Chemical sensors and measuring devices

Abstract

To obtain a chemical sensor that can stably and accurately measure the concentration of a specific substance contained in a measurement medium. [Solution] The chemical sensor 1 comprises a silicon substrate 2 on which a diaphragm 21 is formed, a strain sensor 3 provided on the silicon substrate 2, and a storage film 4 provided on the diaphragm 21 whose volume changes when it absorbs a specific substance. The strain sensor 3 includes a vacuum chamber formed in the diaphragm 21 and an oscillator formed inside the vacuum chamber.

Description

Technical Field

[0001] The present disclosure relates to chemical sensors and measuring devices.

Background Art

[0002] There is a chemical sensor that measures the concentration of a specific substance contained in a measurement medium using an occlusion film that occludes a specific substance. For example, Patent Document 1 discloses a chemical sensor in which a vibrator having a PZT (lead zirconate titanate) vibrator structure is formed on a silicon substrate, and an occlusion film is directly formed on the vibrator. In the chemical sensor disclosed in Patent Document 1, the concentration of a specific substance is calculated by measuring the change in the resonance frequency of the vibrator based on the mass change of the occlusion film that has occluded the specific substance.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the above-described chemical sensor, since the occlusion film is directly formed on the vibrator, the vibrator comes into contact with the measurement medium. Therefore, the influence of the change in the state of the measurement medium on the change in the resonance frequency of the vibrator is large, and the measurement accuracy of the concentration may decrease.

[0005] An object of the present disclosure is to obtain a chemical sensor that can stably and accurately measure the concentration of a specific substance contained in a measurement medium.

Means for Solving the Problems

[0006] The chemical sensor according to this disclosure comprises a silicon substrate on which a diaphragm is formed, a strain sensor provided on the silicon substrate, and a storage film provided on the diaphragm whose volume changes when it absorbs a specific substance, wherein the strain sensor includes a vacuum chamber formed in the diaphragm and an oscillator formed inside the vacuum chamber. [Effects of the Invention]

[0007] According to this disclosure, it is possible to obtain a chemical sensor that can stably and accurately measure the concentration of a specific substance contained in a medium. [Brief explanation of the drawing]

[0008] [Figure 1] This is a plan view of the chemical sensor according to Embodiment 1. [Figure 2] Figure 1 shows a cross-sectional view of the chemical sensor cut along the line II-II. [Figure 3] This is a partially enlarged cross-sectional view of portion A shown in Figure 2. [Figure 4] This is a plan view of the chemical sensor according to Modification Example 1. [Figure 5] Figure 4 shows a cross-sectional view of the chemical sensor cut along the VV line. [Figure 6] This is a cross-sectional view of a chemical sensor according to modified example 2. [Figure 7] This is a cross-sectional view showing the schematic configuration of a measuring device equipped with a chemical sensor according to Embodiment 1. [Figure 8] This is a flowchart showing the procedure for measuring hydrogen concentration using a single measuring device. [Figure 9] This is a flowchart showing the procedure for measuring hydrogen concentration using two measuring devices. [Modes for carrying out the invention]

[0009] A chemical sensor and measuring device according to one embodiment of this disclosure will be described in detail below with reference to the drawings. However, the present invention is not limited to the embodiments described below.

[0010] 〔Embodiment 1〕 〔Schematic Configuration of Chemical Sensor〕 FIG. 1 is a plan view of a chemical sensor according to Embodiment 1. FIG. 2 is a cross-sectional view of the chemical sensor taken along line II-II shown in FIG. 1. The chemical sensor 1 includes a silicon substrate 2, a strain sensor 3, and an occlusion film 4.

[0011] 〔Regarding the Silicon Substrate〕 The silicon substrate 2 is formed of silicon. The silicon substrate 2 has a diaphragm 21 and a rim portion 22. The diaphragm 21 is formed in a thin film shape. The diaphragm 21 has a first surface 21a and a second surface 21b that is the back surface of the first surface 21a. The diaphragm 21 is deformed when pressure is applied to the first surface 21a or the second surface 21b, or when the volume of the occlusion film 4 described later changes.

[0012] The rim portion 22 is formed so as to surround the periphery of the diaphragm 21 in a plan view. The rim portion 22 is formed thicker than the diaphragm 21.

[0013] 〔Regarding the Strain Sensor〕 The strain sensor 3 is provided on the first surface 21a side of the silicon substrate 2. As the strain sensor 3, a first strain sensor 31 provided at a position overlapping the diaphragm 21 in the plan view shown in FIG. 1 and a second strain sensor 32 provided at the boundary between the diaphragm 21 and the rim portion 22 are provided.

[0014] The first strain sensor 31 and the second strain sensor 32 have a common structure. Therefore, in the following description of the structure of the strain sensor 3, the first strain sensor 31 and the second strain sensor 32 will be described as the strain sensor 3 without distinction.

[0015] Figure 3 is a partial enlarged cross-sectional view showing an enlarged view of portion A shown in Figure 2. The strain sensor 3 has a vacuum chamber 3a and a vibrator 3b. The vacuum chamber 3a is formed on the first surface 21a of the silicon substrate 2. The vacuum chamber 3a is a space surrounded by a cavity 3a1 formed on the first surface 21a of the silicon substrate 2. The inside of the vacuum chamber 3a is in a vacuum state.

[0016] The vibrator 3b is housed in the vacuum chamber 3a. As shown in Figure 2, the strain sensor 3 is formed in an H-shaped configuration in a plan view, and the vibrator 3b and the vacuum chamber 3a are also formed in an H-shaped configuration. The vibrator 3b has its ends fixed to the silicon substrate 2. A gap is formed between the vibrator 3b and the inner wall surface of the vacuum chamber 3a except for the fixed both ends. The resonance frequency of the vibrator 3b changes due to the strain generated in the vibrator 3b.

[0017] The silicon substrate 2 is provided with a wiring 51 connected to the vibrator 3b. A terminal 52 to which an external wiring such as a bonding wire is connected is provided at an end of the wiring 51. Note that the shape of the strain sensor 3 provided in the chemical sensor 1 is not limited to the exemplified H-shaped configuration as long as the vibrator 3b is housed in the vacuum chamber 3a. For example, the strain sensor 3 may be formed in an I-shaped configuration. Note that the number and position of the wiring 51 and the terminal 52 formed on the silicon substrate 2 are appropriately changed according to the shape of the strain sensor 3 and the like.

[0018] 〔Regarding the occlusion film〕 The occlusion film 4 is provided on the second surface 21b of the diaphragm 21. The occlusion film 4 changes its volume by occluding a specific substance. Hydrogen is exemplified as the specific substance occluded by the occlusion film 4.

[0019] The hydrogen storage film 4 is formed from a material that readily absorbs and releases hydrogen, and whose volume changes as hydrogen is absorbed and released. Examples of such materials include palladium, magnesium, titanium, vanadium, zirconium, lanthanum, iron, nickel, tantalum, or alloys containing these metals. Furthermore, to enhance the hydrogen absorption and release properties, the material used for the storage film 4 may be an amorphous material rather than a crystalline material. By using an alloy for the material used for the storage film 4, the hydrogen embrittlement resistance of the storage film 4 can be improved.

[0020] The specific substances that the storage film 4 absorbs are not limited to hydrogen. For example, carbon monoxide and carbon dioxide are examples of specific substances that the storage film 4 absorbs. For example, lithium composite oxides such as lithium zirconate are examples of materials used in the storage film 4 that absorb carbon dioxide. In addition, the storage film 4 absorbs not only specific substances in a gaseous state, but also specific substances that are dissolved in liquids as molecules or ions.

[0021] [Regarding the measurement of the concentration of specific substances using chemical sensors] The chemical sensor 1 can measure the concentration of a specific substance contained in the medium in contact with the storage film 4.

[0022] The storage film 4 increases in volume by absorbing a specific substance. Returning to Figure 2, the increase in volume of the storage film 4 causes tensile stress to be applied to the second surface 21b of the diaphragm 21, resulting in tensile strain. At this time, compressive stress is applied to the first surface 21a, which is the back surface of the second surface 21b, resulting in compressive strain. The first strain sensor 31 is provided on the first surface 21a of the diaphragm 21. The compressive strain on the first surface 21a also causes compressive strain to be applied to the oscillator 3b of the first strain sensor 31. The occurrence of compressive strain changes the resonant frequency of the oscillator 3b.

[0023] Furthermore, at the boundary between the diaphragm 21 and the rim portion 22 on the first surface 21a side of the silicon substrate 2, stress in the tensile direction is applied, causing tensile strain. A second strain sensor 32 is provided at the boundary between the diaphragm 21 and the rim portion 22. When tensile strain occurs at the boundary between the diaphragm 21 and the rim portion 22, tensile strain also occurs in the vibrator 3b of the second strain sensor 32. When tensile strain occurs, the resonant frequency of the vibrator 3b changes.

[0024] Here, the larger the amount of the specific substance absorbed by the absorption film 4, the greater the volume change of the absorption film 4, and the greater the strain generated in the oscillator 3b. Furthermore, as the strain generated in the oscillator 3b increases, the change in the resonant frequency also increases. The amount of the specific substance absorbed by the absorption film 4 is proportional to the amount of the specific substance contained in the medium in which the absorption film 4 is in contact. Therefore, the chemical sensor 1 makes it possible to measure the concentration of the specific substance contained in the medium by measuring the resonant frequency of the oscillator 3b. From the viewpoint of accurately measuring the concentration, it is preferable that the oscillator 3b of the first strain sensor 31 and the oscillator 3b of the second strain sensor 32 are designed so that they do not coincide within the range of their respective changing resonant frequencies. It is also possible to measure the concentration of the specific substance by placing only the first strain sensor 31. In addition, if the absorption film 4 is made thicker, the amount of the specific substance that can be absorbed increases. Therefore, concentration measurement becomes possible even in environments where the concentration of the specific substance is high. On the other hand, if the storage film 4 is made too thick, the absorption and release rates of certain substances may decrease, potentially worsening the responsiveness of concentration measurements. Therefore, it is desirable to form the storage film 4 as thin as possible while still allowing for concentration measurement of specific substances.

[0025] In the chemical sensor 1 according to Embodiment 1, the oscillator 3b is located inside a vacuum chamber 3a covered by a cavity 3a2. Therefore, the oscillator 3b does not come into contact with the medium whose concentration is to be measured. As a result, the change in the resonant frequency of the oscillator 3b is not affected by whether the medium is in a gaseous or liquid state. Consequently, the chemical sensor 1 can stably and accurately measure the concentration of a specific substance contained in a medium, even if the state of the medium is different.

[0026] [Regarding pressure measurement using chemical sensors] In chemical sensor 1, strain is generated in the oscillator 3b due to the pressure (static pressure) received from the medium. The strain generated in oscillator 3b is proportional to the static pressure received from the medium. Therefore, in chemical sensor 1, it is possible to measure the static pressure of the medium by measuring the resonant frequency of oscillator 3b.

[0027] [Regarding the effect of specific substances on the storage capacity of the storage film] The amount of a specific substance absorbed into the storage film 4 varies depending on the concentration of that substance, but is also affected by fluctuations in pressure and temperature. As mentioned above, the chemical sensor 1 can measure the pressure of the medium, making it possible to calibrate the concentration measurement based on the measured pressure.

[0028] Furthermore, a diode is formed between the silicon substrate 2, which is made of silicon, and the wiring 51. Therefore, the resistance value of the diode changes with temperature. As a result, it is possible to measure the temperature by measuring the resistance value of the silicon substrate 2. Consequently, it is possible to measure the temperature with the chemical sensor 1 itself and calibrate the concentration measurement value based on the measured temperature, without having to separately provide a thermometer or the like.

[0029] In this way, the chemical sensor 1 can perform more accurate concentration measurements by calibrating the concentration measurement value by measuring pressure and temperature.

[0030] [Regarding Variation 1] Figure 4 is a plan view of the chemical sensor according to Modification 1. Figure 5 is a cross-sectional view of the chemical sensor cut along the VV line shown in Figure 4. In the chemical sensor 1 according to Modification 1, the second strain sensor 32 is positioned in a plan view that avoids the diaphragm 21 and overlaps with the rim portion 22. The vibrator 3b of the second strain sensor 32, which is positioned that avoids the diaphragm 21 and overlaps with the rim portion 22, does not experience strain due to the deformation of the diaphragm 21. That is, even if the diaphragm 21 deforms due to a change in the volume of the storage film 4, no strain occurs in the vibrator 3b of the second strain sensor 32. In this way, the strain generated in the vibrator 3b of the second strain sensor 32 can be limited to the compressive strain generated by the static pressure applied from the medium. Therefore, by measuring the resonance frequency of the vibrator 3b of the second strain sensor 32, it becomes possible to measure the static pressure applied to the medium more accurately.

[0031] [Regarding Variation 2] Figure 6 is a cross-sectional view of the chemical sensor according to Modification 2. The cross-section shown in Figure 6 corresponds to the cross-sections shown in Figures 2 and 5. In the chemical sensor 1 according to Modification 2, an absorption film 4 is provided on the first surface 21a of the diaphragm 21. Therefore, the first strain sensor 31 is covered by the absorption film 4.

[0032] When the storage film 4 provided on the first surface 21a absorbs a specific substance and its volume increases, tensile stress is applied to the first surface 21a of the diaphragm 21, causing tensile strain. As a result, tensile strain is also generated in the oscillator 3b of the first strain sensor 31. Therefore, even with a configuration in which the storage film 4 is provided on the first surface 21a, the concentration of a specific substance can be measured.

[0033] As shown in Figure 6, if the second strain sensor 32 is formed on the rim portion 22, avoiding the diaphragm 21, similar to the first modification, then no strain occurs in the vibrator 3b of the second strain sensor 32 due to deformation of the diaphragm 21.

[0034] Here, when using the chemical sensor 1 in an environment where high pressure is applied to the medium, it is necessary to prevent buckling of the transducer 3b. Let ε0 be the initial tension applied to the transducer 3b, and let ε be the compressive strain generated by the static pressure of the medium. p The compressive strain generated by the deformation of the diaphragm 21 is ε d In this case, the conditions under which buckling occurs in oscillator 3b are expressed by the following equation (1). Buckling strain of oscillator 3b < ε0 - ε p -ε d ...(1)

[0035] In the chemical sensor 1 according to modified example 2, the strain generated in the oscillator 3b of the first strain sensor 31 due to the deformation of the diaphragm 21 is tensile strain, not compressive strain. Also, no strain is generated in the oscillator 3b of the second strain sensor 32 due to the deformation of the diaphragm 21. Therefore, in either the oscillator 3b of the first strain sensor 31 or the oscillator 3b of the second strain sensor 32, the ε generated by the deformation of the diaphragm 21 in the above formula (1) is not generated. d Since it becomes less than or equal to 0, ε0-ε p -ε d The range in which ε does not exceed the buckling strain. p This allows for a wider range to be secured. Therefore, it becomes possible to set a wider pressure range that can be measured by the chemical sensor 1.

[0036] [Regarding the formation of a permeability-blocking film] In the chemical sensor 1 illustrated above, a permeability-blocking film (not shown) that prevents the permeation of a specific substance may be formed to cover at least one of the first surface 21a and the second surface 21b of the silicon substrate 2. In the region where the storage film 4 is provided, a permeability-blocking film is formed between the storage film 4 and the diaphragm 21.

[0037] The permeation-blocking film is, for example, a hydrogen permeation-blocking film that prevents the permeation of hydrogen. By forming a hydrogen permeation-blocking film, it is possible to prevent hydrogen from permeating through the silicon substrate 2 and adversely affecting the strain sensor 3. It is desirable that the hydrogen permeation-blocking film be formed from a material that has characteristics such as a low hydrogen diffusion coefficient, good film adhesion, low film stress on the diaphragm 21 after film formation, and few film defects. Examples of films formed from materials that satisfy these conditions include films made of gold, or ceramic films such as nitride films and alumina films.

[0038] If the permeability-blocking film is formed on at least one of the first surface 21a and the second surface 21b, it is possible to prevent hydrogen contained in the medium from permeating through that surface to the silicon substrate 2 and adversely affecting the strain sensor 3.

[0039] [Examples of chemical sensor implementations] In the chemical sensor 1 exemplified so far, the same medium is in contact with both the first surface 21a and the second surface 21b, and there is no deformation of the diaphragm 21 due to pressure from the medium; the deformation of the diaphragm 21 is used to measure the concentration of a specific substance. On the other hand, the chemical sensor 1 can also be implemented in a measuring device configured so that different pressures are applied to the first surface 21a and the second surface 21b of the diaphragm 21. In the measuring device, the diaphragm 21 deforms due to the difference between the pressure applied to the first surface 21a and the pressure applied to the second surface 21b. The measuring device uses the deformation of the diaphragm to measure the differential pressure, which is the difference between the pressure applied to the first surface 21a and the pressure applied to the second surface 21b. Such a measuring device is also called a differential pressure sensor.

[0040] Figure 7 is a cross-sectional view showing an example of a measuring device on which a chemical sensor according to Embodiment 1 is mounted. The measuring device 6 is the differential pressure sensor described above.

[0041] In the measuring device 6, the chemical sensor 1, base 61, base 62, cap 66, yoke 67, magnet 68, and magnet holder 69 are housed inside the housing 8.

[0042] In the measuring device 6, the chemical sensor 1 is fixed to a base 61. The base 61 is fixed to a base 62. The rim portion 22 of the chemical sensor 1 (see also Figure 2, etc.) is in contact with the base 61. Since the rim portion 22 is formed to surround the periphery of the diaphragm 21, the space between the second surface 21b and the base 61 is separated from the space where the first surface 21a is exposed by the rim portion 22. The gap between the second surface 21b and the base 61 is filled with oil, which is the medium. The oil filled in the gap between the second surface 21b and the base 61 is in contact with the second surface 21b of the diaphragm 21. A passage 63 is formed between the base 62 and the base 61 that communicates with the space where the second surface 21b is exposed.

[0043] The measuring device 6 is equipped with a hermetic terminal 64 that protrudes through the base 62 and avoids the pedestal 61. The hermetic terminal 64 is electrically connected to a terminal 52 (see also Figure 1, etc.) formed on the first surface 21a of the chemical sensor 1 via a bonding wire 65. The chemical sensor 1 emits an electrical signal indicating the resonant frequency of the oscillator 3b. The electrical signal emitted from the chemical sensor 1 is transmitted to the outside of the measuring device 6 via the bonding wire 65 and the hermetic terminal 64.

[0044] A cap 66 is attached to the base 62. The attachment of the cap 66 creates a space between the cap 66 and the base 62 that houses the chemical sensor 1 and the base 61. A yoke 67, a magnet 68, and a magnet holder 69 are provided in the space that houses the chemical sensor 1 and the base 61. The yoke 67 and the magnet 68 are held by the magnet holder 69. The yoke 67 and the magnet 68 are held in a position facing the first surface 21a of the silicon substrate 2.

[0045] An oil medium is filled between the yoke 67 and magnet 68 and the first surface 21a of the silicon substrate 2. The oil filled between the yoke 67 and magnet 68 and the first surface 21a of the silicon substrate 2 comes into contact with the first surface 21a of the diaphragm 21.

[0046] The yoke 67 and magnet 68, which are positioned opposite the first surface 21a of the diaphragm 21, function as an excitation unit that excites the oscillator 3b of the strain sensor 3. This driving method of the chemical sensor 1, which uses an excitation unit having a yoke 67 and a magnet 68 to excite the oscillator 3b, is also called an electromagnetic driving method. In the electromagnetic driving method chemical sensor 1 shown in Figure 7, a chemical sensor 1 equipped with an H-shaped strain sensor 3 as shown in Figures 1 and 4 is used.

[0047] In electromagnetically driven measuring devices 6, the gap between the first surface 21a of the silicon substrate 2 and the yoke 67 may be as narrow as about 10 μm, and the pathways through which a specific substance can penetrate the first surface 21a are complex. As a result, when measuring the concentration of a specific substance using the absorption film 4 provided on the first surface 21a, the response tends to be poor. Therefore, in electromagnetically driven chemical sensors 1, it is sometimes preferable to form the absorption film 4 on the second surface 21b and measure the concentration of the medium in contact with the second surface 21b.

[0048] On the other hand, in a chemical sensor 1 having a strain sensor 3 formed in the shape of an I, a structure for exciting the oscillator 3b is formed in the chemical sensor 1 itself. This driving method, in which the oscillator 3b is excited by a structure formed in the chemical sensor 1 itself, is also called an electrostatic driving method. When an electrostatic driving chemical sensor 1 is used in a measuring device 6, it becomes unnecessary to provide a yoke 67 and a magnet 68 for exciting the oscillator 3b. Therefore, compared to the electromagnetic driving method, a wider space can be secured for filling the medium around the first surface 21a on which the strain sensor 3 is formed. This makes it easier for specific substances to penetrate the first surface 21a. For this reason, in an electrostatic driving chemical sensor 1, it is sometimes preferable to form an absorbance film 4 on the first surface 21a and measure the concentration of the medium in contact with the first surface 21a.

[0049] The housing 8 has a first pressure-receiving diaphragm 81 and a second pressure-receiving diaphragm 82 formed within it. In the measuring device 6, the medium that comes into contact with the first pressure-receiving diaphragm 81 and the second pressure-receiving diaphragm 82 from the outside of the housing 8 is the medium whose differential pressure is measured by the measuring device 6. The first pressure-receiving diaphragm 81 and the second pressure-receiving diaphragm 82 are formed in a membrane-like manner with a space formed inside them, and they deform under pressure from the medium.

[0050] The space formed inside the first pressure-receiving diaphragm 81 is connected to the space where the first surface 21a of the chemical sensor 1 is exposed, through the first housing passage 83 formed inside the housing 8. Therefore, in the measuring device 6, the space inside the first pressure-receiving diaphragm 81 and the first housing passage 83 are filled with oil, as is the space where the first surface 21a is exposed.

[0051] The space formed inside the second pressure-receiving diaphragm 82 is connected to the space where the second surface 21b of the chemical sensor 1 is exposed, through the second housing passage 84 and passage 63 formed inside the housing 8. Therefore, in the measuring device 6, the space inside the second pressure-receiving diaphragm 82, the second housing passage 84, and passage 63 are filled with oil, as is the space where the second surface 21b is exposed.

[0052] The space where the first surface 21a is exposed and the space where the second surface 21b is exposed are separated and do not communicate with each other. Therefore, when the pressure received by the first pressure-receiving diaphragm 81 from the medium is different from the pressure received by the second pressure-receiving diaphragm 82 from the medium, the pressure received by the first surface 21a and the pressure received by the second surface 21b will be different, causing the diaphragm 21 of the chemical sensor 1 to deform. By detecting the deformation of the diaphragm 21 with the strain sensor 3, the differential pressure, which is the difference between the pressure received by the first pressure-receiving diaphragm 81 from the medium and the pressure received by the second pressure-receiving diaphragm 82 from the medium, can be measured.

[0053] On the other hand, in the measuring device 6, since the storage film 4 is provided on the first surface 21a or the second surface 21b of the diaphragm 21 of the chemical sensor 1, the concentration of a specific substance in the medium in contact with that surface can also be measured. The storage film 4 stores not only specific substances in a gaseous state, but also molecules or ions of specific substances dissolved in liquids such as oil. Therefore, even when oil is in contact with the storage film 4, as in the measuring device 6, the concentration of a specific substance can be measured.

[0054] Furthermore, as described above, in the chemical sensor 1, the oscillator 3b is located inside the vacuum chamber 3a covered by the cavity 3a1, making it possible to stably and accurately measure the concentration of a specific substance contained in a medium even if the state of the medium is different. Therefore, it is possible to measure the concentration of a specific substance even in a medium in which liquid and gas coexist. This makes it possible to stably measure the concentration even when bubbles are generated in the liquid medium. For example, bubbles are generated when a part of the liquid medium changes state, or when the amount of substance dissolved in the liquid medium exceeds the soluble amount.

[0055] The measuring device 6 can measure both differential pressure and the concentration of a specific substance by switching between a mode that measures the differential pressure of the medium in contact with the first pressure-receiving diaphragm 81 and the second pressure-receiving diaphragm 82 (differential pressure measurement mode) and a mode that measures the concentration of a specific substance in the medium (oil) in contact with the surface on which the storage film 4 is provided (concentration measurement mode). The processing performed by the calculation unit that processes the signals acquired from the chemical sensor 1 differs between the differential pressure measurement mode and the concentration measurement mode.

[0056] In the following explanation, we will assume that the specific substance is hydrogen. Hydrogen may be mixed into the oil filling the inside of the housing 8, having permeated through the first pressure-receiving diaphragm 81 and the second pressure-receiving diaphragm 82. When hydrogen is mixed into the oil, it will dissolve in the oil up to its soluble limit, but if it exceeds this limit, hydrogen bubbles will be generated. If the mixed hydrogen is able to dissolve in the oil, there will be no problem in measuring the differential pressure. However, if the amount of hydrogen exceeds the soluble limit and bubbles are generated, the pressure received by the first pressure-receiving diaphragm 81 and the second pressure-receiving diaphragm 82 will no longer be accurately transmitted to the diaphragm 21 of the chemical sensor 1. In other words, the generation of bubbles in the oil may cause problems such as the sudden inability to measure pressure.

[0057] Here, if hydrogen is mixed into the oil while the device is operating in differential pressure measurement mode, the hydrogen is absorbed by the storage membrane 4, causing a change in the volume of the storage membrane 4. This change in the volume of the storage membrane 4 causes the diaphragm 21 to deform, resulting in an abnormal differential pressure measurement. When this abnormal value is detected, switching to the concentration measurement mode and measuring the hydrogen concentration makes it possible to foresee the generation of bubbles and the inability to measure the differential pressure.

[0058] The detection of hydrogen contamination in oil can be performed using either one measuring device 6 or two measuring devices 6. First, the procedure for measuring hydrogen concentration using one measuring device 6 will be explained.

[0059] Figure 8 is a flowchart showing the procedure for measuring hydrogen concentration using a single measuring device. First, the measuring device 6 operates in differential pressure measurement mode to measure the differential pressure (step S1). Specifically, the differential pressure is calculated based on the resonance frequencies of the oscillators 3b of the first strain sensor 31 and the second strain sensor 32, and the resistance value of the silicon substrate 2.

[0060] Next, the zero point value of the calculated differential pressure is checked (Step S2). If the zero point value of the differential pressure is normal (Step S2, Yes), the operation continues in differential pressure measurement mode.

[0061] On the other hand, if there is an abnormality in the zero point value of the differential pressure (step S2, No), the operation of the measuring device 6 is switched to the concentration measurement mode and the hydrogen concentration is measured (step S3). In the concentration measurement mode, as in the differential pressure measurement mode, the hydrogen concentration of the oil is calculated based on the resonant frequency of the oscillator 3b and the resistance value of the silicon substrate 2.

[0062] If the calculated hydrogen concentration is close to the amount of hydrogen that can dissolve in the oil, it is foreseeable that bubbles will soon form in the oil, making differential pressure measurement impossible. Thus, by implementing the chemical sensor 1 in the measuring device 6, it is possible to foresee the occurrence of problems caused by hydrogen contamination and take preventative measures. Furthermore, even if differential pressure measurement becomes impossible, calculating the hydrogen concentration makes it possible to determine whether or not the cause of the inability to measure differential pressure is due to hydrogen contamination.

[0063] Next, we will describe the procedure for measuring hydrogen concentration using two measuring devices 6. Figure 9 is a flowchart showing the procedure for measuring hydrogen concentration using two measuring devices.

[0064] First, the differential pressure calculated by each of the two measuring devices 6 is obtained (step S21). The calculation of the differential pressure in the measuring device 6 is performed using the same procedure as in step S1 shown in Figure 9. Next, the differential pressure calculated by each of the two measuring devices 6 is compared (step S22). If the differential pressure calculated by each of the two measuring devices 6 matches (step S23, Yes), the operation in differential pressure measurement mode continues.

[0065] On the other hand, if there is an error in the differential pressure calculated by each of the two measuring devices 6 (step S23, No), it is possible that hydrogen has been absorbed into the absorption membrane 4 by one of the measuring devices 6, so the operation of the measuring device 6 is switched to concentration measurement mode.

[0066] In concentration measurement mode, the hydrogen concentration is calculated based on the difference in differential pressure calculated by each of the two measuring devices 6 (step S24).

[0067] If the calculated hydrogen concentration is close to the amount of hydrogen that can dissolve in the oil, it is foreseeable that bubbles will soon form in the oil, making differential pressure measurement impossible. Thus, by implementing the chemical sensor 1 in the measuring device 6, it is possible to foresee the occurrence of problems caused by hydrogen contamination and take preventative measures. Furthermore, even if differential pressure measurement becomes impossible, calculating the hydrogen concentration makes it possible to determine whether or not the cause of the inability to measure differential pressure is due to hydrogen contamination.

[0068] Furthermore, the storage film 4 may be formed on both the first surface 21a and the second surface 21b. In the measuring device 6, as described above, the space where the first surface 21a of the silicon substrate 2 is exposed and the space where the second surface 21b is exposed are separated. That is, the medium in contact with the first surface 21a and the medium in contact with the second surface 21b are different. If the storage film 4 is formed on both the first surface 21a and the second surface 21b, it becomes possible to measure the concentration based on the change in volume of the storage film 4, regardless of which medium is mixed with hydrogen.

[0069] 〔others〕 Some examples of the combinations of technical features that will be disclosed are listed below.

[0070] (1) A silicon substrate on which a diaphragm is formed, A strain sensor provided on the silicon substrate, The diaphragm is provided with a storage membrane whose volume changes when it absorbs a specific substance, The strain sensor is a chemical sensor comprising a vacuum chamber formed in the diaphragm and an oscillator formed inside the vacuum chamber.

[0071] (2) The diaphragm has a first surface on which the strain sensor is provided and a second surface which is the back surface of the first surface, The storage film is the chemical sensor described in (1) above, provided on the second surface.

[0072] (3) The chemical sensor according to (1) or (2) above, wherein the drive method for exciting the vibrator is an electromagnetic drive.

[0073] (4) The chemical sensor according to any one of (1) to (3) above, further comprising a permeability-preventing film provided on the second surface and covering the second surface to prevent the permeation of the specific substance.

[0074] (5) The chemical sensor according to any one of (1) to (4) above, wherein the permeability-preventing film is also provided on the first surface to prevent the permeation of the specific substance.

[0075] (6) The diaphragm has a first surface on which the strain sensor is provided and a second surface which is the back surface of the first surface, The storage film is provided on the first surface and is the chemical sensor described in (1) above.

[0076] (7) The chemical sensor according to (1) or (6) above, wherein the drive method for exciting the vibrator is an electrostatic drive type.

[0077] (8) The chemical sensor according to (6) or (7) above, further comprising a permeability-preventing film provided on the first surface and covering the first surface to prevent the permeation of the specific substance.

[0078] (9) The chemical sensor according to any one of (6) to (8) above, wherein the permeability-preventing film is also provided on the second surface to prevent the permeation of the specific substance.

[0079] (10) The chemical sensor according to any one of (1) to (9) above, wherein the specific substance absorbed by the absorption film is hydrogen.

[0080] (11) A chemical sensor as described in any one of (2) to (9) above, The system comprises a housing that houses the chemical sensor inside, The housing is provided with a first pressure-receiving diaphragm, a second pressure-receiving diaphragm, a first housing passage connecting the inside of the first pressure-receiving diaphragm to the space where the first surface is exposed, and a second housing passage connecting the inside of the second pressure-receiving diaphragm to the space where the second surface is exposed. A measuring device in which the space where the first surface is exposed, the first housing passage, the space where the second surface is exposed, and the second housing passage are filled with oil. [Explanation of Symbols]

[0081] 1. Chemical Sensor 2. Silicon substrate 21 Diaphragm 21a 1st page 21b 2nd side 22 Rim section 3. Strain Sensor 3a Vacuum chamber 3a1 Cavity 3b vibrator 31. First strain sensor 32. Second strain sensor 4. Absorption film 51 Wiring 52 terminals 6. Measuring device 61 Pedestal 62 base 63 aisle 64 Hermetic terminals 65 Bonding Wire 66 caps 67 York 68 Magnets 69 Magnetic Holder 8 cabinets 81 First pressure-receiving diaphragm 82 Second pressure-receiving diaphragm 83 First cabinet aisle 84 Second cabinet aisle

Claims

1. A silicon substrate on which a diaphragm is formed, A strain sensor provided on the silicon substrate, The diaphragm is provided with a storage membrane whose volume changes when it absorbs a specific substance, The strain sensor is a chemical sensor comprising a vacuum chamber formed in the diaphragm and an oscillator formed inside the vacuum chamber.

2. The diaphragm has a first surface on which the strain sensor is provided and a second surface which is the back surface of the first surface. The chemical sensor according to claim 1, wherein the storage film is provided on the second surface.

3. The chemical sensor according to claim 2, wherein the drive method for exciting the vibrator is an electromagnetic drive method.

4. The chemical sensor according to claim 2, further comprising a permeability-preventing film provided on the second surface and covering the second surface to prevent the permeation of the specific substance.

5. The chemical sensor according to claim 4, wherein the permeability-preventing film is also provided on the first surface to prevent the permeation of the specific substance.

6. The diaphragm has a first surface on which the strain sensor is provided and a second surface which is the back surface of the first surface. The chemical sensor according to claim 1, wherein the storage film is provided on the first surface.

7. The chemical sensor according to claim 6, wherein the drive method for exciting the vibrator is an electrostatic drive method.

8. The chemical sensor according to claim 6, further comprising a permeability-preventing film provided on the first surface and covering the first surface to prevent the permeation of the specific substance.

9. The chemical sensor according to claim 8, wherein the permeability-preventing film is also provided on the second surface to prevent the permeation of the specific substance.

10. The chemical sensor according to any one of claims 1 to 9, wherein the specific substance absorbed by the absorption membrane is hydrogen.

11. The chemical sensor according to claim 2, The system comprises a housing that houses the chemical sensor inside, The housing is provided with a first pressure-receiving diaphragm, a second pressure-receiving diaphragm, a first housing passage connecting the inside of the first pressure-receiving diaphragm to the space where the first surface is exposed, and a second housing passage connecting the inside of the second pressure-receiving diaphragm to the space where the second surface is exposed. A measuring device in which the space where the first surface is exposed, the first housing passage, the space where the second surface is exposed, and the second housing passage are filled with oil.

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