JPH08210977A - Infrared ray type gas analyzing device - Google Patents

Abstract

PURPOSE: To provide an infrared ray type gas analyzing device which has high analyzing precision and good analyzing responsiveness even when it is downsized. CONSTITUTION: This infrared ray type gas analyzing device has a light source, a sample cell and a detector. At least either one of the sample cell 11 and the detector 16 is formed of a connected body formed by laminating and connecting worked silicon plates 1, 2, 3 together, a measuring-side gas passage 12A and detecting chamber 20A and a comparing-side gas passage 12B and a detecting chamber 20B are provided in the thickness direction in parallel to each other. It is particularly desired that the sample cell 11 and the detector 16 are integrally formed of a connected body formed by laminating and connecting three worked silicon monocrystal plates 1, 2, 3 together, and a differential pressure sensor 1 capable of measuring the differential pressure between the measuring-side and comparing-side detecting chambers 20A, 20B is formed on the plate 2 in the center part forming a bulkhead.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared gas analyzer which has a high analysis accuracy and a good analysis response even if it is downsized.

[0002]

2. Description of the Related Art Conventionally, an infrared gas analyzer is generally used for analysis of pollution gas and gas analysis of industrial furnaces. Gas molecules composed of different atoms such as CO, CO ₂ , CH ₄ , SO _{4 and} NO _x have their own vibrations. When such a molecule is irradiated with infrared rays by continuously changing the wavelength, infrared rays having the same frequency as the natural vibration of the molecule are absorbed and a spectrum corresponding to the structure of the molecule is obtained. A method of analyzing the structure of a molecule from this spectrum is called an infrared absorption spectrum method, and the infrared gas analysis is based on this method, and quantitatively and qualitatively analyzes gas molecules composed of different atoms as described above.

As a conventional infrared gas analyzer, for example, one having a structure shown in a schematic vertical sectional view of FIG. 3 is widely known. This gas analyzer basically includes light sources 54A and 54B, a sample cell 51, and a detector 56. The sample cell is usually an aluminum body 51A.
Two stainless steel pipes 51B are longitudinally arranged in parallel with each other at predetermined intervals in the longitudinal direction, one of the pipes is used as a measurement gas passage 52A, and the other is used as a reference gas passage 52B. Has a structure in which infrared transmitting windows 53 and 53 'made of calcium fluoride or sapphire are attached. Further, the detector 56 has two detection chambers, a measurement side detection chamber 60A and a comparison side detection chamber 60B, which are formed of a metal such as aluminum or an aluminum alloy or stainless steel, and a metal thin film capacitor 59 is provided between them. It is provided. In addition, both detection chambers 60A and 6A
A measurement component or a gas having the same infrared absorption band as that component is enclosed in 0B. In the figure, reference numeral 58 is an infrared transmitting window portion, and reference numeral 55 is an optical chopper.

In the infrared gas analyzer having such a structure, the infrared rays emitted from the two light sources 54A and 54B become intermittent light by the chopper 55, and the infrared ray transmitting window portion 53 of the sample cell 51 and the gas passage. 52A, 5
The detector 56 is reached via 2B. Comparative gas passage 52B
Inert gas is present in the reference gas passage 52.
In B, irradiation infrared rays are not absorbed. On the other hand, when the measurement gas flowing through the measurement gas passage 52 contains the component to be measured, infrared absorption is caused by this component. Therefore,
As described above, the absorption of infrared rays in the measurement side detection chamber 60A and the comparison side detection chamber 60B in which the measurement component or the gas having the same infrared absorption band as that component is sealed becomes smaller on the measurement side than on the comparison side. The difference in heat energy is
The pressure difference between the two chambers results in the displacement of the membrane capacitor 59. This capacitance change is detected, and after signal processing, it is taken out as an output signal.

However, when the sample cell and the detector are made of metal such as aluminum or aluminum alloy and stainless steel as described above, a welding technique or the like is required, and downsizing is structurally difficult. Even if the size can be reduced, there is a high possibility that the performance will be deteriorated.

The present invention has high analysis accuracy even if it is downsized,
It is an object of the present invention to provide an infrared gas analyzer having a good analysis response.

[0007]

In order to achieve the above object, an infrared gas analyzer according to the present invention comprises at least one of a sample cell and a detector in which processed silicon plate materials are laminated and joined. Formed by the joined body,
It is characterized in that a gas passage or detection chamber on the measurement side and a gas passage or detection chamber on the comparison side are provided in parallel in the thickness direction.

In the infrared gas analyzer, in particular, a sample cell and a detector are constructed by laminating and bonding three processed silicon single crystal plate materials, and both sides of the plate material at the center of the bonded body are joined. A measurement gas passage and a measurement-side detection chamber, and a comparison gas passage and a comparison-side detection chamber are formed on the two joint surface portions formed on the surfaces, on both sides of the central plate member,
Moreover, it is preferable that a pressure sensor capable of measuring the differential pressure between the measurement side detection chamber and the comparison side detection chamber is formed on the plate material at the central portion which becomes the partition wall.

[0009]

In the present invention, at least one of the sample cell and the detector is formed by laminating and joining the processed silicon plate materials, and the gas passage on the measurement side or the detection chamber and the comparison side are formed in the thickness direction. The gas passage or the detection chamber is provided in parallel. For example, on a surface of a single crystal silicon chip (silicon wafer) having a thickness of about 1 mm, a recess having a U-shaped or semi-elliptical cross section is formed by anisotropic etching or the like, and two pieces of the same shape are formed. By bonding another silicon chip, which serves as a partition, to the central portion of the silicon chip, the sample cell or detection chamber can be obtained which is smaller and lighter.

By using the laminated joined body of the silicon plate materials processed in this way, the size can be reduced more accurately than the conventional detector, and the formation of the sample cell and the detection chamber and the formation of the pressure sensor etc. can be performed by the semiconductor technology. Since it can be performed simultaneously by the micromachining technology centering on the anisotropic etching, it is advantageous not only for downsizing but also for mass productivity.

Further, if the sample cell and the detector are formed by a laminated assembly of three processed silicon substrates, and the sample cell portion and the detector are integrated, the size can be further reduced. Moreover, the number of manufacturing steps can be significantly reduced. Further, when a pressure sensor capable of measuring the differential pressure between the measurement chamber on the measurement side and the detection chamber on the comparison side is formed on the plate member at the central portion which becomes the partition wall, a highly accurate analyzer can be obtained with a simpler configuration.

[0012]

EXAMPLES The present invention will be described in detail below based on examples. 1A and 1B show the configurations of a sample cell and a detector of an infrared gas analyzer according to an embodiment of the present invention. FIG. 1A is a perspective view, and FIG. 1B is a longitudinal sectional view. Figure 1
(C) is a cross-sectional view in the width direction.

This gas analyzer is a double-beam type infrared gas analyzer, and is basically a light source 14A,
14B, the sample cell 11, and the detector 16. As shown in FIG. 1, the sample cell 11 and the detection chamber 16 in this apparatus are each processed into a predetermined shape, for example, three single crystal silicon wafers 1 each having a length of 60 mm, a width of 30 mm, and a thickness of 1.0 mm. It is formed by laminating and joining 2 and 3. More specifically, among these three single-crystal silicon wafers, the first silicon wafer 1 and the third silicon wafer 3 located outside each have the crystal plane of the surface as the (100) plane, Second located in the center
On each of the mirror-finished bonding surfaces facing the silicon wafer 2 of FIG. 1, two anisotropic concave grooves 4A and 4B to 5A and 5B extending along the length direction are formed, for example, by anisotropic etching. They are integrally formed by micromachining technology. In addition, among the anisotropic concave grooves, through holes penetrating in the thickness direction of the wafer are formed in the vicinity of both longitudinal end portions of the grooves 4A and 5A that will form the gas passage portions 12A and 12B of the sample cell. 6A, 6
B to 7A and 7B are formed. These will respectively constitute a gas inlet and a gas outlet for each gas passage of the sample cell. Further, in the first silicon wafer 1, a feedthrough hole 8 for forming a wiring is further formed behind the groove 4B which constitutes the detection chamber in the longitudinal direction.

Further, the second silicon wafer 2 located at the central portion is formed by the anisotropic concave grooves 4B and 5B in the first and third silicon wafers when laminated and bonded. Similarly, anisotropic through holes are formed in the detection chambers 20A and 20B by anisotropic etching or the like, and a general semiconductor process is used for the detection chambers on the measurement side and the comparison side. A pressure-sensitive portion (differential pressure sensor) 19 of a pressure sensor capable of measuring the differential pressure is formed.

Then, these silicon wafers 1, 2,
3 are laminated and bonded so that their ends are aligned, and the two gas passage portions 12A and 12B as described above are attached.
Sample cells 11 in which are arranged in parallel in the thickness direction of the joined body
A laminated structure in which the detection chamber 16 in which the two detection chambers 20A and 20B are arranged in parallel in the thickness direction of the bonded body is integrally formed is obtained. The silicon substrates may be bonded to each other by anodic bonding of SiO ₂ layers generated by thermal oxidation at their interfaces in a measurement target gas atmosphere.
Alternatively, it is also possible to deposit an Au thin film on the bonding surface of the silicon substrate and perform the diffusion bonding process in the measurement target gas atmosphere.

On the surface of the second silicon wafer 2 facing the first silicon wafer 1, a signal output provided in the pressure sensor pressure sensitive portion 19 and the feedthrough hole 8 of the first silicon wafer 1. The wiring connecting the terminal and the power input terminal is formed using a general semiconductor process.

FIG. 2 is a drawing showing in detail the construction of the differential pressure sensor 19 in the embodiment shown in FIG. As shown in FIG. 2, the differential pressure sensor 19 in this embodiment is a thin film type pressure sensor using four polycrystalline silicon strain gauges. In this sensor 19, four strain gauges 2 are provided so as to cover the rectangular pressure introduction hole 23 formed by the anisotropic through hole formed in the second silicon wafer 2.
A circular thin film diaphragm 24 on which 5 is loaded is provided. In this sensor, a circular sacrifice layer (not shown) having a thickness of about 1 μm is formed on the surface of a predetermined portion of the silicon wafer 2 with SiO ₂ or the like, and a thickness of 0.2 μ is formed on the sacrificial layer.
An insulating film such as a Si ₃ N ₄ film 24a having a thickness of about m
It is formed by the VD method, and further four strain gauges 25 made of polycrystalline silicon are formed on a predetermined portion of the upper portion of the Si ₃ N ₄ film 24a, and the upper portion thereof is further covered with, for example, a plasma CV.
Si ₃ N ₄ film 24 having a thickness of about 1 μm formed by the D method
The silicon substrate is covered with an insulating film such as b, and the silicon substrate is etched by anisotropic etching to form a rectangular pressure introduction hole 23, and a void portion 26 is formed by selective etching of the sacrificial layer. When a circular diaphragm is formed in this way, the sensor part can be manufactured with higher accuracy than when a rectangular diaphragm is manufactured by anisotropic etching, high accuracy can be achieved, and stress concentration is less likely to occur due to the circular shape. Will be things. However, of course, this diaphragm may be rectangular. The strain gauges 25 formed on the diaphragm and made of four polycrystalline silicon are piezoresistors RA, RB, RC in the bridge circuit which is a part of the signal processing circuit.
And RD are connected so that the differential pressure can be output.

In the infrared gas analyzer of the present invention,
The pressure-sensitive portion of the differential pressure sensor 19 for measuring the differential pressure between the measurement chamber on the measurement side and the detection chamber on the comparison side does not necessarily have to be provided on the second silicon wafer 2 located at the center of the bonded body as described above. , A pressure sensitive portion of a pressure sensor having four or two strain gauges mounted on such a diaphragm on the surface of each of the first silicon wafer 1 and the third silicon wafer 3 located outside. It is also possible, of course, to provide these and to connect these strain gauges to form a bridge circuit of the signal processing circuit. However, if the pressure-sensitive portion of the pressure sensor is provided on the outside of the bonded body in this way, two pressure-sensitive portions must be formed, and the detected signal will have temperature dependence. Since it becomes necessary to provide a temperature compensating circuit and a signal processing circuit becomes complicated, it is preferable that the second silicon wafer 2 located at the center of the bonded body, that is, the bonded body as described above. It is desirable to form a pressure sensitive portion of the pressure sensor capable of measuring the differential pressure of the detection chambers on the measurement side and the comparison side inside.

In the apparatus of this embodiment, the sample cell 11
Is configured by bonding three silicon wafers together as described above, and has a measurement gas passage 12A and a comparison gas passage 12B. Since the silicon of the material of the sample cell 11 is substantially transparent to infrared rays, the infrared light emitted from the light source passes through the silicon wall and passes through the gas channel 12A,
It reaches the detector 16 via 12B. Therefore, the infrared light transmitting window conventionally required for a sample cell made of stainless steel or the like can be omitted in this sample cell. Further, in the measurement side detection chamber 20A and the comparison side detection chamber 20B of the detector 16 formed integrally with this sample cell, a measurement component or a gas having the same infrared absorption band as that component is sealed. For the same reason as described above, the detector 16 according to the present invention does not include the infrared light transmitting window conventionally required for a detector made of stainless steel or the like. In the figure, reference numeral 15 is an optical chopper.

In the infrared gas analyzer having such a structure, the infrared rays radiated from the two light sources 14A and 14B become intermittent light by the chopper 15 and are detected through the gas passages 12A and 12B of the sample cell 11. Bowl 16
Reach The reference gas passage 12B contains an inert gas, and the reference gas passage 12B does not absorb irradiation infrared rays. On the other hand, when the measurement gas flowing through the measurement gas passage 12A contains the component to be measured, infrared absorption due to this component occurs. Therefore, as described above, the measurement-side detection chamber 20A and the comparison-side detection chamber 20 in which the measurement component or the gas having the same infrared absorption band as that component is enclosed.
The absorption of infrared rays in B is smaller on the measurement side than on the comparison side.
A change in capacity (pressure) caused by the absorbed heat energy can be detected by the strain gauges 25 of the differential pressure sensor 19, and the differential pressure can be output by the signal processing circuit.

The present invention has been described above based on the embodiments, but the present invention is not limited to the above-mentioned embodiments. For example, in the embodiment shown in FIG. 1, the sample cell and the detector are provided. Although they are integrally formed on the same silicon wafer bonded body, the sample cell and the detector may be formed by separate silicon wafer bonded bodies, or only one of them may be formed by the silicon wafer bonded body. It is also possible to form the bonded body constituting such a sample cell or detector by four or more silicon plate materials. However, from the viewpoint of thinning and downsizing the device, a structure in which the sample cell and the detector are integrally formed by a bonded body of three silicon wafers as shown in FIG. 1 is most desirable. Further, although the differential pressure sensor 19 of the above-described embodiment is of the strain gauge type, it may be of the electrostatic capacitance type. Further, instead of such a differential pressure sensor, a communication pipe that connects both detection chambers of this detector is formed, and the pressure difference or the capacity difference is detected by detecting the flow velocity in the communication pipe. You can also That is, the measurement component or the gas having the same infrared absorption band as that component is enclosed in each detection chamber by being heated by the thermal energy absorbed in the measurement side detection chamber and the comparison side detection chamber. A gas flow that expands and is generated in the communication tube according to the concentration of the gas of the component to be measured is converted into an electric signal by a heat ray element arranged in the communication tube portion and detected. You can also

In addition, in the above-mentioned embodiment, since silicon has infrared transparency, no special infrared transmission windows were formed at both ends of each detection chamber of the detector and each gas passage of the sample cell. It is also optional to form an infrared transmitting window portion made of calcium fluoride, sapphire, germanium, or the like. Further in the present invention,
In order to prevent a decrease in sensitivity due to miniaturization, it is also possible to apply an application technique in which each gas passage of the sample cell is coated with a highly reflective film made of Au, Ag, Pt, Al or an alloy of these metals. It is possible.

The infrared gas analyzer of the present invention thus manufactured is used for monitoring the exhaust gas of soot and smoke generating facilities such as large boilers, monitoring automobile exhaust gas, monitoring the working environment, monitoring and controlling the atmosphere of the firing furnace, and energy saving of the power generation boiler. It can be used for applications such as performance quality control of burning appliances, and monitoring of fruit and vegetable storage.

[0024]

INDUSTRIAL APPLICABILITY The infrared gas analyzer of the present invention can be miniaturized with high accuracy as compared with the conventional analyzer, and therefore,
It is not limited in space, can be easily carried and installed, can be made compact and lightweight, and exhibits excellent performance and convenience. Further, since the formation of the detection chamber and the formation of the pressure sensor and the heat ray element can be performed simultaneously by the semiconductor technology and the micromachining technology, not only is it advantageous for downsizing, but also excellent in mass productivity, and the detector and the sample If the cell part and the same silicon plate material are formed integrally with each other, the size can be further reduced and the number of manufacturing steps can be significantly reduced. If it is formed on the silicon plate material that constitutes the bonded body, the size can be further reduced.

[Brief description of drawings]

1A and 1B show configurations of a sample cell and a detector of an infrared gas analyzer according to an embodiment of the present invention, FIG. 1A is a perspective view, and FIG. 1B is a longitudinal sectional view. , Figure 1
(C) is a cross-sectional view in the width direction.

2A and 2B show in detail the structure of a pressure sensor portion in the detector of the embodiment shown in FIG. 1, where FIG. 2A is a sectional view thereof, and FIG. 2B is a plan view thereof.

FIG. 3 is a schematic vertical cross section of an example of a conventional infrared gas analyzer.

[Explanation of symbols]

 1, 2, 3 ... Silicon wafer 4A, 4B, 5A, 5B ... Anisotropic concave groove 6A, 6B, 7A, 7B ... Through hole 8 ... Feed through hole 11 ... Sample cell 12A ... Measurement gas passage 12B ... Comparison gas passage 14A, 14B ... Light source 15 ... Optical chopper 16 ... Detector 19 ... Differential pressure sensor 20A, 20B ... Detection chamber 23 ... Pressure introduction hole 24 ... Thin film diaphragm 25 ... Strain gauge

Claims (2)

[Claims] 1. An infrared gas analyzer comprising a light source, a sample cell, and a detector, wherein at least one of the sample cell and the detector is laminated and joined with a processed silicon plate material. An infrared gas analyzer, characterized in that the gas passage or detection chamber on the measurement side and the gas passage or detection chamber on the comparison side are provided in parallel in the thickness direction. 2. The sample cell and the detector are configured by laminating and joining three processed silicon single crystal plate materials, and two bondings are formed on both side surfaces of the plate material at the center of the bonded body. The measurement gas passage and the measurement side detection chamber, and the comparison gas passage and the comparison side detection chamber are formed on the surface portion on both sides of the central plate member, respectively, and the central plate member serving as a partition wall is provided with the measurement side detection chamber. The infrared gas analyzer according to claim 1, wherein a pressure sensor capable of measuring a differential pressure with respect to the comparison side detection chamber is formed.