JPWO2006011202A1 - Semiconductor gas sensor - Google Patents

Abstract

Provided is a semiconductor gas sensor having improved performance such as detection sensitivity and responsiveness. This semiconductor gas sensor is provided with a sensing element A containing a metal oxide semiconductor as a sensing element A that produces a change in electric resistance value in response to a gas to be detected, and at least Pt and Pd are contained inside the sensing element A. The metal oxide insulator supporting one is dispersed. This makes it possible to exert the catalytic action of Pt and Pd throughout the sensitive element A while suppressing the adverse effect of Pt and Pd on the metal oxide semiconductor.

Description

  The present invention relates to a semiconductor gas sensor including a sensitive element that includes a metal oxide semiconductor as a sensitive element that changes a resistance value in response to a gas to be detected.

  In recent years, semiconductor gas sensors that use metal oxide semiconductors that produce a change in electrical resistance value in response to the gas to be detected have been attracting attention as small and inexpensive gas sensors, and gas of combustible gas for household and industrial use has been attracting attention. It has come to be widely used as a leak sensor, a bad breath sensor, a hydrogen gas sensor for controlling fuel cells, an exhaust gas sensor for automobiles, and the like.

  Of these, for example, as an exhaust gas sensor for automobiles, one that detects nitrogen oxides (NOx) or the like exhausted from a diesel engine, one that detects hydrocarbons exhausted from a gasoline engine, or the like There are provided gas detectors and the like, which are used, for example, for automatic control of a control valve used to supply outside air into the vehicle.

  In such a semiconductor gas sensor, a catalyst such as Pt or Pd is added to the sensitive element in order to improve the detection sensitivity or the response at the time of detection, or to eliminate the influence of interfering gas and improve the selectivity. May be included. Such Pt and Pd improve the performance of the semiconductor gas sensor by, for example, decomposing an interfering gas or converting the gas to be detected into a substance that is easily detected by the metal oxide semiconductor due to its catalytic action. Contribute to.

  As a mode in which Pt or Pd is contained, it may be considered that Pt or Pd is wholly dispersed in a sensitive element containing a metal oxide semiconductor. However, in this case, the electric resistance value of the sensitive element is increased. It is known from experience that it is easy to invite, so it is not possible to achieve the expected performance improvement, and conversely, the detection sensitivity and responsiveness decrease, or these performances deteriorate over time. It was a thing.

Therefore, when Pt or Pd is added to the sensitive element of the semiconductor gas sensor for the purpose of imparting a catalytic action, it contains a metal oxide semiconductor as disclosed in, for example, Japanese Patent Publication No. 9-503587. A coating layer made of a metal oxide carrying Pt or Pd has been provided outside the sensitive element. This Japanese National Publication of International Patent Application No. 9-503587 describes a semiconductor gas sensor for detecting nitrogen oxides contained in exhaust gas and the like, and its sensitive element is a metal oxide semiconductor such as SnO _2. It is configured by forming a coat layer (conversion layer) of a metal oxide supporting Pt or Pd on the outer layer of the metal oxide layer mainly composed of. With such a configuration, the metal oxide semiconductor and Pt or Pd are prevented from coming into contact with each other so that the above-mentioned adverse effect does not occur.

  However, when forming a coat layer as described above, the catalytic action of Pt or Pd works only when the gas passes through the coat layer, and therefore passes through the coat layer without being subjected to the catalytic action of Pt or Pd. A large amount of the component remains, which limits the improvement in performance such as detection sensitivity and responsiveness.

  The present invention has been made in view of the above points, and a first object of the present invention relates to a semiconductor gas sensor in which Pt or Pd is contained in a sensitive element for improving performance such as detection sensitivity and responsiveness. Another object of the present invention is to provide a semiconductor gas sensor that can achieve a significant performance improvement due to the catalytic action of Pd and Pd.

  A second object of the present invention is to detect the sensitivity and responsiveness to nitrogen oxides, hydrocarbons or carbon monoxide as a semiconductor gas sensor capable of achieving a significant performance improvement due to the catalytic action of Pt and Pd as described above. It is an object of the present invention to provide a semiconductor gas sensor which has improved performance and can be suitably used particularly for exhaust gas detection applications such as automobiles.

  As a result of earnest studies, the present inventors have made it possible to disperse Pt and Pd in the sensitive element A, thereby making it possible to exert a catalytic action by Pt and Pd throughout the sensitive element A, and The present invention has been completed by finding a structure of the sensitive element A capable of eliminating the adverse effect of Pt and Pd on the metal oxide semiconductor.

  That is, the semiconductor gas sensor according to the present invention is a semiconductor gas sensor including a metal oxide semiconductor-containing one as a sensitive element A that produces a change in electric resistance value in response to a gas to be detected. In, the metal oxide insulator carrying at least one of Pt and Pd is dispersed.

  In such a semiconductor gas sensor, at least one of Pt and Pd is dispersedly present in the sensitive element A, so that the catalytic action of at least one of Pt and Pd is exerted over the entire inside of the sensitive element A. Moreover, since the Pt and Pd exist in a state of being supported by the metal oxide insulator, direct contact between Pt and Pd and the metal oxide semiconductor in the sensitive element A is suppressed, and Pt and Pd are suppressed. It is possible to suppress the adverse effect on the metal oxide semiconductor due to the influence of Pt and Pd, and to prevent the resistance of the sensitive element A from being increased and the sensitivity thereof to be lowered, and such performance deterioration occurs over time. It is also excellent in stability over time. Therefore, when the performance of the sensitive element A, such as the detection sensitivity and responsiveness, is improved by utilizing the catalytic action of Pt and Pd, a significant performance improvement can be achieved.

In the sensitive element A as described above, the metal oxide semiconductor is at least one of SnO ₂ , In ₂ O ₃ , and WO ₃ , and the metal oxide insulator is Al ₂ O ₃ , SiO ₂ , and high temperature. It can be at least one of the calcined SnO ₂ .

In the sensitive element A having such a composition, if the metal oxide insulator carries Pt, Pt is due to its catalytic action in the sensitive element A particularly when detecting nitrogen oxide (NOx). Oxidize NO to convert it to NO ₂ or further convert it to N ₂ O ₄ to a substance having a large fluctuation range of electric resistance value of the metal oxide semiconductor when adsorbed to the metal oxide semiconductor. It is possible to improve the detection sensitivity of nitrogen oxides, and it is also possible to improve the responsiveness at the time of detection.

  Further, in the sensitive element A, when the metal oxide insulator carries Pd, the hydrocarbon or carbon monoxide (CO) is detected particularly when detecting hydrocarbon or carbon monoxide (CO). It is possible to improve the adsorptivity of the metal oxide semiconductor to the metal oxide semiconductor to significantly improve the detection sensitivity thereof, and to improve the responsiveness at the time of detection.

When the metal oxide semiconductor is SnO ₂ and the metal oxide insulator carries Pt, one or more metals selected from alkaline earth metals and rare earth elements are added to the sensitive element A. When contained, the detection sensitivity of nitrogen oxides (NOx) can be further improved.

Further, in the case where the metal oxide semiconductor contains SnO ₂ , if the sensitive element A contains sulfur, the detection sensitivity of nitrogen oxide (NOx), hydrocarbon, carbon monoxide (CO) and the like can be further improved. In particular, if one or more metals selected from alkaline earth metals and rare earth elements are added to the sensitive element A at this time, the sensitivity of detection of nitrogen oxides (NOx) improved by the action of these metals. Can be further improved.

In the sensitive element A, particularly, the metal oxide semiconductor contains In ₂ O ₃ , the metal oxide insulator is at least one of Al ₂ O ₃ and SiO ₂ , and the metal oxide is To a molded body containing a semiconductor material and the metal oxide insulator carrying at least one of Pt and Pd, followed by firing after adding at least one selected from alumina sol, silica sol and ammonium metatungstate. It is also preferable to obtain the sensitive element A by doing so. In this case, by adding alumina sol, silica sol or ammonium metatungstate, it is possible to improve the detection sensitivity of nitrogen oxide (NOx), hydrocarbon, etc., especially when alumina sol or silica sol is added. The responsiveness at the time of detection can also be improved.

  In these cases, the performance of the semiconductor gas sensor such as detection sensitivity and responsiveness to nitrogen oxides, hydrocarbons or carbon monoxide can be remarkably improved, and it is particularly suitable for exhaust gas detection applications such as automobiles.

It is a principal part schematic diagram of the semiconductor gas sensor which shows an example of embodiment of this invention. It is a partially broken front view of the above semiconductor gas sensor. The principal part of the other example of embodiment of this invention is shown, (a) is the perspective view seen from one surface side, (b) is the perspective view seen from the other surface side. It is a perspective view of the semiconductor gas sensor which the above same partially fractured. 3 is a graph showing a detection sensitivity evaluation (a) and a responsiveness evaluation (b) of the semiconductor gas sensor of Example 1. 5 is a graph showing detection sensitivity evaluation (a) and response evaluation (b) of the semiconductor gas sensor of Example 2. 9 is a graph showing detection sensitivity evaluation (a) and response evaluation (b) of the semiconductor gas sensor of Example 3. 9 is a graph showing detection sensitivity evaluation (a) and response evaluation (b) of the semiconductor gas sensor of Example 4. 9 is a graph showing detection sensitivity evaluation (a) and response evaluation (b) of the semiconductor gas sensor of Example 5. 9 is a graph showing detection sensitivity evaluation (a) and response evaluation (b) of the semiconductor gas sensor of Example 6. 9 is a graph showing detection sensitivity evaluation (a) and response evaluation (b) of the semiconductor gas sensor of Example 7. 9 is a graph showing detection sensitivity evaluation (a) and response evaluation (b) of the semiconductor gas sensor of Example 8. 9 is a graph showing detection sensitivity evaluation (a) and response evaluation (b) of the semiconductor gas sensor of Example 9. 13 is a graph showing a detection sensitivity evaluation (a) and a responsiveness evaluation (b) of the semiconductor gas sensor of Example 10. 13 is a graph showing detection sensitivity evaluation (a) and response evaluation (b) of the semiconductor gas sensor of Example 11. 13 is a graph showing a detection sensitivity evaluation (a) and a responsiveness evaluation (b) of the semiconductor gas sensor of Example 12. 16 is a graph showing detection sensitivity evaluation (a) and response evaluation (b) of the semiconductor gas sensor of Example 13. 16 is a graph showing a detection sensitivity evaluation (a) and a responsiveness evaluation (b) of the semiconductor gas sensor of Example 14. 16 is a graph showing detection sensitivity evaluation (a) and response evaluation (b) of the semiconductor gas sensor of Example 15. 16 is a graph showing the detection sensitivity evaluation (a) and the responsiveness evaluation (b) of the semiconductor gas sensor of Example 16. 16 is a graph showing the evaluation of detection sensitivity of the semiconductor gas sensor of Example 17. 20 is a graph showing a detection sensitivity evaluation (a) and a responsiveness evaluation (b) of the semiconductor gas sensor of Example 18. 20 is a graph showing evaluation of detection sensitivity of the semiconductor gas sensor of Example 19. 21 is a graph showing evaluation of detection sensitivity of the semiconductor gas sensor of Example 20. 20 is a graph showing the evaluation of detection sensitivity of the semiconductor gas sensor of Example 21. 5 is a graph showing a detection sensitivity evaluation (a) and a responsiveness evaluation (b) of the semiconductor gas sensor of Comparative Example 1. 9 is a graph showing a detection sensitivity evaluation (a) and a responsiveness evaluation (b) of the semiconductor gas sensor of Comparative Example 2. 9 is a graph showing a detection sensitivity evaluation (a) and a responsiveness evaluation (b) of the semiconductor gas sensor of Comparative Example 3. 9 is a graph showing a detection sensitivity evaluation (a) and a responsiveness evaluation (b) of the semiconductor gas sensor of Comparative Example 4. 9 is a graph showing detection sensitivity evaluation (a) and response evaluation (b) of the semiconductor gas sensor of Comparative Example 5. 9 is a graph showing detection sensitivity evaluation (a) and response evaluation (b) of the semiconductor gas sensor of Comparative Example 6.

Explanation of symbols

  A sensitive element

  Hereinafter, the present invention will be described based on the best mode for carrying out the invention.

  The sensitive element A of the semiconductor gas sensor according to the present invention contains a metal oxide semiconductor and a metal oxide insulator carrying at least one of Pt and Pd.

  The metal oxide semiconductor may be any one as long as it changes the electric resistance value in response to the gas to be detected and is appropriately selected according to the gas to be detected.

  Further, the Pt and Pd are contained for the purpose of achieving an improvement in detection sensitivity and an improvement in responsiveness due to the catalytic action thereof, and are appropriately selected depending on the combination of the type of metal oxide semiconductor and the gas to be detected. To be selected.

  Further, as the metal oxide insulator, one that does not affect the change in the electric resistance value of the sensitive element A during gas detection is appropriately selected.

  The sensitive element A contains the above metal oxide semiconductor and a metal oxide insulator carrying at least one of Pt and Pd in a mixed and dispersed state. At this time, the metal oxide insulator carries at least one of Pt and Pd in the sensitive element A, and thereby has a function of suppressing contact between Pt and Pd in the sensitive element A and the metal oxide semiconductor. It also fulfills the function of adjusting the electric resistance value and strength of the sensitive element A at the same time.

  The sensitive element A having the above-described structure is a mixture obtained by mixing a material containing particles of a metal oxide insulator supporting at least one of Pt and Pd and particles of a metal oxide semiconductor, for example. Can be manufactured through a process of molding and firing.

  In the semiconductor gas sensor having such a sensitive element A, when the sensitive gas is detected based on the change in the electric resistance value of the sensitive element A when the sensitive element A is exposed to the gas to be sensed, the sensitive element Since Pt and Pd are dispersed in A, the catalytic action of Pt and Pd is exerted over the entire inside of the sensitive element A, and the Pt and Pd are supported by the metal oxide insulator. The presence of Pt or Pd is prevented from directly contacting the metal oxide semiconductor in the sensitive element A, and the adverse effect of Pt or Pd on the metal oxide semiconductor can be suppressed. Therefore, it is possible to achieve remarkable performance improvement in improving the detection sensitivity and response of the sensitive element A by utilizing the catalytic action of Pt and Pd, and prevent deterioration of these characteristics with time.

  The semiconductor gas sensor includes the sensitive element A as described above, and any conventionally known appropriate element can be used as long as it can detect a change in electric resistance value when the sensitive element A is exposed to the gas to be detected. A configuration can be adopted.

  In this semiconductor gas sensor, it is preferable that a heater and an electrode made of platinum (Pt), a platinum alloy (Pt alloy) or the like be used as a sensor base, and the sensitive element A be provided so as to cover the sensor base.

  The electrodes are provided for measuring the electric resistance of the sensitive element A. The electric resistance value between the electrodes is measured in a state where the sensitive element A is placed in an atmosphere containing a gas to be measured, and the electric resistance is measured. The gas concentration can be detected based on the value.

  The heater is provided to keep the sensitive element A at a constant temperature. That is, the sensitive element A has a suitable temperature (element temperature) for detecting a gas depending on the composition, and when the element temperature changes, the gas sensitivity changes and it becomes difficult to detect an accurate concentration. In detecting the gas concentration, the element temperature is kept at a suitable temperature by the heater, so that the gas concentration can be accurately detected.

  Hereinafter, a specific structure of the semiconductor gas sensor will be illustrated.

In the semiconductor gas sensor shown in FIGS. 1 and 2, a coil-shaped heater/electrode 25 and a core wire-shaped electrode 20 are used as a sensor base, and a substantially spherical shape (spherical shape, ellipsoidal shape, etc.) is provided so as to cover the heater/electrode 25 and the electrode 20. ), the sensitive element A is formed. In the illustrated example, the heater/electrode 25 is formed so that its coil portion is embedded in the sensitive element A, and the electrode 20 is formed in the sensitive element A so as to penetrate the center of the coil portion of the heater/electrode 25. Embedded therein, the sensitive element A is miniaturized. The heater/electrode 25 is made of platinum (Pt), a platinum alloy (Pt alloy) or the like, and is provided between the lead wires 20 ₁ and 20 ₃ made of platinum (Pt), a platinum alloy (Pt alloy) or the like. The heater/electrode 25 and the lead wires 20 ₁ and 20 ₃ are integrally formed. The electrode 20 is formed by a lead wire 20 ₂ made of platinum (Pt), platinum alloy (Pt alloy), or the like.

Then, three terminals 10 ₁ , 10 ₂ , 10 ₃ are provided so as to penetrate a base 30 formed of resin or the like, and lead wires 20 ₁ , 20 ₂ , 20 are connected to the terminals 10 ₁ , 10 ₂ , 10 _3. By connecting _{3 the} sensitive element A is fixed and supported. A semiconductor gas sensor is constructed by fitting a bottomed cylindrical sensor housing 40 on the side of the base 30 on which the sensitive element A is supported and fixed. An opening 41 for introducing gas is provided on the top surface of the sensor housing 40, and a metal net 41 made of stainless steel or the like for introducing gas is stretched over the opening 41 as needed.

  In the semiconductor gas sensor shown in FIGS. 3 and 4, an insulating substrate 1 such as an alumina substrate is used as a sensor base (flat type base), and a sensitive element A is formed in a film shape on one surface of the insulating substrate 1 to form a sensing unit. B is configured. Here, electrodes 4A and 4B made of gold or the like connected to electrodes 4A' and 4B' made of gold or the like on the other surface by through holes are provided on one surface of the insulating substrate 1 as shown in FIG. A sensitive element A is formed so as to extend between the electrodes 4A and 4B. A lead wire 5 is connected to each of the electrodes 2A, 2B, 4A' and 4B' on the other side of the insulator substrate 1. The sensing part A has electrodes 4A', 4B' and a heater electrode 2A, on the other surface of the square insulator substrate 1 having a thickness of 0.3 mm and a side length of 2 mm, as shown in FIG. 3(b). 2B is provided, and a heater 25' made of a platinum printed film or the like is formed between the electrodes 2A and 2B.

  Then, the sensing part B is connected to the terminal 10 having the lead wire 5 penetrating the base 30 and mounted on the base 30, and the side of the base 30 on which the sensing part B is mounted has a cylindrical sensor housing with a bottom. A semiconductor gas sensor is formed by fitting the body 40. An opening 41 for introducing gas is provided on the top surface of the sensor housing 40, and a metal net 41 made of stainless steel or the like for introducing gas is stretched over the opening 41 as needed.

  The configurations of these semiconductor gas sensors are examples, and semiconductor gas sensors having other appropriate structures can be formed.

  Next, an example of a specific composition of the sensitive element A will be described. The specific example of the sensitive element A described below is particularly suitable for use in exhaust gas detection from automobiles and the like, but when used in other applications, by appropriately changing the composition as necessary, A semiconductor gas sensor suitable for detecting a desired gas to be detected can be obtained.

As the metal oxide semiconductor, for example, SnO ₂ , In ₂ O ₃ , and WO ₃ can be used, and these can be used alone or in combination of two or more.

When SnO ₂ is used as the metal oxide semiconductor, the SnO ₂ is obtained by, for example, hydrolyzing an aqueous solution of SnCl ₄ with NH ₄ to obtain a stannic acid sol, which is dried, for example, in air to, for example, 550 to 700. It can be prepared by firing at 0.5° C. for 0.5 to 3 hours. In addition, SnO ₂ as the metal oxide semiconductor can be prepared by another method, but in that case, it is preferable that the crystallite size of SnO ₂ is in the range of 20 to 30 nm.

  These metal oxide semiconductors can be applied to applications other than exhaust gas detection, but the change in electric resistance is large when nitrogen oxides, hydrocarbons, carbon monoxide, etc. are adsorbed. A semiconductor gas sensor having high detection sensitivity when used for exhaust gas detection applications can be obtained.

As the metal oxide insulator, for example, Al ₂ O ₃ , SiO ₂ or the like can be used, and these can be used alone or in combination of two or more.

Further, when the metal oxide semiconductor using SnO ₂ as described above, can also be used SnO ₂ was fired at a high temperature as the metal oxide insulator. Here SnO ₂ was fired at a high temperature, the metal oxide SnO ₂ of 800 ° C. or more high temperature which is used as a semiconductor as described above, it preferably obtained by firing 0.5-3 hours in the range of 900 to 1100 ° C. Which has higher electrical insulation than SnO ₂ which is a metal oxide semiconductor. Further, SnO ₂ as the metal oxide insulator can be prepared by other methods, but in that case, it is preferable that the crystallite size of SnO ₂ is in the range of 50 to 130 nm.

  The content of such a metal oxide insulator in the sensitive element A is appropriately adjusted, but in order to make the sensitive element A contain a sufficient amount of Pt or Pd, the metal oxide in the sensitive element A should be contained. When the content (mass) of the semiconductor is 1, it is preferable that the content (mass) of the metal oxide insulator is in the range of 0.2 to 1.5.

  When Pt or Pd is loaded on the metal oxide insulator, only one of Pt and Pd may be loaded, or Pt and Pd may be loaded together.

When Pt is supported on a metal oxide insulator, Pt in the sensing element A oxidizes NO by its catalytic action and converts it into NO ₂ when detecting nitrogen oxides (NOx), or Further, it is converted into N ₂ O ₄ , and each time it is converted into N ₂ O ₄ , it changes into a substance having a large fluctuation range of the electric resistance value of the metal oxide semiconductor when adsorbed to the metal oxide semiconductor, The detection sensitivity is improved, and at the same time, the responsiveness when detecting nitrogen oxides is also improved. Such an improvement in the detection performance is remarkably exhibited especially in the low concentration region where the concentration of nitrogen oxide is about 1 ppm or less. Further, when it is desired to detect only nitrogen oxide which is an oxidizing gas, hydrocarbons such as reducing gas and carbon monoxide (CO) work as interfering gases, but these gases act as a catalytic action of Pt. As a result, the detection sensitivity decreases due to decomposition and combustion, and as a result, nitrogen oxides are selectively detected. Therefore, by supporting Pt on the metal oxide insulator, it is possible to obtain a semiconductor gas sensor for nitrogen oxide (NOx) detection which is excellent in detection sensitivity and responsiveness. Such a semiconductor gas sensor is preferably used as an exhaust gas sensor for a diesel engine, for example.

  In supporting Pt on the metal oxide insulator in this manner, if the content thereof is too small, the nitrogen oxide detection performance cannot be sufficiently improved, and if this content is too large, Although the detection sensitivity of reducing gases such as hydrocarbon and carbon monoxide (CO) can be further suppressed to improve the selective detection performance of nitrogen oxides, the detection sensitivity of nitrogen oxides tends to decrease. .. Therefore, it is preferable to appropriately adjust the amount of Pt supported on the metal oxide insulator so that the sensitive element A can be provided with desired characteristics in consideration of the balance between the improvement in detection sensitivity and the selectivity intelligence. The content of Pt supported on the metal oxide insulator in the sensitive element A is preferably 0.05 to 5 mass% with respect to the total amount of the metal oxide insulator, and more preferably 0.2 to 1%. The range is 0.5% by mass. In this range, a remarkable improvement in the performance of the semiconductor gas sensor is recognized.

  In addition, when Pd is supported on a metal oxide insulator, it can also serve to improve the nitrogen oxide detection performance by a mechanism similar to that of Pt, but in particular hydrocarbon, carbon monoxide (CO), etc. In the case of detecting, the detailed mechanism is not clear, but it is possible to improve the adsorptivity to hydrocarbons, carbon monoxide (CO), and other metal oxide semiconductors and significantly improve the detection sensitivity. At the same time, the responsiveness when detecting hydrocarbons, carbon monoxide (CO), etc. can be improved. Therefore, by supporting Pd on the metal oxide insulator, it is possible to obtain a semiconductor gas sensor for detecting hydrocarbons, carbon monoxide (CO), etc., which has excellent detection sensitivity and responsiveness. Such a semiconductor gas sensor is suitably used as an exhaust gas sensor for a gasoline engine, for example.

  In supporting Pd on the metal oxide insulator in this manner, the amount of Pd is appropriately adjusted so as to impart desired performance to the semiconductor gas sensor, but preferably it is supported on the metal oxide insulator. The amount of Pd is 0.05 to 5% by mass, more preferably 0.2 to 1.5% by mass, based on the total amount of the metal oxide insulator. In this range, a remarkable improvement in the performance of the semiconductor gas sensor is recognized.

  Further, when both Pt and Pd are used together and supported on a metal oxide insulator, the action of Pt for improving the detection sensitivity of nitrogen oxides (NOx) and the action of Pd for hydrocarbons and monoxides are achieved. A semiconductor gas sensor capable of detecting both nitrogen oxides, hydrocarbons, carbon monoxide (CO) and the like can be obtained by simultaneously exhibiting the action of improving the detection sensitivity of carbon (CO) and the like. it can.

In the case where the sensitive element A contains Pt and Pd in this way to obtain a dual-use semiconductor gas sensor, the amounts of Pt and Pd to be carried on the metal oxide insulator are appropriately set according to the characteristics required for the sensitive element A. When the metal oxide semiconductor contained in the sensitive element A is In ₂ O ₃ or WO ₃ , for example, the amount of Pt supported on the metal oxide insulator is preferably adjusted. The amount of Pd supported on the metal oxide insulator is 0.05 to 5% by mass, more preferably 0.2 to 1.5% by mass, based on the total amount of the metal oxide insulator. In the range of 0.05 to 5% by mass, more preferably 0.2 to 1.5% by mass, and the mass ratio of Pt and Pd is in the range of 1:9 to 9:1. It is preferable that

  Such a sensitive element A can be manufactured by an appropriate method. For example, first, particles of a metal oxide insulator are mixed with a solution containing at least one of Pt and Pd (for example, aqua regia solution), and the mixture is fired to carry a metal carrying at least one of Pt and Pd. Obtain oxide insulator particles. Although the firing conditions are appropriately adjusted, for example, the firing conditions can be set to 500 to 700° C. and 0.5 to 3 hours under an air atmosphere. Next, the particles of the metal oxide semiconductor are mixed with the particles of the metal oxide insulator, and an organic solvent such as terpineol is added to the particles to prepare a pasty molding material. Then, the desired sensitive element A can be manufactured by applying this molding material to the sensor base and baking it. Although the firing conditions are appropriately adjusted, the firing conditions may be, for example, 500 to 700° C. for 1 to 60 minutes in an air atmosphere.

  In the sensitive element A thus formed, it is preferable that Pt and Pd be supported only on the metal oxide insulator and not on the metal oxide semiconductor. It is permissible to support it on the body, and inevitably a small amount of Pt or Pd is deposited on the metal oxide semiconductor, such as when a small amount of Pt or Pd is loaded on the metal oxide semiconductor during the molding process. It is also allowed to be carried. However, in this case, the total amount of Pt and Pd supported on the metal oxide semiconductor is preferably 0.5% by mass or less, more preferably 0.2% by mass or less of the total amount of the metal oxide semiconductor. To do.

  In addition to the above components, the sensitive element A may contain appropriate additives as necessary.

For example, particularly when the metal oxide semiconductor is SnO ₂ , in the sensitive element A, an alkaline earth metal such as Mg, Ca, Sr, and Ba and Y, Sc, La, Pr, Nd, Sm, Er, and Gd are contained. One or more metals selected from rare earth elements such as These metals can be contained in the sensitive element A in the form of divalent or trivalent ions (oxides).

  When such a metal is added to the sensitive element A, the detection sensitivity of various gases can be improved, and particularly the detection sensitivity of nitrogen oxide (NOx) can be improved. At this time, regarding the detection sensitivity of nitrogen oxides (NOx), the detection sensitivity in the case of a low concentration of 1 ppm or less is remarkably improved.

  When Pt is supported on the metal oxide insulator, Pt improves the detection sensitivity and response of nitrogen oxide (NOx) as described above, and the metal as described above is added to the sensitive element A. By further adding nitrogen oxide (NOx) to improve the detection sensitivity of nitrogen oxide (NOx), particularly at low concentration, a semiconductor gas sensor for nitrogen oxide detection having extremely excellent detection performance can be obtained.

In this way, when one or more metals selected from alkaline earth metals and rare earth elements are added to the sensitive element A, the amount of addition is appropriately adjusted so as to impart desired characteristics to the sensitive element A. However, if the added amount is too small, the gas detection sensitivity cannot be sufficiently improved, and if the added amount is too large, the electric resistance value of the sensitive element A is increased or the gas detection sensitivity is rather deteriorated. It may decrease. Therefore, for example, when an alkaline earth metal such as Mg, Ca, Sr, or Ba is added as the metal, 3×10 ⁻⁶ to 1× with respect to the total amount of the metal oxide semiconductor and the metal oxide insulator. The content is preferably in the range of 10 ⁻⁴ mol/g, and when at least one of Y and Sc in the rare earth is added, the ratio to the total amount of the metal oxide semiconductor and the metal oxide insulator is 4 It is preferably contained in the range of ×10 ^{-6 to} 1.5 ×10 ^-4 mol/g. When La, Pr, Nd, Sm, Er, Gd, etc. are contained, the ratio to the total amount of the metal oxide semiconductor and the metal oxide insulator is 4×10 ^{−6 to} 1.5×10 ⁻⁴ mol/. It is preferable to contain it so as to be in the range of g. In these ranges, a remarkable improvement in the performance of the semiconductor gas sensor is recognized. Further, when at least one of Y and Sc is used together with a lanthanoid, such as when Y and La are used together, a component composed of at least one of Y and Sc and a component composed of lanthanoid are respectively It is preferable that the content of the former component and the latter component is within the range of 1:2 to 2:1 while the content of 2×10 ^{−6 to} 7×10 ⁻⁵ mol/g.

  When adding the metal to the sensitive element A, an appropriate method can be used. For example, with respect to a molded body obtained by mixing the particles of the metal oxide semiconductor and the particles of the metal oxide insulator carrying at least one of Pt and Pd by the method described above and molding and firing. The metal can be added to the sensitive element A by coating and impregnating a solution containing the above metal (for example, a nitric acid solution in which the above metal is dissolved) and baking it. Although the firing conditions at this time are appropriately adjusted, for example, firing can be performed at 500 to 700° C. for 1 to 60 minutes in an air atmosphere.

Further, when the metal oxide semiconductor is SnO ₂ , sulfur (S) may be added to the sensitive element A. Sulfur (S) can be contained in the sensitive element A, for example, in the state of sulfate ion.

  By adding sulfur to the sensitive element A as described above, the detection sensitivity of hydrocarbons and carbon monoxide (CO) can be improved. Further, a semiconductor gas sensor formed by supporting Pd on a metal oxide insulator to detect hydrocarbons or carbon monoxide (CO), or a gas sensor for both of Pt and Pd supported on a metal oxide insulator. In the semiconductor gas sensor formed as described above, by adding sulfur to the sensitive element A, it is possible to further improve the detection sensitivity when detecting hydrocarbons or carbon monoxide (CO).

  Further, when sulfur is added as described above, the detection sensitivity of nitrogen oxide (NOx) can be improved, and particularly when an alkaline earth metal or a rare earth element is added to the sensitive element A, the sensitive element is further improved. When sulfur is added to A, the detection sensitivity of nitrogen oxide (NOx) can be further improved as compared with the case where only the metal is added. Therefore, in a semiconductor gas sensor in which Pt is supported on a metal oxide insulator, if one or more metals selected from alkaline earth metals and rare earth elements are added to the sensitive element A, and further sulfur is added, nitrogen oxidation will occur. It is possible to further improve the detection sensitivity of substances (NOx) and also the detection sensitivity of hydrocarbons and carbon monoxide (CO), whereby a dual-use semiconductor gas sensor having excellent detection characteristics can be obtained.

As described above, when sulfur is added to the sensitive element A, if the amount of addition is too small, the gas detection sensitivity cannot be sufficiently improved, and if the amount of addition is increased, especially in the case of a dual-purpose semiconductor gas sensor, nitrogen is added. Since the detection sensitivity of hydrocarbons may be higher than the detection sensitivity of oxides, or the responsiveness at the time of detection of nitrogen oxides may be reduced, the amount of sulfur added depends on the desired characteristics of the sensitive element A. It is adjusted appropriately so that it can be given. For example, it is preferably contained in the range of 2×10 ⁻⁶ to 1×10 ⁻⁴ mol/g in terms of sulfur atom based on the total amount of the metal oxide semiconductor and the metal oxide insulator.

  When adding the sulfur to the sensitive element A, an appropriate method can be used. For example, with respect to a molded body obtained by mixing the particles of the metal oxide semiconductor with the particles of the metal oxide insulator supporting at least one of Pt and Pd by the above-described method, molding and firing the mixture. By applying and impregnating a solution containing sulfur (such as an aqueous solution of sulfuric acid) and firing the solution, sulfur can be added to the sensitive element A. Although the firing conditions at this time are appropriately adjusted, for example, firing can be performed at 500 to 700° C. for 1 to 60 minutes in an air atmosphere.

  When one or more metals selected from alkaline earth metals and rare earth elements and sulfur are added to the sensitive element A, for example, at least the particles of the metal oxide semiconductor and Pt and Pd are prepared by the method described above. A solution containing the metal (for example, a nitric acid solution in which the metal is dissolved) is applied to the molded body obtained by mixing the particles of the metal oxide insulator supporting one of them, molding and firing. The metal is added to the sensitive element A by impregnation and firing. Then, the molded body is further coated and impregnated with the above-mentioned solution containing sulfur (for example, an aqueous solution of sulfuric acid), and is baked to add sulfur to the sensitive element A.

  Further, in the case of adding one or more metals selected from alkaline earth metals and rare earth elements and sulfur, prepare a mixed solution in which the metals and sulfur are mixed in one solution, and for example, by the method described above. Metal oxide semiconductor particles and particles of a metal oxide insulator carrying at least one of Pt and Pd are mixed, and the molded body obtained by molding and firing is mixed with the metal and sulfur. The metal and sulfur may be added to the sensitive element A by coating and impregnating a mixed solution containing the same and firing it.

Further, when the metal oxide semiconductor is In ₂ O ₃ and the metal oxide insulator is at least one of Al ₂ O ₃ and SiO ₂ , in particular, when manufacturing the sensitive element A, A molded body containing the above metal oxide semiconductor and a metal oxide insulator supporting at least one of Pt and Pd is prepared, and alumina sol (colloidal alumina) and silica sol ( The sensitive element A can be manufactured by performing a step of firing after adding at least one of colloidal silica) and ammonium metatungstate. For example, with respect to a molded body obtained by mixing the particles of the metal oxide semiconductor with the particles of the metal oxide insulator carrying at least one of Pt and Pd by the above-described method, and molding and firing the mixture. At least one of alumina sol, silica sol, and ammonium metatungstate is applied and impregnated, and then baked to add the above components to the sensitive element A. The firing conditions at this time are appropriately adjusted, but for example, firing can be performed at 650° C. for 10 minutes in an air atmosphere.

  At this time, among the above additives, alumina sol and silica sol can be further added to the sensitive element A to further improve the detection sensitivity when detecting nitrogen oxides (NOx) and hydrocarbons by the semiconductor gas sensor, In addition, the responsiveness at the time of detection can be improved. Further, when ammonium metatungstate is added to the sensitive element A, the detection sensitivity when detecting nitrogen oxides (NOx) by the semiconductor gas sensor can be further improved.

When obtaining a semiconductor gas sensor for detecting nitrogen oxides (NOx), at least one of Al ₂ O ₃ and SiO ₂ is used as a metal oxide insulator, Pt is supported on the metal oxide insulator, and If at least one of alumina sol, silica sol and ammonium metatungstate is used as an additive, the sensitivity of detecting nitrogen oxides (NOx) can be further improved by the action of the additive, and particularly, among alumina sol and silica sol. When at least one of them is added, the responsiveness can be further improved.

When obtaining a semiconductor gas sensor for detecting hydrocarbons or carbon monoxide, at least one of Al ₂ O ₃ and SiO ₂ is used as the metal oxide insulator, and Pd is loaded on the metal oxide insulator. When at least one of alumina sol and silica sol is used as the additive, the sensitivity of hydrocarbon detection can be further improved by the action of the additive.

Further, in the case of obtaining a dual-purpose semiconductor gas sensor, at least one of Al ₂ O ₃ and SiO ₂ is used as a metal oxide insulator, Pt and Pd are both supported on the metal oxide insulator, and an additive is added. If at least one of alumina sol, silica sol, and ammonium metatungstate is used as the material, the sensitivity of nitrogen oxide (NOx) detection can be further improved by the action of the additive. When is added, the sensitivity of detecting hydrocarbon can be further improved and the responsiveness can be improved.

The amount of alumina sol, silica sol, or ammonium metatungstate to be added to the sensitive element A is appropriately adjusted so as to give desired characteristics to the sensitive element A. For example, a metal oxide semiconductor, When adding the above-mentioned components to a molded body containing a metal oxide insulator supporting at least one of Pt and Pd, when an alumina sol is added, a metal oxide semiconductor (In ₂ O ₃ ) Alumina sol is added in an amount of preferably 0.1 to 50 mass% and more preferably 0.5 to 5 mass% in terms of Al ₂ O _{3 based on the} total amount. When silica sol is added, the silica sol is preferably 0.1 to 50% by mass, more preferably 0.5 to 5% by mass in terms of SiO ₂ with respect to the total amount of the metal oxide semiconductor (In ₂ O ₃ ). Add in the range of. When ammonium metatungstate is added, it is preferable to add ammonium metatungstate in the range of 0.1 to 5 mass% in terms of WO ₃ with respect to the total amount of the metal oxide semiconductor (In ₂ O ₃ ).

  Hereinafter, the present invention will be specifically described based on Examples. It should be noted that these are merely examples and do not limit the present invention.

(Examples 1 to 21, Comparative Examples 1 to 6)
For each example and comparative example, the particles of the metal oxide semiconductor shown in Tables 1 to 3 and the particles of the metal oxide insulator were mixed at a ratio shown in the table, and terpineol was added to form a paste-like molding material. Prepared.

At this time, in the case of using SnO ₂ as the metal oxide semiconductor, first, to obtain a stannic acid sol by hydrolysis with NH ₄ an aqueous solution of SnCl _4, at 600 ° C. in air this stannate sol after drying It was calcined for 1 hour to obtain SnO ₂ which is a metal oxide semiconductor, and this SnO ₂ was crushed and used.

When using high-temperature-baked SnO ₂ as the metal oxide insulator, SnO ₂ which is the metal oxide semiconductor obtained as described above is baked in an air atmosphere at 1000° C. for 1 hour. I was there.

  When using particles of a metal oxide semiconductor carrying at least one of Pt and Pd and particles of a metal oxide insulator, an aqua regia solution obtained by dissolving at least one of Pt and Pd in these particles is used. It was impregnated and calcined in air at 500° C. for 1 hour to support at least one of Pt and Pd in the supported amount shown in the following table.

  The paste-like molding material obtained as described above is applied to a sensor substrate as shown in FIG. 1 and then baked at 600° C. for 10 minutes in an air atmosphere to give a minor axis length of 0.3 mm and a long axis length of 0.3 mm. A substantially elliptic spherical shaped body having an axial length of 0.5 mm was obtained.

  Next, in the case where the additive is clearly shown in the column of additive 1 in the table, this additive was applied to the above-mentioned molded body and baked at 650° C. for 10 minutes in the air atmosphere. The content of each additive at this time is shown in the table.

Here, when the additive 1 was La and Y, the La and Y were applied to the above-mentioned molded body in a state where each nitrate was made into an aqueous solution. When the additive 1 is silica sol or alumina sol, this silica sol or alumina sol is applied to the above-mentioned molded body, and the compounding amount in the table is calculated as SiO _{2 in} the case of silica sol and Al _{2 in} the case of alumina sol. It is converted to O ₃ .

  Next, in the case where the additive is clearly indicated in the column of additive 2 in the table, this additive 2 is applied to the molded body after the addition of the additive 1, and the mixture is heated at 650° C. in an air atmosphere. It was baked for 10 minutes. At this time, the content of each additive 2 in the sensitive element A was adjusted to be as shown in the table.

  Here, when the additive 2 is sulfur (S), this S is applied to the above-mentioned molded body in the state of sulfuric acid aqueous solution, and the compounding amount in the table is converted into sulfur atom. .

When the additive 2 is ammonium metatungstate, an aqueous solution of ammonium metatungstate is applied to the above-mentioned molded body, and the compounding amount in the table is in terms of WO ₃ .

  The sensitive element A was formed as described above, and the semiconductor gas sensor having the structure shown in FIG. 2 was produced using this.

(Detection sensitivity evaluation)
For each semiconductor gas sensor, the element temperature is 250° C. for Examples 1 to 7, 19 to 21 and Comparative Examples 1 to 3, and the element temperature is 200° C. for Examples 8 to 10, Examples 11 to 17 and Comparative Examples 4 to. In the case of 6, the detection sensitivity at 350° C. and in the case of Example 18 were examined at 350° C. Here, the detection sensitivity is the electrical resistance value (Rair) of the sensitive element A when the sensitive element A is exposed to clean air and the electrical resistance value (Rs) of the sensitive element A when exposed to the sample gas. It was represented by the ratio (Rs/Rair).

The following were used as sample gas.
-Sample gas 1: Nitrogen dioxide is mixed into clean air and the nitrogen dioxide concentration is changed.
-Sample gas 2: Nitrogen dioxide and carbon monoxide were mixed into clean air, the carbon monoxide concentration was fixed at 30 ppm, and the nitrogen dioxide concentration was varied.
Sample gas 3: Carbon monoxide mixed in clean air and the concentration of carbon monoxide varied.
Sample gas 4: Nitrogen dioxide and carbon monoxide were mixed in clean air, the nitrogen dioxide concentration was fixed at 1 ppm (3 ppm for Examples 11 to 16), and the carbon monoxide concentration was varied.
-Sample gas 5: A mixture of decane as hydrocarbons in clean air and the decane concentration varied.
-Sample gas 6: Nitrogen dioxide and decane were mixed in clean air, the nitrogen dioxide concentration was fixed at 1 ppm, and the decane concentration was varied.

  The result about each Example and a comparative example is shown to (a) in each figure of FIGS. 5-20,22,26-31, and the graph of FIGS. The vertical axis of the graph shows the value of Rs/Rair, and the horizontal axis shows the concentration of the sample gas.

  Further, in the graph, □ shows the results for the sample gas 1, ■ for the sample gas 2, Δ for the sample gas 3, ▲ for the sample gas 4, ◯ for the sample gas 5, and ● for the sample gas 6.

(Responsiveness evaluation)
The semiconductor gas sensors obtained in each of the examples and comparative examples are placed in a container, and the temperature of the sensitive element A is set to the same as in the case of the above-mentioned detection sensitivity evaluation. A sample gas containing nitrogen dioxide or carbon monoxide mixed therein was jetted toward the clean air, and then the clean air was jetted. The results of measuring the electric resistance value (Rs) of the sensitive element A at this time are shown in the graphs of (b) in each of FIGS. 5 to 20, 22, and 26 to 31. The vertical axis of the graph represents the electric resistance value (Rs) of the sensitive element A, and the horizontal axis represents time. In addition, the graph also shows the concentration of nitrogen dioxide or carbon monoxide in the sample gas and the time at which the sample gas was ejected.

In Examples 1 to 4, SnO ₂ was used as the metal oxide semiconductor, Al ₂ O ₃ was used as the metal oxide insulator, Pt was supported on the metal oxide insulator, and La and Y were used as additives. In comparison with Comparative Examples 1 and 2 in which Pt or Pd is not supported on the metal oxide insulator and Comparative Example 3 in which Pt is supported on the metal oxide semiconductor, the detection sensitivity of nitrogen dioxide is particularly 1 ppm or less. , A semiconductor gas sensor capable of selectively detecting nitrogen dioxide when hydrocarbon or carbon monoxide becomes an interfering gas is obtained. .. Further, these were also excellent in responsiveness when detecting nitrogen dioxide. These semiconductor gas sensors can be suitably used for selectively detecting nitrogen oxides.

Among these, particularly, the amount of Pt supported on the metal oxide insulator is in the range of 0.2 to 1.5 mass% with respect to the metal oxide insulator, and the contents of La and Y are each metal oxide. In Example 1 in which the total amount of the insulator and the metal oxide semiconductor was in the range of 5×10 ⁻⁶ to 2×10 ⁻⁵ mol/g, the detection sensitivity of nitrogen oxide and its selective detection performance were It was well-balanced and had excellent responsiveness.

In Examples 5 to 7, SnO ₂ was used as the metal oxide semiconductor, Al ₂ O ₃ was used as the metal oxide insulator, Pt was supported on the metal oxide insulator, and La and Y were added as additives. It is used and further sulfur is added. The addition of sulfur further improves the detection sensitivity of nitrogen oxides and also the detection sensitivity of hydrocarbons and carbon monoxide. These semiconductor gas sensors can be suitably used as a dual-purpose sensor capable of detecting both nitrogen oxide and hydrocarbon or carbon monoxide.

Of these, in particular, in Example 5 in which the sulfur content was in the range of 5×10 ⁻⁶ to 4×10 ⁻⁵ mol/g with respect to the total amount of the metal oxide insulator and the metal oxide semiconductor, nitrogen was used. The detection sensitivity of oxide and the detection sensitivity of hydrocarbon and carbon monoxide are sufficiently improved, and the detection sensitivity is well balanced.

  Further, in Examples 8 to 10, Pd was supported on the metal oxide insulator, and therefore, the detection sensitivity of carbon monoxide was improved. In particular, in Example 9 in which the amount of Pt supported on the metal oxide insulator is less than 50% by mass of the amount of Pd used, or in Example 10 in which Pt is not supported on the metal oxide insulator, nitrogen oxide The detection sensitivity is reduced and the detection sensitivity for carbon monoxide is high. These semiconductor gas sensors can be suitably used for selectively detecting nitric oxide and hydrocarbons.

Further, in Examples 11 to 13, In ₂ O ₃ was used as the metal oxide semiconductor, Al ₂ O ₃ was used as the metal oxide insulator, Pt was supported on the metal oxide insulator, and silica sol was used as an additive. In comparison with Comparative Examples 4 to 6 in which Pt and Pd are not supported on the metal oxide insulator, the detection sensitivity of nitrogen oxide is good and the detection sensitivity of hydrocarbon and carbon monoxide is reduced. There is. In particular, Example 11 in which the amount of Pt supported on the metal oxide insulator was in the range of 0.2 to 1.5 mass% with respect to the metal oxide insulator, and ammonium metatungstate was used together with silica sol as an additive. , 12, the detection sensitivity of nitrogen dioxide was improved particularly in the concentration range of 1 ppm or less, and the detection sensitivity of hydrocarbons and carbon monoxide, especially the detection sensitivity of carbon monoxide was reduced, and A semiconductor gas sensor capable of selectively detecting nitrogen dioxide when it becomes an interfering gas has been obtained. Further, the responsiveness when detecting nitrogen dioxide was also excellent. These semiconductor gas sensors can be suitably used for selectively detecting nitrogen oxides.

  In Comparative Examples 5 and 6, silica sol and alumina sol are added in Comparative Example 4, respectively, and the detection sensitivity of nitrogen dioxide is improved as compared with Comparative Example 4.

In addition, in Examples 14 to 16, In ₂ O ₃ was used as the metal oxide semiconductor, Al ₂ O ₃ was used as the metal oxide insulator, Pt and Pd were both supported on the metal oxide insulator, and as an additive. This is a combination of silica sol and ammonium metatungstate, and the detection sensitivity of nitrogen dioxide is improved especially in the concentration range of 1 ppm or less, and the detection sensitivity of hydrocarbon and carbon monoxide is also improved. Particularly, in Examples 14 and 15 in which the total amount of Pt and Pd supported on the metal oxide insulator is in the range of 0.2 to 1.5 mass %, excellent detection sensitivity is obtained. These semiconductor gas sensors can be suitably used as a dual-purpose sensor capable of detecting both nitrogen oxide and hydrocarbon or carbon monoxide.

In Example 17, In ₂ O ₃ was used as the metal oxide semiconductor, Al ₂ O ₃ was used as the metal oxide insulator, Pd was supported on the metal oxide insulator, and silica sol was used as the additive. The detection sensitivity of nitrogen dioxide is reduced and the detection sensitivity of carbon monoxide and hydrocarbon is improved. This semiconductor gas sensor can be suitably used for selectively detecting nitric oxide and hydrocarbons.

In Example 18, WO ₃ was used as the metal oxide semiconductor, Al ₂ O ₃ was used as the metal oxide insulator, both Pt and Pd were supported on the metal oxide insulator, and silica sol was used as an additive. The detection sensitivity of nitrogen dioxide is improved especially in the concentration range of 1 ppm or less, and the detection sensitivity of hydrocarbon and carbon monoxide is also improved.

In Example 19, SnO ₂ was used as the metal oxide semiconductor, Al ₂ O ₃ was used as the metal oxide insulator, Pt was supported on the metal oxide insulator, and Sr was used as the additive. Is. Further, in Examples 20 and 21, SnO ₂ was used as the metal oxide semiconductor, SiO ₂ or high-temperature baked SnO ₂ was used as the metal oxide insulator, Pt was supported on the metal oxide insulator, and further as an additive. La and Y are used. Compared with Comparative Examples 1 and 2 in which Pt or Pd is not supported on the metal oxide insulator and Comparative Example 3 in which Pt is supported on the metal oxide semiconductor, the concentration of nitrogen dioxide is particularly 1 ppm or less. A semiconductor gas sensor has been obtained which is improved in the region and has a reduced detection sensitivity for hydrocarbons and carbon monoxide, and is capable of selectively detecting nitrogen dioxide when hydrocarbons or carbon monoxide become an interfering gas. Further, these were also excellent in responsiveness when detecting nitrogen dioxide. These semiconductor gas sensors can be suitably used for selectively detecting nitrogen oxides.

  INDUSTRIAL APPLICABILITY The semiconductor gas sensor according to the present invention is used for an appropriate application such as a gas leak sensor for combustible gas for household or industrial use, a breath odor sensor, a hydrogen gas sensor for fuel cell control, an exhaust gas sensor for automobiles, etc. be able to.

Claims (8)

  In a semiconductor gas sensor including a sensing element containing a metal oxide semiconductor as a sensing element that causes a change in electric resistance value in response to a gas to be detected, at least one of Pt and Pd is provided inside the sensing element. A semiconductor gas sensor characterized in that a supported metal oxide insulator is dispersed. The metal oxide semiconductor in the sensitive element is at least one of SnO ₂ , In ₂ O ₃ , and WO ₃ , and the metal oxide insulator is Al ₂ O ₃ , SiO ₂ , or high-temperature fired SnO ₂ . The semiconductor gas sensor according to claim 1, wherein the semiconductor gas sensor is at least one of them.   The semiconductor gas sensor according to claim 2, wherein the metal oxide insulator carries Pt.   The semiconductor gas sensor according to claim 2, wherein the metal oxide insulator carries Pd. The metal oxide semiconductor in the sensitive element is SnO ₂ , and the sensitive element contains at least one metal selected from an alkaline earth metal and a rare earth element. Semiconductor gas sensor. The semiconductor gas sensor according to claim 1, wherein the metal oxide semiconductor in the sensitive element is SnO ₂ , and the sensitive element contains sulfur. The metal oxide semiconductor in the sensitive element is In ₂ O ₃ , the metal oxide insulator is at least one of Al ₂ O ₃ and SiO ₂ , and the sensitive element is the metal oxide. To a molded body containing a semiconductor and the metal oxide insulator carrying at least one of Pt and Pd, one or more selected from alumina sol, silica sol and ammonium metatungstate is added, followed by firing. The semiconductor gas sensor according to claim 1, wherein the semiconductor gas sensor is obtained.   In a semiconductor gas sensor including a metal oxide semiconductor-containing one as a sensitive element that causes a change in electric resistance value in response to a gas to be detected, the sensitive element carries at least one of Pt and Pd. A semiconductor gas sensor, which is obtained through a step of mixing a material containing particles of a metal oxide insulator and particles of a metal oxide semiconductor and molding and firing the resulting mixture.

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