JP5601700B2 - Ozone detection sensor - Google Patents

Description

  The present invention relates to an ozone detection sensor, and more particularly to an ozone detection sensor that detects an ozone concentration in an ozone-containing fluid using a zinc oxide thin film.

Ozone (O ₃ ) has a strong oxidizing power and is used in the gas phase or in various consumer and industrial applications such as sterilization and washing of food and cooking equipment, purification and deodorization of living rooms and wastewater treatment facilities, and bleaching of clothes. Widely used as a liquid phase. However, use at an inappropriate concentration may cause adverse effects on the human body or deterioration of equipment / equipment, so use at an appropriate ozone concentration (for example, 0.1 ppm or less) is required. Recently, there are cases where it is required not only to use ozone, but also to manage the ozone concentration in the natural environment and the workplace environment for the purpose of environmental conservation and occupational health. In order to detect the ozone concentration in the gas phase or the liquid phase, an ultraviolet absorption type ozone concentration detection device utilizing the property that the maximum absorption band of ozone is in a specific wavelength region (near 254 nm) of ultraviolet light. (Hereinafter, sometimes referred to as an ozone detection sensor) has been developed (see Non-Patent Document 1 and Patent Document 1).

  For example, in Patent Document 1, as shown in FIG. 8, a hollow cylindrical measurement cell 33 and a standard cell 34 are respectively opposed to a lamp 31 (for example, a low-pressure mercury lamp that outputs monochromatic light centered on an ozone maximum absorption band). The ozone light O and the standard water R are allowed to flow into the hollow portions of the cells 33 and 34, respectively, and the lamp light is irradiated into the hollow portions from the light transmitting windows 33A and 34A, and the amount of transmitted light in the hollow portions Is detected by detection sensors 35 and 46 (for example, a photodiode having a detection sensitivity near the ozone maximum absorption band, a phototube, a photomultiplier tube, etc.) provided in each of the cells 33 and 34 to detect the ozone concentration in the ozone water O. An apparatus is disclosed. Specifically, the light amount output value of the detection sensor 46 of the target cell 34 is input to the comparison amplification circuit 48, and the power supply 32 of the lamp 31 is always kept constant by the comparison amplification circuit 48. To control the voltage. Further, the output value of the detection sensor 35 is input to the ozone concentration calculation processing circuit 36, and the calculation processing circuit 36 converts the output value of the detection sensor 35 into the ozone concentration in the ozone water O and outputs it to the display 44. By controlling the lamp 31 so that the amount of light is constant on the target cell 34 side, it is possible to accurately detect the ozone concentration on the measurement cell 33 side while avoiding the influence of lamp deterioration and the like.

JIS-B-7957 “Automatic measuring instrument for ozone and oxidant in the atmosphere” Japanese Standards Association, March 2006, Internet <URL: http: // www. jisc. go. jp / app / pager? id = 57773>

JP 2001-056292 A JP 2003-254957 A JP 2008-039665 A

  However, a conventional ultraviolet absorption type ozone detection sensor needs to incorporate relatively large detection sensors 35 and 46 such as photodiodes as shown in FIG. In addition, the photodiodes used as the detection sensors 35 and 46 are sensitive to wavelength regions other than the ozone maximum absorption band (visible light having a wavelength longer than the ozone maximum absorption band). It is also necessary to incorporate the optical filters 33B and 34B for blocking. For this reason, although the ozone concentration detection accuracy is high, there is a problem that the structure is complicated and it is difficult to reduce the size. Ozone detection sensor by using a method other than ultraviolet absorption, for example, a chemiluminescence method (see Non-Patent Document 1 and Patent Document 2) that detects the ozone concentration by using chemiluminescence of a reaction material of ozone and another chemical substance. However, it is difficult to detect ozone concentration with high accuracy as in the UV absorption method, and it is necessary to exchange chemical substances that have already reacted with ozone. It becomes difficult. In order to apply to the detection of the concentration of ozone used in various environments and devices, it is necessary to develop an ozone detection sensor that can detect ozone concentration with a small size that is portable or can be installed inside devices. is there.

  Accordingly, an object of the present invention is to provide a compact ozone detection sensor capable of accurately detecting the ozone concentration.

  The inventor of the present invention paid attention to an ultraviolet detection element utilizing a change in resistance value (photoconductive effect) caused by ultraviolet light irradiation of a zinc oxide (ZnO) thin film. For example, Patent Document 3 uses a P-type or N-type semiconductor zinc oxide thin film whose sensitivity to ultraviolet light is increased by doping or intrinsic defects, and is insensitive to visible light (resistance value hardly changes). A detection element is proposed. If such a thin-film ultraviolet detection element is used in place of the detection sensors 35 and 46 in FIG. 8, for example, the optical filters 33B and 34B that obstruct the downsizing of the ozone detection sensor can be omitted.

  However, the ultraviolet detection element disclosed in Patent Document 3 has a maximum sensitivity frequency (maximum frequency of the photosensitivity spectrum) in the A region (wavelength 400 to 315 nm, hereinafter referred to as UVA region) of ultraviolet light, Sensitivity to the C region (having a wavelength of less than 280 nm, hereinafter sometimes referred to as UVC region) including the ozone maximum absorption band (near 254 nm) is relatively small. Although the maximum sensitivity frequency of the zinc oxide thin film can be shifted somewhat by controlling the doping amount or the intrinsic defect amount (see Patent Document 3), it is difficult to shift the maximum sensitivity frequency from the UVA region to the UVC region. is there. As shown in FIG. 5, the present inventor can adjust the ratio of the ultraviolet light sensitivity of the UVC region to the UVA region by controlling the film thickness of the zinc oxide thin film having the maximum sensitivity frequency in the UVA region. It was found experimentally. If a zinc oxide thin film having a high sensitivity ratio of the UVC region to the UVA region is used, it can be expected to improve the detection accuracy of the concentration of ozone having a maximum absorption band in the UVC region. The present invention has been completed as a result of research and development based on this finding.

Referring to the embodiment of FIG. 1, an ozone detection sensor according to the present invention includes a measurement cell 4 in which a pair of translucent substrates 4a and 4b facing each other in a gap 5 is filled with an ozone-containing fluid O, and one substrate of the measurement cell 4. A light source 20 for irradiating ultraviolet light UV on 4a, a P-type or N-type film thickness d of which the ultraviolet light sensitivity is increased by doping or intrinsic defect provided on the light transmitting side of the other substrate 4b of the measurement cell 4 it comprises a measuring circuit 16 for detecting the zinc oxide thin film 10, the electrode pairs 11 and 12 for applying a constant voltage to the zinc oxide thin film 10, and the current between the electrode pair 11 and 12, and the thickness d of the zinc oxide thin film 10 A proportional coefficient with the sensitivity ratio (UVC / UVA) of the C area ultraviolet light to the A area ultraviolet light is experimentally obtained, and a predetermined film thickness d of the zinc oxide thin film 10 is obtained so that a necessary sensitivity ratio is obtained based on the proportional coefficient. Is selected.

Preferably, a proportional coefficient between the film thickness d of the zinc oxide thin film and the sensitivity ratio of the C region ultraviolet light to the A region ultraviolet light (UVC / UVA) is experimentally determined, and the film thickness d of the zinc oxide thin film 10 and the electrode pair A proportional coefficient with the time constant of the current between 11 and 12 is experimentally obtained, a necessary time is obtained based on both proportional coefficients, and the sensitivity ratio of the C area ultraviolet light to the A area ultraviolet light (UVC / UVA) The predetermined film thickness d of the zinc oxide thin film 10 is selected so as to be maximized. The zinc oxide thin film 10 can be provided in contact with the other substrate 4 b of the measurement cell 4 as shown in FIG. 2A, for example, and the electrode pairs 11 and 12 can be provided in contact with the thin film 10. Alternatively, as shown in FIG. 2C, the electrode pairs 11 and 12 may be provided in contact with the other substrate 4b of the measurement cell 4, and the zinc oxide thin film 10 may be provided in contact with the electrodes 11 and 12. Good.

  The ultraviolet light sensitivity of the zinc oxide thin film 10 can be increased by doping with, for example, B, Al, Ga, In, Zn, H, a group I element, or a group IV element. The zinc oxide thin film 10 may be either a P-type or N-type semiconductor film. For example, as shown in FIG. 3C, a PIN-type thin film in which a P-type and an N-type are stacked with an insulating layer 26 interposed therebetween. The electrode pairs 11 and 12 can be arranged separately on the P-type surface and the N-type surface of the PIN-type thin film.

  Desirably, as shown in FIG. 4, a control cell 7 for loading a non-ozone-containing fluid R is provided in the opposing gap 8 of the pair of translucent substrates 7 a and 7 b, and one of the measurement cell 4 and the control cell 7 is provided by the light source 20. Each of the substrates 4a and 7a is irradiated with ultraviolet light UV, and the zinc oxide thin films 10 and 13 and the electrode pairs (10, 11) and (14, 15) are transferred to the other substrates 4b and 7b of the measurement cell 4 and the control cell 7, respectively. The current difference between the electrode pairs 10 and 11 of the measurement cell 4 and the electrode pairs 14 and 15 of the reference cell 7 is detected by the measurement circuit 16.

  Each of the measurement cell 4 and the control cell 7 has a cylindrical shape having a hollow portion 5 that can be filled with an ozone-containing fluid O or a non-ozone-containing fluid R, and a pair of translucent substrates 4a and 4b that face each other through the hollow portion 5. Cell 2 can be used. Moreover, the measurement cell 4 and the control cell 7 can be made into the integral cylindrical cell 2, for example, as shown in FIG. 4, the single cylindrical shape by which the hollow part 5 was divided by the intermediate partition 3 into the two passages. Cell 2 can be used. The ultraviolet light sensitivity of the zinc oxide thin film 13 can also be increased by doping with, for example, B, Al, Ga, In, Zn, H, a group I element, or a group IV element.

The ozone detection sensor of the present invention is provided with a pair of translucent substrates 4a and 4b facing a measurement cell 4 with a gap 5 therebetween, and a predetermined film on the outer side (opposite side of the gap 5) of one translucent substrate 4b. A zinc oxide thin film 10 having a thickness d is provided, and electrode pairs 11 and 12 for applying a constant voltage to the thin film 10 are provided. The thickness d of the zinc oxide thin film 10 obtained experimentally and the C region ultraviolet light with respect to the A region ultraviolet light. After selecting a predetermined film thickness d of the zinc oxide thin film 10 based on a proportionality factor with respect to the sensitivity ratio (UVC / UVA), the outer side (gap 5) of the other translucent substrate 4a is selected. The ozone-containing fluid O is filled in the opposing gap 5 between the substrates 4a and 4b while irradiating the ultraviolet light UV from the opposite side), and the resistance value of the zinc oxide thin film 10 is irradiated by the ultraviolet light UV transmitted through the opposing gap 5. Change (photoconductive effect) electrode pair 11, 12 And detects the ozone concentration of the ozone-containing fluid O is detected by the measuring circuit 16 connected, the following effects.

(A) Since the ozone concentration is detected using the extremely thin zinc oxide thin film 10, an extremely compact ozone detection sensor having a size capable of storing the measurement cell 4 and the light source 20 substantially filled with the ozone-containing fluid O is obtained. be able to.
(B) Since the zinc oxide thin film 10 that is substantially insensitive to visible light is used, it is not necessary to use an optical filter or the like that blocks visible light, and the ozone detection sensor is miniaturized and the structure is simplified. be able to.
(C) Since the film thickness d of the zinc oxide thin film 10 is selected so that the required sensitivity ratio (UVC / UVA) of the UVC region to the UVA region is obtained according to the required detection accuracy of the ozone concentration , the ozone maximum absorption It is possible to detect the current change occurring in the band (near 254 nm), that is, the ozone concentration in the ozone-containing fluid with sufficient accuracy.

(D) When the film thickness d of the zinc oxide thin film 10 is increased, the time constant of the current flowing through the zinc oxide thin film 10 (time until the current rises to 63% of the maximum value) becomes longer, and as a result, the ozone concentration is detected. Although it may be delayed , the proportional coefficient between the film thickness d of the zinc oxide thin film and the sensitivity ratio of the C region ultraviolet light to the A region ultraviolet light (UVC / UVA) is experimentally obtained, and the film of the zinc oxide thin film 10 is obtained. A proportional coefficient between the thickness d and the time constant of the current between the electrode pairs 11 and 12 is experimentally obtained. Based on the proportional coefficient, the necessary time is obtained and the sensitivity ratio of the UVC region to the UVA region is maximized. Thus, by selecting the film thickness d of the zinc oxide thin film 10, both the detection time and accuracy of the ozone concentration can be optimized.
(E) The control cell 7 filled with the non-ozone-containing fluid R is provided, and the ozone concentration of the ozone-containing fluid O is detected by the current difference between the measurement cell 4 and the reference cell 7, resulting in deterioration of the light source 20 and the like. Detection errors can be prevented, and the ozone concentration detection accuracy can be further improved.
(F) In addition, by using the single cylindrical cell 2 in which the hollow portion 5 is divided into two passages by the intermediate partition wall 3 as the measurement cell 4 and the control cell 7, ozone detection accompanying the addition of the control cell 7 An ozone detection sensor with high detection accuracy can be obtained while avoiding an increase in size of the sensor.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments and examples for carrying out the present invention will be described with reference to the accompanying drawings.
It is explanatory drawing of one Example of the ozone detection sensor by this invention. It is explanatory drawing of the other Example which shows arrangement | positioning of the zinc oxide thin film 10 in an ozone detection sensor. It is explanatory drawing of the Example which shows arrangement | positioning of the electrode pairs 11 and 12 with respect to the zinc oxide thin film 10. FIG. It is explanatory drawing of the other Example of the ozone detection sensor by this invention. It is an example of the graph which shows the difference in the ultraviolet light detection sensitivity (detection current change) according to frequency with respect to the film thickness of a zinc oxide thin film. It is an example of the graph which shows the relationship between the film thickness of a zinc oxide thin film, and the photosensitivity ratio (UVC / UVA) of the UVC area | region with respect to a UVA area | region. It is a graph which shows the relationship between the film thickness of a zinc oxide thin film, and the time constant of the electric current which flows into a zinc oxide thin film at the time of ultraviolet light irradiation. It is explanatory drawing of an example of the conventional ozone concentration detection apparatus.

  FIG. 1 shows an embodiment of the ozone detection sensor of the present invention. The ozone detection sensor 1 of the example of illustration has the cylindrical measurement cell 4 which has the hollow part 5, and the light source 20 which light-emits ultraviolet light UV. The measurement cell 4 in the illustrated example has at least a part of the peripheral walls facing each other through the hollow part 5 as a light-transmitting substrate pair 4a, 4b, and provided with the opening 6a, 6b communicating with the outside in the hollow part 5, The opposing gap 5 (that is, the hollow portion 5) between the substrate pair 4a and 4b can be filled with the ozone-containing fluid O. The light source 20 is disposed so as to face the outer surface of one translucent substrate 4a of the measurement cell 4 so that the ultraviolet light UV is incident in the facing gap 5. In the illustrated measurement cell 4, a P-type or N-type zinc oxide thin film 10 having a predetermined film thickness d provided on the translucent side (outer surface side) of the other translucent substrate 4b and the thin film 10 are fixed. A pair of electrodes 11 and 12 to which a voltage is applied, and a measuring circuit 16 for detecting a photocurrent (resistance value of the zinc oxide thin film 10) flowing in the zinc oxide thin film 10 between the electrode pairs 11 and 12 are provided.

  The measurement cell 4 is, for example, a hollow cylindrical cell 2 made of transparent glass (quartz glass, heat-resistant glass, tempered glass, etc.) or transparent plastic (polyvinyl chloride, polyethylene terephthalate (PET), polycarbonate, polymethyl methacrylate, etc.). The pair of opposing wall surfaces of the cylindrical cell 2 can be the translucent substrates 4a and 4b. However, it is sufficient that the translucent substrates 4a and 4b are provided on at least a part of the opposing wall surface, and the other part may be the non-translucent wall surface 4c. Further, the measurement cell 4 used in the present invention is not limited to the one made of a cylindrical cell, and any cell can be used as long as it can fill the opposed gap 5 between the translucent substrates 4a and 4b with the ozone-containing fluid O. For example, glass or plastic substrates 4a and 4b, which are at least partially transparent, are held facing each other with a predetermined gap 5, and the ozone-containing fluid O is fed into the facing gap 5 from the periphery of both the substrates 4a and 4b and filled. The measurement cell 4 may be used. If necessary, a feeding or suction device (such as a pump) for introducing the ozone-containing fluid O into the facing gap 5 may be included in the measurement cell 4.

  The light source 20 can be, for example, a low-pressure mercury lamp similar to that shown in FIG. 8 having an emission center in the ozone maximum absorption band (near 254 nm). However, as will be described later, in the present invention, since the ultraviolet light sensitivity ratio (UVC / UVA) of the UVC region to the UVA region of the zinc oxide thin film 10 can be increased, the influence other than the ozone maximum absorption band can be suppressed to be small. However, it is also possible to use an ultraviolet lamp other than the ozone maximum absorption band. It is expected that the ozone detection sensor 1 can be downsized by widening the selection range of the light source 20.

The zinc oxide thin film 10 is made of ultraviolet light by doping with one or more impurities selected from, for example, B, Al, Ga, In, Zn, H, a group I element (alkali metal element), or a group IV element (Si, Ge, etc.). Zinc oxide with increased sensitivity, or additive-free zinc oxide with increased ultraviolet light sensitivity due to intrinsic defects lacking oxygen atoms, for example, on a suitable substrate (for example, made of glass or plastic) with a predetermined film thickness d It can be formed by stacking. Zinc oxide also has sensitivity in the visible light region. For example, the carrier concentration is 10 × 10 ¹⁸ cm ⁻³ or more (preferably 1 × 10 ¹⁹ cm ⁻³ or more, more preferably 1 × 10 ²⁰ cm ^−3. By controlling the amount of doping or the amount of oxygen atoms lost so as to achieve the above, an impurity band is formed and the maximum frequency band is shifted to the lower wavelength (high energy) side, and is substantially transparent to visible light. The zinc oxide thin film 10 can be obtained. Preferably, a zinc oxide thin film 10 doped with Ga as an impurity is used.

  The film thickness d of the zinc oxide thin film 10 is selected so that the ultraviolet light sensitivity ratio (UVC / UVA) of the UVC region to the UVA region of the thin film 10 is not less than a predetermined ratio. In order to accurately detect the ozone concentration by the zinc oxide thin film 10, it is desirable to use the thin film 10 having high sensitivity (photoconductive effect) in the ozone maximum absorption band (near 254 nm). However, as shown in FIG. 5, the maximum frequency of the photocurrent (sensitivity) flowing through the zinc oxide thin film 10 exists in the UVA region (around 350 to 360 nm), and the photocurrent (sensitivity) in the ozone maximum absorption band is relative. Small. FIG. 5 shows an experiment in which the zinc oxide thin film 10 having film thicknesses d = 5 nm, 65 nm, 120 nm, and 205 nm is irradiated with ultraviolet light UV while sweeping the frequency, and the photocurrent (arbitrary unit) flowing through each thin film 10 is measured for each frequency. The result (photosensitivity spectrum) is shown. For example, in the thin film 10 having a film thickness d = 5 nm, the sensitivity of the ozone maximum absorption band is extremely small, so that the detection error of the ozone concentration can be large. On the other hand, FIG. 5 shows that the photocurrent (sensitivity) at the maximum sensitivity frequency of the zinc oxide thin film 10 is substantially constant regardless of the film thickness d, but the photocurrent (sensitivity) in the UVC region including the ozone maximum absorption band is the film thickness. It shows that it increases depending on d. If the film thickness d of the zinc oxide thin film 10 is selected to increase the photosensitivity ratio of the UVC region to the UVA region, the detection accuracy of the photocurrent change that occurs in the ozone maximum absorption band is increased, and the accuracy necessary for detecting the ozone concentration is increased. Can be secured.

  FIG. 6 shows the change in the ratio (UVC / UVA) of the photocurrent (sensitivity) in the UVC region to the photocurrent (sensitivity) in the UVA region depending on the film thickness d of the zinc oxide thin film 10 based on the experimental results of FIG. It is a plot. The graph of FIG. 6 shows that the photosensitivity ratio (UVC / UVA) of the zinc oxide thin film 10 is substantially proportional to the film thickness d of the thin film 10, that is, the photosensitivity ratio is adjusted by selecting the film thickness d of the thin film 10. It shows what you can do. Accordingly, the photosensitivity ratio is determined according to the required ozone concentration detection accuracy, and the ozone concentration is detected with the required accuracy by selecting a film thickness d that is equal to or greater than that ratio based on FIG. The zinc oxide thin film 10 can be obtained. For example, when sufficient accuracy is obtained at a light sensitivity ratio of 0.05 to 0.1, 25 to 50 nm is selected as the film thickness d of the zinc oxide thin film 10, and the light sensitivity ratio is required when higher accuracy is required. A film thickness d = 50 to 80 nm is selected such that = 0.15 to 0.2. Note that the proportionality coefficient between the photosensitivity ratio (UVC / UVA) and the film thickness d shown in FIG. 6 and other specific numerical values differ depending on the film forming conditions, the doping amount, and the like of the zinc oxide thin film 10. It is desirable to experimentally create and determine a graph similar to FIG. 6 after determining the doping amount and the like.

  However, according to the experiments by the present inventors, when the film thickness d of the zinc oxide thin film 10 increases, the time constant of the photocurrent of the zinc oxide thin film 10 during irradiation with ultraviolet rays UV (until the photocurrent rises to 63% of the maximum value). As a result, the detection of the photocurrent (ozone concentration detection) flowing through the thin film 10 during the irradiation with the ultraviolet light UV is delayed. The graph of FIG. 7 shows the experimental results of measuring the time constant of the detected current during irradiation with ultraviolet light having a wavelength of 350 nm while changing the film thickness d of the zinc oxide thin film 10. As can be seen from FIG. 7, the time constant of the photocurrent is about 50 seconds when the thin film 10 is about d = 10 nm, whereas the time constant is about 200 seconds when the film thickness d = 20 nm. When the film thickness d is about 50 nm, the time constant becomes as long as about 400 seconds.

  Therefore, when prompt detection of the ozone concentration is required, the range of the film thickness d that provides the required detection accuracy is determined based on FIG. 6, and an allowable time constant is obtained based on FIG. The range of the film thickness d is determined, and the film thickness d is selected so as to satisfy both ranges. Preferably, the ozone concentration is detected by selecting the film thickness d that maximizes the photosensitivity ratio (UVC / UVA) of the UVC region to the UVA region within the range of the film thickness d that provides an acceptable time constant. Optimize both time and accuracy. For example, when it is necessary to detect the ozone concentration in about 250 seconds, the film thickness d in FIG. 7 needs to be about 28 nm or less. Therefore, the film having the maximum photosensitivity ratio within the range based on FIG. A thickness d = 28 nm is selected. Note that the proportionality coefficient between the time constant and the film thickness d shown in FIG. 7 and other specific numerical values also differ depending on the film forming conditions, doping amount, and the like of the zinc oxide thin film 10, so the film forming conditions, the doping amount, and the like were determined. It is desirable to determine experimentally.

  The electrode pairs 11 and 12 can be provided in contact with the surface of the zinc oxide thin film 10 laminated with a film thickness d as described above, and can be, for example, ohmic electrodes. For example, the electrode pairs 11 and 12 are formed by vapor-depositing a metal (for example, aluminum, indium, gold, silver, zinc, or an alloy thereof) that easily obtains ohmic contact on the surface of the thin film 10. However, the electrode pairs 11 and 12 may be Schottky electrodes (MS structure) or Schottky electrodes (MIS structure) with an insulating layer 25 interposed therebetween as shown in FIG. May be an ohmic electrode and the other may be a Schottky electrode.

  In FIG. 1, the electrode pairs 11 and 12 are formed by vapor deposition on one side of the zinc oxide thin film 10. For example, as shown in FIG. 3B, the electrode pairs 11 and 12 are formed on one side of the zinc oxide thin film 10. And may be formed separately on the opposite side. In the present invention, either the P-type or N-type zinc oxide thin film 10 can be used. For example, as shown in FIG. 3C, the P-type and the N-type are laminated via the insulating layer 26. A PIN-type zinc oxide thin film 10 can be used, and the electrode pairs 11 and 12 can be formed separately on the P-type surface and the N-type surface of the PIN-type thin film. By using the PIN type zinc oxide thin film 10, the thin film 10 can be operated at high speed, and the time constant of the photocurrent of the thin film 10 generated upon irradiation with ultraviolet rays UV can be expected to be shortened. The range of selection of d can be expanded.

  The ozone detection sensor of FIG. 1 uses a zinc oxide thin film 10 which is laminated on a suitable transparent substrate (for example, glass or plastic) with a predetermined film thickness d and electrode pairs 11 and 12 are vapor-deposited on the laminated surface. By locking the zinc thin film 10 to the holding member 22 provided in the measurement cell 4, the transparent base of the zinc oxide thin film 10 is held facing the light transmitting side of the light transmitting substrate 4b. In this embodiment, the transmitted ultraviolet light UV of the translucent substrate 4b is irradiated to the zinc oxide thin film 10 via the transparent substrate, and the current flowing through the thin film 10 at the time of irradiation is detected by the electrode pairs 11 and 12. However, as shown in FIG. 2B, the zinc oxide thin film 10 is held facing the translucent substrate 4b, and the ultraviolet light UV transmitted through the translucent substrate 4b is directly irradiated onto the zinc oxide thin film 10. It is also possible to hold it.

  In addition, instead of using the zinc oxide thin film 1 previously laminated on the substrate as shown in FIG. 1, the zinc oxide thin film 10 is placed on the translucent substrate 4 b of the measuring cell 4 as shown in FIG. Direct lamination is also possible. The method for forming the zinc oxide thin film 10 on the translucent substrate 4b is not particularly limited as long as it is a method capable of forming the film on the translucent substrate 4, but is preferably a metal vapor (zinc vapor evaporated in a vacuum). Alternatively, an ion plating method is used in which the zinc oxide thin film 10 is grown on the surface of the translucent substrate 4b by a plasma assisted reaction between the zinc oxide vapor) and the reaction gas (oxygen gas and / or impurity gas). In the ion plating method, since the temperature rise of the substrate 4b is small and the thin film 10 having high adhesion strength can be grown even at a low temperature of 200 ° C. or less, the zinc oxide thin film 10 is also formed on the plastic substrate 4b that is weak at high temperature. There is an advantage that can be formed.

  Alternatively, as shown in FIG. 2C, the electrode pairs 11 and 12 are provided in contact with the translucent substrate 4b of the measurement cell 4 and stacked on an appropriate substrate (including non-transparent materials). It is also possible to place the zinc thin film 10 in contact with the electrodes 11 and 12. In this embodiment, a pair of metals (for example, gold) 23 and 24 are vapor-deposited on the translucent substrate 4b, and the metal pairs 23 and 24 and the electrode pairs 11 and 12 vapor-deposited on the zinc oxide thin film 10 are bonded. By doing so, the zinc oxide thin film 10 is held on the light transmitting side of the light transmitting substrate 4b. As shown in FIGS. 2A and 2C, the translucent substrate 4b and the zinc oxide thin film 10 or the electrode pairs 11 and 12 are brought into contact with each other to hold the holding member as shown in FIGS. 1 and 2B. The ozone detection sensor can be further downsized by omitting 22.

  When detecting the ozone concentration using the ozone detection sensor 1 of FIG. 1 or FIG. 2, the ozone-containing fluid O that is the concentration detection target is filled in the opposing gap 5 of the sensor 1, and then the electrode pair 11 is applied to the zinc oxide thin film 10. , 12 while applying a constant voltage to the outer surface of the translucent substrate 4a of the sensor 1 from the light source 20 to the ultraviolet light UV in the UVC region (preferably, the ultraviolet light UV centered on the ozone maximum absorption band near 254 nm). ) And the measurement circuit 16 detects a current value (resistance value of the zinc oxide thin film 10) flowing between the electrode pairs 11 and 12 of the thin film 10 in accordance with irradiation of the transmitted light through the facing gap 5.

  In the embodiment of FIG. 1, an arithmetic device 18 such as a computer is connected to the measurement circuit 16, and the current value detected by the measurement circuit 16 is input to the arithmetic device 18 to detect the ozone concentration in the ozone-containing fluid O. In the arithmetic unit 18, for example, by a preliminary experiment using an ozone-containing fluid O having a known ozone concentration, a relational expression between the detected current value of the measuring circuit 16 for the ultraviolet light UV in the UVC region and the ozone concentration of the ozone-containing fluid O ( Table etc.) 18a can be obtained and stored in advance. The calculation means 18 in the illustrated example converts the detected current value input from the measurement circuit 16 into an ozone concentration based on the relational expression 18a, and outputs the converted ozone concentration to a display device 19 such as a display.

  Alternatively, as indicated by the dotted line in FIG. 1, the ozone detection sensor 1 includes a light source 20 that irradiates ultraviolet light UV in the UVC region and a light source 21 that irradiates ultraviolet light UV in the UVA region. The zinc oxide thin film 10 is sequentially irradiated with ultraviolet light in the UVA region and UVC region through the substrates 4a and 4b, and the current value flowing between the electrode pairs 11 and 12 of the zinc oxide thin film 10 in response to the irradiation of both ultraviolet light. The ratio can also be detected by the measurement circuit 16 (or the arithmetic device 18). In this case, a preliminary experiment using an ozone-containing fluid O with a known ozone concentration shows a relationship between the ratio of the detected current value of the measurement circuit 16 due to ultraviolet light irradiation in the UVA region and the UVC region and the ozone concentration of the ozone-containing fluid O. Expression 18a is obtained in advance and stored in the arithmetic unit 18, and the ozone concentration is obtained from the current ratio detected by the measurement circuit 16 based on the relational expression 18a.

  The ozone detection sensor 1 of the present invention uses a zinc oxide thin film 10 that is substantially transparent to visible light, so there is no need to incorporate an optical filter or the like, and the measurement cell 4 and the zinc oxide thin film 10 for detecting the ozone concentration are provided. Since it can be configured integrally, the structure is simpler and more compact than the conventional ozone detection sensor as shown in FIG. Further, since the film thickness d of the zinc oxide thin film 10 is selected so that the sensitivity ratio of the UVC region to the UVA region (UVC / UVA) is increased, the change in the photocurrent generated in the ozone maximum absorption band in the UVC region is sufficient. It is possible to detect the ozone concentration with sufficient accuracy.

  Thus, it is possible to provide the “compact ozone detection sensor capable of accurately detecting the ozone concentration” which is an object of the present invention.

  FIG. 4 shows another embodiment of the ozone detection sensor 1 of the present invention in which the control cell 7 is provided together with the measurement cell 4. The control cell 7 is a cell in which the non-ozone-containing fluid R is loaded into the opposing gap 8 between the translucent substrates 7a and 7b. For example, the control cell 7 is a cylindrical cell 2 having a hollow portion 5 similar to the measurement cell 4 in FIG. be able to. On one translucent substrate 7b of the reference cell 7, as in the measurement cell 4, a zinc oxide thin film 13 is laminated with the same film thickness d, and electrode pairs 14 and 15 for applying a constant voltage to the thin film 13 are used. Is provided. In addition, ultraviolet light UV is irradiated from the light source 20 onto one of the substrates 4 a and 7 a of the measurement cell 4 and the control cell 7, and flows into the zinc oxide thin film 10 between the electrode pairs 10 and 11 of the measurement cell 4 by the measurement circuit 16. The current difference between the current and the current flowing in the zinc oxide thin film 13 between the electrode pairs 14 and 15 of the reference cell 7 is detected.

  When the ozone detection sensor 1 is configured by only the measurement cell 4 as shown in FIG. 1, there is a possibility that a detection error may occur in the ozone concentration due to, for example, deterioration of the light source 20m or contamination of the translucent substrates 4a and 4b of the measurement cell 4. is there. On the other hand, in the embodiment of FIG. 4, by comparing the photocurrent detected by the measurement cell 4 with the photocurrent detected by the control cell 7, as in the case of FIG. By avoiding the influence of deterioration and dirt on the light-transmitting substrates 4 and 7, detection errors can be prevented, and deterioration of ozone concentration detection accuracy can be prevented. In the illustrated example, the ultraviolet light UV is irradiated from the single light source 20 to the measurement cell 4 and the control cell 7, but separate light sources 20 may be provided to the measurement cell 4 and the control cell 7. If necessary, an appropriate optical system can be provided between the light source 20 and the measurement cell 4 and the reference cell 7. As shown in FIG. 8, the measurement cell 4 and the control cell 7 can be arranged on both sides of the single light source 20.

  Further, as shown in FIG. 4B, a single cylindrical cell 2 in which the hollow portion 5 is divided into two passages by the intermediate partition wall 3 is used, and one and the other passages are respectively used as the measurement cell 4 and the control cell 7. Thus, the measurement cell 4 and the control cell 7 can be integrated. By using a single cylindrical cell 2 as shown in FIG. 4 and integrating the measurement cell 4 and the control cell 7, the size of the ozone detection sensor 1 associated with the addition of the control cell 7 can be avoided, and the FIG. It can be set as the compact ozone detection sensor 1 substantially the same magnitude | size.

DESCRIPTION OF SYMBOLS 1 ... Ozone detection sensor 2 ... Cylindrical cell 3 ... Blocking part 4 ... Measurement cell 4a, 4b ... Translucent substrate (translucent wall) 4c ... Non-translucent wall 5 ... Opposite gap (hollow part) 6, 6a, 6b ... Opening 7 ... Control cell 7a, 7b ... Translucent substrate (translucent wall)
8 ... Opposite gap (hollow part) 9, 9a ... Opening 10 ... Zinc oxide thin film 11, 12 ... Electrode 13 ... Zinc oxide thin film 14, 15 ... Electrode 16 ... Measuring circuit 17 ... Measuring circuit (amplifier)
DESCRIPTION OF SYMBOLS 18 ... Arithmetic device 19 ... Display device 20, 21 ... Light source 22 ... Holding member 23, 24 ... Contact electrode 25, 26 ... Insulating layer 31 ... Mercury lamp 32 ... High voltage generating power source 33 ... Measuring cell 33A ... Translucent window 33B ... Optical Filter 34 ... Standard cell 34A ... Translucent window 34B ... Optical filter 35 ... Detection sensor (photodiode) 36 ... Processing circuit 37 ... Arithmetic circuit 38 ... Preamplifier 39 ... Comparison amplifier 40 ... Comparison amplifier 41 ... Reference setting circuit 42 ... Reference setting Circuit 43 ... Counter 44 ... Display 45 ... Timer 46 ... Detection sensor 47 ... Preamplifier 48 ... Comparative amplifier circuit

Claims (11)

Measuring cell for filling ozone-containing fluid into the opposing gap of a pair of translucent substrates, a light source for irradiating ultraviolet light on one substrate of the measuring cell, doping provided on the translucent side of the other substrate of the measuring cell Alternatively, a P-type or N-type zinc oxide thin film having a predetermined film thickness with increased ultraviolet light sensitivity due to intrinsic defects, an electrode pair for applying a constant voltage to the zinc oxide thin film, and a measuring circuit for detecting a current between the electrode pairs The proportional coefficient between the film thickness of the zinc oxide thin film and the sensitivity ratio of the C region ultraviolet light to the A region ultraviolet light is experimentally determined, and the required sensitivity ratio is obtained based on the proportional coefficient. An ozone detection sensor that selects a predetermined thickness of a zinc oxide thin film. 2. The detection sensor according to claim 1, wherein a proportionality coefficient between the film thickness of the zinc oxide thin film and the sensitivity ratio of the C region ultraviolet light to the A region ultraviolet light is experimentally determined, and the film thickness of the zinc oxide thin film and the electrode pair are determined. The coefficient of proportionality with the current time constant is obtained experimentally, and the oxidation is performed so that the necessary time is obtained based on both proportional coefficients and the sensitivity ratio of the C region ultraviolet light to the A region ultraviolet light is maximized. An ozone detection sensor formed by selecting a predetermined thickness of a zinc thin film . The detection sensor according to claim 1 or 2, wherein the zinc oxide thin film is brought into contact with the other substrate of the measurement cell, and the electrode pair is brought into contact with the thin film. The detection sensor according to claim 1 or 2, wherein the electrode pair is brought into contact with the other substrate of the measurement cell, and the zinc oxide thin film is brought into contact with the electrode. 5. The detection sensor according to claim 1, wherein the zinc oxide thin film is a PIN thin film in which a P type and an N type are stacked via an insulating layer, and the electrode pair is a P type surface of the PIN thin film. An ozone detection sensor arranged separately from the N-type surface. The detection sensor according to any one of claims 1 to 5, wherein the light source sequentially irradiates A region ultraviolet light and C region ultraviolet light, and the measurement circuit detects a current ratio at the time of both ultraviolet light irradiations. Sensor. 6. The detection sensor according to claim 1, wherein a reference cell for filling a non-ozone-containing fluid is provided in a gap between a pair of translucent substrates, and the light source is provided on one substrate of the measurement cell and the control cell, respectively. Irradiate with ultraviolet light, the zinc oxide thin film and the electrode pair are provided on the other substrate of the measurement cell and the control cell, respectively, and the current difference between the electrode pair of the measurement cell and the electrode pair of the reference cell is measured by the measurement circuit. Detected ozone detection sensor. 8. The detection sensor according to claim 7, wherein each of the measurement cell and the control cell is a cylindrical cell having a hollow part that can be filled with ozone or a non-ozone-containing fluid and a pair of translucent substrates facing each other through the hollow part. Ozone detection sensor. 9. The detection sensor according to claim 8, wherein the measurement cell and the control cell are formed as a single cylindrical cell having a hollow portion divided into two passages by an intermediate partition. 10. The detection sensor according to claim 7, wherein the light source sequentially irradiates A region ultraviolet light and C region ultraviolet light, and the measurement circuit detects a ratio of a current difference during both ultraviolet light irradiations. Ozone detection sensor. 11. The detection sensor according to claim 1, wherein the zinc oxide is doped with B, Al, Ga, In, Zn, H, a group I element or a group IV element.