JP6224311B2 - Semiconductor gas sensor element - Google Patents

Description

  The present invention relates to a semiconductor gas sensor element used for detecting a gas to be detected by a change in electric resistance value of a gas sensitive body containing a metal oxide semiconductor.

  The semiconductor gas sensor element is suitable for detecting a small amount of gas components in the gas phase and is used for various applications. Various types of semiconductor gas sensor elements have been proposed. Among them, semiconductor gas sensor elements constructed by embedding electrodes made of platinum, platinum alloys, etc. in a spherical gas-sensitive body mainly composed of metal oxide semiconductors have high strength and durability. Used (see Patent Document 1). In such a semiconductor gas sensor element, when the gas sensitive body is exposed to a gas to be detected while being heated by a heater or the like, the electrical resistance value of the gas sensitive body changes due to the adsorption of the gas. A change in the resistance value is detected using the electrode, and thereby the gas to be detected is detected. It is also possible to measure the gas concentration in the gas phase based on the amount of change in the electrical resistance value.

JP 2008-46091 A

  In order to accurately detect the gas using the semiconductor gas sensor element or to accurately measure the gas concentration, the electric resistance value measured using the electrode is stable and the electric resistance according to the gas concentration. It is required that the amount of change in value is constant.

  However, the electrical resistance value measured using the electrodes and the amount of change may vary depending on the environmental change or the like. For example, if the heating temperature of the gas sensitive body, the temperature and humidity of the gas phase to which the gas sensitive body is exposed, and the like change, the measured value of the electrical resistance value may change accordingly. In addition, there is a possibility that the gas to be detected is oxidized in the high temperature gas sensitive body, so that the electric resistance value does not change according to the original gas concentration.

  This invention is made | formed in view of the said reason, The subject is providing the semiconductor gas sensor element which a change of the sensitivity resulting from the change of an environment etc. does not arise easily.

  A semiconductor gas sensor according to the present invention includes a gas sensitive body containing a metal oxide semiconductor and an electrode embedded in the gas sensitive body, and the electrode is formed of platinum or a platinum alloy, and on the surface thereof. A gold film is formed.

  According to the present invention, when detecting a gas to be detected using a semiconductor gas sensor element or measuring its concentration, the sensitivity is improved, and a change in sensitivity due to a change in environment is less likely to occur. There is an effect.

It is sectional drawing which shows the semiconductor gas sensor element in one Embodiment of this invention. It is the partially broken front view which shows the gas detection apparatus provided with the said semiconductor gas sensor element. It is a graph which shows the result of having investigated the temperature dependence of the electrical resistance value _Rair between the heater combined electrode and the core wire electrode in the atmosphere for Example 1. It is a graph which shows the result of having investigated the temperature dependence of the electrical resistance value _Rair between the heater combined electrode and the core wire electrode in the atmosphere for Comparative Example 1. The electrical resistance value R _s between the heater combined electrode and the core wire electrode in the gas phase containing the gas to be detected and the electricity between the heater combined electrode and the core wire electrode in the atmosphere for Example 1 the temperature dependence of the ratio R _air / R _s of the resistance value R _air is a graph showing the results of the investigation. For Comparative Example 1, electrical between the heater combined electrode and the wire-shaped electrode in an electric resistance value R _s and the atmosphere between the heater combined electrode and the wire-shaped electrode in the gas phase comprises a gas detection target the temperature dependence of the ratio R _air / R _s of the resistance value R _air is a graph showing the results of the investigation. For Example 1 and Comparative Example 1, a heater combined electrode and the wire-shaped electrode in an electric resistance value R _s and the atmosphere between the heater combined electrode and the wire-shaped electrode in the gas phase comprises a gas detection target FIG. 7A is a graph showing the result of investigating the ratio R _air / R _s with respect to the electric resistance value R _air between FIG. 7A and FIG. 7B when the detection target gas is methane. 7 (c) shows the case where the detection target gas is hydrogen, FIG. 7 (d) shows the case where the detection target gas is ethylene, and FIG. 7 (e) shows the case where the detection target gas is carbon monoxide. 7 (f) shows the case where the detection target gas is ethanol, FIG. 7 (g) shows the case where the detection target gas is toluene, and FIG. 7 (h) shows the detection target gas. FIG. 7 (i) shows the results when the detection target gas is trimethylamine. Show. For Example 2 and Comparative Example 2, a heater combined electrode and the wire-shaped electrode in an electric resistance value R _s and the atmosphere between the heater combined electrode and the wire-shaped electrode in the gas phase comprises a gas detection target it is a graph showing the results of the examination of the ratio R _s / R _air between the electric resistance value R _air between. For Example 2 and Comparative Example 2, the electrical resistance value R ₀ between the heater electrode and the core wire electrode in the atmosphere when the temperature and humidity conditions are 20 ° C. and 60% RH, and the temperature and humidity conditions are as follows: it is a graph showing the results of the examination of the ratio R _s / R ₀ of the electric resistance R _s between the heater combined electrode and the wire-like electrode when changing. For Example 2 and Comparative Example 2, in the gas phase containing ammonia, the electrical resistance value R ₀ between the heater combined electrode and the core wire electrode when the temperature and humidity condition is 20 ° C. and 60% RH, it is a graph showing the results of the examination of the ratio R _s / R ₀ of the electric resistance R _s between the heater combined electrode and the wire-shaped electrode in the case of changing the temperature and humidity conditions. The heater at the applied voltage of 0.5 V in the gas phase containing the gas to be detected when the voltage of 0.5 V and the voltage of 0.9 V are alternately applied to the heater combined electrode in Comparative Example 3 is a graph showing the results of the examination of the gas concentration dependence of the electrical resistance R _s between the combined electrode and the wire-shaped electrode. In Example 3, when a voltage of 0.5 V and a voltage of 0.9 V are alternately applied to the heater combined electrode, the applied voltage is 0.5 V in the gas phase containing the gas to be detected. is a graph showing the results of the examination of the gas concentration dependence of the electrical resistance R _s between the heater combined electrode and the wire-shaped electrode. In Comparative Example 3, when a voltage of 0.5 V and a voltage of 0.9 V are alternately applied to the heater combined electrode, the applied voltage is 0.9 V in the gas phase containing the gas to be detected. is a graph showing the results of the examination of the gas concentration dependence of the electrical resistance R _s between the heater combined electrode and the wire-shaped electrode. The heater at the applied voltage of 0.9 V in the gas phase containing the gas to be detected when the voltage of 0.5 V and the voltage of 0.9 V are alternately applied to the heater combined electrode in Example 3. is a graph showing the results of the examination of the gas concentration dependence of the electrical resistance R _s between the combined electrode and the wire-shaped electrode.

  The semiconductor gas sensor element according to the present embodiment includes a gas sensitive body containing a metal oxide semiconductor and an electrode embedded in the gas sensitive body. The electrode is made of platinum or a platinum alloy, and a gold film is formed on the surface thereof.

  In general, the gas sensitive body of the semiconductor gas sensor element is exposed to the gas to be detected, and the electrical resistance value of the gas sensitive body is measured using an electrode, so that the gas to be detected is based on the change in the electrical resistance value. And the concentration of the gas to be detected can be measured based on the amount of change in the electrical resistance value. In the present embodiment, the amount of change in the electrical resistance value that occurs when the gas sensitive body is exposed to the gas to be detected is increased, and thus the detection sensitivity is increased. Furthermore, when the temperature and humidity of the gas phase around the gas sensitive body fluctuate and when the temperature of the gas sensitive substance fluctuates, the amount of change in the electrical resistance value is reduced. For this reason, it is difficult for a change in sensitivity due to an environmental change or the like to occur.

  The reason why the above action occurs is not sufficiently clear, but the catalytic activity on the surface of the electrode is suppressed by covering the electrode formed of platinum or a platinum alloy with a gold film, thereby reducing the gas. It is inferred that this is due to the fact that the gas to be detected in the phase is less likely to be oxidized.

  Note that the gold coating hardly affects the electric resistance value of the electrode formed of platinum or a platinum alloy. For this reason, the temperature of the electrode when the voltage is applied to the electrode (heating temperature of the gas sensitive body) is hardly affected by the presence or absence of the gold coating. For this reason, the above action is not caused by the temperature change of the gas sensitive body due to the change of the electric resistance value of the electrode.

  In the present embodiment, the type of gas to be detected is not limited, but a remarkable effect is exhibited particularly when the gas to be detected is a reducing gas. Further, when the detection target gas is ammonia, amine, or the like that is easily oxidized among the reducing gases, a particularly remarkable effect is exhibited. That is, when the gas to be detected is a reducing gas, particularly ammonia that is easily oxidized, amine, etc., in this embodiment, the detection sensitivity is greatly improved as compared with the case where no gold coating is formed on the electrode, In addition, the change in detection sensitivity with respect to environmental changes is particularly small.

  Hereinafter, this embodiment will be described in more detail. FIG. 1 shows a semiconductor gas sensor element 1 according to the present embodiment, and FIG. 2 shows a gas detection device 15 including the semiconductor gas sensor element 1. The semiconductor gas sensor element 1 includes a gas sensitive body 4 and two electrodes 2 and 3 embedded in the gas sensitive body 4. The gas detection device 15 includes a semiconductor gas sensor element 1, three lead wires 5, 6, 7, three terminals 8, 9, 10, and a sensor housing 13.

  The electrodes 2 and 3 are formed from platinum or a platinum alloy. Further, a gold film is formed on the surfaces of the electrodes 2 and 3.

  In the present embodiment, one of the two electrodes 2 and 3 is a coiled heater combined electrode 2, and the other is a linear core wire electrode 3. The heater combined electrode 2 is formed, for example, in a range of 0.1 to 0.5 mm in diameter, 0.05 to 0.7 mm in length, and 2 to 11 turns. The length is a dimension in a direction perpendicular to the radial direction of the coil. Two lead wires 5 and 6 respectively project from both ends of the heater combined electrode 2. That is, the two lead wires 5 and 6 and the heater combined electrode 2 are formed from a single wire made of platinum or a platinum alloy, and the heater combined electrode 2 is formed between the two lead wires 5 and 6. The core wire electrode 3 is provided inside the coiled heater combined electrode 2. A lead wire 7 protrudes from an end portion of the core wire electrode 3. That is, the lead wire 7 and the core wire electrode 3 are formed from a single wire made of platinum or a platinum alloy, one end of the wire rod is the core wire electrode 3, and the portions other than the core wire electrode 3 are lead wires. 7 The lead wires 5, 6 and 7, and the wire diameters of the heater combined electrode 2 and the core wire electrode 3 are preferably in the range of 15 to 25 μm.

  The gold film is formed by an appropriate method. For example, a gold film can be formed by depositing an aqueous solution of a gold compound such as chloroauric acid on the surfaces of the electrodes 2 and 3 and then heating and baking it. Further, a gold film may be formed on the surfaces of the electrodes 2 and 3 by gold plating (electrolytic gold plating or electroless gold plating).

  The gas sensitive body 4 contains a metal oxide semiconductor. The metal oxide semiconductor contains a metal oxide selected from, for example, tin oxide, tungsten oxide, indium oxide, zinc oxide, titanium oxide, strontium titanate, barium titanate, and barium stannate.

  The gas sensitive body 4 may further contain an appropriate additive such as an inorganic insulator and a catalyst. The inorganic insulator can contain at least one selected from alumina and silica, for example. The catalyst can contain at least one selected from, for example, ruthenium, palladium, antimony, lanthanum, cerium, and molybdenum.

  The shape of the gas sensitive body 4 is not particularly limited, and is formed into a spherical shape such as an ellipsoidal shape or a spherical shape as in the illustrated example. Although the dimension of the gas sensitive body 4 is set suitably, Preferably the diameter is formed in the range of 0.2-0.7 mm. For example, the gas sensitive body 4 is formed in an ellipsoidal shape having a major axis of 0.5 mm and a minor axis of 0.3 mm.

  The gas sensitive body 4 is formed, for example, by molding a molding material containing a metal oxide semiconductor powder and firing the molding material. In addition to the metal oxide semiconductor powder, the molding material may contain an inorganic insulator powder, a catalyst, and the like. Furthermore, the molding material may contain an appropriate organic solvent, a binder, and the like as necessary. The binder contains at least one selected from, for example, colloidal silica, organic silica, and alumina sol.

  When the gas sensitive body 4 is formed, first, for example, in a state where the core wire electrode 3 is disposed inside the heater electrode 2, the electrodes 2, 3 are covered on the electrodes 2, 3. A molding material is applied to the substrate. When the molding material is heated in a state where the molding material is attached to the electrodes 2 and 3 in this way, the molding material is sintered. Thereby, the gas sensitive body 4 is formed.

  In forming the gas sensitive body 4, a molding material is first molded and further fired to form a sintered body, and an appropriate additive is applied to the sintered body after adding a solvent as necessary, Further, the gas sensitive body 4 may be formed by firing. As an additive in this case, for example, at least one selected from a catalyst, colloidal silica, and alumina sol is used.

  In the gas detection device 15, the end of the lead wire 5 is fixed and electrically connected to the terminal 8, and the end of the lead wire 6 is fixed and electrically connected to the terminal 9, and the lead wire 7 is fixed to the terminal 10 and electrically connected thereto.

  The terminals 8, 9, and 10 pass through the resin base 11 that also serves as the bottom of the sensor housing 13, and one end thereof protrudes inside the sensor housing 13 and the other end protrudes outside the sensor housing 13. It is provided as follows. Accordingly, the terminals 8, 9 and 10 are supported by the sensor housing 13. The cap body 12 that constitutes the sensor housing 13 together with the base 11 is formed in a cylindrical shape that is open at the top and bottom, and a stainless steel wire mesh 14 for exposure protection is provided in the upper opening. By attaching the base 11 to the lower opening of the cap body 12, the lower opening is closed by the base 11, thereby configuring the sensor housing 13. The semiconductor gas sensor element 1 is disposed inside the sensor housing 13.

  This gas detection device 15 is used in a state connected to a measurement circuit, for example. The measurement circuit is a circuit that applies a voltage to the heater combined electrode 2 of the semiconductor gas sensor element 1 through the terminals 8 and 9 and the lead wires 5 and 6 to energize and heat the heater combined electrode 2. Further, the measurement circuit outputs a concentration signal of the gas to be detected based on the change in the electric resistance value generated in the gas sensitive body 4. That is, for example, the measurement circuit intermittently stops the application of the voltage to the heater combined electrode 2, and a constant voltage is applied to the circuit in which the heater combined electrode 2, the core wire electrode 3, and an appropriate resistor are connected in series. Is generated, a signal corresponding to the amount of voltage drop generated between the heater combined electrode 2 and the core wire electrode 3 is generated, and this signal is A / D converted and transmitted to a microcomputer or the like. Since this voltage drop varies depending on the change in the electrical resistance value of the gas sensitive body 4, a change in the electrical resistance value is detected based on this voltage drop, and a change in the electrical resistance value based on the voltage drop. The quantity is measured. The detection target gas is detected based on the change in the electrical resistance value, and the concentration of the detection target gas is measured based on the amount of change in the electrical resistance value.

  When detecting the detection target gas, first, the measurement circuit applies a voltage to the heater combined electrode 2 via the terminals 8 and 9 and the lead wires 5 and 6 to heat the heater combined electrode 2. Thereby, the temperature of the gas sensitive body 4 is heated to a temperature suitable for detection of the detection target gas. In this state, when the gas detection device 15 is exposed to the gas phase containing the gas to be detected, and thereby the gas sensitive body 4 is exposed to the gas phase, the electric resistance value of the gas sensitive body 4 becomes the value in the gas phase. It fluctuates according to the concentration of the gas to be detected. Based on the electric resistance value of the gas sensitive body 4 between the heater combined electrode 2 and the core wire electrode 3, the measurement circuit outputs a concentration signal of the gas to be detected.

[Example 1]
A heater combined electrode and a core wire electrode were formed from a platinum wire having a wire diameter of 20 μm. The heater combined electrode was formed in a coil shape, the length was 0.5 mm, the diameter was 0.3 mm, and the number of turns was 7.

  An aqueous solution containing chloroauric acid in a proportion of 2.6% by mass in terms of gold atom was prepared. Each electrode was heated by immersing the electrode serving as a heater and the core wire electrode in this aqueous solution for 1 second, and then applying a voltage of 1.0 V across the electrodes for 60 seconds. As a result, a gold coating was formed on the surface of each electrode.

  Next, the tungsten oxide powder and the α-alumina powder were mixed at a mass ratio of 2: 1, and terpineol was further added thereto to obtain a paste-like molding composition.

  In a state where the core wire electrodes are arranged inside the heater electrode, these electrodes were covered with the molding composition, and then the molding composition was heated at 500 ° C. for 10 minutes. Thereby, the molding composition was sintered to obtain a sintered body.

  Subsequently, colloidal silica was applied to the surface of the sintered body, and then the sintered body was heated at 700 ° C. for 10 minutes. Thus, an ellipsoidal gas sensitive body having a major axis of about 0.5 mm and a minor axis of about 0.3 mm was obtained.

  Thus, a semiconductor gas sensor element including a gas sensitive body, a heater combined electrode, and a core wire electrode was obtained. A total of five semiconductor gas sensor elements having the same structure were produced.

[Example 2]
A heater combined electrode and a core wire electrode were formed from a platinum wire having a wire diameter of 20 μm. The heater combined electrode was formed in a coil shape, the length was 0.5 mm, the diameter was 0.3 mm, and the number of turns was 7.

  An aqueous solution containing chloroauric acid in a proportion of 2.6% by mass in terms of gold atom was prepared. Each electrode was heated by immersing the electrode serving as a heater and the core wire electrode in this aqueous solution for 1 second, and then applying a voltage of 1.0 V across the electrodes for 60 seconds. As a result, a gold coating was formed on the surface of each electrode.

  Next, the tungsten oxide powder and the α-alumina powder were mixed at a mass ratio of 2: 1, and terpineol was further added thereto to obtain a paste-like molding composition.

  In a state where the core wire electrodes are arranged inside the heater electrode, these electrodes were covered with the molding composition, and then the molding composition was heated at 500 ° C. for 10 minutes. Thereby, the molding composition was sintered to obtain a sintered body.

  Subsequently, colloidal silica was applied to the surface of the sintered body, and then the sintered body was heated at 700 ° C. for 10 minutes.

  Then, after attaching ruthenium chloride aqueous solution (metal Ru conversion density | concentration of 0.15 mass%) to the surface of the sintered compact, the sintered compact was heated at 700 degreeC for 10 minute (s). Thus, an ellipsoidal gas sensitive body having a major axis of about 0.5 mm and a minor axis of about 0.3 mm was obtained.

  Thus, a semiconductor gas sensor element including a gas sensitive body, a heater combined electrode, and a core wire electrode was obtained. A total of five semiconductor gas sensor elements having the same structure were produced.

[Example 3]
In Example 2, when attaching the ruthenium chloride aqueous solution to the surface of the sintered body, a ruthenium chloride aqueous solution having a metal Ru equivalent concentration of 0.2% by mass was used. Other than that was obtained in the same manner as in Example 2 to obtain a semiconductor gas sensor element comprising a gas sensitive body, a heater combined electrode, and a core wire electrode. A total of five semiconductor gas sensor elements having the same structure were produced.

[Comparative Example 1]
In Example 1, the gold coating was not formed on the surfaces of the heater combined electrode and the core wire electrode. Otherwise, the same method as in Example 1 was used to obtain a semiconductor gas sensor element including a gas sensitive body, a heater combined electrode, and a core wire electrode. A total of five semiconductor gas sensor elements having the same structure were produced.

[Comparative Example 2]
In Example 2, the gold coating was not formed on the surfaces of the heater combined electrode and the core wire electrode. Otherwise, the same method as in Example 2 was used to obtain a semiconductor gas sensor element including a gas sensitive body, a heater combined electrode, and a core wire electrode. A total of five semiconductor gas sensor elements having the same structure were produced.

[Comparative Example 3]
In Example 3, no gold coating was formed on the surfaces of the heater combined electrode and the core wire electrode. Otherwise, the same method as in Example 3 was used to obtain a semiconductor gas sensor element including a gas sensitive body, a heater combined electrode, and a core wire electrode. A total of five semiconductor gas sensor elements having the same structure were produced.

[Element temperature dependency evaluation]
For each of Example 1 and Comparative Example 1, a voltage was applied across the heater-cum-use electrode of the semiconductor gas sensor element, and the gas sensitive body of the semiconductor gas sensor element was exposed to the atmosphere. In this state, the electrical resistance value (R _air ) between the heater combined electrode and the core wire electrode was measured.

  FIGS. 3 and 4 show the measurement results of the respective electric resistance values when the voltages applied between both ends of the heater electrode are 0.7V, 0.8V, and 0.9V. FIG. 3 shows the results for Example 1, and FIG. 4 shows the results for Comparative Example 1. In addition, the result shown by these figures is an average value of the result obtained about five semiconductor gas sensor elements.

For each of Example 1 and Comparative Example 1, a voltage was applied between both ends of the electrode serving as a heater of the semiconductor gas sensor element, and the gas sensitive body of the semiconductor gas sensor element was placed in an atmosphere having an ethanol concentration of 100 volume ppm and an ethanol concentration of 10 volume ppm. The electrical resistance value (R _s ) between the heater combined electrode and the core wire electrode when exposed to an atmosphere, an atmosphere having an ammonia concentration of 100 vol ppm, and an atmosphere having an ammonia concentration of 10 vol ppm was measured.

The values of R _air / R _s when the voltages applied across the heater electrode are 0.7V, 0.8V, and 0.9V are shown in FIGS. FIG. 5 shows the results for Example 1, and FIG. 6 shows the results for Comparative Example 1. In addition, the result shown by these figures is an average value of the result obtained about five semiconductor gas sensor elements.

  According to these results, compared with the case of the comparative example 1, in the case of the example 1, the change amount of the electric resistance value with respect to the change amount of the applied voltage value (that is, the temperature change amount of the gas sensitive body) is small. For this reason, compared with the case of the comparative example 1, in the case of Example 1, even if the temperature of a gas sensitive body changes, an electrical resistance value does not change easily, ie, the element temperature dependency of an electrical resistance value is low. It is judged.

[Various gas sensitivity evaluation 1]
For each of Example 1 and Comparative Example 1, a voltage of 0.9 V was applied between both ends of the heater electrode of the semiconductor gas sensor element, and the gas sensitive body of the semiconductor gas sensor element was exposed to the atmosphere. In this state, the electrical resistance value (R _air ) between the heater combined electrode and the core wire electrode was measured.

In addition, for each of Example 1 and Comparative Example 1, a voltage of 0.9 V is applied between both ends of the heater electrode of the semiconductor gas sensor element, and the gas sensitive body of the semiconductor gas sensor element is an atmosphere containing the gas to be detected. The electrical resistance value (R _s ) between the heater combined electrode and the core wire electrode when exposed to (concentration: 10 ppm by volume) was measured.

FIG. 7 shows the values of R _air / R _s when the detection target gases are methane, carbon monoxide, hydrogen, ethylene, ammonia, ethanol, toluene, hydrogen sulfide, and trimethylamine. FIG. 7A shows a case where the detection target gas is methane, FIG. 7B shows a case where the detection target gas is carbon monoxide, and FIG. 7C shows a case where the detection target gas is hydrogen. 7D shows a case where the detection target gas is ethylene, FIG. 7E shows a case where the detection target gas is ammonia, and FIG. 7F shows a case where the detection target gas is ethanol. (G) shows the case where the detection target gas is toluene, FIG. 7 (h) shows the case where the detection target gas is hydrogen sulfide, and FIG. 7 (i) shows the case where the detection target gas is trimethylamine. Results are shown. In addition, the result shown by these figures is an average value of the result obtained about five semiconductor gas sensor elements.

According to these results, the value of R _air / R _s was greater in Example 1 than in Comparative Example 1 regardless of the detection target gas. For this reason, it is determined that the detection sensitivity of Example 1 is higher than that of Comparative Example 1.

[Various gas sensitivity evaluation 2]
For each of Example 2 and Comparative Example 2, a voltage of 0.9 V was applied across the heater-cum-use electrodes of the semiconductor gas sensor element, and the gas sensitive body of the semiconductor gas sensor element was exposed to the atmosphere. In this state, the electrical resistance value (R _air ) between the heater combined electrode and the core wire electrode was measured.

Further, for each of Example 2 and Comparative Example 2, a voltage of 0.9 V is applied between both ends of the heater electrode of the semiconductor gas sensor element, and the gas sensitive body of the semiconductor gas sensor element is an atmosphere containing the gas to be detected. The electrical resistance value (R _s ) between the heater combined electrode and the core wire electrode was measured.

When the gas to be detected is ammonia (concentration 10 volume ppm), trimethylamine (concentration 1 ppm), hydrogen (concentration 10 ppm), carbon monoxide (concentration 10 ppm), and ethanol (concentration 10 ppm), each R _s / The value of R _air is shown in FIG. These results are average values of the results obtained for the five semiconductor gas sensor elements.

According to these results, the value of R _s / R _air was smaller in Example 2 than in Comparative Example 2 regardless of the detection target gas. For this reason, it is determined that the detection sensitivity of Example 2 is higher than that of Comparative Example 2.

[Ambient temperature and humidity dependency evaluation]
For each of Example 2 and Comparative Example 2, a voltage of 0.8 V was applied between both ends of the heater serving electrode of the semiconductor gas sensor element, and the gas sensitive body of the semiconductor gas sensor element was exposed to the atmosphere. The temperature and humidity conditions of the atmosphere are set to −10 ° C., 5 ° C. 40% RH, 20 ° C. 60% RH, and 40 ° C. 90% RH, and in each case, the electricity between the heater combined electrode and the core wire electrode The resistance value (R _s ) was measured.

The ratio R _s / R ₀ of the electrical resistance value (R _s ) in each condition to the electrical resistance value (R ₀ ) in this case is based on the case where the atmospheric temperature and humidity conditions are 20 ° C. and 60% RH. As shown in FIG. These results are average values of the results obtained for the five semiconductor gas sensor elements.

  According to these results, in the atmosphere, there was no significant difference between Example 2 and Comparative Example 2 in the degree of change in electrical resistance value with respect to changes in the temperature and humidity of the atmosphere.

For each of Example 2 and Comparative Example 2, a voltage of 0.8 V was applied between both ends of the heater-cum-use electrode of the semiconductor gas sensor element, and the gas sensitive body of the semiconductor gas sensor element was subjected to an atmosphere (concentration) containing ammonia. 100 ppm by volume). The temperature and humidity conditions of this atmosphere are set to −10 ° C., 5 ° C. 40% RH, 20 ° C. 60% RH, and 40 ° C. 90% RH, and in each case, the electricity between the heater combined electrode and the core wire electrode The resistance value (R _s ) was measured.

FIG. 10 shows the ratio R _s / R ₀ of the electrical resistance value (R _s ) to the electrical resistance value (R ₀ ) based on the case where the temperature and humidity conditions of the atmosphere are 20 ° C. and 60% RH. These results are average values of the results obtained for the five semiconductor gas sensor elements.

  According to these results, in the atmosphere containing ammonia, the amount of change in the electrical resistance value with respect to changes in the temperature and humidity of the atmosphere was smaller in Example 2 than in Comparative Example 2.

  Based on the above, it is determined that the dependence of the electrical resistance value on the ambient temperature and humidity is lower in the case of Example 2 than in Comparative Example 2.

[Gas concentration dependency evaluation]
For each of Example 3 and Comparative Example 3, a voltage of 0.5 V and a voltage of 0.9 V were alternately applied between both ends of the heater combined electrode of the semiconductor gas sensor element for 1 second, while the semiconductor gas sensor element The gas sensitive body was exposed to an atmosphere containing the gas to be detected, and the electrical resistance value (R _s ) between the heater combined electrode and the core wire electrode was measured. As the gas to be detected, carbon monoxide, methanethiol, ammonia, nitrogen dioxide, n-valeraldehyde (indicated as “n-barrel” in FIGS. 11 to 14), and decane are used, and the concentration of the gas is varied. When the applied voltage was 0.5 V and 0.9 V, the electric resistance value (R _s ) was measured. The electrical resistance value (R _s ) was measured immediately before switching the voltage.

  The results are shown in FIGS. 11 shows the result when the applied voltage is 0.5 V in Comparative Example 3, FIG. 12 shows the result when the applied voltage is 0.5 V in Example 3, and FIG. FIG. 14 shows the results when the applied voltage is 0.9V, and FIG. 14 shows the results when the applied voltage is 0.9V in Example 3.

According to these results, the electric resistance value (R _s ) with respect to the concentration of the gas to be detected is higher in the case of Example 3 than in Comparative Example 3 regardless of whether the applied voltage is 0.5 V or 0.9 V. The amount of change was large.

According to the above, the concentration of the gas to be detected can be measured more accurately in the case of Example 3 than in Comparative Example 3 based on the amount of change in the electrical resistance value (R _s ). Judgment.

1 Semiconductor gas sensor element 2 Electrode (heater combined electrode)
3 Electrode (core wire electrode)
4 Gas sensitive body

Claims (1)

A gas-sensitive body containing a metal oxide semiconductor; and two electrodes embedded in the gas-sensitive body, the two electrodes being formed of platinum or a platinum alloy, and on the surfaces of the two electrodes. A gold film is formed,
Of the two electrodes, one is a coiled heater combined electrode, the other is a linear core wire electrode,
The metal oxide semiconductor consists only of tungsten oxide ,
The gas sensitive body contains ruthenium,
The gas sensitive body further contains alumina,
The shape of the gas sensitive body is spherical,
Colloidal silica is applied to the surface of the gas sensitive body,
A semiconductor gas sensor element.

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