JPH0569667U - Gas sensor - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain a gas sensor in which the oxidant in the atmosphere is thermally decomposed and the sensitivity to the oxidant is reduced to a negligible level. [Structure] A substrate 2 made of Al ₂ O ₃ , a heater 3 made of a Pt thin film provided on the lower surface of the substrate 2, and a substrate 2
An electrode 4 formed of a Pt thin film provided on the upper surface of the substrate, a gas-sensitive thin film 5 formed by covering the upper surface of the substrate 2 and the electrode 4 with a metal oxide semiconductor, and an upper portion of the gas-sensitive thin film 5. The gas sensor 1 is characterized in that the gas sensor 1 is composed of a fine particle layer 6 that is covered with a fine particle layer 6 through which a test gas can pass and that has a heat-resistant substance as a main component that thermally decomposes an oxidant in the atmosphere by heating the heater 2. .

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a gas sensor having reduced sensitivity to oxidants in the atmosphere.

[0002]

[Prior Art]

 Thin-film gas sensors that use metal oxide semiconductors as gas-sensing materials have extremely high sensitivity to oxidants in the atmosphere in any manufacturing method such as physical vapor deposition, chemical vapor deposition, and thermal decomposition. Therefore, when used in an oxidant atmosphere in the atmosphere, it often causes malfunctions of alarm devices.

Therefore, conventionally, a thermal reactor (a device that heats a quartz tube having an inner diameter of 6 mm and a length of 10 cm to several hundred degrees to thermally decompose the oxidant in the atmosphere) is installed in front of the gas sensor, and the gas sensor is exposed to the oxidant. I was trying not to be.

FIG. 4 is a longitudinal sectional view showing an example of a conventional humidity sensor disclosed in Japanese Utility Model Laid-Open No. 59-84461, in which a humidity sensor 32 is drawn out on a base 31 and attached by a terminal 33, and a case body 34 is attached. Is formed of a non-breathable material, a window hole 35 is formed in the peripheral wall of the case body 34, and a net 36 is stretched in the window 35 to provide air permeability, and the ozone decomposing substance 37 is attached to the net 36. It is either applied to the surface of, or mixed and dispersed in the material forming the net 36.

As shown in FIG. 4, the humidity sensor 32 is incorporated in an electronic device in a state where the humidity sensor 32 is housed in the case body 34, and the humidity in the device is detected by a change in the resistance value of the humidity sensor 32. Since the case body 34 is provided with the ozone decomposing substance 37 at the portion where the air passes inside and outside, ozone in the air is decomposed and removed without directly acting on the humidity sensor 32. It is possible to prevent deterioration of the detection accuracy of the humidity sensor 32 due to ozone.

[0006]

[Problems to be solved by the device]

 The gas sensor using the conventional thermal reactor has a large sensing unit. Power of about 20 W is required. It is practically impossible to use a flameproof structure. If an alarm device is installed in a well-ventilated area, when the air flows backward, the gas sensor may be exposed to the oxidant in the atmosphere and cause the gas alarm device to malfunction.

In the case of the conventional humidity sensor disclosed in Japanese Utility Model Laid-Open No. 59-84461, an ozone decomposable substance applied or mixed on the surface of the net body 36 forming the case body 34. No. 37 decomposes ozone at room temperature to change it to oxygen, but its decomposition efficiency is low and not perfect at room temperature. Moreover, since this method is a catalytic decomposition method, the catalytic activity is lowered by dust and poisonous gas, and the decomposition efficiency of ozone is lowered.

Further, since it is necessary to convert the case main body 34 having the net body 36 coated with the ozone decomposing substance 37, it is troublesome and costly. Moreover, since the case main body 34 is used, the case main body 34 is made large in size and is pressure proof. There was a problem that it was difficult to make a structure.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a gas sensor in which the oxidant in the atmosphere is thermally decomposed to reduce the sensitivity to the oxidant to a negligible level. To do.

[0010]

[Means for Solving the Problems]

 The gas sensor according to the present invention comprises a gas-sensitive thin film made of a metal oxide semiconductor, a heater for heating the gas-sensitive thin film, and a heat-resistant substance on the surface of the gas-sensitive thin film for thermally decomposing the oxidant in the atmosphere by heating the heater. In the present invention, a fine particle layer, through which a test gas can pass, which is mainly composed of one kind or a mixture of several kinds, is closely coated.

[0011]

[Operation] In the present invention, since the fine particle layer made of a heat-resistant substance and capable of passing the test gas is heated by the heater, it acts to thermally decompose the oxidant in the atmosphere and reduce the sensitivity to the oxidant. To do.

[0012]

【Example】

FIG. 1 is a side sectional view showing an embodiment of the present invention, 1 is the whole gas sensor, 2 is a substrate made of Al ₂ O ₃ , and 3 is a Pt thin film provided on the lower surface of the substrate 2. The heater 4 is an electrode made of a Pt thin film provided on the upper surface of the substrate 2 and the gas sensitive thin film 5 covers the upper surface of the substrate 2 and the electrode 4. In ₂ O ₃ , Ag _0.04 V ₂ O ₅ It is formed of a metal oxide semiconductor comprising one of Zn O or Sn O _2. Reference numeral 6 is a fine particle layer formed on the gas sensitive thin film 5, which contains one or a mixture of Al ₂ O ₃ , SiO ₂ , Al ₂ O ₃ .Si O ₂ , Al N, and Si ₃ N _4. The main component is a fine particle layer through which the test gas can pass.

Table 1 concretely shows the constitution of the gas sensor 1. Examples of the components of the gas sensitive thin film 5, the fine particle layer 6 and the number of the fine particle layer 6 and the particle diameter which are constituted for each gas to be measured. Is shown.

[0014]

[Table 1] The gas sensor 1 configured as described above is heated by energization of the heater 3. In this state, when the oxidant in the atmosphere comes into contact with the fine particle layer 6 and is thermally decomposed, the sensitivity of the gas sensor 1 to the oxidant in the atmosphere is lowered. As an example of this measurement result, the gas sensor 1 according to the embodiment of the present invention for ozone, which is one of the oxidants in the atmosphere, and the oxidant in the atmosphere, and the conventional gas sensor (without the fine particle layer 6 in FIG. 1) 2 and FIG. 3 show comparisons with the responses of FIG. The gas sensor 1 (of the embodiment) used was Cl _{2 as} the gas to be measured, In ₂ O _{3 as} the gas-sensitive thin film component, the number of fine particle layers 6 was 3, and the particle size was 0.05- It is 1 μm.

FIG. 2 shows a response value obtained by experimentally measuring the sensitivity (in arbitrary units) of ozone of the gas sensor with respect to elapsed time, and FIG. 3 shows the sensitivity of the gas sensor to oxidant in the atmosphere outside the room with respect to elapsed time. Shows the response value measured by experiment.

In FIG. 2, 11 is the response value of the gas sensor 1 of the present invention to ozone, and 12 is the response value of the conventional gas sensor. Further, in FIG. 3, 21 is a response value of the gas sensor 1 to an oxidant in the atmosphere, 22 is a response value of a conventional gas sensor, and 23 is a value of an alarm level of a gas to be measured.

As described above, in the conventional gas sensor, the response value 12 to ozone and the response value 22 to oxidant are very high, and in particular, in FIG. 3, the response value 22 to oxidant in the atmosphere is higher than the alarm level value 23. Also, there are many high parts, which causes malfunction. On the other hand, when the gas sensor 1 of the present invention is used, the response value 11 to ozone and the response value 21 to the oxidant in the atmosphere decrease as shown in FIGS. Therefore, as shown in Fig. 3, it hardly responds to the oxidant in the atmosphere, and it is much smaller than the alarm level value 23 of the gas to be measured. No alarm signal is issued.

If the fine particle layer 6 that lowers the sensitivity to oxidants in the atmosphere is formed of one kind or a mixture of several kinds of the materials shown in Table 1, various characteristics of the original gas sensor are not impaired.

Further, although the number of layers of the fine particle layer 6 and the allowable range of the particle size are large as shown in Table 1, the activity of the fine particle layer 6 is increased and the number of layers can be reduced by decreasing the particle size. Although these values vary depending on the gas to be measured, it is appropriate that the particle size is 0.01 to 10 μm and the number of layers is single to several tens.

[0020]

[Effect of the device]

 As described above, the present invention provides a gas-sensitive thin film made of a metal oxide semiconductor, a heater for heating the gas-sensitive thin film, and a heat-resistant material for thermally decomposing the oxidant in the atmosphere by heating the heater on the surface of the gas-sensitive thin film. Since a fine particle layer, which contains one or several mixtures of volatile substances as main components and allows the test gas to pass through, was adhered and covered, decomposition of the oxidant became remarkable, and the sensitivity to the oxidant decreased to a negligible level. It's a real thing. Therefore, it is not necessary to install a thermal reactor in front of the gas sensor, and the gas sensing unit can be downsized. Therefore, electric power for heating the thermal reactor is not required, it is not necessary to provide a circuit and wiring for it, and a flameproof structure is possible. Furthermore, the zero point of the gas sensor is stable, malfunction of the alarm device is eliminated, and there is long-term stability. Also, a gas sensor integrated with a fine particle layer that decomposes the oxidant can be configured, and almost all of the oxidant reaching the sensor contacts the fine particle layer, so that the oxidant is almost completely decomposed and the decomposition efficiency of the oxidant is improved. Moreover, the long-term stability is greatly improved because the gas-sensitive film is not directly exposed to the atmosphere by forming the fine particle layer. Further, since it is easy to manufacture, it can be mass-produced, and it has various practical advantages such as cost reduction.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the elapsed time of the present invention sensor and the conventional gas sensor and the response value for 1 ppm of ozone.

FIG. 3 is a diagram showing the relationship between the elapsed time of the gas sensor of the present invention and the conventional gas sensor and the response value to an oxidant in the air outdoors.

FIG. 4 is a vertical cross-sectional view showing an example of a conventional humidity sensor.

[Explanation of symbols]

 1 gas sensor 2 substrate 3 heater 4 electrode 5 gas sensitive thin film 6 fine particle layer

Claims (1)

[Scope of utility model registration request] 1. A gas sensitive thin film comprising a metal oxide semiconductor,
In a gas sensor provided with a heater for heating a gas-sensitive thin film, the main component of the gas-sensitive thin film is one or a mixture of heat-resistant substances capable of thermally decomposing the oxidant in the atmosphere by heating the heater. The gas sensor is characterized in that a fine particle layer through which the test gas can pass is adhered and coated.