JP4359311B2 - Semiconductor gas sensor - Google Patents

Description

  The present invention relates to a semiconductor gas sensor including a metal oxide semiconductor-containing sensor as a sensitive element that generates a change in electrical resistance in response to a gas to be detected.

  In recent years, semiconductor gas sensors using metal oxide semiconductors that generate a change in electrical resistance in response to the gas to be detected have been attracting attention as small and inexpensive gas sensors. It is widely used as a leak sensor, a bad breath sensor, a hydrogen gas sensor for controlling a fuel cell, an exhaust gas sensor for automobiles, and the like.

  Among these, as exhaust gas sensors for automobiles, for example, those detecting nitrogen oxide (NOx) exhausted from diesel engines, etc., those detecting hydrocarbons exhausted from gasoline engines, etc., both A gas detection device is provided. For example, it is used 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 used for the sensitive element in order to improve the detection sensitivity and the response at the time of detection, or to improve the selectivity by eliminating the influence of the interfering gas. May be included. Such Pt and Pd can improve the performance of the semiconductor gas sensor by, for example, decomposing the interfering gas or converting the gas to be detected into a substance that can be easily detected by the metal oxide semiconductor. It contributes to.

  As an aspect in the case of containing Pt and Pd, it is conceivable that Pt and Pd are entirely dispersed in a sensitive element including a metal oxide semiconductor. However, in this way, an increase in the electric resistance value of the sensitive element is considered. It is known from experience that it is easy to invite, and as a result, the expected performance improvement cannot be achieved, and conversely, the detection sensitivity and responsiveness decrease, or these performances deteriorate over time. It was a thing.

Therefore, when Pt and Pd are included in the sensitive element of the semiconductor gas sensor for imparting a catalytic action, a metal oxide semiconductor is conventionally included, as disclosed, for example, in 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. In Japanese Patent Publication No. 9-503589, a semiconductor gas sensor for detecting nitrogen oxides contained in exhaust gas or the like is described. The sensitive element is a metal oxide semiconductor such as SnO _2. Is formed by forming a coat layer (conversion layer) with a metal oxide carrying Pt or Pd on the outer layer of the metal oxide layer composed mainly of the above. With such a configuration, the metal oxide semiconductor is prevented from coming into contact with Pt or Pd so that the above-described adverse effects do not occur.

  However, when the coating layer is formed as described above, the catalytic action of Pt and Pd works only when the gas passes through the coating layer, and therefore passes through the coating layer without receiving the catalytic action of Pt or Pd. Many components remain, and there is a limit to 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 thereof relates to a semiconductor gas sensor in which Pt or Pd is contained in a sensitive element in order to improve performance such as detection sensitivity and responsiveness. Another object of the present invention is to provide a semiconductor gas sensor capable of achieving a significant performance improvement by the catalytic action of Pd and Pd.

  The second object of the present invention is to provide a semiconductor gas sensor capable of achieving a significant performance improvement by the catalytic action of Pt and Pd as described above, such as detection sensitivity and responsiveness to nitrogen oxide, hydrocarbon or carbon monoxide. An object of the present invention is to provide a semiconductor gas sensor that has improved performance and can be suitably used for exhaust gas detection applications such as automobiles.

  As a result of diligent research, the present inventors have made it possible to exhibit the catalytic action of Pt and Pd over the entire inside of the sensitive element A by dispersively arranging Pt and Pd in the sensitive element A, and The structure of the sensitive element A capable of eliminating the adverse effect of Pt and Pd on the metal oxide semiconductor has been found, and the present invention has been completed.

  That is, the semiconductor gas sensor according to the present invention is a semiconductor gas sensor that includes a metal oxide semiconductor as a sensitive element A that changes in electrical resistance in response to a gas to be detected. Is characterized in that a metal oxide insulator carrying at least one of Pt and Pd is dispersed.

  In such a semiconductor gas sensor, since at least one of Pt and Pd is dispersed in the sensitive element A, the catalytic action of at least one of Pt and Pd is exhibited throughout the sensitive element A. In addition, since the Pt and Pd exist in a state of being supported on the metal oxide insulator, the direct contact between the Pt and Pd and the metal oxide semiconductor in the sensitive element A is suppressed, and Pt and Pd The adverse effect on the metal oxide semiconductor due to the influence of Pt and Pd can be suppressed to prevent the sensing element A from increasing in resistance and the sensitivity from decreasing, and such a performance deterioration occurs with time. This is also prevented and the stability over time is excellent. For this reason, in order to improve the performance such as the detection sensitivity and responsiveness of the sensitive element A using the catalytic action of Pt or 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 , high temperature. It can be at least one of the calcined SnO ₂ .

In the sensitive element A having such a composition, when the metal oxide insulator supports Pt, particularly in the case of detecting nitrogen oxide (NOx), Pt is caused by the catalytic action in the sensitive element A. NO is oxidized and converted to NO ₂ , or further converted to N ₂ O _4, to a substance having a large fluctuation range of the electric resistance value of the metal oxide semiconductor when adsorbed on the metal oxide semiconductor The detection sensitivity of nitrogen oxides can be improved, and the responsiveness at the time of detection can also be improved.

  Further, in the sensitive element A, when the metal oxide insulator supports Pd, particularly when detecting hydrocarbon, carbon monoxide (CO), etc., the hydrocarbon or carbon monoxide (CO). Therefore, the detection sensitivity can be remarkably improved by improving the adsorptivity to the metal oxide semiconductor, and the response at the time of detection can also be improved.

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

Further, when the metal oxide semiconductor contains SnO ₂ , if the sensing element A contains sulfur, the detection sensitivity of nitrogen oxide (NOx), hydrocarbon, carbon monoxide (CO), etc. can be further improved. At this time, particularly when one or more metals selected from alkaline earth metals and rare earth elements are added to the sensitive element A, the detection sensitivity of nitrogen oxide (NOx) improved by the action of these metals. Can be further improved.

In the sensitive element A, in particular, 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 semiconductor Firing after adding at least one selected from alumina sol, silica sol and ammonium metatungstate to a molded body containing a physical semiconductor and the metal oxide insulator supporting at least one of Pt and Pd It is also preferable to obtain the sensitive element A. In this case, by adding alumina sol, silica sol or ammonium metatungstate, the detection sensitivity of nitrogen oxides (NOx), hydrocarbons, etc. can be improved, especially when alumina sol or silica sol is added. 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 the front view which fractured | ruptured partially the semiconductor gas sensor same as the above. The principal part of the other example of embodiment of this invention is shown, (a) is the perspective view seen from the one surface side, (b) is the perspective view seen from the other surface side. It is a perspective view of the semiconductor gas sensor fractured partially. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 1. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 2. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 3. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 4. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 5. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 6. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 7. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 8. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 9. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 10. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 11. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 12. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 13. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 14. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 15. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 16. It is a graph which shows the detection sensitivity evaluation of the semiconductor gas sensor of Example 17. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of Example 18. 22 is a graph showing evaluation of detection sensitivity of the semiconductor gas sensor of Example 19. It is a graph which shows the detection sensitivity evaluation of the semiconductor gas sensor of Example 20. 22 is a graph showing evaluation of detection sensitivity of the semiconductor gas sensor of Example 21. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of the comparative example 1. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of the comparative example 2. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of the comparative example 3. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of the comparative example 4. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of the comparative example 5. It is a graph which shows the detection sensitivity evaluation (a) and responsiveness evaluation (b) of the semiconductor gas sensor of the 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 is not particularly limited as long as it changes the electric resistance value in response to the gas to be detected, and is appropriately selected depending on the gas to be detected.

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

  In addition, the metal oxide insulator is appropriately selected from those that do not affect the change in the electrical resistance value of the sensitive element A during gas detection.

  The sensitive element A contains the above-described 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 has a function of suppressing contact between Pt and Pd in the sensitive element A and the metal oxide semiconductor by supporting at least one of Pt and Pd in the sensitive element A. It can also fulfill the function of adjusting the electrical resistance value and strength of the sensitive element A at the same time.

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

  In the semiconductor gas sensor having such a sensitive element A, when detecting the gas to be detected based on the change in the electrical resistance value of the sensitive element A when the sensitive element A is exposed to the gas to be detected, the sensitive element Since Pt and Pd exist in a dispersed manner in A, the catalytic action by Pt and Pd is exhibited over the entire inside of the sensitive element A, and the Pt and Pd are supported on the metal oxide insulator. Therefore, the direct contact between Pt and Pd and the metal oxide semiconductor in the sensitive element A is suppressed, and the adverse effect of Pt and Pd on the metal oxide semiconductor can be suppressed. For this reason, in order to improve the detection sensitivity and response of the sensitive element A by utilizing the catalytic action of Pt and Pd, a significant performance improvement can be achieved, and deterioration of these characteristics over time can be prevented.

  As long as the semiconductor gas sensor includes the sensitive element A as described above and can detect a change in the electrical resistance value when the sensitive element A is exposed to the gas to be detected, the semiconductor gas sensor may be a conventionally known appropriate element. A configuration can be employed.

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

  The electrode is provided for measuring the electric resistance of the sensitive element A, and the electric resistance value between the electrodes is measured in a state where the sensitive element A is arranged in the atmosphere containing the gas to be 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 gas according to the composition, and if the element temperature varies, the gas sensitivity varies and it becomes difficult to detect an accurate concentration. In detecting the gas concentration, the gas temperature can be accurately detected by keeping the element temperature at a suitable temperature with a heater.

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

In the semiconductor gas sensor shown in FIGS. 1 and 2, the coil-shaped heater combined electrode 25 and the core wire-shaped electrode 20 are used as a sensor base, and the substantially spherical shape (spherical shape, elliptic spherical shape, etc.) is formed so as to cover the heater combined electrode 25 and electrode 20. ) Is formed with the sensitive element A. In the illustrated example, the heater electrode 25 is formed so that the coil portion is embedded in the sensitive element A, and the electrode 20 is in the sensitive element A so as to penetrate the center of the coil portion of the heater electrode 25. Thus, the sensitive element A is miniaturized. The heater combined electrode 25 is platinum (Pt), is formed from a platinum alloy (Pt alloy) or the like, and platinum (Pt), provided between the leads 20 _1, 20 ₃ made of platinum alloy (Pt alloy) or the like, The heater combined 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 through 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 , respectively. By connecting ₃ , the sensitive element A is fixed and supported. A semiconductor gas sensor is configured 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. A gas introduction opening 41 is provided on the top surface of the sensor housing 40, and a metal mesh 41 made of stainless steel for gas introduction is stretched over the opening 41 as necessary.

  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 substrate (flat substrate), and a sensing 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 are provided on one surface of the insulator substrate 1 as shown in FIG. A sensitive element A is formed so as to extend between the electrodes 4A and 4B. Lead wires 5 are connected to the electrodes 2A, 2B, 4A 'and 4B' on the other surface side of the insulating substrate 1, respectively. As shown in FIG. 3B, the sensing part A has electrodes 0.3A and 4B 'and heater electrodes 2A, 2A, 4B on the other surface of the square insulating substrate 1 having a thickness of 0.3 mm and a side length of 2 mm. 2B is provided, and a heater 25 'made of a platinum printed film or the like is formed between the electrodes 2A and 2B.

  The sensing portion B is mounted on the base 30 by connecting the lead wire 5 to the terminal 10 penetrating the base 30, and a bottomed cylindrical sensor housing is mounted on the side of the base 30 on which the sensing portion B is mounted. The semiconductor gas sensor is configured by covering the body 40. A gas introduction opening 41 is provided on the top surface of the sensor housing 40, and a metal mesh 41 made of stainless steel for gas introduction is stretched over the opening 41 as necessary.

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

  Next, an example of a specific composition of the sensitive element A will be described. Specific examples of the sensitive element A described below are particularly suitable for exhaust gas detection applications from automobiles and the like, but when used for 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.

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

When SnO ₂ is used as the metal oxide semiconductor, this SnO ₂ is obtained by, for example, hydrolyzing an aqueous solution of SnCl ₄ with NH ₄ to obtain a stannic acid sol, and drying the stannic acid sol. It can be prepared by baking at a temperature of 0.5 to 3 hours. SnO ₂ can also be prepared as a metal oxide semiconductor by other methods. In that case, the crystallite size of SnO ₂ is preferably in the range of 20 to 30 nm.

  These metal oxide semiconductors can be applied to uses other than those for exhaust gas detection, but the electrical resistance value changes greatly 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.

Further, as the metal oxide insulator, for example, Al ₂ O _3, SiO ₂ or the like can be used, these are well used singly, may be used 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, preferably obtained by firing 0.5-3 hours in the range of 900 to 1100 ° C. This has higher electrical insulation than SnO ₂ which is a metal oxide semiconductor. In addition, SnO ₂ as a metal oxide insulator can be prepared by other methods. In that case, it is preferable that the crystallite size of SnO _{2 be} in the range of 50 to 130 nm.

  The content of such a metal oxide insulator in the sensitive element A is appropriately adjusted. In order to contain a sufficient amount of Pt and Pd in the sensitive element A, the metal oxide in the sensitive element A When the content (mass) of the semiconductor is 1, the content (mass) of the metal oxide insulator is preferably in the range of 0.2 to 1.5.

  When Pt or Pd is supported on the metal oxide insulator, not only Pt and Pd but also Pt and Pd can be supported together.

When Pt is supported on a metal oxide insulator, particularly when nitrogen oxide (NOx) is detected, Pt in the sensitive element A oxidizes NO by its catalytic action and converts it into NO ₂ , or Furthermore, every time it is converted into N ₂ O ₄ and converted in this way, it changes into a substance with a large fluctuation range of the electric resistance value of this metal oxide semiconductor when adsorbed on the metal oxide semiconductor, The detection sensitivity is improved, and at the same time, the response when detecting nitrogen oxides is improved. Such an improvement in detection performance is remarkably exhibited particularly in a low concentration region where the concentration of nitrogen oxide is about 1 ppm or less. In addition, when it is desired to detect only nitrogen oxides, which are oxidizing gases, hydrocarbons, carbon monoxide (CO), etc., which are reducing gases, act as interfering gases. As a result of decomposition and combustion, the detection sensitivity decreases, and nitrogen oxides are selectively detected. For this reason, a semiconductor gas sensor for detecting nitrogen oxide (NOx) having excellent detection sensitivity and responsiveness can be obtained by supporting Pt on a metal oxide insulator. Such a semiconductor gas sensor is suitably used as an exhaust gas sensor for a diesel engine, for example.

  Thus, when Pt is supported on the metal oxide insulator, if the content is too small, the detection performance of nitrogen oxides cannot be sufficiently improved, and if this content is excessive, Although the detection sensitivity of reducing gases such as hydrocarbon and carbon monoxide (CO) can be further suppressed and the nitrogen oxide selection detection performance increases, the nitrogen oxide detection sensitivity tends to decrease. . For this reason, it is preferable to appropriately adjust the amount of Pt supported on the metal oxide insulator so that desired characteristics can be imparted to the sensitive element A in consideration of the balance between improvement in detection sensitivity and selection right intelligence. Preferably, the content of Pt supported on the metal oxide insulator in the sensitive element A is 0.05 to 5% by mass, more preferably 0.2 to 1%, based on the total amount of the metal oxide insulator. The range is 5 mass%. In this range, a remarkable improvement in performance of the semiconductor gas sensor is recognized.

  In addition, when Pd is supported on a metal oxide insulator, it can also improve the performance of detecting nitrogen oxides by the same mechanism as in the case of Pt, but in particular, hydrocarbon, carbon monoxide (CO), etc. Although the detailed mechanism is not clear in the case of detecting CO, it is possible to improve the adsorptivity to metal oxide semiconductors such as hydrocarbon and carbon monoxide (CO) and to improve the detection sensitivity remarkably. At the same time, responsiveness when detecting hydrocarbons, carbon monoxide (CO), etc. can be improved. Therefore, by supporting Pd on a metal oxide insulator, it is possible to obtain a semiconductor gas sensor for detecting hydrocarbons, carbon monoxide (CO), etc. having 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 this way, when Pd is supported on the metal oxide insulator, the amount thereof is appropriately adjusted so as to give a desired performance to the semiconductor gas sensor, but it is preferably supported on the metal oxide insulator. The amount of Pd is 0.05 to 5 mass%, more preferably 0.2 to 1.5 mass%, based on the total amount of the metal oxide insulator. In this range, a remarkable improvement in performance of the semiconductor gas sensor is recognized.

  In addition, when Pt and Pd are used in combination and both are supported on a metal oxide insulator, the action of improving the detection sensitivity of nitrogen oxide (NOx) by Pt, and the hydrocarbon and monoxide by Pd are improved. It is possible to obtain a semiconductor gas sensor capable of detecting both nitrogen oxide and hydrocarbon, carbon monoxide (CO), etc. by simultaneously exerting the effect of improving the detection sensitivity such as carbon (CO). it can.

Thus, when Pt and Pd are contained in the sensitive element A to obtain a semiconductor gas sensor for both, the amounts of Pt and Pd supported on the metal oxide insulator as appropriate according to the characteristics required for the sensitive element A For example, when the metal oxide semiconductor contained in the sensitive element A is In ₂ O ₃ or WO ₃ , the amount of Pt supported on the metal oxide insulator is preferably set. The amount of Pd supported on the metal oxide insulator is in the range of 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. The range is 0.05 to 5% by mass, more preferably 0.2 to 1.5% by mass, and the mass ratio of Pt and Pd is 1: 9 to 9: 1 with respect to the total amount of the insulator. It is preferable that

  Such a sensitive element A can be produced by an appropriate method. For example, first, a metal oxide insulator particle and a solution containing at least one of Pt and Pd (for example, an aqua regia solution) are mixed and fired to form a metal supporting at least one of Pt and Pd. Oxide insulator particles are obtained. Although this baking condition is adjusted suitably, it can be 0.5 to 3 hours, for example at 500-700 degreeC by an air atmosphere. Next, the metal oxide semiconductor particles are mixed with the metal oxide insulator particles, and an organic solvent such as terpineol is added thereto to prepare a paste-like molding material. And after apply | coating this molding material to a sensor base | substrate, it bakes, The desired sensitive element A can be produced. Although this baking conditions are adjusted suitably, it can be made into 1 to 60 minutes at 500-700 degreeC, for example by an air atmosphere.

  In the sensing element A thus formed, it is preferable that Pt and Pd are supported only on the metal oxide insulator and not on the metal oxide semiconductor, but a small amount of Pt and Pd is supported on the metal oxide insulator. It is allowed to be supported on the body, and a small amount of Pt or Pd is inevitably contained in the metal oxide semiconductor such as a small amount of Pt or Pd is supported on the metal oxide semiconductor in the molding process. It is allowed to be supported. 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 in the case where the metal oxide semiconductor is SnO ₂ , an alkaline earth metal such as Mg, Ca, Sr, Ba and the like, Y, Sc, La, Pr, Nd, Sm, Er, Gd are included in the sensitive element A. One or more metals selected from rare earth elements such as can be added. 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 in particular, the detection sensitivity of nitrogen oxide (NOx) can be improved. At this time, as for the detection sensitivity of nitrogen oxide (NOx), the detection sensitivity in the case of a low concentration of 1 ppm or less is remarkably improved.

  When Pt is supported on a metal oxide insulator, the detection sensitivity and responsiveness of nitrogen oxide (NOx) are improved by Pt as described above, and the above metal is added to the sensing element A. By adding it and further improving the detection sensitivity of nitrogen oxide (NOx), in particular, the detection sensitivity at a low concentration, a semiconductor gas sensor for detecting nitrogen oxide having very excellent detection performance can be obtained.

Thus, when one or more metals selected from alkaline earth metals and rare earth elements are added to the sensitive element A, the amount added is appropriately adjusted so that desired characteristics can be imparted to the sensitive element A. However, if the addition amount is too small, the gas detection sensitivity cannot be sufficiently improved, and if the addition amount is excessive, the electrical resistance value of the sensitive element A is increased or the gas detection sensitivity is not good. It may decrease. Thus, 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. It is preferable to contain in the range of 10 ⁻⁴ mol / g, and when adding at least one of Y and Sc among the rare earths, the ratio to the total amount of the metal oxide semiconductor and the metal oxide insulator is 4 It is preferable to contain so that it may become the range of * 10 < ^-6 > -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 so that it may become the range of g. In these ranges, a significant improvement in the performance of the semiconductor gas sensor is observed. Moreover, when using Y and Sc together with a lanthanoid, as in the case of using Y and La in combination, a component consisting of at least one of Y and Sc and a component consisting of a lanthanoid respectively While containing in the range of 2 * 10 < ^-6 > -7 * 10 < ^-5 > mol / g, it is preferable to make the ratio of the former component and the latter component into the range of 1: 2 to 2: 1.

  In adding the metal to the sensitive element A, an appropriate method can be used. For example, the metal oxide semiconductor particles and the metal oxide insulator particles supporting at least one of Pt and Pd are mixed, molded, and fired by the above-described technique. The metal can be added to the sensitive element A by applying and impregnating a solution containing the metal (for example, a nitric acid solution in which the metal is dissolved) and firing the solution. 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 form of sulfate ions.

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

  In addition, when sulfur is added in this way, the detection sensitivity of nitrogen oxide (NOx) can also be improved. In particular, 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, when one or more metals selected from alkaline earth metals and rare earth elements are added to the sensitive element A, and sulfur is further added, nitrogen oxidation is performed. The detection sensitivity of substances (NOx) can be further improved, and the detection sensitivity of hydrocarbons and carbon monoxide (CO) can be improved, whereby a dual-use semiconductor gas sensor having excellent detection characteristics can be obtained.

Thus, when sulfur is added to the sensitive element A, if the addition amount is too small, the gas detection sensitivity cannot be sufficiently improved, and if the addition amount is increased, nitrogen is particularly used in the case of a dual-use semiconductor gas sensor. Since the detection sensitivity of hydrocarbons may increase compared to the detection sensitivity of oxides, or the responsiveness at the time of detection of nitrogen oxides may be reduced, the amount of sulfur added has the desired characteristics for the sensing element A. It adjusts suitably so that it can provide. For example, it is preferable to make it contain in 2 * 10 < ^-6 > -1 * 10 < ^-4 > mol / g in conversion of a sulfur atom with respect to the total amount of a metal oxide semiconductor and a metal oxide insulator.

  In adding the sulfur to the sensitive element A, an appropriate technique can be used. For example, the metal oxide semiconductor particles and the metal oxide insulator particles supporting at least one of Pt and Pd are mixed, molded, and fired by the above-described method. Then, sulfur can be added to the sensitive element A by applying and impregnating a solution containing sulfur (for example, a sulfuric acid aqueous solution) and firing the solution. 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.

  In addition, in the case where one or more metals selected from alkaline earth metals and rare earth elements and sulfur are added to the sensitive element A, for example, the metal oxide semiconductor particles and at least one of Pt and Pd 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 a molded body obtained by mixing, molding, and firing the metal oxide insulator particles supporting one of them. The metal is added to the sensitive element A by impregnating it and firing it. Next, sulfur can be added to the sensitive element A by further impregnating and impregnating the molded body with a solution containing sulfur (for example, an aqueous sulfuric acid solution) and firing it.

  In addition, when adding one or more metals selected from alkaline earth metals and rare earth elements and sulfur, a mixed solution in which the metal and sulfur are mixed in one solution is prepared, for example, by the method described above. A metal oxide semiconductor particle and a metal oxide insulator particle supporting at least one of Pt and Pd are mixed, and the molded product 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 applying and impregnating a mixed solution containing the mixture and firing the mixture.

In particular, 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 , A molded body including the metal oxide semiconductor as described above and a metal oxide insulator supporting at least one of Pt and Pd is manufactured, and alumina sol (colloidal alumina), silica sol ( The sensitive element A can be manufactured through a step of baking after adding at least one of colloidal silica) and ammonium metatungstate. For example, with respect to a molded body obtained by mixing, molding, and firing metal oxide semiconductor particles and metal oxide insulator particles supporting at least one of Pt and Pd by the method described above. In addition, at least one of alumina sol, silica sol, and ammonium metatungstate is coated and impregnated and baked to add the components to the sensitive element A. The firing conditions at this time are appropriately adjusted. For example, the firing can be performed at 650 ° C. for 10 minutes in an air atmosphere.

  At this time, among the above-mentioned additives, alumina sol and silica sol can be further improved in detection sensitivity when nitrogen oxide (NOx) or hydrocarbon is detected by the semiconductor gas sensor by adding to the sensitive element A. In addition, responsiveness at the time of detection can be improved. Further, when ammonium metatungstate is added to the sensitive element A, the detection sensitivity at the time of detecting nitrogen oxide (NOx) by the semiconductor gas sensor can be further improved.

When obtaining a semiconductor gas sensor for detecting nitrogen oxide (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, When at least one of alumina sol, silica sol, and ammonium metatungstate is used as an additive, the detection sensitivity of nitrogen oxides (NOx) can be further improved by the action of the additive, particularly among alumina sol and silica sol. When at least one of them is added, the responsiveness can be further improved.

In addition, 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 a metal oxide insulator, and Pd is supported on the metal oxide insulator. Further, when at least one of alumina sol and silica sol is used as an additive, the detection sensitivity of the hydrocarbon can be further improved by the action of the additive.

Furthermore, when obtaining a dual-use semiconductor gas sensor, at least one of Al ₂ O ₃ and SiO ₂ is used as a metal oxide insulator, and both Pt and Pd are supported on the metal oxide insulator, and further an additive When at least one of alumina sol, silica sol and ammonium metatungstate is used, the detection sensitivity of nitrogen oxides (NOx) can be further improved by the action of the additive, particularly at least one of alumina sol and silica sol. In addition, it is possible to improve the detection sensitivity of the hydrocarbon and improve the responsiveness.

The addition amount in the case of adding alumina sol, silica sol or ammonium metatungstate to the sensitive element A is appropriately adjusted so that desired characteristics are imparted to the sensitive element A, for example, a metal oxide semiconductor, In adding the component to a molded body including a metal oxide insulator supporting at least one of Pt and Pd, when adding an alumina sol, a metal oxide semiconductor (In ₂ O ₃ ) is added. The alumina sol is preferably added in an amount of 0.1 to 50% by mass, more preferably 0.5 to 5% by mass in terms of Al ₂ O ₃ with respect to the total amount. Further, 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. Also it is preferably added in an amount of 0.1 to 5 wt% of a metal oxide semiconductor (In ₂ O ₃₎ WO ₃ in terms ammonium metatungstate with respect to the total amount in the case of addition of ammonium metatungstate.

  Hereinafter, the present invention will be specifically described based on examples. In addition, these are illustrations and do not limit the present invention.

(Examples 1-21, Comparative Examples 1-6)
About each Example and Comparative Example, the metal oxide semiconductor particles shown in Tables 1 to 3 and the metal oxide insulator particles are mixed in the ratio shown in the table, and terpineol is 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 By firing for 1 hour, thereby obtaining SnO ₂ which is a metal oxide semiconductor, a pulverized SnO ₂ was used.

In addition, when high-temperature fired SnO ₂ is used as the metal oxide insulator, SnO ₂ , which is a metal oxide semiconductor obtained as described above, is fired at 1000 ° C. for 1 hour in an air atmosphere. It was.

  Further, when using metal oxide semiconductor particles and metal oxide insulator particles carrying at least one of Pt and Pd, an aqua regia solution in which at least one of Pt and Pd is dissolved in these particles. It was impregnated and calcined in the air at 500 ° C. for 1 hour, and at least one of Pt and Pd was supported in a 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. A substantially oval spherical shaped body having an axial length of 0.5 mm was obtained.

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

Here, when additive 1 was La and Y, La and Y were applied to the molded body in a state in which each nitrate was in an aqueous solution. Further, when the additive 1 is silica sol or alumina sol, the silica sol or alumina sol is applied to the molded body, and the blending amount in the table is SiO ₂ conversion in the case of silica sol, and Al _{2 in} the case of alumina sol. O ₃ equivalent.

  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 at 650 ° C. in an air atmosphere. 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 molded body in the state of an aqueous sulfuric acid solution, and the blending amount in the table is converted to sulfur atoms. .

In addition, when the additive 2 is ammonium metatungstate, an aqueous solution of ammonium metatungstate is applied to the 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 a semiconductor gas sensor having the configuration shown in FIG.

(Detection sensitivity evaluation)
About each semiconductor gas sensor, about Examples 1-7, 19-21, and Comparative Examples 1-3, element temperature is 250 degreeC, In the case of Examples 8-10, element temperature is 200 degreeC, Examples 11-17, and Comparative Examples 4- In the case of 6, the detection sensitivity was investigated at 350 ° C., and in the case of Example 18, the detection sensitivity at 350 ° C. was investigated. Here, the detection sensitivity is the electric resistance value (Rair) of the sensitive element A when the sensitive element A is exposed to clean air, and the electric resistance value (Rs) of the sensitive element A when exposed to the sample gas. The ratio (Rs / Rair).

The following was used as the sample gas.
Sample gas 1: A mixture of nitrogen dioxide mixed with clean air and varying the nitrogen dioxide concentration.
Sample gas 2: A mixture of nitrogen dioxide and carbon monoxide mixed in clean air, with the carbon monoxide concentration fixed at 30 ppm, and the nitrogen dioxide concentration varied.
Sample gas 3: Carbon monoxide mixed in clean air and the concentration of carbon monoxide was changed.
Sample gas 4: A mixture of nitrogen dioxide and carbon monoxide mixed in clean air, the nitrogen dioxide concentration fixed at 1 ppm (3 ppm for Examples 11 to 16), and the carbon monoxide concentration 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 mixed in clean air, nitrogen dioxide concentration fixed at 1 ppm, and decane concentration 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 indicates the value of Rs / Rair, and the horizontal axis indicates the concentration of the sample gas.

  Further, in the graph, □ indicates the result of the sample gas 1, ■ indicates the sample gas 2, Δ indicates the sample gas 3, ▲ indicates the sample gas 4, ○ indicates the sample gas 5, and ● indicates the result for the sample gas 6.

(Response evaluation)
The semiconductor gas sensor obtained in each of the examples and comparative examples was placed in a container, and was first placed in clean air with the temperature of the sensitive element A being the same as in the case of the above-described detection sensitivity evaluation. A sample gas in which nitrogen dioxide or carbon monoxide was mixed into clean air was jetted out, and then clean air was jetted out. The result of measuring the electrical resistance value (Rs) of the sensitive element A at this time is shown in the graph 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. The graph also shows the concentration of nitrogen dioxide or carbon monoxide in the sample gas and the time when the sample gas was ejected.

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

Among these, in particular, the amount of Pt supported on the metal oxide insulator is in the range of 0.2 to 1.5% by mass with respect to the metal oxide insulator, and the contents of La and Y are respectively metal oxides. In Example 1 which became the range of 5 * 10 < ^-6 > -2 * 10 < ^-5 > mol / g with respect to the total amount of an insulator and a metal oxide semiconductor, the detection sensitivity of nitrogen oxide and its selective detection property are It was improved in a well-balanced manner and had excellent responsiveness.

In Examples 5 to 7, SnO ₂ is used as the metal oxide semiconductor, Al ₂ O ₃ is used as the metal oxide insulator, Pt is supported on the metal oxide insulator, and La and Y are added as additives. Used and further added with sulfur. By adding sulfur, the detection sensitivity of nitrogen oxides is further improved, and the detection sensitivity of hydrocarbons and carbon monoxide is also improved. 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 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, The detection sensitivity of oxides and the detection sensitivity of hydrocarbons and carbon monoxide are sufficiently improved, and the balance of these detection sensitivities is good.

  In Examples 8 to 10, Pd is supported on a metal oxide insulator, and thus the detection sensitivity of carbon monoxide is 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, 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 of carbon monoxide is high. These semiconductor gas sensors can be suitably used for selectively detecting nitrogen monoxide and hydrocarbons.

In Examples 11 to 13, In ₂ O ₃ is used as the metal oxide semiconductor, Al ₂ O ₃ is used as the metal oxide insulator, Pt is supported on the metal oxide insulator, and silica sol is used as an additive. Compared with Comparative Examples 4 to 6 in which Pt and Pd are not supported on a metal oxide insulator, the detection sensitivity of nitrogen oxide and the detection sensitivity of hydrocarbon and carbon monoxide are reduced. Yes. 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 in combination with silica sol as an additive. , 12, the detection sensitivity of nitrogen dioxide is improved particularly in the concentration range of 1 ppm or less, and the detection sensitivity of hydrocarbons and carbon monoxide, particularly the detection sensitivity of carbon monoxide is reduced. A semiconductor gas sensor capable of selectively detecting nitrogen dioxide in the case of interfering gas was obtained. Moreover, the responsiveness at the time of nitrogen dioxide detection 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 were added in Comparative Example 4, respectively. Compared with Comparative Example 4, the detection sensitivity of nitrogen dioxide was improved.

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, and Pt and Pd were both supported on the metal oxide insulator, and used as additives. This is a combination of silica sol and ammonium metatungstate. The detection sensitivity of nitrogen dioxide is improved particularly in a concentration range of 1 ppm or less, and the detection sensitivity of hydrocarbon and carbon monoxide is also improved. In particular, in Examples 14 and 15 where 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 an 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 or hydrocarbon.

In Example 18, WO ₃ is used as the metal oxide semiconductor, Al ₂ O ₃ is used as the metal oxide insulator, both Pt and Pd are supported on the metal oxide insulator, and silica sol is used as an additive. Therefore, the detection sensitivity of nitrogen dioxide is improved particularly in a concentration region 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 an additive. It is. In Examples 20 and 21, SnO ₂ was used as the metal oxide semiconductor, SiO ₂ or high-temperature fired 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 and Pd are not supported on a metal oxide insulator, and Comparative Example 3 in which Pt is supported on a metal oxide semiconductor, the concentration of nitrogen dioxide is particularly 1 ppm or less. A semiconductor gas sensor was obtained that was improved in the region, and the detection sensitivity of hydrocarbons and carbon monoxide was reduced, and nitrogen dioxide can be selectively detected when hydrocarbons and carbon monoxide are interfering gases. Moreover, these were also excellent in the responsiveness at the time of nitrogen dioxide detection. These semiconductor gas sensors can be suitably used for selectively detecting nitrogen oxides.

  The semiconductor gas sensor according to the present invention is used for appropriate applications such as a gas leak sensor for combustible gas for home use and industrial use, a bad breath sensor, a hydrogen gas sensor for controlling a fuel cell, an exhaust gas sensor for automobile use, etc. be able to.

Claims (9)

In a semiconductor gas sensor comprising a metal oxide semiconductor-containing sensor as a sensitive element that generates a change in electrical resistance in response to a gas to be detected, the gas to be detected is nitrogen oxide, and the sensitive element is SnO ₂ is contained as a metal oxide semiconductor, and a metal oxide insulator carrying Pt is dispersed inside the sensitive element, and the metal oxide insulator is Al ₂ O _3. , SiO ₂ , at least one of high-temperature fired SnO ₂ , and the sensitive element contains at least one of alkaline earth metal and rare earth. In a semiconductor gas sensor comprising a metal oxide semiconductor containing a sensitive element that generates a change in electrical resistance in response to a gas to be detected, the sensitive element contains SnO ₂ as the metal oxide semiconductor, A metal oxide insulator carrying Pt is dispersed inside the sensitive element, and the metal oxide insulator is made of Al ₂ O ₃ , SiO ₂ , high-temperature fired SnO ₂ . And the sensitive element contains at least one of alkaline earth metal and rare earth and sulfur. In a semiconductor gas sensor comprising a metal oxide semiconductor-containing sensor as a sensitive element that generates a change in electrical resistance in response to a gas to be detected, the gas to be detected is nitrogen oxide, and the sensitive element is In ₂ O ₃ is contained as a metal oxide semiconductor, and a metal oxide insulator carrying Pt is dispersed inside the sensitive element, and the metal oxide insulator is Al ₂ O. ₃ and at least one of SiO ₂ , and the sensitive element includes the metal oxide semiconductor and the metal oxide insulator supporting Pt, an alumina sol, silica sol, and metatungstic acid. A semiconductor gas sensor obtained by baking after adding at least one selected from ammonium. In a semiconductor gas sensor comprising a sensing element containing a metal oxide semiconductor as a sensitive element that generates a change in electrical resistance in response to a gas to be detected, the gas to be detected is nitrogen oxide, hydrocarbon, and carbon monoxide, The sensitive element contains In ₂ O ₃ as the metal oxide semiconductor, and a metal oxide insulator carrying Pt and Pd is dispersed inside the sensitive element. A molded body including a material insulator that is at least one of Al ₂ O ₃ and SiO ₂ , and wherein the sensitive element includes the metal oxide semiconductor and a metal oxide insulator supporting Pt and Pd. A half obtained by baking after adding at least one selected from alumina sol, silica sol and ammonium metatungstate Body gas sensor. In a semiconductor gas sensor comprising a metal oxide semiconductor-containing sensor as a sensitive element that generates a change in electrical resistance in response to a gas to be detected, the gas to be detected is nitrogen oxide, and the sensitive element is WO ₃ is contained as a metal oxide semiconductor, a metal oxide insulator carrying Pt is dispersed inside the sensitive element, and the metal oxide insulator is Al ₂ O _3. A semiconductor gas sensor, which is at least one of SiO ₂ . In a semiconductor gas sensor equipped with a metal oxide semiconductor-containing sensitive element that generates a change in electrical resistance in response to the gas to be detected, the gas to be detected is nitrogen oxide, hydrocarbon, and carbon monoxide. The sensitive element contains WO ₃ as the metal oxide semiconductor, and a metal oxide insulator carrying Pt and Pd is dispersed inside the sensitive element. A semiconductor gas sensor, wherein the oxide insulator is at least one of Al ₂ O ₃ and SiO ₂ . An exhaust gas sensor for a gasoline engine, comprising the semiconductor gas sensor according to claim 2 . An exhaust gas sensor for a diesel engine comprising the semiconductor gas sensor according to any one of claims 1 to 6 . An exhaust gas sensor for both a gasoline engine and a diesel engine, comprising the semiconductor gas sensor according to claim 2 .

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