of 5.0 V and a current of 0.5 A or less from the outside. I did some experiments. When the explosion did not occur, the nichrome wire was energized to confirm the hydrogen explosion, which was proved that the inside of the container 35 was filled with hydrogen gas at a concentration leading to the explosion. The concentration of hydrogen gas was theoretically about 30% at which all the hydrogen and oxygen inside the container 35 burned out.

  The explosion test sample S1 having the same mounting structure as the combustible gas sensor according to the first embodiment shown in FIG. 8 is provided with a metal cap 6 and a waterproof moisture-permeable material 9, and in this hydrogen explosion experiment, An explosion test sample S1 was used. The diameter of the hole 8 formed in the upper part of the metal cap 6 is 1.5 mm, the hole diameter of the waterproof and moisture-permeable material 9 is 1 μm, and the thickness thereof is 0.3 mm. The explosive experiment comparative sample RS1 formed by the present inventors for comparison shown in FIG. 9 is provided with the metal cap 6 with respect to the explosive experiment sample S1, but not with the waterproof and moisture permeable material 9. . In addition, the explosive experiment comparative sample RS2 formed by the present inventors for comparison shown in FIG. 10 does not include the metal cap 6 and the waterproof moisture-permeable material 9 with respect to the explosive experiment sample S1. Further, as shown in FIGS. 8 to 10, in all these samples S1, RS1, and RS2, a tungsten filament wire 38 is used as a hydrogen gas ignition source, and both ends of the tungsten filament wire 38 penetrate the stem 2 respectively. Are connected to different lead terminals 4 installed in the same manner.

  The experimental results are summarized in Table 1. In the explosive experiment comparative sample RS1 in which only the metal cap 6 is mounted and the waterproof moisture-permeable material 9 is not mounted, and in the explosive experiment comparative sample RS2 in which the metal cap 6 and the waterproof moisture-permeable material 9 are not mounted, When energized by applying a voltage of 5 V and a current of 0.5 A, an explosion occurred instantaneously. On the other hand, in the explosion test sample S1, no explosion occurred even when a voltage of 5 V and a current of 0.5 A were applied from the outside to energize. For the explosion test sample S1, the tungsten filament wire 38 is burned and disconnected, and then the nichrome wire is energized to cause a hydrogen explosion. It was confirmed that it was charged. In addition, in the explosion experiment sample S1, it is confirmed that the inside of the container 35 burns red from the hole 8 provided in the upper portion of the metal cap 6 until the tungsten filament wire 38 is burned out.

  In another hydrogen explosion experiment, the diameter of the hole 8 formed in the upper part of the metal cap 6 was used in the range of 0.5 to 3 mm. However, no significant difference was observed in the explosion-proof property within this range. Moreover, although the hole diameter of the waterproof moisture-permeable raw material 9 was used in the range of 1-4 micrometers, and the thickness was used in the range of 0.3-1 mm, the difference in explosion-proof property was not seen in each range. From these experimental results, it is considered that mounting using the waterproof and moisture-permeable material 9 having a hole diameter of 1 to 4 μm and a thickness of 0.3 to 1 mm is effective against explosion.

  Strictly speaking, this hydrogen explosion experiment shows that it does not ignite and explode to the outside of the container 35 until 23 to 50 seconds, but the tungsten filament wire 38 and hydrogen gas are burned inside the container 35 for a longer time. When this happens, there still remains a problem such as whether the container 35 ignites and explodes or the waterproof and moisture-permeable material 9 melts. However, in reality, the combustible gas sensor GS1 is not exposed to a high temperature for a long time, so it is considered that there is no problem.

  By the way, in many flammable gas sensors, mounting technology that protects the flammable gas sensor from disturbance (humidity, salinity, NOx gas or dust) due to the outside air is strong to guarantee the reliability of the flammable gas sensor. Is essential.

Next, the salt damage resistance performance of the combustible gas sensor according to the first embodiment will be described. Below, the method of the salt damage test which the present inventors conducted and its result are demonstrated. In addition, it has been proved so far that the waterproof and moisture-permeable material is strong in water resistance (not H ₂ O gas) or chemical resistance. The salt damage test complied with JIS standard salt damage test C60068-2-52 for equipment always installed on the coast or on the ocean. The salt damage test C60068-2-52 has severity (1) and severity (2) shown in Table 2 due to the difference in salt damage strength, but both were applied.

  FIGS. 11A and 11B are a cross-sectional view and a bottom view of the main part of the combustible gas sensor according to the first embodiment used in the salt damage test. In the combustible gas sensor GS2 used for the salt damage test, in addition to the combustible gas sensor GS1 shown in FIG. 1 described above, a tube-shaped waterproof and moisture-permeable material is provided on the side of the metal cap 6 in order to confirm the role of the waterproof and moisture-permeable material. 39, and a tube-shaped waterproof and moisture-permeable material 39 is fastened by a stainless steel wire 40. As the tube-shaped waterproof and moisture-permeable material 39, two types (2 μm and 3.5 μm) of tube-shaped waterproof and moisture-permeable materials 39 having different hole diameters were used. The thickness of the tube-shaped waterproof and moisture-permeable material 39 is, for example, 0.8 mm.

  FIG. 12 shows a SEM (Scanning Electron Microscope) photograph after the salt damage test of the combustible gas sensor according to the first embodiment. FIGS. 12 (a), (b) and (c) are SEM photographs of samples not subjected to the salt damage test, SEM photographs of samples after the salt damage test of severity (1), and severity (2), respectively. It is a SEM photograph of the sample after performing a salt damage test.

  The side of the metal cap 6 not covered with the tube-shaped waterproof and moisture-permeable material 39 of the combustible gas sensor GS2, the welded portion of the collar portion 6a of the metal cap 6 and the stem 2, and the connection between the lead terminal 4 and the stem 2 The glass material 2a was corroded by red rust, and the sensor chip 1 malfunctioned due to the influence of the stem 2. Further, red rust was generated in the lead terminal 4 and it was easily broken even with a slight force.

  Further, at locations indicated by a, b and c in FIG. 12B and at locations indicated by d, e, f and g in FIG. 12C, EDX (Energy Dispersive X-ray Fluorescence: Energy Dispersive Fluorescence X) When the constituent elements were analyzed by the line analysis method), only Au plating the surface of the metal cap 6 was detected at the locations indicated by b, d and g, but at the locations indicated by c, e and f, Au plating was peeled off, and Fe and the like were detected. In the welded portion between the flange portion 6a of the metal cap 6 and the stem 2, corrosion due to red rust is remarkably advanced at a location a where the Au plating is peeled off during welding. There is a portion where the corrosion at the welded portion also spreads on the surface of the stem 2. Corrosion is also observed in the twelve lead terminals 4 and the glass material 2a provided in the stem 2. In the salt damage test of severity (2), red rust was also widely observed on the surface of the side portion of the metal cap 6.

  On the other hand, the portion covered with the tube-shaped waterproof and moisture-permeable material 39 has no rust in the salt damage test of severity (1) and severity (2). Rust generation was not observed for the stainless steel wire 40 as well.

  Also, the hydrogen response characteristics were measured for 6 samples, and after the salt damage test of severity (2), the hydrogen response characteristics ΔVg and response speed were not changed in 4 samples, but 2 samples The response speed was reduced and the response speed was not saturated even after 600 seconds. In addition, after the salt damage test of severity (1), both the hydrogen response characteristic ΔVg and the response speed were remarkably reduced, but when the metal cap 6 was removed and the wire 5 was reconnected, the response speed remained lowered. However, the hydrogen response characteristic ΔVg recovered to some extent. Causes of this phenomenon include salt and water intrusion from the location where the corrosion of the welded portion between the collar portion 6 a of the metal cap 6 and the stem 2 has progressed, and between the metal cap 6 and the stem 2. Red rust or red rust generated around the lead terminals 4 can be considered. In this salt damage test, no significant change was observed in the threshold voltage Vth of the sensor n-channel MIS 16 of the sensor chip 1.

  Rust generated in the glass material 2a connecting the lead terminal 4 and the stem 2 can be prevented by covering the back surface of the stem 2 with a molding material such as an epoxy resin.

  In another salt damage test, the diameter of the hole 8 formed in the upper part of the metal cap 6 was used in the range of 0.5 to 3 mm, but no significant difference was observed in the hydrogen response characteristic ΔVg in this range. . Moreover, although the hole diameter of the waterproof and moisture-permeable material 9 was used in the range of 1 to 4 μm and the thickness in the range of 0.3 to 1 mm, no significant difference was seen in the hydrogen response characteristic ΔVg in each range. . From these experimental results, it is considered that mounting using the waterproof and moisture-permeable material 9 having a hole diameter of 1 to 4 μm and a thickness of 0.3 to 1 mm is effective against salt damage.

  When there is no need to consider salt damage, a metal cap 6 and a Kovar stem 2 can be used. On the other hand, when salt damage needs to be taken into account, the metal cap 6 and the stem 2 can be prevented from corroding by covering the outside of the metal cap 6 and the stem 2 with the waterproof and moisture-permeable material 39. Another example of the combustible gas sensor in which the outer sides of the metal cap 6 and the stem 2 are covered with the waterproof and moisture-permeable material 39 will be described in a second embodiment to be described later. In place of the metal cap 6 and the stem 2, a ceramic or stainless steel cap and stem can be used.

  Next, the dust resistance performance of the combustible gas sensor mounting structure according to the first embodiment will be described. Below, the method of the dust test which the present inventors conducted and its result are demonstrated. We tested the ability of waterproof and moisture-permeable materials to prevent atmospheric dust, especially particulate matter discharged from automobiles and various facilities into the atmosphere. A sensor chip and a combustible gas sensor, which is a mounted product, were installed at an actual hydrogen station located about 80 meters from the coast, right next to the expressway, and the deterioration of these samples was observed for half a year.

  FIG. 13 shows an SEM photograph of the sensor chip after 12 days of the dust test. As shown in FIG. 13, the particulate matter 41 discharged into the atmosphere directly hits the catalytic metal gate 28 (gate length: 20 μm) of the sensor n-channel MIS 16, and is notable for the operational characteristics of the sensor n-channel MIS 16. Deterioration was observed. However, no foreign matter was observed in the gate region of the combustible gas sensor by observation with an optical microscope. From this result, it can be seen that mounting using a waterproof and moisture-permeable material is also effective for dust prevention. In addition, it was confirmed that the operational characteristics of the sensor n-channel MIS 16 are stable and the fluctuation of the hydrogen response characteristic ΔVg is small.

  From the explosion-proof test, the salt damage test and the dust-proof test described above, the flammable gas sensor GS1 shown in FIG. 1 is effective for explosion-proof and dust-proof, and the flammable gas sensor GS2 shown in FIG. It can be said that it is effective against dust.

  As described above, according to the first embodiment, the combustible gas sensor GS1 is configured using the sensor chip 1, and the sensor chip 1 is disposed on the stem 2 via the heat insulating material 3 and covered with the metal cap 6. By adopting the mounting structure, the internal volume of the mounting structure is 10 mL or less (for example, the volume of the combustible gas sensor GS1 shown in FIGS. 4 to 6 described above), which is 1/10 or less of a gas sensor employing a conventional explosion-proof structure. Can be about 0.5 mL). Moreover, a hole 8 for introducing outside air is formed in the upper part of the metal cap 6. By covering the hole 8 with a waterproof and moisture-permeable material 9 from the inside of the metal cap 6, an explosion-proof effect is exerted on the combustible gas sensor GS 1. And it can have a dustproof effect. Thereby, the combustible gas sensor GS1 which is light and small and has explosion-proof properties can be realized. Furthermore, by covering the outer side of the metal cap 6 with a tube-shaped waterproof and moisture-permeable material 39, the combustible gas sensor GS2 having a higher salt damage resistance than the combustible gas sensor GS1 can be realized.

  By the way, the flame arrester having an explosion-proof and explosion-proof construction is designed so that heat is taken away when the flame passes through the gap of the flame arrester, so that the temperature is lower than the explosion temperature and the flame does not leak to the outside. To prevent explosion, it is necessary to take heat when the flame passes through the gap of the flame arrestor and to keep it below the explosion temperature. In the combustible gas sensor GS1 according to the first embodiment, the waterproof and moisture-permeable material 9 having a thickness of 0.3 to 1 μm is used, but the maximum nominal filtration diameter is as small as 1 to 4 μm, and the metal cap Since the space inside 6 is also as small as 0.5 mL, it is possible to prevent the gas explosion from leaking to the outside, considering that the energy of the gas explosion is proportional to the volume of the space inside the metal cap 6. In view of small size and light weight, a resin-based material is more preferable than metal. Although resin materials generally have a problem of poor heat resistance, the use of waterproof and moisture-permeable materials is not a problem because combustible gas sensors are not exposed to high temperatures for a long time.

(Embodiment 2)
In the second embodiment, a combustible gas sensor in which the outside of a metal cap is also covered with a waterproof and moisture-permeable material will be described. A basic structure of the combustible gas sensor according to the second embodiment will be described with reference to FIGS. 14 and 15. FIG. 14 is a cross-sectional view of a main part of a first example of the combustible gas sensor according to the second embodiment, and FIG. 15 is a cross-sectional view of a main part of a second example of the combustible gas sensor according to the second embodiment.

  A combustible gas sensor GS3 shown in FIG. 14 has a waterproof and moisture permeable material 9 disposed on the inner side of the metal cap 6 in contact with the upper portion of the metal cap 6 in the same manner as the combustible gas sensor GS1 described above. The metal cap 6 has a mounting structure in which the side portions of the metal cap 6 including the welded portion with the collar portion 6 a are wrapped with a waterproof and moisture-permeable material 39. Rust generated in the glass material 2 a connecting the lead terminal 4 and the stem 2 can be prevented by covering the back surface of the stem 2 with a molding material, for example, an epoxy resin 42.

  The combustible gas sensor GS4 shown in FIG. 15 does not include the waterproof and moisture permeable material 9 inside the metal cap 6, and includes the welded portion between the stem 2 and the collar portion 6a of the metal cap 6, and the metal cap 6 side. All parts are encased in a waterproof / breathable material 39, and the upper part of the metal cap 6 is also encased in a waterproof / breathable material 39. In this case, the waterproof and moisture permeable material 39 that covers the side portion of the metal cap 6, the waterproof and moisture permeable material 9 disposed in contact with the upper portion of the metal cap 6, and the connection portion are caulked by the heat insulating material 10. The heat insulating material 10 is formed by hollowing a PEEK material into a cylindrical shape having a height of 3 to 5 mm and bonding the PEEK material to the upper surface and the side surface of the metal cap 6. Rust generated in the glass material 2 a connecting the lead terminal 4 and the stem 2 can be prevented by covering the back surface of the stem 2 with a molding material, for example, an epoxy resin 42.

  In the second embodiment, the hole 8 formed in the metal cap 6 is provided in the upper part of the metal cap 6 as in the first embodiment. However, the present invention is not limited to this. You may form in the 6 side part. Also in this case, the waterproof and moisture-permeable material 39 can be attached to the outside of the metal cap 6.

  As described above, according to the second embodiment, the hole 8 provided in the upper portion of the metal cap 6 is covered with the waterproof and moisture-permeable material 9 from the inside of the metal cap 6, and the side portion of the metal cap 6 is waterproofed and transparent from the outside. By covering with the moisture material 39 or covering the upper and side portions of the metal cap 6 with the waterproof moisture-permeable material 39 from the outside, it is possible to have an explosion-proof effect, a salt-damage effect, a dust-proof effect, and the like. Thereby, combustible gas sensor GS3, GS4 with which the salt damage-proof effect improved rather than combustible gas sensor GS1, GS2 is realizable.

(Embodiment 3)
A sensor chip provided in the combustible gas sensor according to the third embodiment will be described with reference to FIGS. 16 and 17. FIGS. 16A and 16B are a cross-sectional view and a plan view of the main part of the heater wiring region in which the sensor n-channel MIS is arranged, respectively. FIG. It is principal part sectional drawing. Pt is used for the catalyst metal gate of the Si-MOSFET type hydrogen gas sensor. Since the Pt gate Si-MOSFET type hydrogen gas sensor is disclosed in Japanese Patent Application No. 2008-156427 (2008.6.6.16 application) of Usagawa et al., The detailed description here will be repeated in principle. Suppose there is nothing. Hereinafter, a case will be described in which the present invention is applied to an n-channel MIS having a gate length (Lg) of, for example, 20 μm and a gate width (Wg) of, for example, 300 μm.

  First, the heater wiring region in which the sensor n-channel MIS is disposed will be described. As shown in FIGS. 16A and 16B, in the substrate of the sensor chip, a buried insulating layer 23 is formed on the silicon substrate 22, and a channel silicon layer 24 is further formed on the buried insulating layer 23. A so-called SOI wafer is used. The thickness of the silicon substrate 22 is, for example, 200 to 750 μm, the thickness of the buried insulating layer 23 is, for example, 0.1 to 5 μm, and the thickness of the channel silicon layer 24 is, for example, 0.1 to 20 μm. For example, a silicon oxide film can be used for the buried insulating layer 23.

A local oxide film SiO ₂ 26 made of a silicon oxide film is formed on the main surface of the channel silicon layer 24 by using a local oxidation method in order to define the gate region 25 of the sensor n-channel MIS 16. A catalytic metal gate 28 made of, for example, Pt is formed on the main surface of the channel silicon layer 24 in the gate region 25 via a gate insulating film 27. A lead electrode is electrically connected to the catalyst metal gate 28, but the illustration is omitted. In the channel silicon layer 24 below the local oxide film SiO ₂ 26, a source region 28S and a drain region 28D made of an n ⁺ type semiconductor region are formed. The threshold voltage Vth of the sensor n-channel MIS 16 is, for example, 1.0V. In FIG. 16A, the extraction electrode of the catalyst metal gate 28 is not shown.

Except for the gate region 25, the channel silicon layer 24 and the local oxide film SiO ₂ 26 are covered with an interlayer insulating film 29 and are electrically connected to the source region 28 </ b> S through a connection hole 30 formed in the interlayer insulating film 29. A source electrode 31S and a drain electrode 31D electrically connected to the drain region 28D are formed. The interlayer insulating film 29 can be formed of, for example, a phosphorus-doped glass PSG (Phospho Silicate Glass) film. A heater wire 32 is formed on the local oxide film SiO ₂ 26 and on the interlayer insulating film 29. The heater wiring 32 is formed of an Al alloy film, and has a line width of, for example, 5 μm and a height of, for example, 0.5 μm. The heater wiring 32 is arranged in a folded state between the catalytic metal gate 28 and the source electrode 31S and between the catalytic metal gate 28 and the drain electrode 31D. For example, between the catalytic metal gate 28 and the source electrode 31S, the heater wiring 32 is formed in a 15-folded state at intervals of 5 μm with a length of 320 μm as a unit, and similarly, for example, between the catalytic metal gate 28 and the drain electrode 31D. When the heater wirings 32 are formed in a 15-folded state at intervals of 5 μm with a length of 320 μm as a unit, the total length of the heater wirings 32 is about 1 mm.

  Further, except for the gate region 25, the source electrode 31 </ b> S, the drain electrode 31 </ b> D, and the heater wiring 32 are covered with a surface protective film 33. As the surface protective film 33, for example, a silicon nitride film can be used.

  Further, a silicon substrate 22 located under a region (hereinafter referred to as a genuine sensor region) 34 including the main portion of the gate region 25 and the heater wiring 32 is cut out. Thus, by reducing the thickness of the authentic sensor region 34 that is a heated region to about 0.1 to 20 μm, for example, when the heater wiring 32 is energized and heated, The amount of heat that has flowed in is difficult to escape to the surroundings, and as a result, the temperature of the genuine sensor region 34 can be set to about 100 to 200 ° C. with low power. The silicon substrate 22 can be cut through by performing anisotropic dry etching and wet etching with a KOH solution on the silicon substrate 22.

  Next, the heater wiring region in which the reference n-channel MIS 17 is disposed will be described. As shown in FIG. 17, the structure of the heater wiring region in which the reference n-channel MIS 17 is disposed is substantially the same as the structure of the heater wiring region in which the sensor n-channel MIS 16 is disposed. The difference is that the catalytic metal gate 28 of the sensor n-channel MIS 16 is not covered with the interlayer insulating film 29 and the surface protective film 33, but the catalytic metal gate 28 of the reference n-channel MIS 17 is not covered with the interlayer insulating film 29 and the surface protective film. It is covered with the film 33.

  In addition, since the distance between the catalytic metal gate 28 and the source electrode 31S and between the catalytic metal gate 28 and the drain electrode 31D is as long as several tens of μm, the source / gate resistance is increased, but the operating region of the combustible gas sensor is the source / drain current. Is used in a small area, so it is not considered to be a major obstacle.

  Further, although the sensor n-channel MIS 16 and the reference n-channel MIS 17 are formed in the sensor chip, a p-channel MIS may be used instead of the n-channel MIS, and the sensor chip can be similarly realized.

  Next, the power consumption of the combustible gas sensor according to the third embodiment will be described.

  In the combustible gas sensor according to the third embodiment, as shown in FIG. 16 described above, the structure of the sensor chip includes the distance between the catalyst metal gate 28 and the source electrode 31S and the distance between the catalyst metal gate 28 and the drain electrode 31D. The distance of the gap is increased, and the heater wiring 32 made of metal wiring is bent and inserted into this gap, and the silicon substrate 22 located under the genuine sensor region 34 including the main part of the gate region 25 and the heater wiring 32. The peripheral silicon substrate 22 is hard to be heated by the heat generated by heating the gate region 25, and the heat insulating material 3 is inserted between the sensor chip 1 and the stem 2 as shown in FIG. To do. With such a structure, the area to be actually heated can be 1/50 or less of the total area of the sensor chip and 1/1000 or less of the total volume.

  FIG. 18 is a graph illustrating the relationship between the resistance of the heater wiring and the power consumption of the combustible gas sensor according to the third embodiment.

  For example, in the sensor n-channel MIS 16 shown in FIG. 16 described above, when a current of 12.5 mA is passed between the extraction electrodes (electrode pads 20) of the heater wiring 32, the gate region 25 is 25. However, since the voltage between the extraction electrodes (electrode pads 20) of the heater wiring 32 is less than 1 V, the power consumption is 12 mW. Further, even if the current is increased and the power consumption is 20 mW, the temperature in the gate region 25 is about 200 ° C. Accordingly, even when the vicinity of the catalyst metal gate 28 (gate region 25) of the sensor chip is heated to 100 to 200 ° C., the power consumption is 25 mW or less, the rated voltage is 1.2 V or less, and the rated current is 0.1 A or less. Can do.

  Although an Al alloy is used as the material of the heater wiring 32, a Mo / Au / Mo laminated structure can be used as disclosed in, for example, the above-mentioned Patent Application No. 2008-156427. As a result of conducting a reliability test of the wiring made of the Al alloy and the wiring made of the Mo / Au / Mo laminated structure, a predicted life of 5 years or more is obtained in both.

  As described above, according to the third embodiment, the structure of the sensor chip is configured such that the surrounding silicon substrate 22 is not easily heated, and the heat insulating material is inserted between the sensor chip and the stem (for example, as described above). 1), even when the vicinity of the catalyst metal gate 28 of the sensor chip is heated to 100 to 200 ° C., the power consumption is 25 mW or less, the rated voltage is 1.2 V or less, and the rated current is 0.1 A or less. . Thereby, the sensor chip which has explosion-proof property is realizable. Although only the sensor chip shown in the third embodiment can have explosion resistance, the mounting structure of the flammable gas sensors GS1 and GS2 shown in the first embodiment described above or the combustible shown in the second embodiment described above. The metal cap 6 provided with the waterproof and moisture-permeable material 9, 39 may be used as in the mounting structure of the gas sensor GS3, GS4. Thereby, the explosion-proof effect is further improved, and further, salt damage resistance, dust resistance, and the like can be obtained.

(Embodiment 4)
Since the sensor chip described in the third embodiment described above exhibits low power consumption of, for example, 25 mW or less, it can be incorporated into a sensor kit that is cordless by battery driving. Therefore, in the fourth embodiment, a sensor kit of an explosion-proof sensor node in which a sensor chip, a peripheral circuit, a power supply (for example, a battery), and the like are combined into one will be described.

  A basic configuration of a sensor kit having a simple explosion-proof structure according to the fourth embodiment will be described with reference to FIGS. 19 is a system development view of the sensor node according to the fourth embodiment, FIG. 20 is a schematic sectional view of a sensor kit having a simple explosion-proof structure according to the fourth embodiment, and FIGS. 21 (a), (b) and (c) are FIG. 3 is a cross-sectional view of a main part of a sensor portion including a sensor chip, a perspective view of a socket provided in the sensor node board module, and a plan view of a socket provided in the sensor node board module.

  As shown in FIG. 19, the sensor node SN mainly includes a sensor module 100, a communication control module 200, and a power supply system 300. The sensor node technology of the sensor network is disclosed in, for example, Japanese Patent Application Laid-Open No. 2006-155209 (gas inspection system), and details thereof are not mentioned, but the sensor 101 and its drive circuit 102, heater 103, thermometer 104 are not mentioned. The analog signals from the thermometer 104 and its drive circuit 105 are taken into the controller (microcomputer) 201 via the A / D converters 202 and 203, and information is transmitted from the antenna 207 through the communication system 206 to the server 208 by radio. This technology detects gas leaks in real time. In FIG. 19, reference numeral 204 denotes a threshold value, and 205 denotes a comparator.

  The sensor module 100 can be manufactured by one IC (Integrated Circuit) chip. However, since the sensor 101 is a consumable part and needs to be replaced periodically, it is desirable that the sensor 101 can be easily replaced from the sensor node board module. In the fourth embodiment, a sensor kit having a simple explosion-proof structure in which the sensor 101 can be easily removed from the sensor node board module is illustrated.

  As shown in FIG. 20, in the sensor kit GSK according to the fourth embodiment, the sensor module 100, the communication control module 200, and the power supply system 300 are mounted on the sensor node board module 43. The sensor 101, the heater 103, and the thermometer 104 in the sensor module 100 are integrated on one silicon chip as described in the third embodiment. The temperature of the sensor 101 is measured from the temperature characteristic of the resistance of the heater wiring, and the drive circuits 102 and 105 in the sensor module 100 are mounted on the sensor node board module 43 by another IC chip. A portion in which the sensor 101, the heater 103, and the thermometer 104 are integrated on an IC chip is referred to as a sensor chip 47, and is a consumable that can be easily removed from the sensor node board module 43 as a sensor 106 that is simply mounted as described below.

  The sensor node board module 43 is installed on the housing board 44 via the buffer 45, and the sensor 106 is installed on the sensor node board module 43 so that it can be easily removed using a socket as will be described later. . The sensor node board module 43 and the sensor 106 are covered with, for example, the metal cap 6 on which the waterproof and moisture permeable material 9 according to the first embodiment described above is mounted, and the metal cap 6 is attached to the housing board 44 using the stopper 46. It is fixed. The shape of the metal cap 6 is not a columnar shape but can be a rectangular parallelepiped or a similar shape. The external dimensions of the metal cap 6 not including the mounting bracket are, for example, 25 (W) × 20 (H) × 20 (D) mm, and its weight is 20 g. The antenna 207 protrudes from the metal cap 6.

  As shown in FIG. 21A, the sensor 106 uses a sensor chip 47, and the sensor chip 47 is disposed on the stem 48 via a heat insulating material 49. The stem 48 is provided with a plurality of lead terminals (in this example, twelve are illustrated) 50 that penetrate the stem 48 and project on both the front surface and the back surface of the stem 48. It is fixed to the stem 48 by a glass material provided on the outer periphery of the lead terminal 50. A plurality of electrode pads formed on the main surface of the sensor chip 47 and a plurality of lead terminals 50 connected to the stem 48 are respectively connected by wires 51. The sensor chip 47, the heat insulating material 49, and the plurality of wires 51 are covered with a stainless wire mesh 52 having a height of about 6 to 12 mm, and the lowermost portion (the brim portion 52 a) on the side of the stainless wire mesh 52 is around the stem 48. It is joined with.

  The sensor chip 47 is only covered with the stainless wire mesh 52, and the stainless wire mesh 52 cannot be expected to have sufficient explosion-proof properties. However, as shown in FIG. 20, since the entire sensor node board module 43 on which the sensor chip 47 is mounted is covered with the metal cap 6 on which the waterproof and moisture-permeable material 9 having explosion-proof properties is attached, the sensor kit GSK. Can have explosion-proof properties.

  In addition, as described above, the sensor 106 is attached to a socket fixed to the sensor node board module 43. Specifically, as shown in FIGS. 21B and 21C, a plurality of socket lead terminals (here, twelve are illustrated) 53 are provided in the socket 54, and the sensor 106 The sensor 106 is mounted on the sensor node board module 43 by inserting the lead terminal 50 included in the sensor node board 43.

  As described above, according to the fourth embodiment, the entire sensor node board module 43 on which the sensor 106 is mounted is covered with the metal cap 6 to which the waterproof and moisture-permeable material 9 having the explosion-proof property is attached. A sensor kit GSK can be realized. Further, since the sensor 106 can be easily replaced by attaching / detaching it to / from the socket 54 fixed to the sensor node board module 43, the workability of replacing the sensor 106 is improved, and when the sensor 106 is consumed. Since the function of the sensor kit GSK can be restored by replacing only the sensor 106, the cost can be reduced.

(Embodiment 5)
A basic configuration of a contact combustion methane gas sensor having a simple explosion-proof structure according to the fifth embodiment will be described with reference to a schematic cross-sectional view shown in FIG.

  In the catalytic combustion type methane gas sensor 56, a detection element 57 and a compensation element 58 are disposed on a stem 59, and a thermal shielding plate 60 is provided between the detection element 57 and the compensation element 58. The detection element 57 has, for example, a structure in which a combustion catalyst is supported on a coiled platinum wire 61, and both ends of the platinum wire 61 are connected to metal lead wires 62 and 63. The compensating element 58 has a structure in which a combustion catalyst is not supported on the coiled platinum wire 64, and both ends of the platinum wire 64 are connected to metal lead wires 65 and 66. The diameters of the platinum wire 61 of the detecting element 57 and the platinum wire 64 of the compensating element 58 are, for example, 10 μm, their length is, for example, 300 μm, and the power consumption can be reduced to 100 mW.

  The stem 59 is provided with four lead terminals 67 that penetrate the stem 59 and protrude on both the front surface and the back surface of the stem 59, and the lead terminal 67 is a glass provided on the outer periphery of the lead terminal 67. It is fixed to the stem 59 by a material. The metal lead wires 62, 63, 65, 66 are connected to different lead terminals 67. Furthermore, the detection element 57, the compensation element 58, and the heat shielding plate 60 are covered with a metal cap 6 on which the waterproof and moisture-permeable material 9 having the same explosion resistance as that of the first embodiment described above is mounted, for example. The lowermost portion of the side portion (the flange portion 6 a) is joined to the periphery of the stem 59.

  In the contact combustion type methane gas sensor having a simple explosion-proof structure according to the fifth embodiment, when the metal cap 6 manufactured with the same dimensions as those described in the first embodiment is employed, even at an operating temperature of around 400 ° C., Stable operation can be obtained.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  For example, in the above-described embodiment, the hydrogen gas sensor using Si-MOSFET is exemplified, but the present invention can also be applied to other types of gas sensors. For example, the present invention can be applied to a hydrogen gas sensor using a MIS type capacitor. The present invention can also be applied to a sensor having a different operation principle, such as a hydrogen gas sensor using an organic pigment or an EMF type hydrogen gas sensor.

  The present invention can be applied to a gas sensor that detects a flammable gas that requires explosion resistance and high reliability (such as salt damage resistance, dust resistance, water resistance, and chemical resistance).

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining the combustible gas sensor by this Embodiment 1, (a), (b) and (c) are the principal part sectional drawing of a combustible gas sensor, a bottom view, and caulking a waterproof moisture-permeable material, respectively. It is a perspective view of components. (A), (b), and (c) are the graph which shows the relationship between the flame strength of a waterproof moisture-permeable material and a metal sintered compact board, respectively, a schematic diagram explaining the internal state of a waterproof moisture-permeable material, and It is a schematic diagram explaining the internal state of a metal sintered compact board. It is an optical microscope photograph of an example of the sensor chip with which the combustible gas sensor by this Embodiment 1 is equipped. It is a top view of the heat insulating material with which the sensor chip with which the combustible gas sensor by this Embodiment 1 is equipped was affixed. It is an optical microscope photograph of the heat insulating material with which the sensor chip with which the combustible gas sensor by this Embodiment 1 is equipped was affixed. It is principal part sectional drawing of the combustible gas sensor by this Embodiment 1. FIG. It is principal part sectional drawing of the container used for the hydrogen explosion-proof experiment by this Embodiment 1. FIG. It is principal part sectional drawing of the sample for an explosion experiment of the same mounting structure as the combustible gas sensor by this Embodiment 1. FIG. It is principal part sectional drawing of the sample for an explosion experiment which the present inventors formed for the comparison. It is principal part sectional drawing of the sample for an explosion experiment which the present inventors formed for the comparison. (A) And (b) shows the principal part sectional drawing and bottom view of the combustible gas sensor by this Embodiment 1 used for the salt damage test, respectively. It is a figure explaining the salt damage resistance of the combustible gas sensor by this Embodiment 1, (a), (b) and (c) are the SEM photograph of the sample which is not performing the salt damage test, respectively, respectively of severity (1) It is the SEM photograph of the sample after performing a salt damage test, and the SEM photograph of the sample after performing the salt damage test of severity (2). It is a figure explaining the dust resistance of the combustible gas sensor by this Embodiment 1, and shows the SEM photograph of the sensor chip after the dust test 12 day progress. It is principal part sectional drawing of the 1st example of the combustible gas sensor by this Embodiment 2. FIG. It is principal part sectional drawing of the 2nd example of the combustible gas sensor by this Embodiment 2. FIG. It is a figure explaining the sensor chip with which the combustible gas sensor by this Embodiment 3 is equipped, (a) And (b) is principal part sectional drawing of the heater wiring area | region where n-channel MIS for sensors of a sensor chip is arrange | positioned, respectively It is a principal part top view. It is a figure explaining the sensor chip with which the combustible gas sensor by this Embodiment 3 is equipped, and is principal part sectional drawing of the heater wiring area | region where the n-channel MIS for reference of a sensor chip is arrange | positioned. The graph figure explaining the relationship between the resistance of the heater wiring of the combustible gas sensor by this Embodiment 3, and power consumption is shown. It is a system development view of the sensor node according to the fourth embodiment. It is a cross-sectional schematic diagram of the sensor kit of the simple explosion-proof structure by this Embodiment 4. It is a figure explaining the sensor kit of the simple explosion-proof structure by this Embodiment 4, (a), (b) and (c) is equipped with the principal part sectional drawing of the sensor part containing a sensor chip, respectively, and a sensor node board | substrate module. It is the perspective view of a socket, and the top view of the socket with which a sensor node board | substrate module is equipped. It is a cross-sectional schematic diagram of the contact combustion type | mold methane gas sensor explaining the basic composition of the contact combustion type methane gas sensor of the simple explosion-proof structure by this Embodiment 5. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sensor chip 2 Stem 2a Glass material 3 Heat insulating material 4 Lead terminal 5 Wire 6 Metal cap 6a Collar part 8 Hole 9 Waterproof moisture-permeable material 10 Heat insulating material 11 Polytetrafluoroethylene 12 Air gap 13 Metal sintered body 14 Air gap 15 Silicon substrate 16 n-channel MIS for sensors
17 n-channel MIS for reference
18 heater 19 pn junction diode 20 electrode pad 21 wiring 22 silicon substrate 23 buried insulating layer 24 channel silicon layer 25 gate region 26 local oxide film SiO ₂
27 Gate insulating film 28 Catalytic metal gate 28S Source region 28D Drain region 29 Interlayer insulating film 30 Connection hole 31S Source electrode 31D Drain electrode 32 Heater wiring 33 Surface protective film 34 Authentic sensor region 35 Container 36 Film 37 Clay 38 Tungsten filament wire 39 Waterproofing Moisture permeable material 40 Stainless steel wire 41 Particulate matter 42 Epoxy resin 43 Sensor node board module 44 Housing board 45 Buffer 46 Stopper 47 Sensor chip 48 Stem 49 Heat insulating material 50 Lead terminal 51 Wire 52 Stainless steel wire 52a Collar part 53 Socket lead Terminal 54 Socket 55 Socket receptacle 56 Contact combustion type methane gas sensor 57 Detection element 58 Compensation element 59 Stem 60 Thermal shielding plate 61 Platinum wire 62, 63 Metal lead wire 64 Platinum wire 65, 66 Gold Lead wire 67 Lead terminal 100 Sensor module 101 Sensor 102 Drive circuit 103 Heater 104 Thermometer 105 Drive circuit 106 Sensor 200 Communication control module 201 Controller 202, 203 A / D converter 204 Threshold value 205 Comparator 206 Communication system 207 Antenna 208 Server 300 Power supply system GS1, GS2, GS3, GS4 Combustible gas sensor GSK Sensor kit SN Sensor node S1 Explosion experiment sample RS1, RS2 Explosion experiment comparison sample

Claims (22)

A gas sensor; a stem on which the gas sensor is mounted; and a cap having an upper portion and a side portion, and a lowermost portion of the side portion joined to an outer periphery of the stem. The stem and the cap surround the gas sensor. A combustible gas sensor,
A flammable gas sensor, wherein a hole is formed in a part of the cap, and a first waterproof and moisture-permeable material that covers the hole is installed inside the cap. A gas sensor; a stem on which the gas sensor is mounted; and a cap having an upper portion and a side portion, and a lowermost portion of the side portion joined to an outer periphery of the stem. The stem and the cap surround the gas sensor. A combustible gas sensor,
A hole is formed in a part of the cap, a first waterproof / breathable material covering the hole is installed inside the cap, and a second waterproof / breathable material is installed outside the side of the cap. A flammable gas sensor. A gas sensor; a stem on which the gas sensor is mounted; and a cap having an upper portion and a side portion, and a lowermost portion of the side portion joined to an outer periphery of the stem. The stem and the cap surround the gas sensor. A combustible gas sensor,
A flammable gas sensor, wherein a hole is formed in a part of the cap, and a second waterproof and moisture-permeable material is installed outside the upper part and the side part of the cap.   The combustible gas sensor according to claim 1 or 2, wherein the first waterproof and moisture-permeable material is a porous film having a hole diameter of 1 to 4 µm and a thickness of 0.3 to 1 mm. Gas sensor.   3. The combustible gas sensor according to claim 1, wherein the first waterproof and moisture-permeable material is a material in which a fluororesin and a polyurethane polymer are combined.   The combustible gas sensor according to claim 2 or 3, wherein the second waterproof and moisture-permeable material is a porous film having a hole diameter of 1 to 4 µm and a thickness of 0.3 to 1 mm. Gas sensor.   4. The combustible gas sensor according to claim 2, wherein the second waterproof and moisture-permeable material is a material in which a fluororesin and a polyurethane polymer are combined.   The combustible gas sensor according to claim 1 or 2, wherein the hole is formed in an upper portion of the cap, and the first waterproof and moisture-permeable material covering the hole is caulked by a heat insulating material. Combustible gas sensor.   4. The combustible gas sensor according to claim 1, wherein a diameter of the hole formed in a part of the cap is 0.5 to 3.0 mm. 5.   4. The combustible gas sensor according to claim 1, wherein the volume of the region surrounded by the stem and the cap is 10 mL or less. 5.   4. The combustible gas sensor according to claim 1, wherein a heat insulating material is inserted between the gas sensor and the stem.   4. A combustible gas sensor according to claim 1, wherein the back surface of the stem is covered with an epoxy resin.   4. The combustible gas sensor according to claim 2, wherein a portion where the lowermost portion of the side portion of the cap is joined to the outer periphery of the stem is covered with the second waterproof and moisture-permeable material. Combustible gas sensor.   4. The combustible gas sensor according to claim 1, 2, or 3, wherein the cap is made of stainless steel or ceramic. A sensor chip having a sensor field effect transistor, a reference field effect transistor, a heater wiring, and a pn junction diode formed on the main surface of the substrate, a stem on which the sensor chip is mounted, and a gap between the sensor chip and the stem A flammable gas sensor including a heat insulating material inserted in
The field effect transistor for a sensor has a catalytic metal gate, a source region, and a drain region, and between the catalytic metal gate and the source region and between the catalytic metal gate and the drain region, respectively. The thickness of the substrate in the region where the heater wiring is arranged and the catalyst metal gate and the heater wiring are arranged is thinner than the thickness of the substrate in the region where the catalyst metal gate and the heater wiring are not arranged. Combustible gas sensor characterized by the above.   The combustible gas sensor according to claim 15, wherein a thickness of the substrate in a region where the catalytic metal gate and the heater wiring are disposed is 0.1 to 20 µm.   16. The combustible gas sensor according to claim 15, wherein the substrate is an SOI substrate in which a silicon substrate, a buried insulating layer and a channel silicon layer are stacked, and the silicon substrate in a region where the catalytic metal gate and the heater wiring are disposed. A flammable gas sensor characterized in that the gas is removed.   The combustible gas sensor according to claim 15, wherein the catalytic metal gate is made of Pt.   16. The combustible gas sensor according to claim 15, wherein the sensor chip is further surrounded by a cap having an upper portion and a side portion, and a lowermost portion of the side portion of the cap is joined to an outer periphery of the stem. A combustible gas sensor is characterized in that a hole is formed in a part of the cap, and a first waterproof and moisture-permeable material covering the hole is installed inside the cap.   16. The combustible gas sensor according to claim 15, wherein the sensor chip is further surrounded by a cap having an upper portion and a side portion, and a lowermost portion of the side portion of the cap is joined to an outer periphery of the stem. A hole is formed in a part of the cap, a first waterproof and moisture permeable material covering the hole is installed inside the cap, and a second waterproof and moisture permeable material is installed outside the side portion of the cap. Combustible gas sensor characterized by the above.   16. The combustible gas sensor according to claim 15, wherein the sensor chip is further surrounded by a cap having an upper portion and a side portion, and a lowermost portion of the side portion of the cap is joined to an outer periphery of the stem. A flammable gas sensor is characterized in that a hole is formed in a part of the cap and a second waterproof and moisture-permeable material is installed outside the upper part and the side part of the cap.   16. The combustible gas sensor according to claim 15, further comprising: the sensor chip mounted on a substrate module, wherein the entire substrate module on which the sensor chip is mounted is surrounded by a cap having an upper portion and a side portion. The lowermost part of the side part is joined to the outer periphery of the stem, a hole is formed in a part of the cap, and a first waterproof and moisture-permeable material covering the hole is installed inside the cap. A combustible gas sensor.