JP2024015656A - Gas physical quantity detection device and gas physical quantity detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas physical quantity detection device and a gas physical quantity detection method that can improve performance by using a thermopile, widely used for temperature measurement, to measure physical quantities such as a degree of vacuum.

SOLUTION: A gas physical quantity detection device includes a substrate 11 having a cavity 13, a membrane section 14 formed on the substrate 11, a thermopile 1 including a series of thermocouples having a plurality of hot junction sections 15 and cold junction sections 16 disposed on the membrane section 14, and a power supply unit 3 that supplies power to the series of thermocouples of the thermopile 1 and causes the thermopile 1 to self-heat, wherein, the thermopile 1 detects changes in the amount of heat loss depending on the thermal conductivity of the atmosphere.

SELECTED DRAWING: Figure 2

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a gas physical quantity detection device and a gas physical quantity detection method.

BACKGROUND ART Conventionally, heat conduction vacuum gauges have been used to measure pressure in vacuum in order to control and improve the quality of products by controlling the vacuum environment to an appropriate state in production equipment such as thin film forming processes. Heat conduction vacuum gauges are also used to measure the pressure of vacuum insulation materials for buildings, medicine transportation bags, etc.

There are Pirani vacuum gauges and thermocouple vacuum gauges as total pressure gauges that utilize this pressure dependence of heat conduction. A Pirani vacuum gauge is a vacuum gauge that measures pressure by detecting temperature changes due to heat conduction of gas in an electrically heated platinum or tungsten filament as changes in its electrical resistance. A thermocouple vacuum gauge, like the Pirani vacuum gauge, is a vacuum gauge that heats a filament with electricity and measures the temperature change of the filament caused by gas with a thermocouple to determine the pressure.

Although these vacuum gauges have a simple structure, they have problems in that stability and accuracy cannot be expected, and they also have poor temporal response. Furthermore, since a heating element such as a filament is required, there is also the problem that the number of parts increases.

By the way, there is a thermopile, which is one type of thermal infrared detection element and utilizes thermoelectromotive force generated by the Seebeck effect. A thermopile generates a thermoelectromotive force proportional to the amount of incident energy of Joule infrared rays, operates at room temperature, has spectral sensitivity characteristics that are independent of wavelength, and can obtain a voltage output according to the amount of incident energy. It is widely used for temperature measurement due to its low cost and long life.

On the other hand, a cantilever method is used to measure physical quantities such as the flow rate, velocity, degree of vacuum, and concentration of gas or liquid surrounding the thermocouple by passing a current through the thermocouple itself and making it act as a heater rather than self-heating due to heat. A temperature measuring device has been proposed (for example, see Patent Document 4).

Japanese Unexamined Patent Publication No. 48-51675 Japanese Unexamined Patent Publication No. 49-54078 JP2015-227880A Patent No. 5076235 Patent No. 4888861

However, the cantilever method and micro air bridge method, which are conventional proposals in which thermocouples are mounted on a cantilever, have the disadvantage that the number of thermocouples cannot be increased, and because the combined resistance of thermocouples is small, a large current is required to obtain a certain degree of sensitivity. This results in problems such as increased power consumption. As described above, the performance is not satisfactory, and further improvement in performance compared to the conventional method is expected.

Embodiments of the present invention utilize a thermopile, which is widely used for temperature measurement using infrared rays, to measure physical quantities such as the degree of vacuum while minimizing the effects of infrared rays, and use a gas that can improve performance. An object of the present invention is to provide a physical quantity detection device and a gas physical quantity detection method.

A gas physical quantity detection device according to an embodiment of the present invention includes a substrate having a cavity, a membrane portion formed on the substrate, and a thermoelectric device having a plurality of hot junction portions and cold junction portions disposed on the membrane portion. and a power supply unit that supplies power to the thermopile of the thermopile to self-heat the thermopile, the thermopile has a heat loss amount that changes depending on the thermal conductivity of the atmosphere. It is characterized by detecting.

The gas physical quantity detection device of this embodiment can be applied to detect atmospheric pressure and wind velocity such as the degree of vacuum of a gas, and gas concentration in a thermal conduction type gas sensor. The physical quantity of the atmosphere to be measured is not particularly limited.

Further, the gas physical quantity detection method according to the embodiment of the present invention includes a substrate having a cavity, a membrane section formed on the substrate, and a plurality of hot junction sections and cold junction sections disposed on the membrane section. a thermopile having a thermopile having a thermopile; and a power supply unit that supplies power to the thermopile of the thermopile to self-heat the thermopile, the power supply unit supplies power to the thermopile, and the thermopile is heated. It is characterized by comprising the steps of self-heating, detecting a temperature change in the thermopile as a change in electromotive force, and outputting the pressure of the atmosphere to be measured as a measurement result based on the change in electromotive force.

According to the embodiments of the present invention, it is possible to provide a gas physical quantity detection device and a gas physical quantity detection method that use a thermopile to measure a physical quantity such as a degree of vacuum and can improve performance.

1 is a perspective view showing a gas physical quantity detection sensor according to an embodiment of the present invention. FIG. 3 is a perspective view showing the gas physical quantity detection sensor with the cap removed. It is a sectional view showing the same gas physical quantity detection sensor. FIG. 2 is a perspective view showing a partially cut away thermopile in the gas physical quantity detection sensor. It is a typical explanatory view for explaining the thermopile in the gas physical quantity detection sensor. 5 is a schematic cross-sectional view taken along line XX in FIG. 4. FIG. FIG. 2 is a wiring diagram showing a schematic wiring state of the gas physical quantity detection sensor. It is a flowchart which shows the operation of the same gas physical quantity detection sensor. It is a graph showing the relationship between atmospheric pressure and output voltage in the atmospheric pressure physical quantity detection device. It is a table showing the relationship between the applied voltage and temperature. It is a table showing a comparison of characteristics between the present embodiment and a comparative example.

Hereinafter, a gas physical quantity detection device and a gas physical quantity detection method according to an embodiment of the present invention will be described with reference to FIGS. 1 to 7. FIG. 1 is a perspective view of a gas physical quantity detection sensor, FIG. 2 is a perspective view of the gas physical quantity detection sensor with the cap removed, and FIG. 3 is a cross-sectional view of the gas physical quantity detection sensor. FIG. 4 is a perspective view showing a part of the thermopile cut away, FIG. 5 is a schematic explanatory view for explaining the thermopile, and FIG. 6 is a schematic diagram along the line XX in FIG. 7 is a cross-sectional view, and FIG. 7 is a schematic wiring diagram of the gas physical quantity detection sensor. Moreover, FIG. 8 is a flow cheat showing the operation of the gas physical quantity detection sensor. In addition, in each figure, the scale of each member is changed as appropriate for explanation purposes in order to make each member a recognizable size. Further, the same or corresponding parts are given the same reference numerals, and redundant explanations will be omitted.

The gas physical quantity detection device of this embodiment is equipped with an atmospheric pressure physical quantity detection sensor, and the atmospheric pressure physical quantity detection sensor uses a thermopile with a membrane structure to detect the pressure of the atmosphere by utilizing the fact that the thermal conductivity of the atmosphere changes depending on the pressure. It is a thermal conduction type atmospheric pressure detection sensor. The thermopile is self-heated to detect changes in heat loss according to the thermal conductivity of the atmosphere, and this temperature change is detected as a change in thermoelectromotive force.
As shown in FIGS. 1 and 2, an atmospheric pressure detection sensor 10 as a gas physical quantity detection sensor includes a thermopile 1 and a package 2 that covers the thermopile 1.

As shown in FIGS. 2 and 4, the thermopile 1 has a substantially square shape with a length of 1 mm or less on each side, and an insulating film 12 made of silicon dioxide or silicon nitride is provided on one surface of a substrate 11. A cavity 13 is formed from the back side of the substrate 11 by anisotropic etching. Substrate 11 is made of silicon material.

A membrane portion 14 made of an insulating film 12 is formed on the cavity portion 13 . Further, a hot junction part 15 of a thermocouple made of different metals is arranged on the membrane part 14, and a cold junction part 16 is arranged in the heat sink part 17 around the membrane part 14, and a plurality of these thermocouples are connected in series. forming a thermopile connected to the Further, an infrared absorber 18 is placed on the hot junction portion 15 of the thermopile. Furthermore, electrode pads 19 are formed on the heat sink portion 17 to which lead wires of the thermopile are connected. It is preferable to form 60 or more pairs of such hot contact portions 15 and cold contact portions 16, and in this embodiment, for example, 96 pairs of hot contact portions 15 and cold contact portions 16 are formed.

The cantilever method and micro air bridge method, which are conventional proposals in which thermocouples are mounted on a cantilever, have the disadvantage that the number of thermocouples cannot be increased, and because the combined resistance of the thermocouples is small, the current tends to be large to obtain a certain degree of sensitivity. As a result, there is a problem that power consumption increases. In this embodiment, for example, 96 pairs of hot junctions 15 and cold junctions 16 are formed, so that the combined resistance value is approximately 65 kΩ, so the current value during operation is extremely small, and as a result, power consumption is reduced. It becomes 1.5mW. The conventional method has a resistance value of 20Ω and power consumption of 10mW.

Next, the connection state of each thermoelectric element will be explained with reference to a schematic explanatory diagram in FIG. 5. On the insulating film 12, that is, on the membrane part 14, an n-type polycrystalline silicon layer 20a and a metal thin film layer 20b made of aluminum or the like are formed radially around the center of the membrane part 14. The hot contact portion 15 of the n-type polycrystalline silicon layer 20a is sequentially connected to the cold contact portion 16 of the adjacent n-type polycrystalline silicon layer 20a through the metal thin film layer 20b. In this way, the hot junction part 15 of the n-type polycrystalline silicon layer 20a is sequentially and continuously connected to the cold junction part 16 of the adjacent n-type polycrystalline silicon layer 20a by the metal thin film layer 20b, and the thermoelectric element is connected to the metal thin film layer 20b. They are connected in series at layer 20b to form a thermoelectric element array. These final ends are connected to electrode pads 19 as shown in FIGS. 2 and 4.

As shown in FIG. 6, an n-type polycrystalline silicon layer 20a and a metal thin film layer 20b are stacked on the membrane portion 14 with an insulating film 12 in between. Further, an infrared absorber 18 is formed at the center of the membrane portion 14 . The infrared absorber 18 is in the form of a film, and is made of polyimide resin, vinyl resin, phenol resin, epoxy resin, acrylic resin, synthetic rubber, or the like. Such a thermopile 1 can be manufactured with a MEMS structure from a silicon semiconductor material using a MEMS (Micro Electro Mechanical System) technology using a semiconductor processing process.

Next, as shown in FIGS. 1 to 3, the package 2 is an envelope that accommodates and covers the thermopile 1, and includes a cap 21 that is made of a heat conductive metal and has a substantially cylindrical shape, and a cap 21 that is also made of a metal and has a substantially cylindrical shape. The stem 22 has a substantially disk shape.

Specifically, the cap 21 includes a shielding portion 21a and a side wall portion 21b. The shielding part 21a faces the infrared absorber 18, which is the light receiving part of the thermopile 1, and has a function of shielding and preventing infrared rays from entering the thermopile 1, that is, from receiving light. Further, an opening 23 is formed in the side wall portion 21b. The opening 23 has the function of making the atmosphere inside and outside the cap 21 the same. The opening 23 is a circular through hole that penetrates and communicates between the inside and outside of the cap 21 . The size of the cap 21 is, for example, an axial length of 4 mm to 6 mm, and a diameter of 5 mm to 7 mm. The opening 23 has a diameter of 0.5 mm to 1.5 mm, preferably 1 mm, and is formed horizontally with respect to the side wall 21b. Specifically, the opening 23 is formed closer to the thermopile 1 than the center in the axial direction, at the same height as the thermopile 1, and in a direction intersecting the axial direction, preferably in a direction perpendicular to the axial direction. This makes it possible to reduce the influence of external light.

Furthermore, a thermistor Ct for temperature compensation is mounted on the stem 22 to improve detection accuracy. Further, four lead terminals 24 are attached to the stem 22 so as to pass through the stem 22 vertically, and the lead terminals 24 are connected to the electrode pad 19 of the thermopile 1 and the thermistor Ct for temperature compensation. As a result, driving power is supplied to the thermopile 1 and the thermistor Ct for temperature compensation, and detection signals are sent out.

Next, the connection state of the atmospheric pressure detection sensor 10 (thermopile 1) in the gas physical quantity detection device will be described with reference to FIG. Note that the thermistor Ct for temperature compensation is omitted. A power supply section 3 is connected in series to the thermopile 1, and an output terminal is connected between them, so that the electromotive force of this output terminal can be detected as an output voltage Vout.

The power supply unit 3 is a constant current source, and has a function of supplying power to the thermopile 1 in the atmospheric pressure detection sensor 10 to cause it to self-heat by supplying power to the thermopile 1 of the atmospheric pressure detection sensor 10 to cause a constant current to flow therethrough. This self-heating allows the atmospheric pressure detection sensor 10 to detect atmospheric pressure without using a heating element such as a filament as in the conventional case.

Next, an outline of the operation of the atmospheric pressure detection sensor 10 will be explained with reference to FIG. The atmospheric pressure detection sensor 10 is placed in the atmosphere to be measured. When the atmospheric pressure detection sensor 10 is activated (step S1), power is supplied from the power supply section 3 to the thermopile 1 of the atmospheric pressure detection sensor 10, and the thermopile 1 is self-heated (step 2). The heat dissipation state of the self-heated thermopile 1 changes depending on the thermal conductivity of the atmosphere to be measured, that is, the amount of heat loss changes (step 3). The output voltage Vout is detected by using this temperature change of the thermopile 1 as a change in electromotive force (step 4). The output voltage Vout is input to a control processing means such as a microcomputer (not shown), and is subjected to arithmetic processing, and the pressure of the atmosphere to be measured is output as a detection output, which is then output as a measurement result (step 5).

According to the configuration of the atmospheric pressure detection sensor 10 as described above, the thermopile 1 is covered with the cap 21 in which the opening 23 is formed in the side wall portion 21b. placed in a state. Furthermore, in this case, the thermopile 1 is protected by the cap 21, and the shielding portion 21a of the cap 21 blocks infrared rays from entering the thermopile 1, so that the influence of external disturbances can be suppressed, and detection accuracy is improved. be able to. Therefore, the cap 21 protects the thermopile 1 and allows the atmosphere to circulate, but has the function of blocking infrared rays from entering the thermopile 1.

Note that when the thermopile 1 is used to detect atmospheric pressure, the infrared absorber 18 is not an essential component, but the presence of the red infrared absorber 18 prevents dirt from adhering to the thermopile 1 and improves the signal. The effect of reducing fluctuations can be expected.
Moreover, the thermopile 1 of this embodiment has a membrane structure. The membrane structure has the following main advantages over the cantilever method described above.

That is, the membrane part 14 has a flat shape and is supported by the substrate 11 on its entire circumference, and the thermopile 1 is formed on this membrane part 14. Therefore, the membrane portion 14 is mechanically and thermally stable, and it is expected that output stability will be ensured. In addition, since a large number of thermocouples can be formed on the membrane portion 14, the response speed tends to be faster.
Next, the output characteristics of the atmospheric pressure detection sensor 10 in the gas physical quantity detection device will be described with reference to FIGS. 9 to 11.
[Atmospheric pressure and voltage]

FIG. 9 shows the relationship between the atmospheric pressure in the atmosphere to be measured and the output voltage, and the change in the output voltage when the atmospheric pressure is changed is measured. In the figure, the horizontal axis shows atmospheric pressure (Pa), and the vertical axis shows voltage (v).

Measurement was performed by constant current driving by applying currents of 1 mA, 0.6 mA, 0.3 mA, and 0.15 mA from a constant current source. The measurement results show that the output voltage decreases as the atmospheric pressure increases. This confirms that changes in atmospheric pressure can be detected by constant current driving.
[Applied voltage and temperature]

FIG. 10(a) shows the applied voltage and power consumption when a constant current is passed through the thermopile 1, and FIG. 10(b) shows the voltage and power consumption when a constant current is passed through the thermopile 1 and a voltage is applied. It shows data obtained by measuring the temperature of the thermopile 1 with a thermo camera before application. This shows that changes in temperature rise can be measured with less power consumption.
[This embodiment and comparative example]

FIG. 11 shows a comparison of characteristics between this embodiment and a comparative example. A comparative example has the characteristics shown in the prior art document Patent Document 4. The case where the atmospheric pressure is changed from atmospheric pressure to 10 Pa is shown.

From this comparison, the gas physical quantity detection device of this embodiment can improve performance. Specifically, it has a fast time constant, low power consumption, and good sensitivity, allowing detection with a small temperature rise.

Note that the gas physical quantity detection device of this embodiment is not limited to being applied to the measurement of atmospheric pressure. For example, it is applicable to a thermal conduction type gas sensor that detects gas concentration, and wind sensing such as wind speed and air volume.

The present invention is not limited to the configuration of the embodiments described above, and various modifications can be made without departing from the gist of the invention. Further, the above embodiments are presented as examples, and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made. These embodiments and their modifications are included within the scope and gist of the invention, as well as within the scope of the invention described in the claims and its equivalents.

1...Thermopile 2...Package 3...Power supply unit 10...Atmospheric pressure detection sensor 11...Substrate 12...Insulating film 13...Cavity Part 14...Membrane part 15...Hot contact part 16...Cold contact part 17...Heat sink part 18...Infrared absorber 19...Electrode pad 21... - Cap 21a... Shielding part 21b... Side wall part 23... Opening 24... Lead terminal

Claims (8)

A thermopile comprising a substrate having a cavity, a membrane formed on the substrate, and a thermopile having a plurality of hot junctions and cold junctions disposed on the membrane;
a power supply unit that supplies power to the thermopile of the thermopile and causes the thermopile to self-heat;
A gas physical quantity detection device, wherein the thermopile detects a change in heat loss according to thermal conductivity of the atmosphere. The gas physical quantity detection device according to claim 1, wherein the power supply section is a constant current source. The gas physical quantity detection device according to claim 1 or 2, wherein the thermopile is manufactured by MEMS technology. 3. The gas physical quantity detection device according to claim 1, wherein the thermopile is covered with a cap, and the cap has a horizontal opening. The gas physical quantity detection device according to claim 4, wherein the cap is made of metal. 3. The gas physical quantity detection device according to claim 1, further comprising a thermistor for temperature compensation. 3. The gas physical quantity detection device according to claim 1, wherein the thermopile includes 60 or more pairs of hot junctions and cold junctions. A thermopile comprising: a substrate having a cavity; a membrane formed on the substrate; and a thermopile arranged on the membrane and having a plurality of hot junctions and cold junctions; and a power supply unit that supplies power to the pair of columns and causes the thermopile to self-heat,
supplying power from the power supply unit to the thermopile to self-heat the thermopile;
detecting a temperature change in the thermopile as a change in electromotive force;
outputting the pressure of the atmosphere to be measured as a measurement result based on the change in the electromotive force;
A method for detecting a gas physical quantity, comprising:

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