JP2005257621A - Infrared detector and analyzer using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infrared detector for detecting infrared rays of an arbitrary wavelength band and having extremely high sensitivity with its miniaturization easily achieved, and an analyzer using the same. <P>SOLUTION: This infrared detector comprises two gas chambers 6a and 6b filled with gas for absorbing infrared rays R<SB>1</SB>and R<SB>2</SB>being detecting objects; a gas flow path 7 for causing the two gas chambers 6a and 6b to communicate with each other; a cantilever 11 having a gas flow sensing part 16 disposed in the flow path 7 for sensing the gas flowing through the flow path 7; and a detection element 13 for finding the flow f of the gas on the basis of a displacement amount d of the cantilever 11. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an infrared detector and an analyzer using the same.

  An infrared detector used in an infrared gas analyzer or the like is filled with, for example, a gas having the same infrared absorption characteristics as the measurement target gas, and is arranged in series or in parallel with each other with respect to the measurement cell. A gas chamber is partitioned by a thin film and a pressure difference between the two is detected by a condenser microphone, or a gas flow path that connects both gas chambers and a flow rate detection element provided in the gas flow path is there.

  The flow rate detecting element preferably detects the gas flow sensitively, and for that purpose, it is desired to reduce the size. That is, in order to increase the sensitivity of the flow rate detection element, it is necessary to increase the flow velocity by making the diameter of the gas flow path as narrow as possible. Patent Document 1 discloses a technique for miniaturizing a thermal flow rate detection element as much as possible by using a substrate on which a heater is patterned by a semiconductor manufacturing process, and increases the resistance change amount of the thermal heater. In order to further increase the sensitivity, a configuration in which the diameter of the gas channel is made as narrow as possible is shown.

On the other hand, Patent Document 2 uses a cantilever having a bimetallic structure made of two kinds of metals having different thermal expansion coefficients, absorbs radiant heat by infrared rays, and measures the amount of deflection caused by the difference in thermal expansion coefficients of both metals. An infrared detector that can detect a minute amount of heat (infrared rays) is shown.
JP 2000-009641 A JP-A-8-184500

  However, as in Patent Document 1, in the case where a heat flow rate type flow rate detecting element is provided in the gas flow path between the gas chambers to obtain the infrared intensity, the sensitivity is increased by narrowing the diameter of the gas flow path. On the other hand, if the area of the heat exchange part between the heater and the gas is too small, there is a drawback that efficient heat exchange cannot be performed. For this reason, the gas flow path serving as a heat exchange part with the heater needs to have a certain length. However, the longer the gas flow path, the higher the flow path resistance, thereby lowering the flow velocity and lowering the sensitivity. There was a problem.

  In addition, in order to detect infrared rays using a thermal flow rate detection element, control is performed to apply a constant voltage to the heater so that the temperature is higher than the temperature of the gas filled in the gas chamber by a certain temperature. In addition, it is necessary to form a bridge circuit or the like for properly capturing the change in the temperature caused by the gas flow as a change in the resistance value of the heater. For this reason, there has been a problem that a relatively complicated electric control circuit is required for detecting the flow rate using the thermal flow rate type flow rate detecting element.

  On the other hand, in the infrared detector of Patent Document 2, it is possible to detect the intensity of infrared light in a wavelength range that can be absorbed by a bimetallic cantilever, but a wavelength range that cannot be absorbed by a bimetallic cantilever, such as low-frequency infrared rays. There was a problem that the intensity of infrared rays could not be detected.

  The present invention has been made in consideration of the above-mentioned matters, and the object thereof is to detect infrared rays in an arbitrary wavelength region, to be extremely sensitive, and to easily achieve downsizing. An infrared detector and an analyzer using the same are provided.

  In order to achieve the above object, an infrared detector according to a first aspect of the present invention includes two gas chambers filled with a gas that absorbs infrared rays to be detected, a gas flow path that connects the two gas chambers, and the gas flow. It is characterized by comprising a cantilever having a gas flow sensing part that senses gas flowing in a gas flow path and a detection element that obtains the flow rate of the gas by the amount of displacement of the free end of the cantilever (claim) Item 1).

  A flow passage restricting portion may be formed in the gas flow passage, and a cantilever may be disposed in the flow passage restricting portion.

  The cantilever may be formed by microfabrication by a semiconductor manufacturing process, and the detection element may be a piezoelectric element formed at a base end portion of the cantilever.

  The detection element may be a light detection element that optically detects the displacement of the free end of the cantilever.

  The cantilever may be made of a material whose spring constant can be changed by doping impurities (Claim 5).

  The analyzer of the second invention is characterized by using the infrared detector according to any one of claims 1 to 5 (claim 6).

  In the infrared detector according to claim 1, when infrared rays are incident on one gas chamber, the infrared rays are absorbed by the gas filled in the gas chamber, and the gas expands to generate a pressure difference between the two chambers. A gas flow occurs in the gas flow path. Then, when this gas hits the gas flow sensing part of the cantilever, the free end part of the cantilever is displaced according to the flow, and this displacement amount is detected by the detection element. In other words, since the cantilever itself forms a resistance in the gas flow path, the free end portion of the cantilever can be displaced according to the flow rate of the gas flowing through the gas flow path, and the displacement amount of the free end portion can be reduced. Based on this, the intensity of infrared rays can be determined.

  That is, in the infrared detector of the present invention, it is possible to freely design the spring constant of the cantilever, the area of the gas flow path in the portion where the cantilever is provided, etc. And higher sensitivity can be achieved. That is, since it is not necessary to heat the gas unlike the thermal type flow rate detecting element, it is not necessary to provide a long flow path that causes an unnecessary increase in resistance, and it is possible to achieve higher speed, higher sensitivity, and smaller size.

  Further, by increasing the sensitivity of the flow rate detection element comprising the cantilever and the detection element for the displacement amount of the cantilever, it becomes possible to reduce the size of the gas chamber and achieve further miniaturization of the infrared detector. be able to.

  In addition, since the infrared detector of the present invention measures the amount of displacement of the free end of the cantilever, a control circuit for heating the gas to an appropriate temperature, such as a thermal flow rate detection element, Since it is not necessary to form a peripheral circuit such as a bridge circuit using a reference resistor in order to capture the flow, the configuration can be simplified and the manufacturing cost can be reduced. In addition, even when the gas flow is fast, the free end of the cantilever is displaced accordingly, and the amount of this displacement can be detected directly, so that the dynamic range can be expanded accordingly and the linearity of the output is improved. The cause of drift due to temperature changes can be reduced.

  When a flow restrictor is formed in the gas flow path and a cantilever is arranged in the flow restrictor (Claim 2), the speed of the gas flow that collides with the gas flow sensing part of the cantilever is increased. In addition, the amount of displacement can be increased and the flow of gas flowing through the cantilever arrangement portion can be adjusted, so that stable and highly sensitive measurement can be performed. The gas flow path other than the flow path restricting portion can be widened so as not to have flow path resistance.

  When the cantilever is formed by microfabrication by a semiconductor manufacturing process and the detection element is a piezoelectric element formed at the base end of the cantilever (Claim 3), the cantilever is in a micron order. It can be formed as small as possible by microfabrication, and by achieving further downsizing, detection with higher sensitivity becomes possible. In addition, since the detection element is a piezoelectric element, it is possible to form a piezoelectric material by forming a film on the base end of the cantilever, and since the detection element has a very simplified configuration, it can be formed at low cost. The bending of the cantilever can be easily detected by an electromotive force caused by distortion of the piezoelectric material.

  When the detection element is a light detection element that optically detects the amount of displacement of the free end portion of the cantilever (Claim 4), the amount of displacement of the free end portion of the cantilever can be accurately determined without coming into contact therewith. Can be measured.

  When the cantilever is made of a material whose spring constant can be changed by doping impurities (Claim 5), the sensitivity of the infrared detector can be easily set.

  The analyzer using the infrared detector according to any one of claims 1 to 5 (claim 6) can perform highly sensitive analysis and can achieve downsizing.

  FIG. 1 is a diagram showing a configuration of an infrared gas analyzer (analyzer) A using the infrared detector 1 of the first embodiment, and FIG. 2 shows an enlarged configuration of a main part of the infrared detector 1. FIG. In FIG. 1, 2a is a comparison cell filled with a reference gas, 2b is a measurement cell through which the sample gas S flows, 3a and 3b are infrared light sources corresponding to the cells 2a and 2b, and 4 is a mechanical chopper. is there.

The infrared detector 1 of the present invention includes two gas chambers 6a and 6b having infrared transmission windows 5a and 5b through which infrared rays R ₁ and R ₂ that have passed through the cells 2a and 2b are incident, and both gas chambers 6a and 6b. A gas flow path 7 to be communicated, a flow path narrowing portion 8 for speeding up the gas flow by narrowing the gas flow in the gas flow path 7, and a gas flow rate detecting element 9 formed in the flow path narrowing portion 8 Have

The gas chambers 6a and 6b contain a gas that absorbs infrared rays having a predetermined wavelength, which is a detection target (in this embodiment, the same gas as the measurement target component of the infrared gas analyzer) and is absorbed by the measurement target component. Can absorb infrared rays in a certain wavelength region. Therefore, depending on the amount of each measurement target component of the reference gas and the sample gas S, infrared rays in a specific wavelength region are absorbed, and there is a difference in the intensity of the infrared rays R ₁ and R ₂ incident on the gas chambers 6a and 6b. Arise. For this reason, a pressure difference is generated in the gas chambers 6 a and 6 b, and the gas flows through the gas flow path 7.

That is, by measuring the flow rate of the gas flowing through the gas flow path 7 with the gas flow rate detecting element 9, the infrared detector 1 can determine the difference in intensity between the infrared rays R ₁ and R ₂ incident thereon. The amount of the measurement target component contained in the sample gas S can be obtained using the difference in infrared intensity.

That is, since the infrared detector 1 of the present invention obtains the intensity of the infrared rays R ₁ and R ₂ by using the absorption of the infrared rays R ₁ and R ₂ by the gas filled in the gas chambers 6a and 6b. By changing the gas, infrared rays in an arbitrary wavelength range can be detected.

In addition, the infrared detector 1 of this embodiment arranges gas chambers 6a and 6b provided with infrared transmitting windows 5a and 5b made of the same material, so that infrared rays R ₁ and R incident on both gas chambers 6a and 6b are arranged. The difference between the _two strengths can be measured, but the present invention is not limited to this configuration. That is, infrared light may be incident only on one gas chamber 6a, and the gas chambers 6a and 6b may be formed in series in the incident direction of infrared light.

  FIG. 2A is an enlarged view showing the configuration of the flow path restricting portion 8, and FIG. 2B is a view showing the configuration of the gas flow rate detecting element 9 arranged in the flow path restricting portion 8. is there.

  2 (A) and 2 (B), 10 is a semiconductor substrate constituting the flow rate detecting element, 11 is a micro cantilever (cantilever) formed on the semiconductor substrate 10 by a semiconductor manufacturing process, and 12 is a periphery of the micro cantilever 11. 13 is a piezoelectric element (detecting means) made of a piezoelectric material formed on the surface of the base end portion 11a of the micro cantilever 11 by a semiconductor manufacturing process, and 14 and 15 are both ends of the piezoelectric element 13. It is the formed lead wire. Reference numeral 16 denotes a gas flow sensing unit formed to have a somewhat larger area by forming the slit 12 to be curved in a C shape.

  The micro cantilever 11 can be made as small as possible by forming it by a semiconductor manufacturing process. For example, the length L can be formed to about 100 μm and the width W can be formed to about 20 μm. . Similarly, the slit 12 can be formed very thin up to about 10 μm, and the cross-sectional area of the slit 12 can be set with high accuracy.

  The piezoelectric element 13 of this example is formed on the base end portion 11 a of the micro cantilever 11 so that a predetermined tension T acts on the displacement d of the micro cantilever 11. The lead wires 14 and 15 are connected to an electric circuit (not shown) so that the electromotive force in the piezoelectric element 13 can be detected from the outside.

Therefore, when the infrared rays R ₁ and R ₂ are incident on the infrared detector 1 and a gas flow is generated in the gas flow path 7, a force F acts on the gas flow sensing unit 16 and the flow rate f from the slit 12. Gas flows. At this time, the free end portion 11a of the micro cantilever 11 is displaced, and a tension T corresponding to the displacement amount d is generated in the piezoelectric element 13, and this can be detected as a voltage value.

  That is, since the infrared detector 1 of the present invention can directly detect a value corresponding to the flow rate f of the gas flowing through the gas flow path 7, an electric circuit provided outside is extremely simple. Further, since the sectional area of the slit 12 is small, the gas flow can be detected with high sensitivity even if the flow rate f of the gas flowing through the gas flow path 7 is very small. Furthermore, since the microcantilever 11 is extremely small, its inertia is so small that it can be ignored, and the response speed can be extremely high.

  In addition, when the gas flow rate f increases, the micro cantilever 11 can be greatly bent, and the dynamic range of the infrared detector 1 can be increased.

  Furthermore, in the present embodiment, a flow restrictor 8 is formed in the middle of the gas flow path 7, and the micro cantilever 11 is disposed in the flow restrictor 8. By restricting the flow of the gas and increasing the flow velocity, the free end portion 11b can be sufficiently displaced by acting on the micro cantilever 11 more strongly and stably.

Further, a gas flow path 7 in the present embodiment, as viewed from the irradiation direction of the infrared R _1, R _2, gas chamber 6a, but is formed so as to communicate the back of 6b, the present invention in this configuration It is not limited.

  FIG. 3 is a diagram showing the configuration of the infrared detector 1 ′ of the second embodiment. In FIG. 3, members denoted by the same reference numerals as those in FIGS. 1 and 2 are the same or equivalent members, and thus detailed description thereof is omitted.

  In FIG. 3, reference numeral 20 denotes a partition wall between two gas chambers 6 a and 6 b, and the micro cantilever 11 is formed in the gas flow path 7 formed in the partition wall 20. That is, since the micro cantilever 11 formed using the semiconductor manufacturing process can be formed extremely small, it can be disposed in the short gas flow path 7 formed in the partition wall 20.

  Therefore, it is possible to further simplify the configuration of the infrared detector 1 ′, thereby reducing the manufacturing cost. Further, by shortening the gas flow path 7, the inertia and flow resistance of the gas flowing through the gas flow path 7 can be reduced.

  In addition, the gas chambers 6a and 6b may be arranged in series with respect to the infrared irradiation direction. In this case, an infrared transmission window can be formed on one surface 1a of the infrared detector 1 ', and the partition wall 20 can be formed of an infrared transmission material. At this time, the infrared ray incident on the gas chamber 6b is attenuated by the amount corresponding to the formation of the gas flow rate detection element 9. However, since the microcantilever 11 constituting the gas flow rate detection element 9 is extremely small, the attenuation amount of the infrared ray due to this is ignored. can do.

  Furthermore, although the throttle channel 8 of the gas channel 7 is formed in this example, the slit 12 formed around the micro cantilever 11 can also be used as a diaphragm. In this case, the gas flow path 7 becomes the slit 12, and the configuration of the infrared detector 1 'can be further simplified.

The detection means for detecting the displacement amount d in the free end portion 11b of the micro-cantilever 11 is not limited to the piezoelectric element 13 described above, occurs when light L ₁ to the free end portion 11b of the microcantilever 11 A light position element (not shown) for optically detecting the reflected lights L ₂ and L ₃ may be provided.

It is a figure which shows 1st Example of the infrared detector of this invention. It is a figure which expands and shows the principal part of the said infrared detector. It is a figure which shows the infrared detector of 2nd Example.

Explanation of symbols

1, 1 'Infrared detector 6a, 6b Gas chamber 7 Gas flow path 8 Flow path restricting part 11 Cantilever 11b Free end part 13 Piezoelectric element (detection element)
16 Gas flow sensor d Displacement f Gas flow rate R ₁ , R ₂ infrared

Claims (6)

  Two gas chambers filled with a gas that absorbs infrared rays to be detected, a gas flow path that connects both gas chambers, and a gas flow sensing unit that is disposed in the gas flow path and senses gas flowing through the gas flow path An infrared detector comprising: a cantilever having a detecting element; and a detection element for obtaining a flow rate of the gas based on a displacement amount of a free end portion of the cantilever.   The infrared detector according to claim 1, wherein a flow path restricting portion is formed in the gas flow path, and a cantilever is disposed in the flow restricting portion.   The infrared detector according to claim 1, wherein the cantilever is formed by microfabrication by a semiconductor manufacturing process, and the detection element is a piezoelectric element formed at a base end portion of the cantilever.   The infrared detector according to claim 1, wherein the detection element is a light detection element that optically detects a displacement amount of a free end portion of a cantilever.   The infrared detector according to claim 1, wherein the cantilever is made of a material capable of changing a spring constant by doping impurities. An analyzer comprising the infrared detector according to claim 1.

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