JP6514875B2 - Method of driving hydrogen gas sensor device and hydrogen gas sensor device using the same - Google Patents

Description

  The present invention relates to a method of driving a hydrogen gas sensor device, and in particular, when the hydrogen-sensitive substance which is the sensitive part of the hydrogen gas sensor is exposed to extremely high concentration hydrogen gas (H2) of several% to nearly 100% at high temperature heating, A hydrogen gas sensor device using this method is provided, as well as a method for preventing deterioration of the characteristics of the hydrogen gas sensor due to deterioration due to hydrogen embrittlement and the like.

  It has been found that there is a danger of explosion in a very wide range of hydrogen gas from 4.0 to 75.0% (vol%) in air. Conventionally, as a gas sensor, a catalytic combustion type hydrogen gas detection sensor (see Patent Document 1) or the like in which the temperature of a catalyst in which fine particle platinum (Pt) or the like is dispersed in an oxide film is increased by a heater there were. In this catalytic combustion type hydrogen gas sensor, in order to accelerate the catalytic reaction, the temperature is generally constantly heated to 100 ° C. or higher. When oxygen and hydrogen come into contact in an oxygen atmosphere such as air, catalytic combustion occurs even at a relatively low temperature of about 100 ° C if there is a catalyst in the sensitive part of the hydrogen gas sensor, and the temperature is further increased. Based on the principle of detecting the hydrogen concentration in the air. However, if the sensitive part of the hydrogen gas sensor is exposed to extremely high concentration hydrogen gas of several percent to nearly 100%, the temperature rises abnormally and the catalyst is reduced by hydrogen, and the catalyst which is a hydrogen sensitive substance is returned to its original state. It is a big problem that it becomes a state of absence and causes sensitivity degradation.

  The inventor of the present invention previously invented “a gas sensor element and a gas concentration measuring device using the same” (see Patent Document 2), and thin film thermally separated from a substrate was covered with one or more temperature sensors and Intended to measure the concentration of hydrogen gas arranged so that it can measure the temperature change due to heat absorption and heat generation during absorption or release of the detection gas by including a gas absorbing substance that absorbs the detection gas A gas sensor element and a gas concentration measuring device were proposed.

  Furthermore, the inventor repeated experiments and improvements, and using two cantilever type thermocouples and heaters, at one tip of the cantilever, palladium, which is a hydrogen absorbing material, was used as a sensitive part of a hydrogen gas sensor. Pd) A thin film is deposited by sputtering to form a detection part, and the other cantilever tip part is not attached with a hydrogen-absorbing material and measured as a reference part with hydrogen gas of low concentration (approximately 5% or less to about 1 ppm) We proposed a hydrogen gas sensor (hydrogen absorption and heat generation type) to be used (Patent Document 3). If the hydrogen gas concentration is measured during heater heating, if the hydrogen concentration is about 5% or more, the thermal conductivity of the hydrogen gas is the largest in the gas, so the hydrogen gas concentration is 5% because of this effect. If it exceeds, even if the heater is driven with a predetermined power, temperature rise stagnates, and if the hydrogen concentration is large, it turns out that the temperature tends to lower the temperature of the sensitive part (hydrogen gas concentration is about 5% It turned out that there was a peak in the output), and it was better to stop the heater heating and to look at the temperature change during the cooling process. For this purpose, prepare two cantilevers of the detection unit with the hydrogen absorption material Pd thin film in the sensitive part of the hydrogen gas sensor and the control unit without the hydrogen absorption material at the high concentration of several% or more. In the hydrogen gas sensor, it has been proposed that the reference portion of the above two cantilevers be used to heat the heater and use it as a heat conduction type hydrogen gas sensor.

  Here, in order to expel the absorbed hydrogen gas from the Pd thin film which is a hydrogen absorbing material, it is intermittently heated to a high temperature of 100 ° C. or higher, but in a high concentration hydrogen gas of several% to nearly 100% The absorbing substance Pd also has the effect of catalytic combustion in the presence of oxygen gas and may become very high temperature. Furthermore, a large amount of hydrogen gas is absorbed by the Pd thin film during cooling and released by heating. Therefore, the density change (volume change) of the Pd thin film is intensified by the heating and cooling cycles, and the micronization is promoted by the crack accompanying the volume change of the Pd thin film at this time, and the hydrogen embrittlement progresses For example, it has been found that the hydrogen gas concentration measurement has a great effect on the measurement of hydrogen gas concentration, which is also a cause of deterioration or peeling of the Pd thin film which is a hydrogen sensitive substance.

Also, conventionally, using hydrogen selectivity of palladium (Pd) film, Pd film is used as a gate electrode of FET, and when hydrogen is absorbed, its work function changes, and drain current changes And hydrogen gas sensor (hydrogen absorption resistance change type) that utilizes the change in the electrical resistance of the Pd film due to the absorption of hydrogen into the Pd film, etc. Hysteresis due to absorption of hydrogen occurs, and exposure to high concentration hydrogen gas has also been a problem as it causes deterioration and deterioration of these hydrogen gas sensors.

Unexamined-Japanese-Patent No. 2006-201100 JP, 2008-111822, A PCT / JP2011 / 70427

  The present invention has been made to solve the above problems, and in particular, in order to detect a hydrogen gas concentration of 100 ppm or less, in general, as described above, a hydrogen absorbing film as a hydrogen sensitive film is used as a hydrogen gas sensor. If this hydrogen absorbing film is exposed to high concentration hydrogen gas of several percent to nearly 100%, especially at a high temperature of about 100 ° C., the hydrogen absorbing film is rapidly degraded and altered, and the sensitivity of the hydrogen gas sensor It has been found that unrecoverable deterioration and deterioration occur, and it is an object of the present invention to provide a method of driving a hydrogen gas sensor device for preventing this and a hydrogen gas sensor device using this method.

In order to achieve the above object, in the method of driving a hydrogen gas sensor device according to claim 1 of the present invention, a hydrogen gas sensor A having a relatively low concentration as compared with the hydrogen gas sensor B,
A hydrogen gas sensor B having a relatively high concentration as compared with the hydrogen gas sensor A,
A driving method of a hydrogen gas sensor device for measuring a hydrogen gas concentration by combining the hydrogen gas sensor device, the hydrogen gas sensor device driving method being configured to be able to judge whether the measurement reference concentration is lower than a predetermined reference value . The hydrogen gas sensor B is a heat conduction type sensor having a heater B and a temperature sensor B and having a structure that does not deteriorate even when exposed to high concentration hydrogen gas close to 100%, and the hydrogen gas sensor A has its hydrogen sensitive substance as, the hydrogen-absorbing material, further comprising a heater a and a temperature sensor a to release the absorbed hydrogen, the switching reference density said a predetermined reference value, the absorption of hydrogen gas at the high concentration side of the hydrogen gas sensor a and the heating and cooling cycle with the release, Dearuko safety limit sense concentration of a degree that does not cause hysteresis deteriorated deteriorated to damage the hydrogen-absorbing material ,
When the hydrogen gas sensor A is exposed to the measurement atmosphere when the measurement of the hydrogen gas concentration is started , and the heater is not heated,
First, the hydrogen gas sensor B is driven, and by measuring the hydrogen gas concentration of the hydrogen gas sensor B, it is judged whether the measurement atmosphere is lower than the switching reference concentration, and it is judged that the judgment result is lower than the switching reference concentration. The hydrogen gas sensor A performs the heating / cooling cycle, releases the hydrogen in the heating cycle heated by the heater A, and measures the hydrogen gas concentration in the cooling cycle, and the switching reference concentration is 1% concentration It is a certain thing.

The hydrogen gas sensor A, which uses an exothermic reaction with a hydrogen-absorbing material such as Pd as a hydrogen-sensitive material, supplies the electric power of the set heater to 100% of the hydrogen- absorbing material at high temperatures of 100 ° C. or higher (here When exposed to hydrogen gas close to the volume%), absorption during cooling of a large amount of hydrogen and release during high-temperature operation at the heater are repeated, resulting in large volume change, causing micronization due to the occurrence of cracks, and hydrogen embrittlement It has been experimentally found that the hydrogen-absorbing material is degraded such that the surface is roughened and blackened, resulting in a phenomenon that leads to deterioration and degradation in the hydrogen sensitivity characteristics.

In order to prevent deterioration and deterioration in such hydrogen sensitivity characteristics, at the beginning of hydrogen concentration measurement, how much hydrogen (H 2) gas is present in the nitrogen gas or air of the gas to be measured which is the atmosphere gas Because we do not know, first, even if there is a hydrogen gas concentration close to 100% at first, the hydrogen gas sensor B, which is placed close to another of different operating principles that does not cause deterioration or deterioration, operates to measure its ambient environment gas ( Check the hydrogen gas concentration in the test gas), that is, the hydrogen gas concentration in the high concentration range which is the measurement range of the hydrogen gas sensor B, or the hydrogen gas concentration whose error is too large in the measurement range of the hydrogen gas sensor B, That is, since the hydrogen gas concentration is lower than a predetermined value (switching reference concentration), it is determined whether it is the measurement range of the hydrogen gas sensor A for low hydrogen gas concentration measurement. When the measurement operation of the hydrogen gas sensor A is suitable (switching reference concentration following hydrogen gas concentration), and is to be an operation to measure the hydrogen gas concentration using the hydrogen gas sensor A. As the hydrogen gas sensor B, a high concentration that hydrogen is a structure that has deteriorated deteriorated even when exposed to gas, a hydrogen gas has the highest thermal conductivity in the gas, from the heater B and the high hydrogen gas concentration heat conduction type of a hydrogen gas sensor for measuring the temperature change of the heat radiation heater B by utilizing the fact intense is preferable. Of course, for use as a leak detector that guarantees that there is no high concentration hydrogen gas, etc., the operation of the hydrogen gas sensor B is omitted, and the hydrogen gas concentration is measured from the beginning using the hydrogen gas sensor A It is preferable that the operation (hydrogen gas sensor A mode) be made to be able to operate at high speed.

  Here, the above-mentioned switching reference concentration is a concentration below the safety limit sense concentration at which the sensor on the high concentration side of the hydrogen gas sensor A is damaged and deteriorated to cause no hysteresis phenomenon. As described later, although the hydrogen gas sensor A can measure at several ppm level on the low concentration side of the measurement area, it is exposed to hydrogen gas having a concentration exceeding 3%, for example, on the high concentration side of the measurement area As a result, damage resulting in deterioration or deterioration of the sensitivity characteristic occurs. Therefore, damage to the hydrogen gas sensor A can be prevented in advance by setting the switching reference concentration to a concentration (e.g., 1% concentration) below the safety limit sense concentration which is a concentration at which such damage does not occur. It becomes. It should be noted that the determination of whether or not the measurement atmosphere is lower than the switching reference concentration is not limited to performing measurement after accurately measuring the concentration of the measurement atmosphere, but at least the measurement atmosphere is lower than the switching reference concentration. It should just be able to judge.

The hydrogen gas sensor A is a sensor for measuring the hydrogen gas concentration in the low hydrogen gas concentration region of at least 1% or less, and although the hydrogen sensitive substance differs depending on the operation principle, it is exposed to a small amount of hydrogen gas. Optical characteristics such as gloss change of hydrogen sensitive substance formed in the sensing area of gas sensor A, electrical characteristics, physical characteristics such as heat generation, expansion deformation, etc., work functions, chemical characteristics such as adsorption state and chemical bonding state Although it is a substance showing a change such as, in this case, it is a case of a physical property change of electrical resistance change or heat generation by hydrogen absorption. The hydrogen absorbing substance as the hydrogen sensitive substance is preferably in the form of a thin film within the same volume from the viewpoint of increasing the contact area with hydrogen gas.

  In the present invention, hydrogen gas concentration measurement of at least several% (volume%) or more is based on a principle different from hydrogen gas sensor A utilizing hydrogen absorption heat generation etc., so that it is difficult to react with hydrogen even at high temperature. This is the case where the heat conduction type hydrogen gas sensor is used as the hydrogen gas sensor B. It utilizes the fact that hydrogen gas has the largest thermal conductivity in the gas, and utilizes the fact that the amount of heat released from the heater-heated sensing region depends on the hydrogen concentration in the surrounding gas, for example, the hydrogen gas concentration is In many cases, the ultimate temperature decreases even if the heater is heated by the same heating power, and if it is attempted to use the same heating temperature, the heating power of the heater is required so much, so measure these temperatures and electric energy The hydrogen gas concentration is obtained based on the calibration data prepared in advance by the hydrogen gas concentration.

According to the method of driving the hydrogen gas sensor device of the present invention, when the measurement of the hydrogen gas concentration is started, the hydrogen gas sensor B is first driven in a state where the hydrogen gas sensor A is exposed to the measurement atmosphere and without heating . It is determined whether the measurement atmosphere is lower than the switching reference concentration.

  In the method of driving a hydrogen gas sensor device according to the present invention, it is determined that the measurement atmosphere is lower than the switching reference concentration while driving the hydrogen gas sensor B to measure the hydrogen gas concentration, and the determination result is lower than the switching reference concentration In this case, the hydrogen gas sensor A is switched to the hydrogen gas sensor A to measure the hydrogen gas concentration.

In the method of driving a hydrogen gas sensor device according to claim 2 of the present invention, it is determined whether the measurement atmosphere is lower than the switching reference concentration while driving the hydrogen gas sensor B to measure the hydrogen gas concentration, and the determination result is the switching reference concentration If it is determined that the hydrogen gas concentration does not fall below the above, the hydrogen gas sensor B continuously measures the hydrogen gas concentration.

The timing of the judgment in the invention according to claims 1 and 2 can be arbitrarily determined, for example, it may be periodically performed at intervals of 10 seconds, and the difference between the previous measurement result and this measurement result is relatively If the difference is small, the measurement interval may be increased, and if the difference is relatively large, the measurement interval may be shortened. According to the first and second aspects of the present invention, even after the measurement by the hydrogen gas sensor B is started once, it is possible to select and measure an appropriate hydrogen gas sensor according to the concentration of the measurement atmosphere.

In the method of driving a hydrogen gas sensor device according to claim 3 of the present invention, the hydrogen gas sensor A is configured to be able to determine whether the hydrogen gas concentration does not exceed the switching limit concentration which is the hydrogen concentration that may exceed the switching reference concentration. During the measurement of the hydrogen gas concentration by driving the hydrogen gas sensor A, it is judged whether the measurement atmosphere exceeds the switching limit concentration, and if it is judged that the judgment result exceeds the switching limit concentration, the hydrogen gas sensor It is a drive method of the hydrogen gas sensor device which switched to B and measured hydrogen gas concentration.

This is a measure to prevent damage to the hydrogen gas sensor A when the concentration of the measurement atmosphere is increased during measurement by the hydrogen gas sensor A. With such a configuration, when the measurement atmosphere exceeds the switching limit concentration, the measurement can be switched to the measurement by the hydrogen gas sensor B, and damage can be prevented by stopping the measurement of the hydrogen gas sensor. The switching limit concentration preferably does not exceed the switching reference concentration. For example, as in the method of driving a hydrogen gas sensor device according to claim 4 of the present invention, the switching limit concentration and the switching reference concentration may be configured to be equal values.

  As a hydrogen gas sensor A, a conventional semiconductor gas sensor, a hydrogen gas sensor (hydrogen absorption heat generation type) using hydrogen absorption and heat generation, etc. are suitable because they can measure extremely low hydrogen gas concentration of about 1 ppm. It is necessary to raise the temperature of the hydrogen-sensitive substance shown in the above by heater heating at about 100.degree. In the semiconductor type gas sensor, hydrogen concentration measurement is performed during heater heating, but when hydrogen absorption is used, heater heating is necessary when discharging hydrogen absorbed by the hydrogen absorbing material.

  The hydrogen gas sensor A is a sensor for measuring the hydrogen gas concentration in a low hydrogen gas concentration region of at least 1% or less, and the hydrogen-sensitive substance mentioned here is exposed to a trace amount of hydrogen gas although it differs depending on the operation principle. Optical characteristics such as gloss change of the hydrogen sensitive substance formed in the sensing area of the hydrogen gas sensor A, physical characteristics such as electrical resistance, heat generation, expansion deformation, work function, adsorption state and chemical bonding state It is a substance that exhibits changes such as chemical properties. The hydrogen sensitive substance is preferably in the form of a thin film within the same volume from the viewpoint of increasing the contact area with hydrogen gas.

In the method of driving a hydrogen gas sensor device according to claim 5 of the present invention, the hydrogen gas concentration is measured by measuring a temperature rise based on hydrogen absorption and heat generation to the hydrogen absorbing material.

In this case, the temperature rise due to the heat of hydrogen absorption into the hydrogen-absorbing material is measured by the mounted temperature sensor A. Since a temperature rise is to be measured as a temperature sensor, it is preferable to use a temperature difference sensor such as a thermocouple or a thermopile.

In the method of driving a hydrogen gas sensor device according to claim 6 of the present invention, the hydrogen-sensitive substance is a substance utilizing a change in electric resistance due to absorption and absorption of hydrogen gas of a semiconductor type gas sensor.

  Conventionally, it is widely used in semiconductor type gas sensors that utilize a change in which the semiconductor surface is generally n-type and the electrical resistance is reduced due to the gas adsorption and absorption reaction on the semiconductor surface such as a tin oxide thin film as a hydrogen sensitive substance. That is, in a semiconductor gas sensor using tin oxide or the like as a hydrogen-sensitive substance, when it is operated at high temperature, adsorption of hydrogen gas causes tin oxide to be reduced to some extent to become a tin (Sn) rich state, resulting in electrical resistance. It is a hydrogen gas sensor that makes use of being smaller. Although the exothermic reaction due to hydrogen is not visible, the change in electrical resistance is converted to a hydrogen concentration based on calibration data prepared in advance. At a high hydrogen concentration close to 100%, the tin oxide film is reduced to become Sn-rich, and this is micronized and brought into contact with each other to form a mass, and a large change occurs in the shape and it does not return to the original state. There was a problem that it would deteriorate.

  A hydrogen gas sensor provided with a hydrogen absorbing substance as a hydrogen sensitive substance can utilize a temperature change based on an exothermic reaction at the time of absorption (including storage and adsorption) of hydrogen gas in gas. In general, hydrogen absorbing materials absorb more hydrogen at lower temperatures. However, when hydrogen is absorbed and the equilibrium state at that temperature is reached, the absorption of hydrogen stops, and an exothermic reaction occurs at the time of hydrogen absorption, so if the absorption stops, the exothermic reaction also stops. Therefore, in order to continuously measure the hydrogen gas concentration due to the exothermic reaction, it is necessary to drive out hydrogen from the hydrogen absorbing material. For example, if palladium (Pd) is used as a hydrogen-absorbing material, the partial pressure of hydrogen in Pd becomes 1 atm when heated to about 160 ° C., so heater heating to such a temperature is required. . When the temperature rise due to such high temperature heater heating is performed in high concentration hydrogen gas, the above-described deterioration and deterioration of the Pd film as the hydrogen absorbing material occur.

  Hydrogen absorption that is a hydrogen absorbing substance (including storage and adsorption) as a hydrogen-sensitive substance is a single metal or alloy such as palladium (Pd) or platinum (Pt), and further nickel (Ni) or niobium (Nb) The reaction when hydrogen is absorbed (including storage and adsorption) is generally an exothermic reaction when metals, organic materials, ceramics, etc. are called alloys, and for example, the reaction heat of the hydrogen storage alloy of LaNi5 is, per mole of hydrogen And about 7 kcal, which is a large value of about 0.048 kcal per 1 g of hydrogen. Conversely, when the temperature is raised by heating the metal-hydrogen compound (at this time, an endothermic reaction occurs), hydrogen is released and returns to the original hydrogen storage alloy. Thus, it is known that the hydrogen absorbing material reversibly absorbs and releases hydrogen, and there is a large amount of heat coming and going with it.

  At the time of absorption of hydrogen gas (H 2) into a hydrogen-absorbing material, it is generally stored not in the state of gas but in the state of monoatomic hydrogen. It is desirable that the surface of the hydrogen absorbing material be easily oxidized, be affected by water vapor and moisture, and that the hydrogen absorbing material does not crack or deform even after repeated heating and cooling. Also, in the case of an alloy, the composition change at the time of production has a large influence on the absorption amount to the characteristics, the calorific value, etc., and there is also a problem on production uniformity and uniformity on the basis of production yield and design. Chemically stable and inert single metals such as palladium (Pd) and platinum (Pt) are suitable as the hydrogen absorbing material of the present invention.

  If the hydrogen absorbing material is formed into a thin film, it can be easily formed by sputtering, electron beam evaporation, etc., the surface area in contact with hydrogen gas becomes large, the heat capacity is small, the response is fast, and the thickness is controlled. It is advantageous from the fact that the time until the completion of absorption can be adjusted, and accordingly, the time for temperature rise due to the exothermic reaction after stopping heating can be adjusted, and it is not always necessary to make it porous or fine particles, and a flat thin film may be used.

A driving method of a hydrogen gas sensor device according to claim 7 of the present invention is a case where a substance containing palladium (Pd) is used as the hydrogen absorbing substance.

  Pd as a hydrogen absorbing material has extremely high selectivity to hydrogen, and by using a Pd film as a hydrogen absorbing material, it is possible to provide a highly selective hydrogen gas sensor to hydrogen gas. In addition, since a Pd film can be easily deposited as a thin film by sputtering deposition or evaporation, deposition and patterning into a sensing region provide a low-power, inexpensive, inexpensive hydrogen gas sensor device with high mass productivity. it can.

In the hydrogen gas sensor device driving method according to claim 8 of the present invention, the heater A and temperature sensor A of the hydrogen gas sensor A, and the heater B and temperature sensor B of the hydrogen gas sensor B both are on the thin film thermally separated from the substrate. If you are prepared for

  When both hydrogen gas sensor A and hydrogen gas sensor B are thermal type sensors, it is desirable to reduce their power consumption and to increase the response speed. The temperature sensor B and temperature sensor B of the sensitive part need to reduce the heat conduction to the outside and reduce their heat capacity, so they need to be formed on a floating structure, ie, a thin film structure thermally isolated from the substrate .

In the method of driving a hydrogen gas sensor device according to claim 9 of the present invention, the hydrogen is absorbed from the hydrogen absorbing material by heating the heater A of the hydrogen gas sensor A, and the heating of the heater A is stopped. Using the output of the temperature sensor A at or after a predetermined time that is greater than the thermal time constant τ of the thin film when hydrogen of the heater A is not present, the hydrogen gas concentration in the atmosphere gas If you try to know

  After stopping the heating of the heater, hydrogen released from the hydrogen-absorbing material by heating starts to be absorbed, and the temperature rise occurs due to the exothermic reaction at the time of hydrogen absorption, which causes the thermal time constant to increase. It slowly returns to the temperature of the original atmosphere gas (room temperature). If pure air containing no hydrogen (hydrogen gas concentration is 0%), there is no absorption of hydrogen even if the hydrogen absorbing material is loaded on the thin film thermally separated from the substrate, so there is no heat of reaction, so it should be It is cooled with a thermal time constant τ of The hydrogen gas may be measured when the thermal time constant τ has elapsed after the heater heating is stopped, but generally, after approximately 4 times the thermal time constant τ, the hydrogen gas concentration is approximately 0%. Since it is considered that the thin film is completely cooled and the thin film has returned to room temperature, the temperature from the room temperature after a lapse of time about 4 times or more the thermal time constant τ after stopping heating (Amount of increase) ΔT can be considered to depend only on the result of the exothermic reaction based on the hydrogen absorption of the hydrogen absorbing material.

In the method of driving a hydrogen gas sensor device according to claim 10 of the present invention, after the heating of the heater A is stopped, the predetermined time greater than or equal to the thermal time constant τ of the thin film when hydrogen does not exist When the output of the temperature difference between the temperature of the atmosphere gas and the temperature of the position of the temperature sensor A is integrated over time and output using the temperature sensor A, and the hydrogen gas concentration is known using the output It is.

  When hydrogen gas is not present, the temperature difference between the temperature of the thin film and the temperature of the thin film at the position of the thin film temperature sensor A at a predetermined time point equal to or greater than the thermal time constant τ of the thin film after stopping heating Becomes very close to zero, and the output voltage based on the temperature difference is very close to zero. However, when hydrogen gas is present, its absorption heat generation causes a temperature rise, causing a temperature difference between the substrate which is considered to be room temperature and the thin film, and an output voltage is generated. The signal output contains noise, and the output at a specific point in time has greatly fluctuated, resulting in measurement with a small S / N. For this purpose, the capacitor C is charged with the signal current based on the temperature difference for a predetermined period, so that the so-called output of the temperature difference is integrated over time and output to improve S / N. The hydrogen gas sensor device of the present invention is provided.

The method of driving a hydrogen gas sensor device according to claim 11 of the present invention is the case where the heater B can also be heated and cooled in a predetermined cycle.

  In the hydrogen gas sensor device of the present invention, since the hydrogen sensitive substance is formed on the thin film suspended from the substrate, the thermal time constant τ as the response speed depends on the size of the thin film, but is about several milliseconds. It operates at high speed. Therefore, since the hydrogen absorbing material is also in the form of a thin film, the process of releasing hydrogen gas by heater heating may be as long as 10 milliseconds in this case. Also, in this case, the cooling process may be as long as 10 milliseconds, and even if it includes the heating and cooling processes, only about 100 milliseconds will be sufficient, and a hydrogen gas sensor device of high speed operation which has not been achieved conventionally Can be provided.

  Also in the heater heating, the thin film may be heated to a predetermined steady temperature, and the thin film may be periodically heated by the heater A or the heater B periodically to a predetermined temperature based on this temperature. The hydrogen absorbing material formed in the thin film of the hydrogen gas sensor A is heated at a room temperature which is the temperature of the atmosphere gas, or at a predetermined electric power further from a predetermined temperature, and the heating is stopped and cooled. . When utilizing the heat absorption effect based on hydrogen absorption, heater heating is expected to work to promote the desorption (release) of hydrogen gas from the hydrogen absorbing substance which is a hydrogen sensitive substance and return it to the initial state At the time of cooling, hydrogen in the atmosphere gas is absorbed to generate heat, and a temperature rise at that time is measured by the temperature sensor A and converted to a hydrogen concentration.

  Since the room temperature which is the temperature of the atmosphere gas differs depending on the environment for each measurement, it is necessary to measure this temperature. For this purpose, an absolute temperature sensor such as a diode is formed on the substrate, and the temperature of the substrate 1 is regarded as the temperature of the atmosphere gas, or the relationship between the temperature of the substrate 1 and the temperature of the atmosphere gas is determined. , And should be configured. In order to make the initial state or initial conditions of measurement constant, the heater A or heater B heats the thin film to a predetermined temperature (for example, 30 ° C.) slightly higher than the ambient temperature of the place to be usually measured. It may be

  As mentioned above, it has been found that the concentration of hydrogen gas in the air is explosive in a wide range of 4.0-75.0%. In the present invention, since the hydrogen gas is released from the hydrogen sensitive substance by the heater and the heater is heated as a heat conduction type sensor, measurement of the hydrogen gas concentration range is indispensable. Therefore, the hydrogen gas sensor device of the present invention needs to be explosion proof. An explosion-proof structure can apply a prior art. That is, a mesh structure of metal or the like is preferable. In the hydrogen gas sensor of the present invention, since the temperature of a thin film floating in the air is measured, the influence of air flow is extremely disliked. Therefore, it is necessary to interrupt the air flow, but the hydrogen gas needs to reach the detection part smoothly and see through. Also for such purpose, a cap having a mesh structure that is porous such as metal that blocks air flow is preferable.

  In order to continuously measure the hydrogen gas concentration in the ambient gas subject to hydrogen concentration measurement, as described in claim 1, the hydrogen gas sensor B is first driven to determine the hydrogen gas concentration in the test gas If the hydrogen gas concentration is higher than a predetermined value, the hydrogen gas sensor B is measured as it is. If the hydrogen gas concentration is lower than the predetermined value, the hydrogen gas sensor A is always cyclically measured to be measured. You may do it. However, if it is determined once whether the hydrogen gas concentration in the ambient gas is higher or lower than a predetermined value, for example, automatically or manually, the measurement mode of the hydrogen gas sensor A or the hydrogen gas sensor It is also possible to switch the measurement mode of B. Of course, it is desirable to be able to set so as to measure in the measurement mode of the hydrogen gas sensor A and the measurement mode of the hydrogen gas sensor B from the beginning.

A hydrogen gas sensor device according to claim 12 of the present invention is characterized in that it is configured to use the method for driving a hydrogen gas sensor device according to any one of claims 1 to 11 .

  Basically, a hydrogen gas sensor device comprising a hydrogen gas sensor A for measuring a hydrogen gas concentration of 1% or less and a hydrogen gas sensor B having an operation principle different from that of the hydrogen gas sensor A capable of measuring a hydrogen concentration of at least 1% When the hydrogen gas concentration is measured, the hydrogen gas sensor B is first driven, and if it is within the range where the hydrogen gas sensor B can measure (hydrogen gas concentration equal to or higher than a predetermined value), the hydrogen gas sensor B When the concentration is measured and it is determined that the hydrogen gas concentration is smaller than the measurement range within the predetermined error of the hydrogen gas sensor B as a result of measurement by the hydrogen gas sensor B (hydrogen gas concentration less than the predetermined value) A hydrogen gas sensor device is characterized in that the hydrogen gas concentration can be measured by the hydrogen gas sensor A.

The hydrogen gas sensor device according to claim 13 of the present invention is the case where the hydrogen gas sensor A and the hydrogen gas sensor B are provided close to each other.

  If the hydrogen gas sensor A and the hydrogen gas sensor B are separated and installed, it is assumed that the hydrogen gas concentration may differ or the ambient temperature may differ depending on the position of the hydrogen gas sensor A and the hydrogen gas sensor B. In that case, the measurement results Will cause a large error. Proximity refers to the case where the hydrogen gas sensor A and the hydrogen gas sensor B are disposed close to each other to the extent that the surrounding environment is considered to be substantially the same.

The hydrogen gas sensor device according to claim 14 of the present invention is the case where the hydrogen gas sensor A and the hydrogen gas sensor B are formed on the same substrate.

  For example, the hydrogen gas sensor A and the hydrogen gas sensor B are formed on the same silicon single crystal substrate. It is preferable that the hydrogen gas sensor A and the hydrogen gas sensor B are thermal sensors and have a thin film thermally separated from the substrate. Using an SOI substrate as a silicon single crystal substrate, the SOI layer of the SOI substrate is a thin film thermally isolated from the substrate as a thin film of cantilever structure, crosslinked structure, diaphragm structure, a heater, a temperature sensor, and a hydrogen sensitive film It is good to form If necessary, the heater and the temperature sensor can be combined.

In the hydrogen gas sensor device according to claim 15 of the present invention, at least the amplifier circuit, the arithmetic circuit, the heater driving circuit, and the determination circuit using the output of the hydrogen gas sensor B are mounted.

  Various circuits (at least an amplifier circuit, an arithmetic circuit, a heater drive circuit, a judgment circuit using the output of hydrogen gas sensor B) necessary for driving the hydrogen gas sensor device and measuring hydrogen concentration are modularized and mounted on the hydrogen gas sensor device Alternatively, integrated circuits may be formed on the same silicon SOI substrate.

  In the method of driving a hydrogen gas sensor device according to the present invention, the hydrogen gas sensor A for measuring low concentration hydrogen gas is particularly characterized in that when exposed to high concentration hydrogen gas in a high temperature condition of about 100 ° C., its characteristics deteriorate and deteriorate. Before hydrogen gas sensor A is operated using hydrogen gas sensor B for measuring high concentration hydrogen gas that hydrogen gas sensor B does not deteriorate characteristics even if exposed to high concentration hydrogen gas to protect hydrogen absorbing material Operation is performed to determine the hydrogen gas concentration of the gas to be measured whether the measurement atmosphere is below the switching reference concentration, which is a predetermined reference value below the safety limit sense concentration at which damage does not occur and hysteresis does not occur. It has the advantage that the hydrogen gas sensor A need not be exposed to high concentration hydrogen gas at high temperature.

  In the hydrogen gas sensor device driving method and hydrogen gas sensor device of the present invention, since the hydrogen gas sensor A for low concentration hydrogen gas measurement and the hydrogen gas sensor B for high concentration hydrogen gas measurement are provided, extremely low concentration of about 1 ppm There is an advantage that measurement of a wide range of hydrogen gas concentration is possible from detection of hydrogen gas to measurement of extremely high hydrogen gas concentration up to 100%.

  According to the method of driving the hydrogen gas sensor device of the present invention, if it is clear in advance that hydrogen gas is in a state of low concentration to the extent that the hydrogen absorbing substance is damaged and altered in the test gas and hysteresis does not occur. Since the operation of the hydrogen gas sensor B for gas concentration measurement can be omitted, there is an advantage that the low hydrogen concentration measurement can be performed at high speed by performing the operation of the hydrogen gas sensor A for low hydrogen gas concentration measurement from the beginning. .

  In the hydrogen gas sensor device of the present invention, the hydrogen gas sensor A for low hydrogen gas concentration measurement and the hydrogen gas sensor B for high hydrogen gas concentration measurement can be mounted close to each other on the same substrate, and an amplification circuit for driving these and calculation Since the circuit, the heater driving circuit, and the determination circuit using the output of the hydrogen gas sensor B can be mounted close to each other, there is an advantage that a very compact hydrogen gas sensor device can be provided.

It is a flowchart for demonstrating the drive method of the hydrogen gas sensor apparatus of this invention. Example 1 It is the plane schematic of one example of the sensor chip of the hydrogen gas sensor used for the drive method of the hydrogen gas sensor device of the present invention. (Example 1, Example 3) It is the cross-sectional schematic which follows the XX line of the part of hydrogen gas sensor A of the sensor chip 100 shown in FIG. 2 of the hydrogen gas sensor apparatus of this invention. Example 1 In the method for driving a hydrogen gas sensor device of the present invention, FIG. 7A is a clock chart of an embodiment of the output of the temperature sensor 20B in heating and cooling cycles of the heater 25B, FIG. It is a time chart of an output waveform of temperature sensor 20B. Example 1 It is a block diagram of an example of a hydrogen gas concentration measuring device as a hydrogen gas sensor used for a method of driving a hydrogen gas sensor device of the present invention. Example 1 It is the schematic of the response waveform from the hydrogen gas sensor A in the cycle of the heating and cooling used for the drive method of the hydrogen gas sensor apparatus of this invention. Example 1 The schematic diagram of one Example of the sensor chip 100 used for the drive method of the hydrogen gas sensor apparatus of this invention is shown, the figure (A) is the plane | planar schematic, and the figure (B) is a cross-sectional schematic. (Example 2) The figure (A) is a plane | planar schematic, and the figure (B) is a cross-sectional schematic with one Example at the time of using the heat conduction type hydrogen gas sensor B of the hydrogen gas sensor apparatus of this invention. (Example 3) The hydrogen gas sensor device of the present invention shows an embodiment in the case of having cantilever-like sensing regions 7A, in which (A) is a schematic plan view and (B) is a schematic sectional view. (Example 3) In the hydrogen gas sensor device of the present invention, in the embodiment of the sensor chip 100 realized as a single hydrogen gas sensor A, the same figure (A) is a schematic plan view, and the same figure (B) is a schematic sectional view. (Example 3) In the hydrogen gas sensor device of the present invention, the sensor chip 100 realized as a single hydrogen gas sensor A is an example in the case of having the sensing area 7A of the cross-linked structure, and FIG. (B) is a cross-sectional schematic view. (Example 3)

  Hereinafter, a method of driving a hydrogen gas sensor device and a hydrogen gas sensor device according to the present invention will be described in detail based on examples. The sensor chip of the hydrogen gas sensor can be formed of a silicon (Si) substrate using mature semiconductor integration technology and MEMS technology. Description will be made with reference to the drawings in the case of using this silicon (Si) substrate, in particular, an SOI substrate.

  FIG. 1 is a flow chart for explaining the driving method of the hydrogen gas sensor device of the present invention. FIG. 2 shows a hydrogen gas sensor A for measuring low concentration hydrogen gas and a high concentration hydrogen gas measurement on a substrate 1 having the same SOI layer (a substrate having a BOX layer which is a buried insulating layer in silicon single crystal) The hydrogen gas sensor B of the present invention is mounted on a schematic plan view of the sensor chip 100 of the hydrogen gas sensor device of the present invention. The hydrogen gas sensor A and the hydrogen gas sensor B share the substrate 1 to measure the hydrogen gas concentration using the cantilever-shaped sensing regions 7A and 7B. Here, the heater 25A as the heater A for the hydrogen gas sensor A and the temperature sensor 20A as the temperature sensor A are formed in the cantilever sensing region 7A, and a hydrogen absorbing material as the hydrogen sensitive material 5 is sensed. It is a case where it forms near the tip of 7A. Also, the heater 25B as the heater B for the hydrogen gas sensor B and the temperature sensor 20B as the temperature sensor B are formed in the cantilevered sensing region 7B, and a heat conduction type hydrogen gas sensor is adopted as the hydrogen gas sensor B. Because of this, no hydrogen absorbing material is provided as the hydrogen sensitive material 5. The temperature sensor 20A and the temperature sensor 20B both use the SOI layer as one of the thermocouples 120a of the thin-film thermocouple and the thin-film thermocouple, which is a temperature difference sensor consisting of the other thermocouple 120b through the insulating film 50, It is a case where it is adopted as a sensor. FIG. 3 is a schematic cross-sectional view along the line XX of the portion of the hydrogen gas sensor A of the sensor chip 100 shown in FIG.

  The driving method of the hydrogen gas sensor device of the present invention will be described with reference to FIG. As shown in FIG. 1, the power is turned on using a hydrogen gas sensor device (hydrogen gas concentration measuring device) provided with a hydrogen gas sensor A and a hydrogen gas sensor B as the ambient gas (test gas) for measuring the hydrogen gas concentration. (S0101). At this time, although the hydrogen gas sensor A and the hydrogen gas sensor B are exposed to the test gas, the hydrogen gas concentration measurement operation is not performed first, and then, for example, the hydrogen gas sensor B for high concentration hydrogen gas measurement automatically. Measurement operation is performed (S0102). Next, whether the measurement result of the hydrogen gas concentration by the hydrogen gas sensor B is higher than a predetermined hydrogen gas concentration value (switching reference concentration) of the safety limit sense concentration to the extent that the hydrogen absorbing substance is damaged and denatured and the hysteresis phenomenon does not occur. It is judged whether it is less than that (S0103). If the hydrogen gas concentration is equal to or higher than the switching reference concentration (No in FIG. 1), the measurement result by the hydrogen gas sensor B is displayed (S0104). If the hydrogen gas concentration is lower than the switching reference concentration (Yes in FIG. 1), measurement of the low hydrogen gas concentration with the hydrogen gas sensor A is started (S0105), and the result is displayed (S0106). The predetermined hydrogen gas concentration value (switching reference concentration) with the hydrogen gas sensor B does not matter in the measurement of the hydrogen gas concentration with the hydrogen gas sensor A, that is, the hydrogen gas in the test gas is a low concentration hydrogen gas Therefore, the hydrogen gas sensor A can measure the hydrogen gas concentration as a stable hydrogen gas sensor A at a hydrogen gas concentration lower than the hydrogen gas sensor A because the hydrogen gas sensor A does not cause deterioration or deterioration.

The hydrogen gas sensor A and the hydrogen gas sensor B formed on the substrate 1 having the same SOI layer shown in FIGS. 2 and 3 can be easily formed by the known MEMS technology. Here, cantilever thin films 10A and 10B are formed using the SOI layer 11 of the SOI substrate, and a thin film thermocouple, which is a temperature difference sensor, is formed as a temperature sensor here. In this embodiment, a heater is used. As an example, a thin film of a nichrome thin film resistor is formed on the silicon oxide film insulating film 50 formed on the SOI layer 11. The tips of cantilever thin films 10A and 10B have a large area, and the resistance of nichrome thin film is formed into a zigzag shape so as to surround the measurement point (hot junction) 26 of the thin film thermocouple so that heat can be uniformly generated. It is arranged. The thin film thermocouple is a silicon oxide film formed by thermally oxidizing the SOI layer 11 on the SOI layer 11 (for example, an n-type silicon single crystal film and having a thickness of about 10 μm) as the first thermal conductor 120a. The second thermal conductor 120b (for example, a nickel thin film or a nichrome thin film) formed through the insulating film 50 is formed to form the ohmic contact 60 as the measurement point (warm contact) 26. . A reference point (cold junction) 27 of the thin film thermocouple is formed on the substrate 1. The length of cantilevers may be about 700 μm. Here, in order to measure the temperature of the substrate 1, a pn junction diode (semiconductor diode) is formed on the substrate 1 and used as an absolute temperature sensor 23 for measuring the absolute temperature of the substrate 1. . In the method of using a semiconductor diode as the absolute temperature sensor 23, a constant forward voltage is applied to the semiconductor diode in measurement of a room temperature which is a relatively low temperature of 150 ° C. or less, and the temperature dependency of the diode current at that time There is a method of obtaining a constant current and a method of obtaining it from the temperature dependency of the diode forward voltage at that time, and in high temperature measurement of 150 ° C. or more, the reverse of the diode at a fixed reverse applied voltage of about 0.5V to 1V. It can be determined from the temperature dependence of the directional current.

  Although the hydrogen gas sensor B for high concentration hydrogen gas measurement is of the heat conduction type, the operation of the hydrogen gas sensor B and the function of determining the hydrogen gas concentration in the test gas will be described. A hydrogen gas sensor device (hydrogen gas concentration measuring device) will be described using a hydrogen gas sensor A and a hydrogen gas sensor B on a substrate 1 having the same SOI layer 11 shown in FIGS. 2 and 3. A current is supplied to the heater 25B of the sensing region 7B formed in the cantilever shape of the hydrogen gas sensor B through the electrode pad 71c and the electrode pad 71b common to the heater 25A of the hydrogen gas sensor A to perform heater heating. The heater temperature at this time is as high as about 200 ° C., and the sensitivity is higher. The above-mentioned thin film thermocouple temperature sensor 20B is used as a temperature sensor. Since the thin film thermocouple temperature sensor 20B is a temperature difference sensor, the reference point 27 (common electrode pad 75) formed on the substrate 1 and the measurement point 26 (electrode pad 70b) at the tip of the sensing region 7B formed in cantilever shape. Output the temperature difference between FIG. 4 shows a time chart of one embodiment of heating and cooling cycles of the heater 25B of the temperature sensor 20B at that time. FIG. 4A is a time chart of a clock pulse for heating and cooling of the heater 25B, and FIG. 4B is a time chart of an output waveform of the temperature sensor 20B.

  As shown in the output waveform of the temperature sensor 20B shown in FIG. 4B, when the hydrogen gas is not present in the test gas (hydrogen gas concentration: 0%), the temperature rise of the sensing area 7B of the hydrogen gas sensor B is supported. The output voltage to be output is the maximum V0 which is a saturated output voltage. However, when the hydrogen gas concentration is high, the saturation output voltage is a voltage Vm smaller than the maximum V0, and as the hydrogen gas concentration increases, the saturation output voltage Vm becomes smaller than V0. From the maximum output voltage V0, which is the saturation output voltage when the hydrogen gas concentration at this time is 0%, the saturation output voltage Vm when the hydrogen gas concentration is low becomes smaller by the output difference ΔV. The hydrogen gas concentration in the test gas is measured by using the previously prepared calibration data of the output difference .DELTA.V (= V0-Vm) and the hydrogen gas concentration. As shown in FIG. 4, if the hydrogen gas concentration in the test gas is a voltage Vm smaller than the saturation output voltage Vc corresponding to the specified value (representation in hydrogen gas concentration) which is a predetermined hydrogen gas concentration value Since the hydrogen gas concentration in the test gas is within the range that can be measured by the hydrogen gas sensor B at the hydrogen gas concentration, it can be measured by the hydrogen gas sensor B as it is. The concentration is converted to the hydrogen gas concentration in the test gas and displayed. However, if the hydrogen gas concentration in the test gas is a voltage Vm (value close to V0) larger than the saturation output voltage Vc corresponding to the specified value which is a predetermined value (for example, 1000 ppm), the test gas contains The error is large for the hydrogen gas concentration to be measured by the hydrogen gas sensor B. For example, a heat conduction type hydrogen gas sensor, which is a heat conduction type hydrogen gas sensor B that is difficult to measure for low hydrogen gas concentrations of 1000 ppm or less, is a specified value where the hydrogen gas concentration in the test gas is a predetermined value (Switching reference concentration) Judged by using the judgment circuit that it is less than or equal to the switching reference concentration, switching to measurement with the hydrogen gas sensor A having high sensitivity even to low hydrogen gas concentration of 1000 ppm or less The concentration of hydrogen gas in the

  FIG. 5 shows a block diagram of a hydrogen gas concentration measuring device as a hydrogen gas sensor device of the present invention provided with a hydrogen gas sensor A and a hydrogen gas sensor B. FIG. 4 illustrates the configuration of a hydrogen gas concentration measuring device and the description of the operation thereof, which illustrates a flowchart of a method of driving a hydrogen gas sensor device according to the present invention shown in FIG. When the hydrogen gas concentration measuring apparatus is turned on, first, the measurement of the hydrogen gas concentration in the test gas of the hydrogen gas sensor B starts by the heater drive of the hydrogen gas sensor B, and its output signal is amplified by the amplifier circuit, The determination circuit determines whether the magnitude of the signal from the hydrogen gas sensor B, that is, whether the output voltage Vm is larger or smaller than the saturation output voltage Vc corresponding to the above-described prescribed value. When the output voltage Vm is smaller than the saturation output voltage Vc (hydrogen gas concentration is larger than the switching reference concentration, ΔV is large), amplification is performed using an amplification circuit as necessary, and calibration data and the like are used. Then, processing is performed by the arithmetic circuit, and the output result of the hydrogen gas sensor B is used to display the hydrogen gas concentration. If the output voltage Vm is larger than the saturation output voltage Vc (ΔV is small), switch to the heater drive circuit of the hydrogen gas sensor A, and measure the low concentration hydrogen gas with the hydrogen gas sensor A as needed. The signal is amplified by using the signal, processed by the arithmetic circuit using calibration data and the like, and the hydrogen gas concentration is displayed by using the output result of the hydrogen gas sensor A. Of course, in applications such as leak detectors, if it is clear that hydrogen gas absorbing substances are damaged and degraded and degraded in the test gas and hydrogen gas is present only in a very low concentration where hysteresis does not occur. It may be made to be able to be performed only by the operation of the hydrogen gas sensor A from the beginning with emphasis on responsiveness. Also, conversely, in the case of the test gas having a high hydrogen gas concentration, the hydrogen gas sensor A may be set so as not to operate.

  The operation of the hydrogen gas sensor A will be described here using an example of a hydrogen absorption / heat generation type as the hydrogen gas sensor A. In this case, an example in which a thin film (referred to as a Pd film) mainly composed of palladium (Pd) which is a hydrogen-absorbing material is used as the hydrogen-sensitive material 5 shown in FIGS. The Pd film can be easily formed to a film thickness of about 1 micrometer (μm) by sputtering deposition. The Pd film is widely used as a metal film that transmits only hydrogen, and is also used for high purification of hydrogen gas. The Pd film causes an exothermic reaction when absorbing hydrogen and the temperature rises. The lower the temperature is, the larger the amount of absorbed hydrogen, and when heated to a high temperature, the absorbed hydrogen is released to reach an equilibrium state. Therefore, when hydrogen gas is absorbed at a certain temperature, it absorbs hydrogen until it is in equilibrium at that temperature, but when it is in equilibrium and saturates, it does not absorb any more, so the exothermic reaction also stops, and hence the temperature rise also stops. In order to cause the exothermic action continuously, it is necessary to drive out hydrogen gas from the Pd film, and it is important to continue the heating / cooling cycle by cyclic heater heating. It is preferable to release hydrogen absorbed in the Pd film at the time of heating, absorb hydrogen at the time of cooling to generate heat, and measure the temperature rise at this time.

  In FIG. 6, a Pd film as a hydrogen-absorbing material as the hydrogen-sensitive material 5 formed in the sensing area 7A as the hydrogen gas sensor A shown in FIGS. 2 and 3 is heated by the heater 25A in the heating / cooling cycle. The schematic diagram of the response waveform from the hydrogen gas sensor A at the time of heating is shown. For example, it shows the case where there is a hydrogen gas concentration of 100 ppm in the test gas, and further, in the test gas, the hydrogen gas from the hydrogen gas sensor A when the hydrogen gas concentration is 0% (for example, pure air) The outline of the response waveform is also shown. If there is a hydrogen gas concentration of 100 ppm in the test gas, the hydrogen gas absorbed in the Pd film is released to the environment as hydrogen gas in the heating cycle (for example, heater heating at 160 ° C.) Although it is in an equilibrium state, since it is exposed to a hydrogen gas concentration of 100 ppm, in the cooling cycle, as it gets cold, it absorbs this and an exothermic reaction occurs. Therefore, the temperature at the time of cooling of sensing area 7A falls by a gentle curve. This temperature is measured by the thin film thermocouple sensor of the temperature difference sensor as the temperature sensor 20A formed in the sensing area 7A of the hydrogen gas sensor A. In heating the heater 25A, a current flows between the electrode pad 71a and the electrode pad 71c, and the temperature sensor 20A measures the thermoelectromotive force between the electrode pad 70a for the temperature sensor 20A and the common electrode pad 75. However, if the hydrogen gas concentration in the test gas is 0% (for example, pure air), there is no heat generation associated with hydrogen absorption, so the sensing region 7A has the original thermal time constant τ when the heater heating is stopped. It is rapidly cooled exponentially. Generally, the temperature difference with the ambient temperature is completely zero after a time that is several times its thermal time constant τ (for example, a time after 4 times τ) Then, when the hydrogen gas concentration in the test gas is measured, the output of the temperature sensor 20A is observed, so this output value ΔV depends on the exothermic reaction by the hydrogen gas in the test gas, and this is measured The hydrogen gas concentration is determined on the basis of calibration data prepared in advance. The sensitivity can be further enhanced by time integration of the output value ΔV by charging the capacitor or the like.

  Here, the case where a semiconductor gas sensor is used as the hydrogen gas sensor A will be described. As the hydrogen gas sensor B in the hydrogen gas sensor device of the present invention, a heat conduction hydrogen gas sensor can be used as described above. In FIG. 7, a semiconductor gas sensor is used as such hydrogen gas sensor A, and the sensing regions 7A and 7B of the heat conduction hydrogen gas sensor are formed on the substrate 1 having the same SOI layer as the hydrogen gas sensor B. The schematic diagram of one Example of the sensor chip 100 is shown, the figure (A) is the plane | planar schematic, and the figure (B) is a cross-sectional schematic. In the above-described embodiment, the sensing areas 7A and 7B are cantilever-shaped, but here, both are cross-linked structures, and in the cantilever structure, since there is one supporting portion, the heater or the Wiring for temperature sensor and wiring for measuring resistance such as tin oxide thin film which is a metal thin film which is a hydrogen absorbing material as hydrogen sensitive substance 5 of semiconductor type gas sensor, etc. are very crowded when introduced on the substrate 1 side. In the case of the crosslinked structure, since there are two supporting portions, there is an advantage that the introduction of the wiring to the substrate 1 side becomes easy. However, since the heat radiation by the heat conduction to the substrate 1 also increases, the length of the sensing regions 7A and 7B needs to be increased, and the size of the sensor chip 100 must be increased.

  The heater 25B of the hydrogen gas sensor B is formed of, for example, a nichrome (NiCr) thin film. The temperature sensor 20B is a thin film thermocouple of an SOI layer and a nichrome film as in the first and second embodiments. The heater 25B can perform heater heating by passing a current between the electrode pad 73a and the electrode pad 73b. Further, in the temperature sensor 20B, a thermoelectromotive force is generated between the electrode pad 74a and the electrode pad 74b when the sensing area 7B is heated by the heater. Also, here, the heater 25A of the hydrogen gas sensor A uses the SOI layer of the sensing area 7A. Furthermore, the temperature sensor 20A is used as a temperature measuring resistor by using the resistance temperature count of the heater 25A. The semiconductor gas sensor as the hydrogen gas sensor A, for example, heats a tin oxide thin film which is a hydrogen absorbing substance as the hydrogen sensitive substance 5 to about 400 ° C., and a reducing gas which is a hydrogen gas is adsorbed and absorbed from the surface. When the tin oxide thin film is reduced to form a metal-rich tin oxide thin film and the electric resistance is reduced, the hydrogen gas in the test gas is prepared using calibration data prepared in advance from the change in the electric resistance. The concentration is calculated. That is, the measurement of the electrical resistance of the tin oxide thin film which is a hydrogen absorbing substance as the hydrogen sensitive substance 5 is carried out between the electrode pad 70a and the electrode pad 70b through the electrodes 80a and 80b of the hydrogen sensitive substance 5 shown in FIG. The change in resistance is measured to measure the hydrogen gas concentration in the test gas. The hydrogen gas concentration in the test gas of the hydrogen gas sensor B is measured, the value is compared with the specified value, and the judgment circuit is used to have a judgment function such as measuring the low hydrogen gas concentration region with the hydrogen gas sensor A The method of driving the hydrogen gas sensor according to the present invention is the same as that of the above-described embodiment, and thus the description thereof is omitted.

  In the present embodiment, an example is shown in which the driving method of the hydrogen gas sensor device of the present invention is implemented using a single hydrogen gas sensor B disposed close to a single hydrogen gas sensor A. As an independent hydrogen gas sensor B, an example in the case of using the heat conduction type hydrogen gas sensor B shown in FIG. 8 is shown. A schematic plan view of the heat conduction type hydrogen gas sensor B shown in FIG. 8 is shown in FIG. 8 (A), and a schematic sectional view thereof is shown in FIG. 8 (B), but as shown in FIG. In the first embodiment, one sensing area 7A in the plan view of FIG. 2 shown in the first embodiment is independent. Therefore, the operation is the same as the case shown in the first embodiment, and the description thereof is omitted here. In this embodiment, as a single hydrogen gas sensor A, FIG. 9 shows an embodiment in the case of having cantilever-like sensing regions 7A, in which (A) is a schematic plan view and (B) is a schematic view. FIG. When a thin film of a hydrogen-absorbing material such as Pd as a hydrogen-absorbing and heat-generating type is formed as the hydrogen-sensitive material 5, the same process as in Example 1 is performed.

  FIG. 10 shows an embodiment of the sensor chip 100 in the case where the hydrogen gas sensor is realized as a single hydrogen gas sensor A and the heater 25A and the temperature sensor 20A are used together, and FIG. The figure and the figure (B) are cross-sectional schematic views. FIG. 11 shows a sensor chip 100 realized as a single hydrogen gas sensor A in a hydrogen gas sensor, having a sensing area 7A of a cross-linked structure, and a heater 25A and a hydrogen gas sensor. It is one Example at the time of making it use the temperature sensor 20A, and the figure (A) is a plane schematic, and the figure (B) is a cross-sectional schematic. In the case where the heater 25A and the temperature sensor 20A are used in the present embodiment, it is preferable to form a thin film of a hydrogen absorbing material such as Pd as a hydrogen absorbing and heat generating type as the hydrogen sensitive material 5. In the case of the hydrogen absorption heat generation type, the heater is heated to drive out the hydrogen absorbed by the hydrogen absorption material, but as shown in Example 1, since the hydrogen absorption heat generation measures its temperature during the cooling cycle, The heater heating cycle, which is the action as the heater 25A for the expulsion, and the cooling cycle for the temperature (difference) measurement action as the temperature sensor 20A differ from each other in time series, which is advantageous. By combining the heater 25A and the temperature sensor 20A, electrical separation of wiring and the like is simplified, the number of manufacturing steps is reduced, and a compact hydrogen gas sensor chip 100 with a simple structure can be provided.

  In the present embodiment, the single hydrogen gas sensor A and the single hydrogen gas sensor B are disposed close to each other to constitute a hydrogen gas concentration measuring device which is a hydrogen gas sensor device, and the same substrate 1 of the above embodiment is used. Since the operation and the formation are essentially the same, the description is omitted.

  In the above-mentioned embodiment, since the heater is heated to measure the hydrogen concentration, the ignition temperature of hydrogen in the air is low, and it is explosive-proof, for example, by covering it with a metal mesh because it is explosive. It is required to use.

  The above-described embodiments are merely examples, and it goes without saying that there are various modifications while the gist, operation and effects of the present invention are similar.

  Hydrogen gas is used in a very wide range, such as being used as a fuel, used in hydrogen reduction processes for substances, used in fuel cells and secondary batteries, or mixed with trace amounts of hydrogen gas as a probe gas, and adopted in leak detectors It is done. However, there is a risk of explosion in the air, etc., so it is necessary to know the concentration of hydrogen gas, and if necessary, measurement of extremely low hydrogen gas concentration of about 1 ppm, up to 100% A very wide range of concentration measurement is required, such as high hydrogen concentration measurement. In particular, heater heating is often required for high-sensitivity hydrogen concentration measurement. Furthermore, in low-hydrogen gas concentration measurement, the hydrogen-absorbing substance as the hydrogen-sensitive substance 5 is exposed to high-concentration hydrogen gas at high temperatures. The hydrogen-sensitive substance 5 is known to deteriorate and deteriorate rapidly, and these measures have been required. Since these problems are eliminated by the method of driving a hydrogen gas sensor of the present invention, it is possible to provide a compact, long-life hydrogen gas sensor device capable of measuring a wide range of hydrogen gas concentration.

DESCRIPTION OF SYMBOLS 1 substrate 5 hydrogen sensitive substance 7A, 7B sensing area 10A, 10B thin film 11 SOI layer 12 island of SOI layer 13 BOX layer 15 base substrate 20A, 20B temperature sensor 23 absolute temperature sensor 25A, 25B heater 26 measurement point (warm contact)
27 reference point (cold junction)
40 cavity 41 groove 50 insulating film 60 ohmic contact 70a, 70b electrode pad 71a, 71b, 71c electrode pad 72a, 72b electrode pad 73a, 73b electrode pad 74a, 74b electrode pad 75 common electrode pad 80a, 80b electrode 100 sensor chip 120 Thermocouple 120a, 120b Thermoconductor

Claims (15)

A hydrogen gas sensor A whose measurement region has a relatively low concentration compared to the hydrogen gas sensor B,
A hydrogen gas sensor B having a relatively high concentration as compared with the hydrogen gas sensor A,
A driving method of a hydrogen gas sensor device for measuring a hydrogen gas concentration by combining the hydrogen gas sensor device, the hydrogen gas sensor device driving method being configured to be able to judge whether the measurement reference concentration is lower than a predetermined reference value . The hydrogen gas sensor B is a heat conduction type sensor having a heater B and a temperature sensor B and having a structure that does not deteriorate even when exposed to high concentration hydrogen gas close to 100%, and the hydrogen gas sensor A has its hydrogen sensitive substance as, the hydrogen-absorbing material, further comprising a heater a and a temperature sensor a to release the absorbed hydrogen, the switching reference density said a predetermined reference value, the absorption of hydrogen gas at the high concentration side of the hydrogen gas sensor a and the heating and cooling cycle with the release, Dearuko safety limit sense concentration of a degree that does not cause hysteresis deteriorated deteriorated to damage the hydrogen-absorbing material ,
When the hydrogen gas sensor A is exposed to the measurement atmosphere when the measurement of the hydrogen gas concentration is started , and the heater is not heated,
First, the hydrogen gas sensor B is driven, and by measuring the hydrogen gas concentration of the hydrogen gas sensor B, it is judged whether the measurement atmosphere is lower than the switching reference concentration, and it is judged that the judgment result is lower than the switching reference concentration. The hydrogen gas sensor A performs the heating / cooling cycle, releases the hydrogen in the heating cycle heated by the heater A, and measures the hydrogen gas concentration in the cooling cycle, and the switching reference concentration is 1% concentration Method of driving a hydrogen gas sensor device While measuring hydrogen gas concentration by driving the hydrogen gas sensor B,
Measurement atmosphere is determined whether the below the switching reference density, the judgment result according to claim 1, wherein which is adapted to measure the hydrogen gas concentration in the hydrogen gas sensor B to continue if it is determined that not less than the switching reference density Method of driving hydrogen gas sensor device The hydrogen gas sensor A is configured to be able to determine whether the hydrogen gas concentration does not exceed the switching limit concentration, which is the hydrogen concentration that may exceed the switching reference concentration,
While measuring hydrogen gas concentration by driving the hydrogen gas sensor A,
Measurement atmosphere is determined whether does not exceed the switching limit concentration, claim 1 or was to measure the hydrogen gas concentration by switching the hydrogen gas sensor B in the case where the determination result is determined to be greater than the switching limit concentration The driving method of the hydrogen gas sensor device according to any one of 2 . The method according to claim 3 , wherein the switching limit concentration and the switching reference concentration are equal to each other. The method for driving a hydrogen gas sensor device according to any one of claims 1 to 4, wherein the hydrogen gas concentration is measured by measuring a temperature rise based on the heat of hydrogen absorption into the hydrogen absorbing substance. The method for driving a hydrogen gas sensor device according to any one of claims 1 to 5, wherein the hydrogen sensitive substance is a substance utilizing a change in electric resistance due to hydrogen gas adsorption and absorption of a semiconductor gas sensor. The method of driving a hydrogen gas sensor device according to any one of claims 1 to 6, wherein the hydrogen absorbing material is a material containing palladium (Pd). The hydrogen according to any one of claims 1 to 7 , wherein the heater A and the temperature sensor A of the hydrogen gas sensor A, and the heater B and the temperature sensor B of the hydrogen gas sensor B are both provided on a thin film thermally separated from the substrate. Method of driving a gas sensor device. After hydrogen is released from the hydrogen absorbing material by the heating of the heater A and the heating of the heater A is stopped, the thermal time constant τ of the thin film when hydrogen of the heater A does not exist is 9. The method of driving a hydrogen gas sensor device according to claim 8 , wherein the output of the temperature sensor A at or after a predetermined time elapses is used to know the hydrogen gas concentration in the atmosphere gas. After the heating of the heater A is stopped, the temperature sensor A is used to measure the temperature of the atmosphere gas and the temperature sensor after a predetermined time has elapsed, which is equal to or more than the thermal time constant τ of the thin film when hydrogen is not present. 10. The method of driving a hydrogen gas sensor device according to claim 9 , wherein the output of the temperature difference with the temperature at A is integrated over time and output, and the output is used to know the hydrogen gas concentration. The method for driving a hydrogen gas sensor device according to any one of claims 1 to 10 , wherein the heater B can also be heated and cooled in a predetermined cycle. A hydrogen gas sensor device configured to use the method for driving a hydrogen gas sensor device according to any one of claims 1 to 11 . The hydrogen gas sensor device according to claim 12 , wherein the hydrogen gas sensor A and the hydrogen gas sensor B are provided in proximity to each other. 14. The hydrogen gas sensor device according to claim 12, wherein the hydrogen gas sensor A and the hydrogen gas sensor B are formed on the same substrate. The hydrogen gas sensor device according to any one of claims 12 to 14 equipped with at least an amplifier circuit, an arithmetic circuit, a heater drive circuit, and a judgment circuit using the output of the hydrogen gas sensor B.

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