JP6879093B2 - Oxidizing gas sensors, gas alarms, controls, and control methods - Google Patents

Description

The present invention relates to an oxidizing gas sensor, a gas alarm, a control device, and a control method.

_{A semiconductor gas sensor that detects an oxidizing gas such as NO 2} by changing the electric resistance value of the semiconductor film is known (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3).
[Patent Document]
[Patent Document 1] Japanese Unexamined Patent Publication No. 2011-75545 [Patent Document 2] International Publication No. 2004/0489557 [Patent Document 3] Japanese Unexamined Patent Publication No. 2006-119014

In the oxidizing gas sensor, it is desirable to increase the sensor sensitivity.

In the first aspect of the present invention, an oxidizing gas sensor is provided. The oxidizing gas sensor may include a gas sensing layer. The oxidizing gas sensor may include a heater. The heater may heat the gas sensing layer. The oxidizing gas sensor may include a heating control unit. The heating control unit may control the heater to control the temperature of the gas sensing layer. The oxidizing gas sensor may include a detection unit. The detection unit may detect the oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer heated to the measurement temperature by the heater. The heating control unit preheats the gas sensing layer so that the temperature of the gas sensing layer is in the range of T _min -100 ° C or higher and T _min + 50 ° C or lower, and then heats the gas sensing layer to the measurement temperature. The heater may be controlled. The minimum temperature may be T _min ° C. The minimum temperature may be the temperature of the gas sensing layer at which the electrical resistance value exhibits the minimum value with respect to the temperature characteristics of the electrical resistance value of the gas sensing layer in clean air.

Preheating may desorb oxygen adsorbed on the surface of the gas sensing layer.

Regarding the temperature characteristics of the electric resistance value of the gas sensing layer in clean air, the measured temperature is the maximum temperature T when the maximum temperature, which is the temperature of the gas sensing layer at which the electric resistance value exhibits the maximum value, is set to T _{max ° C.} It may be lower than _{max ° C.}

The measurement temperature may be higher than the adsorption start temperature of the oxidizing gas to be detected.

The measurement temperature may be T _min + 50 ° C. or lower.

The preheating time may be 10 seconds or more and 10 minutes or less.

The preheating time may be variable.

When the electric resistance value of the gas sensing layer is equal to or higher than a predetermined first threshold value, the heating control unit may change the preheating time to be longer. The detector may detect the oxidizing gas to be detected based on the electrical properties of the gas sensing layer heated to the measurement temperature after the preheating with the time changed for a long time.

The oxidizing gas sensor may detect the first oxidizing gas and the second oxidizing gas. As the measurement temperature, the first measurement temperature and the second measurement temperature may be defined. The detection unit may detect the first oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer heated to the first measurement temperature by the heater. The detection unit may detect the second oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer heated to the second measurement temperature by the heater.

The heating control unit may control the heater so that the gas sensing layer is heated to a temperature higher than the measurement temperature prior to the preheating.

The gas alarm may include an oxidizing gas sensor. The gas alarm may further include an alarm generator. The alarm generating unit may generate an alarm when the oxidizing gas sensor detects the oxidizing gas to be detected.

In the second aspect of the present invention, a control device is provided. The control device may control the oxidizing gas sensor. The oxidizing gas sensor may have a gas sensing layer. The oxidizing gas sensor may have a heater. The heater may heat the gas sensing layer. The oxidizing gas sensor may detect the oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer heated by the heater. The control device may include a heating control unit. The heating control unit preheats the gas sensing layer so that the temperature of the gas sensing layer is in the range of T _min -100 ° C or higher and T _min + 50 ° C or lower, and then heats the gas sensing layer to the measurement temperature. The heater may be controlled. The minimum temperature may be T _min ° C. The minimum temperature may be the temperature of the gas sensing layer at which the electrical resistance value exhibits the minimum value with respect to the temperature characteristics of the electrical resistance value of the gas sensing layer in clean air. The control device may include a detection unit. The detection unit may detect the oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer heated to the measurement temperature by the heater.

In the third aspect of the present invention, a control method is provided. The control method may be a control method of an oxidizing gas sensor. The oxidizing gas sensor may have a gas sensing layer. The oxidizing gas sensor may have a heater. The heater may heat the gas sensing layer. The oxidizing gas sensor may detect the oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer heated by the heater. The control method may include a control step. In the control stage, gas sensing is performed when the minimum temperature, which is the temperature of the gas sensing layer in which the electrical resistance value exhibits the minimum value with respect to the temperature characteristics of the electrical resistance value of the gas sensing layer in clean air, is set to T _min ° C. After preheating the gas sensing layer with a heater so that the temperature of the layer is in the range of T _min -100 ° C or higher and T _min + 50 ° C or lower, the heater is controlled so that the gas sensing layer is heated to the measurement temperature. Good. The control method may include a detection step. In the detection stage, the oxidizing gas to be detected may be detected based on the electrical characteristics of the gas sensing layer heated to the measurement temperature by the heater.

The outline of the above invention does not list all the necessary features of the present invention. Sub-combinations of these feature groups can also be inventions.

It is the schematic of the gas sensor 100 of the 1st Embodiment of this invention. It is the schematic of the gas alarm 102 of the 1st Embodiment of this invention. It is sectional drawing which shows an example of the schematic structure of the detection unit 10. It is a figure which shows the temperature characteristic of the electric resistance value of a gas sensing layer 12 in clean air. It is a figure which shows an example of the intermittent drive of a heater 14. It is a figure which shows an example of the heater drive pattern in the gas sensor 100 of 1st Embodiment of this invention. It is a figure which shows an example of the heater drive pattern in the gas sensor of the comparative example. It is a flowchart which shows an example of the processing content by the gas sensor 100 of 1st Embodiment of this invention. It is a figure which shows an example of the heater drive pattern in the gas sensor 100 of the 2nd Embodiment of this invention. It is a flowchart which shows an example of the processing content by the gas sensor 100 of the 2nd Embodiment of this invention. It is a figure which shows an example of the heater drive pattern in the gas sensor 100 of the 3rd Embodiment of this invention. It is a flowchart which shows an example of the processing content by the gas sensor 100 of the 3rd Embodiment of this invention. It is a figure which shows an example of the heater drive pattern in the gas sensor 100 of 4th Embodiment of this invention. It is a flowchart which shows an example of the processing content by the gas sensor 100 of 4th Embodiment of this invention. It is a figure which shows another example of the heater drive pattern in the gas sensor 100 of 4th Embodiment of this invention.

Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the inventions that fall within the scope of the claims. Also, not all combinations of features described in the embodiments are essential to the means of solving the invention.

FIG. 1 is a schematic view of the gas sensor 100 according to the first embodiment of the present invention. The gas sensor 100 of this example is an oxidizing gas sensor that detects the oxidizing gas to be detected. Examples of the oxidizing gas include nitrogen oxide gas (NO _{X ) such as nitrogen dioxide (hereinafter, NO 2} ), halogen-based gas such as chlorine gas and fluorine gas, and carbon dioxide (hereinafter, CO ₂ ).

The gas sensor 100 includes a detection unit 10 and a control device 200. The detection unit 10 includes a gas sensing layer 12 and a heater 14. The detection unit 10 of this example includes a temperature measurement unit 16 that measures the temperature of the heater 14. Unlike this example, the detection unit 10 does not have to include the temperature measurement unit 16. As another example, the heater 14 and the temperature measuring unit 16 may be combined. Specifically, the temperature dependence of the electric resistance value of the heater may be acquired in advance, and the heater voltage may be adjusted so as to reach a predetermined temperature.

The electrical properties of the gas sensing layer 12 vary depending on the type and concentration of gas present. The electrical characteristic of the gas sensing layer 12 may be the electrical resistance value of the gas sensing layer 12. The electrical characteristic of the gas sensing layer 12 may be the voltage value at both ends of the gas sensing layer 12 when a current is passed through the gas sensing layer 12, and the gas sensing layer when a voltage is applied to both ends of the gas sensing layer 12. It may be the value of the current flowing through 12.

The heater 14 heats the gas sensing layer 12. The heater 14 heats the gas sensing layer 12 to the measurement temperature. The measurement temperature means a temperature at which the electrical characteristics of the gas sensing layer 12 are measured in order to detect the target gas. The gas sensor 100 detects the oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer 12 heated to the measurement temperature by the heater 14. In the gas sensor 100 of the present embodiment, after the gas sensing layer 12 is preheated in order to desorb oxygen adsorbed on the surface of the gas sensing layer 12, the heater 14 is heated so that the gas sensing layer 12 is heated to the measurement temperature. Be controlled.

The control device 200 controls the gas sensor 100. In this example, both the detection unit 10 and the control device 200 are built in the gas sensor 100. However, the control device 200 may be a control device externally attached to the gas sensor 100. The control device 200 includes a detection unit 20 and a heating control unit 30. The detection unit 20 detects the oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer 12 heated to the measurement temperature by the heater 14. The detection unit 20 acquires the electrical characteristics of the gas sensing layer 12. For example, the detection unit 20 measures the electric resistance value of the gas sensing layer 12, which is the sensor resistance. The electrical characteristic of the gas sensing layer 12 may be the electrical resistance value of the gas sensing layer 12, or may be a voltage or current associated with the electrical resistance value.

The heating control unit 30 controls the heater 14 to control the temperature of the gas sensing layer 12. Specifically, the heating control unit 30 may control the voltage applied to the heater 14. In particular, the heating control unit 30 preheats the gas sensing layer 12 to the preheating temperature T1 by the heater 14. Then, the heating control unit 30 controls the heater 14 so that the gas sensing layer 12 is heated to the measurement temperature T2 after the preheating. The heating control unit 30 may be configured by a microcomputer. The preheating temperature T1 and the measurement temperature T2 will be described later.

The control device 200 of this example includes a setting unit 40 and a storage unit 50. The setting unit 40 sets information or parameters necessary for the heating control unit 30 to control the heater 14. The storage unit 50 stores information or parameters necessary for the heating control unit 30 to control the heater 14. The storage unit 50 may store information about the preheating temperature T1, the measurement temperature T2, the preheating time t1, and the measurement temperature duration t2. The preheating time t1 is a time for preheating the gas sensing layer 12. The measurement temperature duration t2 is a time for maintaining the gas sensing layer 12 at the measurement temperature T2. Although the case where the control device 200 of this example includes the setting unit 40 and the storage unit 50 has been described, the control device 200 is not limited to this case. Unlike this example, the control device 200 does not necessarily include each part.

FIG. 2 is a schematic view of the gas alarm 102 according to the first embodiment of the present invention. The gas alarm 102 of this example further includes an alarm generating unit 60 in addition to each configuration of the gas sensor 100 shown in FIG. The alarm generation unit 60 generates an alarm when the gas sensor 100 detects the oxidizing gas to be detected. Specifically, the alarm generation unit 60 generates an alarm when the oxidizing gas to be detected is detected based on the measurement of the electrical characteristics of the gas sensing layer 12 by the detection unit 20. The alarm generation unit 60 may include an alarm sound output unit that emits a sound such as an alarm sound. The alarm sound output unit may be composed of a speaker, a buzzer, or the like. The alarm generation unit 60 may include an alarm display unit that displays an alarm state by blinking or lighting an LED (light emitting diode) or the like.

FIG. 3 is a cross-sectional view showing an example of a schematic configuration of the detection unit 10. The detection unit 10 of this example is a thin film semiconductor type gas sensor. The detection unit 10 of this example includes a silicon substrate 2, a heat insulation support layer 3, a heater layer that functions as a heater 14, an electrical insulation layer 4, and a gas sensing unit 5. The silicon substrate 2 is provided with a through hole 6. The through hole 6 constitutes a diaphragm structure. The gas sensing unit 5 may include a bonding layer 7, a gas sensing layer electrode 8, a gas sensing layer 12, and a catalyst layer 9.

The gas sensing layer 12 is formed as a sensing layer containing metal oxides such as _{SnO 2} , In ₂ O ₃ , WO ₃ , ZnO, and TiO _{2 as main components.} The gas sensing layer 12 is preferably SnO ₂ or WO ₃ , and particularly preferably SnO ₂ . The catalyst layer 9 may be a sintered body carrying at least one kind of catalyst. The catalyst layer 9 selectively burns a gas other than the oxidizing gas to be detected. This makes it easier for the gas sensor 100 to selectively detect the oxidizing gas to be detected. However, the catalyst layer 9 may be omitted.

In the detection unit 10 of this example, a heater structure using MEMS technology is adopted. The heater structure of this example has a silicon substrate 2 in which a space having an opening is formed. In this example, a through hole 6 is formed in the silicon substrate 2 as a space having an opening. The heat insulating support layer 3 is provided on the space having the opening. In this example, the heat insulating support layer 3 may be stretched over the entire opening of the through hole 6 of the silicon substrate 2 to form a diaphragm structure. The heater 14, which is a heater layer, is supported by the heat insulating support layer 3.

The detection unit 10 shown in FIG. 3 is manufactured as follows, for example. _{A silicon nitride (Si 3} N ₄ ) film and a silicon oxide (SiO ₂ ) film are sequentially formed by a plasma CVD method as a support layer having a diaphragm structure on a silicon substrate 2 provided with thermal oxide layers on both sides. As a result, the thermal insulation support layer 3 in which the thermal oxide film, the silicon nitride film, and the silicon oxide film are laminated in this order is formed.

Next, the heater 14 is formed by forming platinum (Pt) -tungsten (W) on the silicon oxide film by a sputtering method. The electrically insulating layer 4 is formed by forming a _{SiO 2} insulating film by a sputtering method so as to cover the heater 14. A bonding layer 7 is formed on the electrically insulating layer 4. Further, a conductive film such as platinum (Pt) is formed by the RF magnetron sputtering method. As a result, the gas sensing layer electrode 8 is formed. Next, as the gas sensing layer 12, a semiconductor film of metal oxides such _{as SnO 2} , In ₂ O ₃ , WO ₃ , ZnO, and TiO _{2 is formed.} A through hole 6 is formed on the back surface side of the silicon substrate 2 by etching or the like.

The gas sensor 100 using the heater 14 that realizes low power consumption is realized by the heater structure using the MEMS technology as described above. However, the structure of the detection unit 10 is not limited to that having a diaphragm structure. The detection unit 10 may have a heater structure called a cavity type.

In the cavity type heater structure, the cavity is formed on the silicon substrate as a space having an opening. The cavity has an opening on the upper surface of the silicon substrate, but the lower surface side of the silicon substrate 2 is not open. The cavity may have a quadrangular pyramid or a quadrangular frustum shape. A thermal insulation support layer is provided on the cavity. The heat insulating support layer may include a central portion located at the center on the cavity and a plurality of bridge portions connecting the central portion and the peripheral portion.

FIG. 4 is a diagram showing the temperature characteristics of the electric resistance value of the gas sensing layer 12 in clean air. Clean air is air that does not contain oxidizing gas or the like to be detected. Clean air contains oxygen. Oxygen is negatively charged on the surface of the gas sensing layer 12 in the thin film semiconductor type gas sensor 100, that is, on the surface of a semiconductor such as _{SnO 2.} When oxygen is adsorbed on the surface of the semiconductor, electrons, which are carriers in the semiconductor, are deprived by oxygen. As a result, the electron density in the semiconductor is reduced, and the electric resistance value of the gas sensing layer 12 is increased.

Detection of reducing gases such as methane, propane, and butane is carried out at a measurement temperature of about 400 ° C. As shown in FIG. 4, when the temperature of the gas sensing layer 12 reaches about 400 ° C., oxygen ions ^O2- are adsorbed on the surface of the gas sensing layer 12, and the electric resistance value of the gas sensing layer 12 becomes high. ing. In this state, if a reducing gas such as methane, propane, or butane is present, the oxygen adsorbed on the negative charge reacts with the reducing gas. During this reaction, the electrons return into the semiconductor, increasing the electron density in the semiconductor. Therefore, the electric resistance value of the gas sensing layer 12 changes so as to be low. The degree of change in the electrical resistance value corresponds to the sensitivity to gas. When the detection target gas is a reducing gas, sufficient sensitivity can be easily obtained.

On the other hand, when the oxidizing gas is present, the oxidizing gas is _{further negatively adsorbed on the surface of the semiconductor such as SnO 2} on which oxygen is already adsorbed, and the electric resistance value of the gas sensing layer 12 becomes high. However, oxygen is adsorbed on the semiconductor surface in clean air, and the gas sensing layer 12 has already increased resistance. Therefore, even if the oxidizing gas is further adsorbed, the change in the electric resistance value of the gas sensing layer 12 is small. Therefore, when the oxidizing gas is detected, the sensitivity is lower than when the reducing gas is detected.

As shown in FIG. 4, in the temperature range from the ambient temperature to 250 ° C., the electric resistance value of the gas sensing layer 12 decreases as the temperature increases. This process of lowering the electric resistance value is caused ^{by the oxygen adsorbed on the gas sensing layer 12 in the form of O −} (or O ₂ ⁻ ) being desorbed as the temperature rises. When the temperature of the gas sensing layer 12 exceeds 250 ° C., the electric resistance value of the gas sensing layer 12 increases as the temperature increases in the temperature range of 250 ° C. to 400 ° C. In particular, the temperature change rate from 250 ° C. to 400 ° C. is higher than the temperature change rate from the ambient temperature to 250 ° C. Increase process in the electrical resistance, to the gas sensing layer 12, oxygen O ^2- embodiment is believed to be due to the adsorption. When the temperature of the gas sensing layer 12 exceeds 400 ° C., the characteristic of the gas sensing layer 12 as a semiconductor is that the electric resistance value decreases as the temperature increases.

As described above, regarding the temperature characteristics of the electric resistance value of the gas sensing layer 12 in clean air, when the temperature of the gas sensing layer 12 is the minimum temperature T _min (° C.), the electrical resistance value of the gas sensing layer 12 Presents a minimum value. When the gas sensing layer 12 is formed of _{SnO 2 as in this example, T min} (° C.) is 250 ° C. T _min (° C.) depends on the material of the gas sensing layer 12. On the other hand, regarding the temperature characteristics of the electric resistance value of the gas sensing layer 12 in clean air, the electric resistance value of the gas sensing layer 12 is maximum when the temperature of the gas sensing layer 12 is the maximum temperature T _max (° C.). Presents a value. T _max (° C.) is 400 ° C. The T _max (° C.) also depends on the material of the gas sensing layer 12.

In the gas sensor 100 of this example, the heating control unit 30 preheats the gas sensing layer 12 so that the temperature of the gas sensing layer 12 becomes the preheating temperature T1 in the range of _{T min} −100 ° C. or higher and T _{min + 50 ° C. or lower.} Let me. That is, the heating control unit 30, in the preheating, the temperature of the gas sensing layer 12, or the temperature minus 100 ° C. from the minimum value temperature _{T min,} and the temperature following the addition of 50 ° C. to minimum value temperature _{T min} The heater 14 is controlled so that the gas sensing layer 12 is heated in the temperature range. Then, the heating control unit 30 controls the heater 14 so that the gas sensing layer 12 is heated to the measurement temperature T2 after the preheating.

The state and the amount of adsorption of O ^2- is reduced ^- by gas sensing layer 12 is preheated, O is oxygen adsorbed on the surface of the gas sensing layer 12. Therefore, the oxidizing gas to be detected is more likely to be adsorbed on the surface of the gas sensing layer 12 than in the state where oxygen is already adsorbed on the surface of the gas sensing layer 12. In particular, nitrogen-sensitive gas (NOx) is more easily adsorbed on the surface of the clean gas sensing layer 12 than oxygen.

Compared with the case where the heater 14 is controlled so that the gas sensing layer 12 is heated to the measurement temperature T2 from the beginning of heating, the heater 14 is heated to the measurement temperature T2 after the preheating. The more controlled, the higher the sensitivity to the oxidizing gas to be detected. That is, it is better to control the heater 14 so that the gas sensing layer 12 is heated to the measurement temperature T2 after preheating for a predetermined preheating time, so that the temperature of the gas sensing layer 12 does not undergo preheating. Compared with the case where the heater 14 is controlled so that the gas is heated to the measurement temperature T2, the increase change of the electric resistance value of the gas sensing layer 12 becomes larger according to the concentration of the oxidizing gas to be detected.

In this example, the measurement temperature T2 is higher than the preheating temperature T1. The measurement temperature T2 is higher than the adsorption start temperature of the oxidizing gas to be detected. On the other hand, the measurement temperature T2 may be lower than the _{maximum temperature T max (° C.).} More preferably, the measurement temperature T2 may be T _min + 50 ° C. or lower. The heating control unit 30 may control the heater 14 so that the temperature of the gas sensing layer 12 is heated in a temperature range equal to or lower than the _{minimum temperature T min plus 50 ° C.} When measuring the electrical characteristics of the gas sensing layer 12 at a temperature equal to or higher than the maximum temperature T _max ^{(° C.), oxygen (O2-} ) is sufficiently adsorbed on the surface of the gas sensing layer 12, and the oxidizing gas. Is hard to adsorb. On the other hand, _{when measuring the electrical characteristics of the gas sensing layer 12 at a temperature lower than the maximum temperature T max} (° C.), more preferably at a temperature of T _min + 50 ° C. or lower, the detection target is added to oxygen in the air. Due to the presence of the oxidizing gas, the electric resistance value of the gas sensing layer 12 tends to be high.

FIG. 5 is a diagram showing an example of intermittent drive of the heater 14. The vertical axis of FIG. 5 shows the temperature of the gas sensing layer 12, and the horizontal axis shows the time. The heating control unit 30 may periodically pulse drive the heater 14. That is, the heating control unit 30 periodically applies a pulsed voltage to the heater 14 as a heater driving voltage.

The heating control unit 30 may apply a pulsed voltage to the heater 14 at a period tk of 30 seconds or more and 24 hours or less. The period tc is determined by the application of the gas sensor 100. When carbon dioxide is detected and the concentration is measured in an air conditioner or a plant factory, the detection frequency is emphasized, and the cycle ct is, for example, 5 minutes or less. On the other hand, when nitrogen oxides are detected and the concentration is measured in environmental measurement applications, the period tk may be, for example, 1 hour or more. As shown in FIG. 5, the heating control unit 30 preheats the gas sensing layer 12 so as to reach the preheating temperature T1, and then controls the heater 14 so that the gas sensing layer 12 reaches the measurement temperature T2.

FIG. 6 is a diagram showing an example of a heater drive pattern in the gas sensor 100 according to the first embodiment of the present invention. FIG. 6 shows an enlarged waveform of one pulse-shaped portion shown in FIG. The vertical axis of FIG. 6 shows the temperature of the gas sensing layer 12, and the horizontal axis shows the time. As shown in FIG. 6, the gas sensing layer 12 is preheated by the heater 14 from the ambient temperature to the preheating temperature T1. The preheating temperature T1 may be predetermined in the range of _{T min} −100 ° C. or higher and T _{min + 50 ° C.} When the material of the gas sensing layer 12 is SnO ₂ , T _min is 250 ° C. Therefore, the preheating temperature T1 may be in the range of 150 ° C. or higher and 300 ° C. or higher.

When the preheating temperature T1 is smaller than 150 °, the surface of the gas sensing layer 12 is affected by moisture. Therefore, the preheating temperature T1 is preferably 150 ° C. or higher. The preheating time t1 may be predetermined. The preheating time t1 may be 10 seconds or more and 10 minutes or less. In order to stabilize the temperature, it is desirable that the preheating time t1 is long. On the other hand, in order to quickly detect the oxidizing gas to be detected, it is desirable that the preheating time t1 is short. The heating control unit 30 controls the heater 14 so that the gas sensing layer 12 reaches the measurement temperature T2 after the lapse of the preheating time t1.

The measurement temperature T2 may be equal to or lower than the _{maximum temperature Tmax.} Further, the measurement temperature T2 may be T _min + 50 ° C. or lower. When the material of the gas sensing layer 12 is SnO ₂ , T _min is 250 ° C. and T _max is 400 ° C. Therefore, when the material of the gas sensing layer 12 is SnO ₂ , the measurement temperature T2 may be 400 ° C. or lower, more preferably 350 ° C. or lower, still more preferably 250 ° C. or higher and 320 ° C. or lower. May be. The measurement temperature duration t2 may be shorter than the preheating time t1. In one example, the measurement temperature duration t2 may be 0.1 seconds or more and 60 seconds or less.

At the timing immediately before the end of the measurement temperature duration t2, the detection unit 20 may acquire the electrical characteristics of the gas sensing layer 12. The detection unit 20 detects the oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer 12 heated to the measurement temperature by the heater 14. Specifically, the current flowing through the gas sensing layer 12 when a known voltage is applied to both ends of the gas sensing layer 12 is measured, and the electrical resistance of the gas sensing layer 12 is obtained from the voltage and current across the gas sensing layer 12. You may get the value. The storage unit 50 may store a look-up table showing the relationship between the electric characteristic value such as the electric resistance value and the oxidizing gas concentration. The detection unit 20 may detect the corresponding gas concentration with reference to the look-up table for the acquired electrical characteristic value.

Next, the effect of the gas sensor 100 of the first embodiment configured as described above will be described with reference to a comparative example. FIG. 7 is a diagram showing an example of a heater drive pattern in the gas sensor of the comparative example. The vertical axis of FIG. 7 shows the temperature of the gas sensing layer 12, and the horizontal axis shows the time. The structure of the gas sensor of the comparative example is the same as the structure of the gas sensor 100 of the first embodiment shown in FIGS. 1 to 3 except for the difference in the heater drive pattern.

In the gas sensor of the comparative example, the heating control unit 30 controls the heater 14 so as to directly heat the gas sensing layer 12 to the measurement temperature T2 without preheating the gas sensing layer 12. Table 1 shows the results of comparing the sensor sensitivities of the gas sensor 100 of Example 1 and the gas sensor of Comparative Example 1. In the first embodiment shown in FIG. 6, the first embodiment has a preheating temperature T1 of 250 ° C., a preheating time t1 of 30 seconds, a measurement temperature of 300 ° C., and a measurement temperature duration t2 of 0.3 seconds. If this is the case. Comparative Example 1 is a case where the preheating is not executed, the measurement temperature is 300 ° C., and the measurement temperature duration t2 is 30 seconds in the comparative example shown in FIG. 7. In Example 1 and Comparative Example 1, the oxidizing gas to be detected was NO _2, and _{the concentration of NO 2} was 4 ppm.

For the gas sensitivity, the electric resistance value of the gas sensing layer 12 in the clean air when heated under the same heater driving conditions was set to Rair, and the electric resistance value of the gas sensing layer 12 in the atmosphere of _{4 ppm NO 2 gas was set to Rgas.} In some cases, it is calculated as the ratio of Rgas to Air, specifically, Rgas / Air. As shown in Table 1, it was found that the gas sensor of Example 1 had higher gas sensitivity than that of Example 1 and Comparative Example 1, although the measurement temperature T2 was the same. In Example 1, it was found that sufficient gas sensitivity was obtained.

FIG. 8 is a flowchart showing an example of processing contents by the gas sensor 100 according to the first embodiment of the present invention. FIG. 8 shows a control method of the gas sensor 100. The heating control unit 30 controls the heater 14 so that the gas sensing layer 12 is heated to the preheating temperature T1 (step S101). Waiting for the preheating time t1 to elapse (step S102: YES), the heating control unit 30 controls the heater 14 so that the gas sensing layer 12 is heated to the measurement temperature T2 (step S103). In steps S101 to S103, the gas sensing layer 12 is preheated by the heater 14 so that the temperature of the gas sensing layer 12 is in the range of T _min -100 ° C. or higher and T _min + 50 ° C. or lower, and then the gas sensing layer 12 is formed. Corresponds to the control stage in which the heater 14 is controlled to be heated to the measurement temperature.

In a state where the gas sensing layer 12 is heated to the measurement temperature T2, waiting for a predetermined time to elapse (step S104: YES), the detection unit 20 acquires the electrical characteristics of the gas sensing layer 12 (step S104: YES). Step S105). The predetermined time may be the measurement temperature duration t2 or shorter than the measurement temperature duration t2. The detection unit 20 detects the oxidizing gas to be detected based on the acquired electrical characteristics (step S106). Specifically, in this example, the electric resistance value of the gas sensing layer 12 increases as the concentration of the oxidizing gas to be detected increases. Steps S104 to S106 correspond to a detection step of detecting an oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer 12 heated to the measurement temperature T2 by the heater 14.

When the oxidizing gas to be detected is present, the oxidizing gas to be detected is adsorbed on the surface of the gas sensing layer 12 together with the oxygen in the air. Therefore, only the oxygen in the air is adsorbed on the surface of the gas sensing layer 12. The electric resistance value of the gas sensing layer 12 is higher than that of the gas sensing layer 12. In particular, in this example, since the surface of the gas sensing layer 12 is cleaned by preheating, the oxidizing gas is easily adsorbed. The detection unit 20 may detect the corresponding gas concentration of the acquired electrical characteristic value such as the electric resistance value by referring to a look-up table or the like. Further, the detection unit 20 may compare the electric resistance value of the gas sensing layer 12 with one or more threshold values stored in the storage unit 50. If the electric resistance value of the gas sensing layer 12 is higher than the threshold value, the detection unit 20 may determine that the oxidizing gas to be detected exists.

Further, when the oxidizing gas to be detected is NO ₂ gas, NO ₂ gas is more easily adsorbed on the surface of the gas sensing layer 12 than oxygen. _{Therefore, the electric resistance value increases when not only oxygen in the air but also NO 2} gas is adsorbed on the surface of the gas sensing layer 12 as compared with the case where oxygen in the air is adsorbed on the surface of the gas sensing layer 12. It tends to occur early. Therefore, the detection unit 20 may determine that _{NO 2} gas is present when the time from when the gas sensing layer 12 starts to be heated to the measurement temperature T2 until the electric resistance value reaches a predetermined value is short. Further, the detection unit 20 may determine that the shorter the time until the electric resistance value reaches a predetermined value, the higher the concentration of _{the NO 2 gas.}

When the detection unit 20 detects the oxidizing gas to be detected (step S106: YES), the control device 200 generates a gas detection signal (step S107). For example, in the gas alarm 102 as shown in FIG. 2, the alarm generation unit 60 issues an alarm to the effect that the oxidizing gas to be detected has been detected. Next, the heating control unit 30 may stop energizing the heater 14 after waiting for the total heating time of the preheating time t1 and the measurement time duration t2 to elapse (step S108). The heating control unit 30 may periodically pulse drive the heater 14. Therefore, the heating control unit 30 waits for the heater drive cycle ct to elapse (step S109: YES), and controls the heater 14 so that the gas sensing layer 12 is heated to the preheating temperature T1 (step S101). ).

As described above, according to the gas sensor 100 of the present embodiment, the gas sensing layer 12 has a minimum temperature in which the electric resistance value of the gas sensing layer 12 in clean air exhibits a minimum value in a temperature range before and after _{T min ° C.} Preheat. By preheating, the amount of oxygen adsorbed on the gas sensing layer 12 is reduced, and the surface of the gas sensing layer 12 becomes clean. By controlling the heater 14 so that the gas sensing layer 12 is heated to the measurement temperature T2 after undergoing the preheating in this way, the sensor sensitivity to the oxidizing gas to be detected can be increased.

FIG. 9 is a diagram showing an example of a heater drive pattern in the gas sensor 100 according to the second embodiment of the present invention. The structure of the gas sensor 100 of the second embodiment is the same as that of the gas sensor 100 of the first embodiment except for the difference in the heater drive pattern. Therefore, repeated explanations of common parts are omitted. FIG. 9 shows an enlarged waveform of one pulse-shaped portion as shown in FIG. 5, similar to FIG. 6 in the first embodiment. The vertical axis of FIG. 9 shows the temperature of the gas sensing layer 12, and the horizontal axis shows the time.

As shown in FIG. 9, the heating control unit 30 controls the heater 14 so as to heat the gas sensing layer 12 to an initial heating temperature T0 higher than the measurement temperature T2 prior to the preheating to the preheating temperature T1. More preferably, the initial heating temperature T0 may be equal to or higher than the _{maximum temperature Tmax.} The initial heating temperature T0 may be a temperature at which the detection target gas is desorbed from the gas sensing layer 12. For example, when the detection target gas is NO ₂ gas, the initial heating temperature T0 may be 400 ° C. or higher and 470 ° C. or lower, and more preferably 420 ° C. or higher and 460 ° C. or lower. The initial heating temperature duration t0 may be shorter than the preheating time t1. In one example, the initial heating temperature duration t0 may be 0.1 seconds or more and 60 seconds or less.

After the initial heating, the same heater drive pattern as in the case of the first embodiment shown in FIG. 6 may be executed. According to this example, the heating control unit 30 heats the gas sensing layer 12 to an initial heating temperature T0 higher than the measurement temperature T2 prior to the preheating to the preheating temperature T1. Therefore, it is possible to release the oxidizing gas to be detected once adsorbed on the surface of the gas sensing layer 12. Therefore, the surface of the gas sensing layer 12 becomes clean. Therefore, the oxidizing gas to be detected is easily adsorbed on the surface of the gas sensing layer 12, so that the sensor sensitivity to the oxidizing gas to be detected can be increased.

Next, the effect of the gas sensor 100 of the second embodiment configured as described above will be described with reference to the comparative example shown in FIG. Table 2 shows the results of comparing the sensor sensitivities of the gas sensor 100 of Example 2 and the gas sensor of Comparative Example 1. In the second embodiment shown in FIG. 9, in the second embodiment, the initial heating temperature T0 is 450 ° C., the initial heating temperature duration t0 is 0.3 seconds, the preheating temperature T1 is 250 ° C., and the preheating time t1 is 30. Second, the measurement temperature is 300 ° C., and the measurement temperature duration t2 is 0.3 seconds. Comparative Example 1 is a case where the initial heating and the preheating are not executed, the measurement temperature T2 is 300 ° C., and the measurement temperature duration t2 is 30 seconds in the comparative example shown in FIG. In Example 2 and Comparative Example 1, the oxidizing gas to be detected was NO _2, and _{the concentration of NO 2} was 4 ppm.

As shown in Table 2, although the measurement temperature T2 is the same in Example 2 and Comparative Example 1, the gas sensor of Example 2 has higher gas sensitivity than the gas sensor of Comparative Example 1. I found it to play. In Example 2, it was found that sufficient gas sensitivity was obtained. In the case of Example 1 of Table 1 in the first embodiment, the gas sensitivity is 2.0, whereas in the case of Example 2 of Table 2 in the second embodiment, the gas sensitivity is 5.0. Is.

FIG. 10 is a flowchart showing an example of processing contents by the gas sensor 100 according to the second embodiment of the present invention. The heating control unit 30 controls the heater 14 so that the gas sensing layer 12 is heated to the initial heating temperature T0 (step S201). Waiting for the initial heating temperature duration t0 to elapse (step S202: YES), the heating control unit 30 controls the heater 14 to heat the gas sensing layer 12 to the preheating temperature T1 (step S203). The processing contents of steps S203 to S211 are the same as the processing contents of steps S101 to S109 in FIG. Therefore, the repetitive description is omitted.

As described above, according to the gas sensor 100 of the present embodiment, the gas sensing layer 12 is heated to the initial heating temperature T0 higher than the measurement temperature T2 prior to the preheating to the preheating temperature T1. Next, the gas sensor 100 of the present embodiment preheats the gas sensing layer 12 in a temperature range of around _{T min} ° C. at a minimum temperature at which the electric resistance value of the gas sensing layer 12 in clean air exhibits a minimum value. As a result, the amount of oxygen adsorbed on the gas sensing layer 12 is reduced, and the surface of the gas sensing layer 12 is brought into a clean state. By controlling the heater 14 so that the gas sensing layer 12 is heated to the measurement temperature T2 after the initial heating and the preheating, the sensor sensitivity to the oxidizing gas to be detected can be increased.

FIG. 11 is a diagram showing an example of a heater drive pattern in the gas sensor 100 according to the third embodiment of the present invention. The structure of the gas sensor 100 of the third embodiment is the same as that of the gas sensor 100 of the first or second embodiment except for the difference in the heater drive pattern. Therefore, repeated explanations of common parts are omitted. FIG. 11 shows an enlarged waveform of one pulse-shaped portion as shown in FIG. 5, similar to FIG. 6 in the first embodiment. The vertical axis of FIG. 11 shows the temperature of the gas sensing layer 12, and the horizontal axis shows the time.

As shown in FIG. 11, in the gas sensor 100 of the third embodiment, the preheating time t1 is variable. In this example, the preheating time is t11 in the initial heater drive, whereas it is the preheating time t12 in the subsequent heater drive. The preheating time t12 is longer than the preheating time t11. The longer the preheating time, the more stable the temperature and the higher the detection accuracy. On the other hand, the longer the preheating time, the lower the detection frequency.

In this example, the preheating time is set in consideration of the detection frequency. Then, the detection unit 20 acquires the electric resistance value of the gas sensing layer 12. When the electric resistance value of the gas sensing layer 12 is equal to or higher than the predetermined first resistance value, there is a possibility that the oxidizing gas to be detected is present. Therefore, when the electric resistance value of the gas sensing layer 12 is equal to or higher than the predetermined first resistance value, the heating control unit 30 changes the preheating time to be longer in consideration of the detection accuracy. The detection unit 20 detects the oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer 12 heated to the measurement temperature after the preheating in which the preheating time t12 is changed to be long. ..

FIG. 12 is a flowchart showing an example of processing contents by the gas sensor 100 according to the third embodiment of the present invention. The processing from step S301 to step S304 is the same as the processing from step S101 to step S104. Next, the detection unit 20 acquires the electric resistance value of the gas sensing layer 12 (step S305). Then, the detection unit 20 determines whether the electric resistance value of the gas sensing layer 12 is equal to or higher than the first threshold value (first resistance value) (step S306). When the gas sensing layer 12 is equal to or higher than the first threshold value (step S306: YES), the heating control unit 30 determines whether the preheating time t1 has already been changed (step S307).

If the preheating time t1 has not been changed yet (step S307: NO), the preheating time t1 is changed to be longer (step S308). On the other hand, when the preheating time t1 has already been changed (step S307: YES), it is assumed that the oxidizing gas to be detected is detected, and a gas detection signal is generated (step S309). Step S310 and step S311 are the same as those of step S108 and step S109 of FIG. Therefore, the description of repetition will be omitted.

FIG. 13 is a diagram showing an example of a heater drive pattern in the gas sensor 100 according to the fourth embodiment of the present invention. The gas sensor 100 of this example detects a plurality of types of oxidizing gases, a first oxidizing gas and a second oxidizing gas. In this example, as the measurement temperature T2, the first measurement temperature T21 and the second measurement temperature T22 are defined according to the type of oxidizing gas. The detection unit 20 detects the first oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer 12 heated to the first measurement temperature T21 by the heater 14. The detection unit 20 detects the second oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer 12 heated to the second measurement temperature by the heater 14.

As shown in FIG. 13, in the drive pattern of the heater 14, the measurement temperature may be switched between the first measurement temperature T21 and the second measurement temperature T22 every time the period changes. FIG. 14 is a flowchart showing an example of processing contents by the gas sensor 100 according to the fourth embodiment of the present invention. In FIG. 14, the processes of steps S401 to S405 are the same as the processes of steps S101 to S105 of FIG. However, in step S403, the measurement temperature may be the first measurement temperature T21 or the second measurement temperature T22.

In step S403, when the measurement temperature T2 is the first measurement temperature T21, the detection unit 20 detects the first oxidizing gas (step S406). On the other hand, in step S403, when the measurement temperature T2 is the second measurement temperature T22, the detection unit 20 detects the second oxidizing gas (step S406). When the detection unit 20 detects the oxidizing gas to be detected (step S406: YES), the control device 200 generates a gas detection signal according to the type of the detected oxidizing gas (step S407). .. The processing of step S408 and step S409 is the same as the processing of step S108 and step S109 in FIG. In step S410, the measurement temperature T2 is switched to either the first measurement temperature T21 or the second measurement temperature T22.

According to this example, a plurality of measurement temperatures are prepared as measurement temperatures. Therefore, it is possible to detect a plurality of types of oxidizing gases corresponding to each measurement temperature.

FIG. 15 is a diagram showing another example of the heater drive pattern in the gas sensor 100 according to the fourth embodiment of the present invention. In the example shown in FIG. 13, a case where the measurement temperature is switched between the first measurement temperature T21 and the second measurement temperature T22 has been described every time the cycle changes. However, the measurement temperature may be sequentially switched to the first measurement temperature T21 and the second measurement temperature T22 in one cycle.

Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various changes or improvements can be made to the above embodiments. It is clear from the description of the claims that such modified or improved forms may also be included in the technical scope of the present invention.

The order of execution of operations, procedures, steps, steps, etc. in the devices, systems, programs, and methods shown in the claims, specification, and drawings is particularly "before" and "prior to". It should be noted that it can be realized in any order unless the output of the previous process is used in the subsequent process. Even if the scope of claims, the specification, and the operation flow in the drawings are explained using "first", "next", etc. for convenience, it means that it is essential to carry out in this order. It's not a thing.

2 ... Silicon substrate, 3 ... Thermal insulation support layer, 4 ... Electrical insulation layer, 5 ... Gas sensing part, 6 ... Through hole, 7 ... Bonding layer, 8 ... Gas sensing layer electrode, 9 ...・ Catalyst layer, 10 ・ ・ detection unit, 12 ・ ・ gas detection layer, 14 ・ ・ heater, 16 ・ ・ temperature measurement unit, 20 ・ ・ detection unit, 30 ・ ・ heating control unit, 40 ・ ・ setting unit, 50 ・・ Storage unit, 60 ・ ・ Alarm generator, 100 ・ ・ Gas sensor, 102 ・ ・ Gas alarm, 200 ・ ・ Control device

Claims (13)

Gas sensing layer and
A heater that heats the gas sensing layer and
A heating control unit that controls the heater to control the temperature of the gas sensing layer,
An oxidizing gas sensor including a detection unit that detects an oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer heated to a measurement temperature by the heater.
Regarding the temperature characteristics of the electric resistance value of the gas sensing layer in clean air, when the minimum temperature, which is the temperature of the gas sensing layer at which the electric resistance value exhibits a minimum value, is set to T _min ° C., the heating control unit Is to preheat the gas sensing layer so that the temperature of the gas sensing layer is in the range of T _min −100 ° C. or higher and T _min + 50 ° C. or lower, and then the gas sensing layer is heated to the measured temperature. An oxidizing gas sensor that controls the heater. The oxidizing gas sensor according to claim 1, wherein oxygen adsorbed on the surface of the gas sensing layer is desorbed by the preheating. The measured temperature when the maximum temperature, which is the temperature of the gas sensing layer at which the electric resistance value exhibits the maximum value, is set to T _{max ° C. with respect to the temperature characteristics of the electric resistance value of the gas sensing layer in the clean air.} The oxidizing gas sensor according to claim 1 or 2, wherein is lower than the maximum temperature T _{max ° C.} The oxidizing gas sensor according to claim 3, wherein the measured temperature is higher than the adsorption start temperature of the oxidizing gas to be detected. The oxidizing gas sensor according to claim 3, wherein the measurement temperature is T _{min + 50 ° C. or less.} The oxidizing gas sensor according to any one of claims 1 to 5, wherein the preheating time is 10 seconds or more and 10 minutes or less. The oxidizing gas sensor according to any one of claims 1 to 6, wherein the preheating time is variable. When the electric resistance value of the gas sensing layer is equal to or higher than a predetermined first threshold value, the heating control unit is changed to lengthen the preheating time.
Any of claims 1 to 7, wherein the detection unit detects the oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer heated to the measurement temperature after the preheating in which the time is changed for a long time. The oxidizing gas sensor according to item 1. An oxidizing gas sensor that detects the first oxidizing gas and the second oxidizing gas.
As the measurement temperature, the first measurement temperature and the second measurement temperature are defined.
The detection unit detects the first oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer heated to the first measurement temperature by the heater, and is heated to the second measurement temperature by the heater. The oxidizing gas sensor according to any one of claims 1 to 8, which detects the second oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer. The oxidizing gas sensor according to any one of claims 1 to 9, wherein the heating control unit controls a heater so that the gas sensing layer is heated to a temperature higher than the measurement temperature prior to the preheating. The oxidizing gas sensor according to any one of claims 1 to 10 is provided.
A gas alarm that further includes an alarm generating unit that generates an alarm when the oxidizing gas sensor detects an oxidizing gas to be detected. A control that has a gas sensing layer and a heater that heats the gas sensing layer, and controls an oxidizing gas sensor that detects an oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer heated by the heater. It ’s a device,
Regarding the temperature characteristics of the electric resistance value of the gas sensing layer in clean air, when the minimum temperature, which is the temperature of the gas sensing layer at which the electric resistance value exhibits a minimum value, is set to T _min ° C., the gas sensing layer After preheating the gas sensing layer with the heater so that the temperature of the gas sensing layer is in the range of T _min -100 ° C. or higher and T _min + 50 ° C. or lower, the heater is heated so that the gas sensing layer is heated to the measurement temperature. The heating control unit to control and
A control device including a detection unit that detects an oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer heated to the measurement temperature by the heater. A control method for an oxidizing gas sensor that has a gas sensing layer and a heater that heats the gas sensing layer, and detects an oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer heated by the heater. There,
Regarding the temperature characteristics of the electric resistance value of the gas sensing layer in clean air, when the minimum temperature, which is the temperature of the gas sensing layer at which the electric resistance value exhibits a minimum value, is set to T _min ° C., the gas sensing layer After preheating the gas sensing layer with the heater so that the temperature of the gas sensing layer is in the range of T _min -100 ° C. or higher and T _min + 50 ° C. or lower, the heater is heated so that the gas sensing layer is heated to the measurement temperature. The control stage to control and
A control method comprising a detection step of detecting an oxidizing gas to be detected based on the electrical characteristics of the gas sensing layer heated to the measurement temperature by the heater.

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