WO2002088698A1 - Capteur de gaz photoacoustique - Google Patents

Capteur de gaz photoacoustique Download PDF

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Publication number
WO2002088698A1
WO2002088698A1 PCT/JP2002/004285 JP0204285W WO02088698A1 WO 2002088698 A1 WO2002088698 A1 WO 2002088698A1 JP 0204285 W JP0204285 W JP 0204285W WO 02088698 A1 WO02088698 A1 WO 02088698A1
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WO
WIPO (PCT)
Prior art keywords
cavity
infrared light
substrate
gas
gas sensor
Prior art date
Application number
PCT/JP2002/004285
Other languages
English (en)
Japanese (ja)
Inventor
Hisatoshi Fujiwara
Nobuaki Honda
Takashi Kihara
Original Assignee
Yamatake Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
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Publication of WO2002088698A1 publication Critical patent/WO2002088698A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/24—Probes
    • G01N29/2418—Probes using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics
    • G01N29/2425—Probes using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics optoacoustic fluid cells therefor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
    • G01N2021/1704—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids in gases
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/028—Material parameters
    • G01N2291/02872—Pressure

Definitions

  • the present invention relates to a small-sized photoacoustic gas sensor having a simple structure with enhanced gas detection sensitivity.
  • Photoacoustic gas sensors use the phenomenon that a specific type of gas absorbs infrared light of a specific wavelength and expands thermally, and uses a specific type of gas, such as air, in a mixed gas such as air.
  • This type of photoacoustic gas sensor basically includes a cavity 1 into which gas (air) is introduced as shown in FIG. 10, a light source 2 for irradiating infrared rays into the cavity 1, and a cavity 1 for the cavity 1. It comprises a microphone 3 that is provided as part of the wall surface (ceiling surface) and is sensitive to the sound pressure in the cavity 1.
  • the cavity 1 is formed by etching a Si substrate transparent to infrared light to form a predetermined space,
  • a gas flow passage 4 for introducing outside air (gas) into the cavity 1 is provided.
  • a gas diffusion filter 5 is usually provided in the gas passage 4. This gas diffusion filter 5 restricts the flow of gas, thereby maintaining the flow (replacement) of gas (air) between the inside and outside of the cavity 1. It plays a role of changing the sound pressure in the cavity 1 according to the thermal expansion of C 0 2 (gas) due to the absorption of the infrared light described above.
  • this gas diffusion filter 5 plays the following two roles. One of them is to act as a large airflow resistor against the rapid pressure change (sound pressure) generated in the cavity 1 by the irradiation of the infrared pulse, and to keep the sound inside the capital 1 substantially closed. This function prevents pressure from being transmitted to the outside of cavity 1. The other is that it does not act as an airflow resistor against slow pressure changes (sound pressure) in the cavity 1 caused by changes in the external environment such as temperature and atmospheric pressure. This function keeps the air open.
  • the present invention increases the efficiency of absorption of infrared light by a gas to be detected in a cavity irradiated with infrared light of limited intensity, thereby improving gas detection sensitivity. It is intended to provide a compact photoacoustic gas sensor having a simple structure.
  • the photoacoustic gas sensor according to the present invention is a small-sized one manufactured by processing a Si substrate or the like using, for example, micromachining technology.
  • a cavity provided with a gas flow opening for introducing outside air and an infrared light introduction window; a gas diffusion filter provided integrally with the cavity in the gas flow opening; and a part of an inner wall surface of the cavity.
  • a microphone that is provided to detect the sound pressure in the cavity, and a light source that irradiates infrared light into the cavity through the infrared light introducing window in a pulsed manner.
  • an infrared light reflecting film is coated on the inner wall surface of the cavity except for the gas flow port and the infrared light introducing window.
  • the cavity is formed by etching a Si substrate having a predetermined thickness to form a concave space having a predetermined internal volume, and anodizing a part of the wall surface to form a porous silicon layer forming the gas diffusion filter. It is realized as something.
  • the microphone microphone is provided with one of a pair of electrodes facing each other so as to cover the concave space of the Si substrate, thereby forming a ceiling surface facing the infrared light introducing window of the cavity. Provided integrally with the cavity.
  • the infrared light reflection film is made of, for example, a thin film of Au or A1, and has an inner wall surface excluding a gas diffusion filter made of the porous silicon layer of the Si substrate in which the concave space is formed, and a wall surface of the cavity. It is provided on the electrode surface of the formed microphone by, for example, vapor deposition or sputtering to a thickness of several / xm.
  • the ceiling of the cavity is formed so that the microphone electrode on which the infrared light reflecting film is coated has a waveform, and the infrared light introduced from the infrared light introducing window is multiply reflected. It is desirable to configure so that
  • the light source configured to include a thin film heater formed on a bridge provided over a recess formed on the surface of the semiconductor substrate, the inner wall surface of the recess and / or An infrared light reflecting film coated on the back surface is provided, and the infrared light emitted from the thin film heater to the back surface side is reflected and condensed to irradiate the infrared light introduction window of the cavity. It is preferable to configure.
  • the light source is thermally isolated from the cavity, and provided so as to face the infrared light introducing window of the cavity so that undesired heat transfer from the light source to the cavity is prevented. Is desirable. BRIEF DESCRIPTION OF THE FIGURES
  • FIG. 1 is a sectional view showing a schematic configuration of a photoacoustic gas sensor according to one embodiment of the present invention.
  • FIG. 2A to 2I are exploded views showing an example of a manufacturing process of the cavity 10 and the microphone 50 in the photoacoustic gas sensor shown in FIG.
  • FIGS. 3A to 3C are diagrams respectively showing examples of masks used to form the first electrode 51 of the microphone 50 into a waveform.
  • FIG. 4A and 4B are exploded views showing an example of a manufacturing process of the gas diffusion filter 40 in the photoacoustic gas sensor shown in FIG.
  • 5A to 5G are exploded views showing another example of the manufacturing process of the gas diffusion filter 40 in the photoacoustic gas sensor shown in FIG.
  • FIG. 6 is a sectional view showing a schematic configuration of a photoacoustic gas sensor according to another embodiment of the present invention.
  • Figure 7 is an electrical equivalent circuit showing the thermal characteristics of cavities.
  • FIG. 8 is a diagram showing a frequency response characteristic to a change in sound pressure in the cavity.
  • Figure 9 is an electrical equivalent circuit showing the characteristics of a gas diffusion filter.
  • FIG. 10 is a diagram showing a general configuration of a photoacoustic gas sensor. BEST MODE FOR CARRYING OUT THE INVENTION
  • FIG. 1 is a cross-sectional view showing a schematic configuration of a photoacoustic gas sensor according to this embodiment.
  • the photoacoustic gas sensor generally includes a cavity (photoacoustic cell) 10 having a gas flow port 20 for introducing outside air and an infrared light introduction window 30, and the gas flow port 20.
  • a gas diffusion filter 40 provided integrally with the cavity 10, and a sound pressure inside the cavity 10 which is provided as a part of an inner wall surface of the cavity 10.
  • a microphone 50 for detection, and a light source 60 for irradiating infrared light into the cavity 10 via the infrared light introducing window 30 are provided.
  • the cavities 10, microphones 50, and light sources 60, etc. are each subjected to micromachining technology, for example, by etching an Si substrate having a predetermined thickness transparent to infrared light. Manufactured. Especially microphone 50
  • the cavity 10 is, for example, anisotropically etched on two Si substrates 11 and 12 having a thickness of 500 m, respectively, and has a square recess (hole) 13 with a side of about l mm.
  • the recesses (holes) 13 and 14 are abutted against each other, and the two Si substrates 11 and 12 are joined by semiconductor and integrated. Eggplant Then, an opening of one Si substrate 11 is closed to form a microphone 50 integrally, and an optical filter forming an infrared light introducing window 30 is provided in the opening of the other Si substrate 12. And has a structure in which an internal space having a predetermined internal volume is formed.
  • the gas flow port 20 is, for example, Si on the side where the infrared light introducing window 30 is provided.
  • the gas diffusion port (groove) 20 is partially filled with an anodized Si substrate 12 into a porous silicon layer, as described later, into a porous silicon layer. 0 is provided on the body. Gas integrated with such a gas diffusion filter 40
  • 25 through hole 20 is, for example, a space which is provided between the two Si substrates 11 and 12 constituting the cavity 10 and forms a part of the cavity 10.
  • another Si substrate serving as a substrate may be provided with holes equivalent to the concave portions (holes) 13 and 14.
  • the microphone 50 is formed on the Si substrate 11 when forming the concave portion (hole) 13 in the Si substrate 11.
  • the microphone 50 includes a first electrode 51 provided so as to cover a concave portion (hole) 13 opened in the Si substrate 11 and a predetermined electrode above the first electrode 51. And a back plate 53 that supports the second electrode 52 from above.
  • the back plate 53 and the second electrode 52 are provided with a plurality of acoustic holes 54 communicating with a space between the first electrode 51 and the second electrode 52. .
  • the photoacoustic gas sensor basically configured as described above is characterized in that the photoacoustic gas sensor according to this embodiment is characterized in that the gas communication port 20 on the inner wall surface of the cavity 10 and the infrared light
  • the area other than the introduction window 30 is coated with an infrared light reflecting film 70 made of Au, A1, or the like. Since the infrared light reflecting film 70 is formed to have a thickness of several meters by vapor deposition, sputtering, or the like, pulse irradiation was performed from the light source 60 into the cavity 10 through the infrared light introducing window 30. Reflecting the infrared light plays a role of increasing the propagation optical path length of the infrared light in the cavity 10.
  • the inner wall surface of the cavity 10 is formed as a slope forming the (111) plane by anisotropic etching of a Si substrate having the (100) plane as a main surface, for example. ing.
  • the electrode surface of the microphone 50 provided as a ceiling surface of the cavity 10 is also provided in a waveform shape using anisotropic etching of the Si substrate as described later.
  • the infrared light reflecting film 70 is provided on the inner wall surface of the cavity 10 forming the above-mentioned slope and on the electrode surface (the ceiling surface of the cavity 10) of the microphone 50 forming the waveform, respectively. Randomly multiplexes infrared light pulsed into the cap It is intended to reflect.
  • the light source 60 has a structure in which, for example, a thin film transistor 64 is formed on an insulating thin film bridge 63 provided over a concave portion 62 formed on the surface of the Si substrate 61, for example. .
  • the inner wall surface of the concave portion 62 of the light source 60 is also coated with an infrared light reflecting film 65 made of Au, A1, or the like.
  • the infrared light reflecting film 65 reflects and condenses infrared light emitted from the thin film light 64 to the rear surface side, and irradiates the infrared light introduction window 30 of the cavity 10. Has a role.
  • an insulating thin film bridge 63 provided with a thin film heater 64 over the upper surface of the concave portion 62 is provided. Therefore, it is preferable to form the infrared light reflecting film 65 by electrolytic plating in order to surely provide the infrared light reflecting film 65 also in a region directly below the insulating thin film bridge 63 in the concave portion 62.
  • the infrared light reflecting film 65 is formed on the back side of the Si substrate 61, the light condensing function for the infrared light emitted from the thin film heater 64 to the back side is similarly obtained. be able to.
  • Au, A1, or the like may be deposited (or sputtered) on the back surface of the Si substrate 61.
  • the side surface of the Si substrate 61 is anisotropically etched, and the back surface of the Si substrate 61 is formed into a trapezoidal shape surrounding the thin-film heater 64, or a pot bottom shape isotropically etched. If formed in such a way, it is possible to increase the efficiency of collecting infrared light by the infrared light reflecting film 65 formed on the rear surface side.
  • FIG. 2A to 2I show the manufacturing steps of the cavity 10 and the microphone 50 in an exploded manner.
  • This microphone 50 is formed integrally with the first Si substrate 11 constituting the cavity 10. Therefore, first, for example, a Si wafer having a (100) plane as a main surface is used as a Si substrate 11 to form the cavity 10. After preparing and growing a thermal oxide film 15 on the Si substrate 11 as shown in FIG. 2A, rectangular holes 16 are formed in the thermal oxide film 15 at a predetermined opening pitch using photolithography.
  • the rectangular holes 16 provided in the thermal oxide film 15 may be formed by arranging minute square holes at equal intervals vertically and horizontally. As shown in FIG. 3, a rectangular hole may be provided in parallel, or as shown in FIG. 3C, a frame may be formed by extending the hole shape from the center to the outside in order. In short, as will be described later, when the Si substrate 11 is anisotropically etched using the thermal oxide film 15 as a mask, a mask pattern may be formed so as to form unevenness having a uniform waveform shape on the surface thereof. .
  • the Si substrate 11 is anisotropically etched using KOH or TMAH (trimethyl ammonium hydride). Then, as shown in FIG. 2B, a plurality of recesses 17 having a triangular cross section are formed on the surface of the Si substrate 11 according to the above-described microphone pattern shape, and the shape of the first electrode 51 in the microphone 50 is defined. A corrugated shape is formed on the surface of the Si substrate 11.
  • first electrode 51 is to form a thermal oxide film of Si0 2 or the like for taking insulation between the substrate 11 (not shown).
  • first electrodes 51 made of, for example, Cr / Au / Cr are formed to a thickness of 4 / 20-4 nm, respectively, and further used as a diaphragm on the first electrodes 51.
  • Photosensitive polyimide (not shown) is formed to a thickness of 1 / xm. That is, a first electrode 51 lined with a diaphragm is insulated from the Si substrate 11 and formed in a waveform along one surface of the Si substrate 11 processed into the waveform.
  • a sacrificial layer 55 is formed on the upper surface of the first electrode 51, as shown in FIG. 2D.
  • Al is formed to a thickness of two.
  • the sacrificial layer (A 1) 55 plays a role in defining a distance (gap) between the second electrode 52 and the first electrode 51 of the microphone 50, and is formed by vacuum evaporation or sputtering. It is formed while controlling the film thickness by the evening ring.
  • a second electrode 52 made of, for example, AuZCr is formed on the sacrificial layer (A1) 55, and the second electrode 52 is covered with the second electrode 52 as shown in FIG. 2F.
  • a photosensitive polyimide forming the back plate 53 is formed to a thickness of about 10 to 20 m.
  • Au / Cr is used here for the second electrode 52 in consideration of the resistance at the time of removing the sacrificial layer 55 by etching described later, the sacrificial layer (A1) 55
  • other electrode materials can be used as long as they have resistance to the etching solution.
  • a predetermined opening is formed by patterning the back plate 53 made of photosensitive polyimide, and the second electrode 52 is selectively etched using the back plate 53 as a mask, as shown in FIG. 2G.
  • a plurality of acoustic holes 54 that function as air vents in the microphone 50 are formed. These acoustic holes 54 are also used for etching and removing the sacrificial layer (A1) 55 described above.
  • a thermal oxide film 18 is grown on the back surface of the Si substrate 11, and a rectangular hole is formed in the thermal oxide film 18 using photolithography.
  • the Si substrate 11 is anisotropically etched from the back side using KOH or TMAH (trimethylammonium hydride) to form the first electrode (diaphragm).
  • KOH or TMAH trimethylammonium hydride
  • a concave portion (hole portion) 13 forming a cavity 10 is formed inside the Si substrate 11 as shown in FIG. 2H.
  • Au is sputtered into the cavity 10 from the back side of the Si substrate 11 to form the exposed surface of the first electrode (diaphragm) 51 and the cavity 10 of the Si substrate 11.
  • An infrared light reflective film 70 having a thickness of several meters is formed on the inner wall surface thus formed.
  • the sacrificial layer 55 is removed through the acoustic hole 54 as shown in FIG.
  • the microphone 50 integrated with the cavity 10 is completed.
  • the sacrificial layer 50 made of A1 is removed by etching, for example, using a mixed solution of phosphoric acid and nitric acid (70 ° C.) as the etching solution.
  • a thermal oxide film is grown on one surface of the second Si substrate 12 forming the cavity 10, and a rectangular hole is formed in the thermal oxide film using photolithography.
  • This thermal oxide film corresponds to the thermal oxide film 18 formed on the back surface of the first Si substrate 11.
  • the second Si substrate 21 is anisotropically etched using KOH or TMAH (trimethylammonium hydride).
  • KOH or TMAH trimethylammonium hydride
  • a recess (hole) 14 forming the cavity 10 is formed.
  • Au is sputtered on the inner surface of the second Si substrate 12, and the inner wall surface of the concave portion (hole) 14 formed in the second Si substrate 12 has an infrared ray of several zm thickness.
  • a light reflection film 70 is formed.
  • a gas flow port 20 is formed on the joint surface side with the first Si substrate 11.
  • the gas diffusion filter 40 is integrally buried in the gas flow port 20.
  • the second Si substrate 12 in which the concave portion (hole) 14 is formed is opposite to the surface on which the gas diffusion filter 40 is formed.
  • heat treatment is performed at approximately 500 ° C. in a vacuum. This A1 film is used as an electrode contact at the time of anodic oxidation described later.
  • a photosensitive polyimide is spin-coated on the surface (surface) of the Si substrate 12 on which the gas diffusion filter 40 is formed, and the photosensitive polyimide is selectively irradiated with ultraviolet light.
  • the photosensitive polyimide is As a mask, the Si substrate 12 is anodized to form a porous layer, and a porous silicon layer 41 forming a gas diffusion filter 40 is formed as shown in FIG. 4A.
  • the selective anodic oxidation of the Si substrate 12 is performed by mechanically covering the back surface of the Si substrate 12 on which the A1 film is formed as described above, or by protecting the back surface with a tape or the like. This is performed by immersing the Si substrate 12 in a hydrofluoric acid solution together with a reference electrode (not shown) serving as a cathode and a current having a predetermined density. At this time, it is preferable to remove ethanol generated during the anodic oxidation of the Si substrate 12 by adding ethanol to the hydrofluoric acid solution.
  • photosensitive polyimide is used as a mask for the Si substrate 12, but it goes without saying that a noble metal or other polymer material may be used.
  • a gas flow passage having the porous silicon layer 41 integrally embedded on the upper surface of the Si substrate 12 is formed. 20 are formed in a groove. At this time, it is desirable to adjust the length (the thickness of the filter) of the porous silicon layer 41 so that the gas diffusion filter 40 has a desired filter characteristic.
  • a resist such as S I_ ⁇ 2 on porous silicon layer 4 1
  • a resist film using the resist film only in the region to be patterned to form a gas diffusion filter 4 0 by photolithography or the like Leave.
  • the record resist film (S i 0 2) as a mask for example by using a weak alkaline etching solution consisting of 1% aqueous solution of Na_ ⁇ _H, or selectively etching the Porous silicon layer 4 1 by dry etching
  • the length (thickness of the filter) of the porous silicon layer 41 is adjusted.
  • a gas diffusion filter 40 having desired filter characteristics is realized.
  • the gas diffusion filter 40 may be formed, for example, on the second Si substrate 12 constituting the cavity 10 as shown in FIG. 5, or on the spacer described above. That is, as shown in FIG. 5A, first, the S i N Protective films 21 and 22 made of a hydrofluoric acid-resistant insulating film such as an x film are provided. Then, as shown in FIG. 5B, a resist film 23 is formed on the protective film (SiN x film) 21 on the lower surface side of the Si substrate 12, and after the resist film 23 is patterned, the resist film 23 is formed. An opening is formed in the protective film (SiN x film) 21 to form a recess (hole) 14 forming a cavity 10 by using the mask as a mask.
  • the Si substrate 12 is deep-etched in the vertical direction from the back side thereof, and as shown in FIG. 5C, a concave portion (cavity 10) is formed on the back side of the Si substrate 12. Holes 14 are formed.
  • a resist film 24 is formed on the surface side of the Si substrate 12, and the resist film 24 is patterned.
  • a resist film is formed so as to cover a portion facing the concave portion (hole portion) 14 and leave an area slightly larger than the size of the concave portion (hole portion) 14 with a protective film (SiN x film) 22. This is done by selectively removing 24.
  • the protective film (SiN x film) 22 is selectively removed as shown in FIG. 5D.
  • the Si substrate 12 is deep-etched in the vertical direction from the surface side thereof, and the cavities 10 are formed on the surface side of the Si substrate 12 as shown in FIG. 5E.
  • a groove-shaped recess 25 is formed outside the recess (hole) 14.
  • the groove-shaped concave portion 25 forms a gas flow port 20 for the cavity 10 formed by the Si substrate 12.
  • a partition wall 26 having a predetermined thickness is formed between the concave portion 25 and the concave portion (hole portion) 14 forming the cavity 10.
  • the thickness of the partition wall 26 is determined by the pattern of the mask formed by the resist films 23 and 24 described above, and is set according to the filter length required for the gas diffusion filter 40.
  • the Si substrate 12 is immersed in a hydrofluoric acid solution while the protective films (SiN x films) 21 and 22 are left, and the partition walls 26 are anodized.
  • This anodization is based on the hydrofluoric acid present on both sides of the Si substrate 12 as shown in Fig. 5F.
  • the peripheral surface of the S ⁇ substrate 12 is sealed in a liquid-tight manner, and between the pair of electrodes provided on both surfaces of the Si substrate 12 in the hydrofluoric acid solution. This is achieved by applying a current of a predetermined density.
  • the Si substrate 12 is insulated at the portion covered with the protective films (SiN x films) 21 and 22, the current flows into the protective film (SiN x film) 21. , 22 flow through the nonexistent bulkhead 26 portion.
  • the S component forming the partition wall 26 is locally anodized and turned into a porous layer to form a porous silicon layer 27.
  • the partition wall 26 When the partition wall 26 is anodized, a current may be applied while irradiating light depending on the anodizing conditions. Also, when the partition wall 26 is anodized, the anodic oxidation current almost always flows through the inner wall surface without masking the inner wall surface of the groove-shaped concave portion 25 forming the gas flow passage 20. Since there is no anodizing, there is no possibility that the inner wall surface of the concave portion 25 (the gas passage 20) is anodized.
  • the partition wall 26 formed as the porous silicon layer 27 in this way is used as a gas diffusion filter 40 of a predetermined thickness integrally formed with the Si substrate 12 forming the cavity 10.
  • the infrared light reflecting film 7 is formed on the wall surface of the concave portion (hole portion) 14 forming the cavity 10 of the second Si substrate 12 formed integrally with the gas diffusion filter 40 as described above.
  • a wall body 28 is provided at a position facing the formation site of the gas diffusion filter 40, and the back surface side of the Si substrate 12 is provided.
  • Au, A1, etc. may be deposited (or sputtered) from diagonally below.
  • the wall body 28 may be formed at the same time as forming a predetermined height when the recess (hole) 14 is formed by etching.
  • the gas diffusion filter 40 formed as a part of the inner wall surface of the cavity 10 is shielded from the source such as Au or A1 by the wall body 28.
  • the infrared light reflection film 70 is not formed. Therefore, the infrared light reflecting film 70 can be formed on the entire inner wall surface of the cavity 10 except for the region where the gas diffusion filter 40 is formed.
  • the second Si substrate 12 integrally formed with the gas diffusion filter 40 as described above and the first Si substrate 11 integrally formed with the microphone 50 as described above are combined. Joining and joining together. Further, an optical filter forming an infrared light introduction window 30 covering the opening of the second Si substrate 12 and being joined to and integrated with one open surface of the second Si substrate 12 to form a predetermined space (sample chamber).
  • the formed cavity 10 is completed.
  • the gas diffusion filter 40 can of course be provided on the side of the first Si substrate 11 on which the microphone 50 is integrally formed. In this case, when the first Si substrate 11 is etched as shown in FIG. 6, if the above-described wall 28 is formed, the entire inner wall surface of the cavity 10 including this wall 28 is formed.
  • the infrared light reflection film 70 such as Au or A1 can be coated except for the filter surface of the gas diffusion filter 40.
  • the inside of the cavity 10 excludes the gas flow port 20 integrally provided with the gas diffusion filter 40 and the infrared light introduction window 30. Therefore, the infrared light reflected from the light source 60 into the cavity 10 is coated with the infrared light reflecting film 70 made of Au, A1, or the like. Multiple reflection occurs. Therefore, the propagation optical path length of the infrared light within the cavity 10 can be sufficiently increased, and the absorption efficiency of the gas (co 2 ) introduced into the cavity 10 can be effectively increased.
  • the thermal expansion of the gas (co 2 ) due to the absorption of the infrared light can be sufficiently increased.
  • the detection sensitivity of the microphone 50 can be sufficiently increased.
  • the detection sensitivity of the photoacoustic gas sensor can be improved by a simple configuration in which the inside of the cavity 10 is coated with the infrared light reflection film 70.
  • the practical advantage is enormous.
  • the inside of the cavity 10 can be easily coated with the infrared light reflecting film 70 as described above, the industrial advantage is also enormous in this respect.
  • the first electrode 51 of the microphone 50 that forms the ceiling of the captivity 10 has a waveform shape, infrared light can be randomly reflected, and infrared light within the capacity 10 can be reflected. Multiple reflection can be effectively generated. Therefore, the first electrode 51 having the above waveform shape greatly contributes to enhancing the detection sensitivity.
  • the modulation frequency of infrared light for thermally expanding a gas such as CO 2 is considered. It is desirable to set the frequency to, for example, 100 Hz or higher in order to avoid a frequency region where a lot of air conditioning-related noise occurs.
  • the thermal time constant of the thin film heater 64 in the light source 60 is Is less than 1.6 mSec.
  • the thermal time constant of the thin-film heater 64 is roughly proportional to a value obtained by dividing the heat capacity of the thin-film heater 64 by the degree of escaping of heat from the thin-film heater 64 (thermal conduction, convection, and radiation). Then it can be considered.
  • the heat capacity of the thin-film heater 64 is reduced while maintaining the surface area by reducing the thickness of the thin film heater 64.
  • increasing the degree of heat release leads to an increase in power consumption, and is not preferable from the viewpoint of reducing the thermal time constant. Accordingly, from the viewpoints of high-speed driving, high efficiency, and long-term stability, if the thin film heater 64 is formed of single-crystal silicon as shown in the above-described embodiment, for example, the thermal time constant is less than Imsec.
  • the frequency response due to the escape of heat in the cavity 10 is determined by the internal volume of the cavity 10 by heat transfer or heat conduction. Therefore, in the small-sized photoacoustic gas sensor as shown in the above-described embodiment, the internal volume of the cavity 10 is sufficiently small, and the frequency response may be handled by heat transfer. If the frequency characteristics of the sound pressure within the cavity 10 due to the escape of heat are replaced with an electrical system, for example, an equivalent circuit as shown in Fig. 7 can be obtained.
  • the constant T is a first-order low-pass filter.
  • the thermal time constant T is represented by the heat capacity C of air and the multiplier R for escaping heat to the Si substrate (housing), where R and C are
  • h is the natural convection heat transfer coefficient of air
  • S is the area of the inner wall surface at cavity 10
  • Cv is the specific heat of constant volume of air
  • p is the density of air
  • V is the internal volume of cavity 10 It is.
  • the frequency response to a change in sound pressure in the cavity 10 can be schematically represented as a first-order low-pass filter characteristic with the straight lines A and B asymptotically as shown in FIG.
  • the cut-off frequency f c indicated by this low-pass filter characteristic is
  • the cutoff frequency fc itself does not change, only the level of the straight line A changes, and the characteristic indicated by the straight line B does not change. Therefore, if the drive frequency of the light source 60 is set to be equal to or higher than the cut-off frequency fc, the sound pressure for the drive frequency changes along the straight line B.
  • the only way to enhance the characteristic itself represented by the straight line B to increase the sound pressure change (sensitivity) is to increase the energy change ⁇ E of infrared light corresponding to the current i in the electric system.
  • the cutoff frequency i c is obtained as 2.3 Hz. Therefore, if the light source 60 is modulated and driven at 70 Hz or higher as described above, even if the internal volume of the cavity 10 is small, a change in the sound pressure can be detected with sufficiently high sensitivity. Since noise is inversely proportional to the modulation drive frequency, it can be said that good S / N detection is possible.
  • the internal pressure in the cavity 10 can be sufficiently maintained, and the gas can be quickly replaced with the outside air and the cavity 10. It is required that sound can be cut off.
  • the holding performance of the internal pressure in the cavity 10 is a first-order high-pass filter having a time constant T determined by the pressure loss coefficient K of the gas diffusion filter 40 and the internal volume V of the cavity 10. Electrically, it is given by an equivalent circuit as shown in FIG.
  • the pressure loss coefficient K of the gas diffusion filter 40 can be set as a resistance component in an equivalent circuit, and the parameter of the internal volume V of the cavity 10 can be expressed by the following equation. Can be considered as the acoustic compliance divided by, and can be placed as a capacitor in the equivalent circuit.
  • the time constant T becomes small, and the cutoff frequency becomes, for example, about 83 Hz. It is quite close to the pulse drive frequency of 100 Hz by infrared light.
  • the ability to maintain the internal pressure in the cavity 10 also deteriorates. Therefore, in order to solve such problems, it is necessary to use a gas diffusion filter 40 with a high pressure loss coefficient K.
  • the pressure loss coefficient K is inversely proportional to the area of the gas diffusion filter 40. Therefore, as shown in the above-described embodiment, a part of the Si substrate 12 on which the cavity 10 is formed is anodized to form a porous body. If the size of the gas diffusion filter 40 is reduced as a porous silicon layer integrated with the tee 10, the pressure loss coefficient K can be increased to achieve desired filter characteristics.
  • the present invention is not limited to the embodiment described above.
  • the manufacturing method of each part constituting the photoacoustic gas sensor and its shape and size may be determined according to the specifications.
  • the means for forming the infrared light reflection film 70 is not particularly limited.
  • the light source 60 may be formed integrally with the cavity 10.
  • various modifications can be made without departing from the scope of the invention. Industrial applicability
  • the infrared light reflecting film coated on the inner wall surface of the cavity is provided, the infrared light introduced into the cavity is subjected to multiple reflection, and the gas (CO 2) is reflected.
  • the absorption efficiency of infrared light can be increased, so that a small-sized photoacoustic gas sensor with a simple configuration that increases the sound pressure change due to thermal expansion and increases its detection sensitivity can be realized.
  • the practical advantages are substantial.

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Abstract

L'invention concerne un capteur de gaz photoacoustique composé d'une cavité (10) présentant un port de flux de gaz (20) destiné à l'alimentation d'air et une fenêtre d'entrée de rayons infrarouges (30), d'un filtre de diffusion de gaz (40) présentant une couche de silicium poreuse disposée dans le port de flux de gaz d'un seul bloc avec la cavité, d'un microphone (50) formant une partie de la surface de la paroi intérieure de la cavité et présentant une première électrode (51) de forme sinusoïdale destinée à détecter la pression acoustique dans la cavité, et d'une source de lumière (60) destinée à émettre par impulsions des rayons infrarouges à l'intérieur de la cavité, au travers d'une fenêtre d'introduction de rayons infrarouges. Le capteur selon l'invention est caractérisé en ce que notamment la surface de la paroi intérieure de la cavité, exception faite du port de flux de gaz et de la fenêtre d'introduction de rayons infrarouges, est revêtue d'une couche (70) réfléchissant les rayons infrarouges, réalisée en Au, Al, ou similaire. Le capteur de gaz photoacoustique selon l'invention est de construction simple et compacte et permet d'améliorer l'efficacité de l'absorption de rayons infrarouges par la détection d'un gaz cible dans la cavité irradiée par des rayons infrarouges d'intensité limitée, et d'améliorer par ailleurs la sensibilité de la détection de gaz.
PCT/JP2002/004285 2001-04-27 2002-04-26 Capteur de gaz photoacoustique WO2002088698A1 (fr)

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GB2511327A (en) * 2013-02-28 2014-09-03 Scytronix Ltd Photoacoustic Chemical Detector
US8848191B2 (en) 2012-03-14 2014-09-30 Honeywell International Inc. Photoacoustic sensor with mirror
CN107462629A (zh) * 2016-06-03 2017-12-12 英飞凌科技股份有限公司 声波检测器
CN112730303A (zh) * 2020-12-18 2021-04-30 Oppo广东移动通信有限公司 气体检测方法及装置、终端设备、存储介质
EP3832301A1 (fr) * 2019-12-06 2021-06-09 Commissariat à l'Energie Atomique et aux Energies Alternatives Dispositif pour la caractérisation photo-acoustique d'une substance gazeuse et procédé de fabrication d'un tel dispositif

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JP5134277B2 (ja) 2007-03-30 2013-01-30 三菱重工業株式会社 超音波検査装置
JP5260130B2 (ja) * 2007-08-10 2013-08-14 三菱重工業株式会社 超音波検査装置、超音波検査方法および原子力プラントの非破壊検査方法
JP5223298B2 (ja) * 2007-10-30 2013-06-26 横河電機株式会社 赤外線光源
JP5260985B2 (ja) * 2008-02-29 2013-08-14 パナソニック株式会社 赤外線放射素子
US8695402B2 (en) * 2010-06-03 2014-04-15 Honeywell International Inc. Integrated IR source and acoustic detector for photoacoustic gas sensor
US10883875B2 (en) 2015-03-05 2021-01-05 Honeywell International Inc. Use of selected glass types and glass thicknesses in the optical path to remove cross sensitivity to water absorption peaks
DE202015002315U1 (de) * 2015-03-27 2015-05-06 Infineon Technologies Ag Gassensor
WO2017044435A1 (fr) 2015-09-10 2017-03-16 Honeywell International Inc. Détecteur de gaz présentant réponse normalisée et sensibilité améliorée
US9606049B1 (en) * 2015-10-09 2017-03-28 Honeywell International Inc. Gas detector using a golay cell
EP3359933A1 (fr) 2015-10-09 2018-08-15 Honeywell International Inc. Détecteur de rayonnement électromagnétique utilisant une cellule de golay plate

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Cited By (9)

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Publication number Priority date Publication date Assignee Title
US8848191B2 (en) 2012-03-14 2014-09-30 Honeywell International Inc. Photoacoustic sensor with mirror
GB2511327A (en) * 2013-02-28 2014-09-03 Scytronix Ltd Photoacoustic Chemical Detector
CN107462629A (zh) * 2016-06-03 2017-12-12 英飞凌科技股份有限公司 声波检测器
US10451589B2 (en) 2016-06-03 2019-10-22 Infineon Technologies Ag Acoustic wave detector
EP3832301A1 (fr) * 2019-12-06 2021-06-09 Commissariat à l'Energie Atomique et aux Energies Alternatives Dispositif pour la caractérisation photo-acoustique d'une substance gazeuse et procédé de fabrication d'un tel dispositif
FR3104259A1 (fr) * 2019-12-06 2021-06-11 Commissariat A L'energie Atomique Et Aux Energies Alternatives Dispositif pour la caractérisation photo-acoustique d’une substance gazeuse et procédé de fabrication d’un tel dispositif
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US11874217B2 (en) 2019-12-06 2024-01-16 Commissariat A L'energie Atomique Et Aux Energies Alternatives Device for photoacoustic characterisation of a gaseous substance and method for manufacturing such a device
CN112730303A (zh) * 2020-12-18 2021-04-30 Oppo广东移动通信有限公司 气体检测方法及装置、终端设备、存储介质

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