JPH09269308A - Heat ray type semiconductor gas detection element and gas detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique efficiently achieving the suppression of power consumption when the heat ray type semiconductor gas detection element is formed so that the vol. thereof becomes small. SOLUTION: A responsive part 3 formed from a semiconductor based on tin oxide so as to cover a noble metal wire coil 2 is provided to this element and formed so that the long diameter d2 thereof becomes 1.5 times or less the short diameter d3 thereof and the vol. thereof becomes 8.2×10<-3> mm<3> or less. Further, the distance from the coil part 2a of the noble metal wire coil 2 to the outer surface of the responsive part 3 is set to 50μm or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-wire semiconductor type gas sensing element having a sensitive portion formed of a semiconductor containing tin oxide as a main component, which covers a noble metal wire coil, and
A gas detector that incorporates a hot-wire semiconductor gas detection element into a gas detection circuit and is provided with a voltage supply unit that supplies a voltage to the gas detection circuit so that the output from the hot-wire semiconductor gas detection element can be detected freely. Regarding the device.

[0002]

2. Description of the Related Art Heretofore, it has been known that a hot wire type semiconductor gas detecting element of this kind is formed in a small volume of about 2.1 × 10 ^-2 mm ^3. A gas detection device has been constructed by incorporating a hot wire semiconductor type gas detection element into a gas detection circuit. As other gas detection elements, there are known a semiconductor thick film type gas detection element having a sensitive portion made of a semiconductor thick film and a microchip having a sensitive portion made of a semiconductor thin film.

[0003]

In the conventional gas detection element described above, the smaller the volume, the smaller the total heat capacity,
It is said to be preferable from the viewpoint that the operating temperature can be maintained with low power consumption. That is, the semiconductor thin film is preferable to the semiconductor thick film in that it consumes less power. However, even if the gas sensing element is formed to have a small volume like a microchip, its power consumption can be reduced, but it is highly sensitive to ozone in the atmosphere. Compared to the sensing element,
There are problems that the output becomes unstable due to the interference gas and the long-term stability becomes poor. In addition, along with this, it is the current situation that gases such as methane and carbon monoxide that need to be detected cannot be detected.

Therefore, in view of the above-mentioned drawbacks, an object of the present invention is to provide a gas detection element which consumes less power and is excellent in output stability against interference gas and long-term stability, or
In addition to this, it is to provide a gas detection element having a high response speed. Still another object of the present invention is to provide a gas detection device which is easy to use because such a hot wire type semiconductor gas detection element has low power consumption.

[0005]

[Means for Solving the Problems] The present inventors have found that when a hot wire type semiconductor gas sensing element having a volume of 6.5 × 10 ⁻⁵ mm ³ or more and 8.2 × 10 ⁻³ mm ³ or less is energized. We obtained a new finding that power consumption and response speed depended largely on the distance from the coil part of the noble metal wire coil to the outer surface of the sensitive part of the hot wire semiconductor gas sensing element. Further, particularly when the distance to the outer surface of the sensitive portion of the hot wire semiconductor type gas detection element is 50 μm or less (0 μm, that is, including the case where the coil portion of the metal wire coil is located on the outer surface of the sensitive portion). We have obtained new knowledge that the response speed can be increased. The present invention is based on these new findings.

[Structure 1] Referring to FIG. 1, the characteristic structure of the hot-wire type semiconductor gas detecting element of the present invention for achieving the above-mentioned object is that the noble metal wire coil 2 is covered with tin oxide. In the hot-wire semiconductor gas detection element provided with a sensitive section 3 formed of a semiconductor as a component, the sensitive section 3 has a major axis d2 of 1.5 times or less of a minor axis d3 and a volume of 6 0.5 × 10 ^-5 mm ³ or more 8.2 × 10 ^-3 m
The coil portion 2 of the precious metal wire coil 2 is formed to have a size of m ³ or less.
The distance from a to the outer surface of the sensitive portion 3 is 50 μm or less, and the average secondary particle diameter is 0.3 μm.
It is preferable that the sensitive portion 3 is formed by sintering a semiconductor containing tin oxide having a thickness of 0.8 μm or less as a main component. Although the drawings are referred to for describing the characteristic configuration of the present invention, the present invention is not limited to the drawings.

[Operation and Effect] That is, since the volume of the sensitive portion is formed to be 8.2 × 10 ⁻³ mm ³ or less, the power consumption is further increased as compared with the above-described conventional hot-wire semiconductor gas detection element. It can be seen that can be reduced. Further, based on the above new knowledge, the distance from the coil part of the precious metal wire coil to the outer surface of the sensitive part (hereinafter referred to as the sensitive part thickness)
Is formed to have a thickness of 50 μm or less, it can be operated with lower power consumption and high responsiveness can be obtained (for example, a gas detection element having a volume of 9.2 × 10 ⁻⁴ mm ³ and a sensitive portion thickness of 20 μm). Exhibits a response speed 40 times that of a conventional gas detection element having a volume of 8.7 × 10 ^-2 mm ³ and a sensitive portion thickness of about 145 μm). In addition, when forming such a hot-wire type semiconductor gas detection element, due to its small volume, the surface area becomes large, such as the major axis of the sensitive section being larger than the minor axis, and the heat absorption and heat dissipation is increased. From the balance of payments etc.,
While it is difficult to form a hot-line semiconductor gas detection element with stable characteristics, a hot-line semiconductor gas detection element with stable characteristics can be obtained by controlling the major axis to be 1.5 times the minor axis or less. Easy to form. In the semiconductor forming the sensitive portion, the smaller the secondary particle diameter, the better the adhesion between the sensitive portion and the precious metal wire coil, and it is considered that the gas detection characteristics can easily set the long-term stability. When is composed of a semiconductor containing tin oxide as a main component, the average secondary particle size is preferably 0.8 μm or less. However, it is considered that the gas detection responsiveness by the hot-wire semiconductor type gas detection element is related to the gas diffusion rate into the sensitive section, and if the sensitive section is too dense, It takes time for the gas diffusion from the outer surface side to the coil side to be hindered and for the outer surface side of the sensitive section and the coil side to have a uniform gas concentration to be detected. Since the output is not stable when the difference is large, the response speed until stable output is expected to be slow. Therefore, the average secondary particle size is 0.3 μm.
It is preferably m or more. In other words, by greatly improving the response speed to gas, it is possible to accurately detect the gas in a steady state without maintaining the temperature of the sensitive section at a high temperature for an unnecessarily long time, and therefore, the temperature of the sensitive section is increased. It becomes possible to perform an operation control that suppresses the energization time for maintaining the temperature in a predetermined temperature range to a necessary minimum, and it is possible to form a sensitive section useful for suppressing power consumption. It became so. The temperature of the sensitive part can be stabilized in about 2 msec by energization [Infrared microscope type thermometer by Birds Co., mo.
del RM-2A (measurement accuracy 2 μsec)], the response speed to the above gas is about 200 msec even with the hot-wire semiconductor gas detection element of the present invention, and the heat of the sensitive part It takes an extremely long time as compared with the response, and the energization time for accurately detecting the gas greatly depends on the response speed to the gas.

[Structure 2] Referring to FIG. 2, a characteristic structure of the gas detecting apparatus of the present invention for achieving the above-mentioned object is that the hot wire semiconductor type gas detecting element 1 is incorporated in a gas detecting circuit. In the gas detecting device configured to freely detect the output from the hot wire semiconductor gas detecting element by providing a voltage supply unit 4 for supplying a voltage to the gas detecting circuit, the hot wire semiconductor gas detecting element 1 is first Using the hot wire semiconductor type gas detection element 1 of the above, and the voltage supply unit 4
Is configured to be able to supply power by a battery,
The circuit switching means 6 is provided for alternately switching between an ON state for supplying electric power to the gas detection circuit and an OFF state for stopping the electric power supply to the gas detection circuit.
Keeping the N state for 1 second or less
It is preferable to provide a control device 7 for controlling the time ratio between the ON state and the OFF state (ON state / OFF state) to 1/10 or less. Further, the setting of the control device 7 is the ON state.
The duration of the state is set to 0.5 seconds or less, and the O
More preferably, the time ratio between the N state and the OFF state (ON state / OFF state) is 1/40 or less. Further, it is preferable that the control device 7 be configured to maintain and control the hot-wire semiconductor gas detection element 1 at a set temperature of 350 ° C. or higher and 550 ° C. or lower. Although the drawings are referred to for describing the characteristic configuration of the present invention, the present invention is not limited to the drawings.

[Operation and Effect] That is, since the gas detection device of the present invention is provided with the above-mentioned hot-wire type semiconductor gas detection element, it becomes easy to detect the gas with a small amount of power and can be driven by a battery. it can. Further, when a circuit switching means for alternately switching between an ON state for supplying electric power to the gas detection circuit and an OFF state for stopping the electric power supply to the gas detection circuit is provided, a hot wire semiconductor incorporated in the gas detection circuit is provided. It is possible to switch between a state in which power is supplied to the gas detector element and a state in which power is stopped. Therefore, it is possible to realize a configuration in which accurate gas detection can be performed in the ON state, and when the gas detection is not performed, power consumption can be suppressed without energizing the hot-wire semiconductor gas detection element. Then, the duration of the ON state is set to 1 second or less, and the time ratio between the ON state and the OFF state (ON state / OFF state) is set to 1/10 or less, and more preferably, the duration of the ON state. 0.
If a controller for controlling the time ratio between the ON state and the OFF state (ON state / OFF state) to 1/40 or less is provided for 5 seconds or less, the hot-wire semiconductor gas detection element Even if the gas detection operation is performed for a long time, the energization time can be set to 1/10 or less or 1/40 or less of the operation time. Therefore, the hot-wire semiconductor type gas detection element can be operated with a smaller amount of electric power, and the life of the battery can be extended even when the battery is operated with the power source. Therefore, the gas detection device can be stably used for a long period of time. Therefore, if the gas detection device is formed by providing a voltage supply unit that uses a battery as a power source, in the case of a gas detection device that uses an outlet as a power source like a conventional gas detection device, there are restrictions on the installation location. In some cases, it may be difficult to install the product, such as having to run a cord around, but it is difficult to be restricted in the installation place and it is possible to use it in a place where it could not be used in the past. In addition, the gas detector can be made portable, the cost required for installing the gas detector can be reduced, and the usability of the gas detector can be improved. In addition to the above-described switching drive, the control device may be arranged so that the hot-wire semiconductor gas detection element is 350 ° C. or higher.
If the temperature can be maintained and controlled at a set temperature of 50 ° C. or less, durability against poisoning by interfering gas can be imparted, and it is difficult to keep the sensitive part at a high temperature due to switching drive, so sintering proceeds. As a result, it is difficult for the inconvenience that the gas detection characteristic is changed to occur, and the long-term stability of the sensitive portion can be enhanced. Since the hot-wire semiconductor gas detection element can perform stable gas detection and it is easy to maintain the hot-wire semiconductor gas detection element itself in an environment where deterioration is difficult, the hot-wire semiconductor can be used even when the gas detection device is used for a long period of time. It is possible to suppress the inconvenience caused by the deterioration of the gas sensor.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An example of an embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 2, the gas detection device of the present invention is configured by incorporating the hot-wire semiconductor gas detection element 1 into a bridge circuit. The gas detection element 1 covers a platinum coil wire 2 having a coil diameter d1 of about 80 μm, a semiconductor containing tin oxide as a main component having an average secondary particle diameter of about 0.6 μm, and a major axis d2 of a minor axis d3. After being provided in a substantially equal spherical shape of approximately 120 μm and dried, the semiconductor containing tin oxide as a main component is baked at 600 ° C. for 1 hour to form the sensitive portion 3. That is, the platinum coil wire 2
The distance d4 from the coil portion 2a to the outer surface of the sensitive portion 3 is 20 μm. Further, in the gas detection device, if a voltage is continuously applied, a voltage supply device 4 capable of applying a voltage capable of making the final temperature of the gas detection device 1 350 to 550 ° C., and the gas detection device. 1
Is connected to the detection circuit unit 5. In addition, according to the control rule, the voltage supply device 4 applies voltage of the pulse voltage (ON) and stops voltage application of the pulse voltage (OF).
F) is provided with a control mechanism 6 for switching control, and the detection circuit unit 5 outputs the output from the gas detection element based on the application of the pulse voltage as detection information (alarm sound) of the gas to be detected. A device (alarm device) 8 is provided.

This gas detection device is switch-controlled by a microcomputer and used for gas detection in accordance with the following control rules, for example. ⊚ First rule: When the duration of voltage application reaches 0.1 seconds (voltage application (ON) duration), the voltage application is stopped. ◎ Second rule: The duration of the state where the voltage application is stopped (voltage application stop (OFF) duration) is the voltage application (O
N) The voltage application is started when the time reaches 200 times (20 seconds) the duration (when the operating time ratio (ON / OFF) becomes 1/200).

That is, when the control is performed according to the first and second rules, a pulse voltage is applied to the gas detecting element 1, and therefore, by repeating the operation of energizing for about 0.1 second for about 20 seconds, , The gas detection element 1
When the output based on the change in the resistance value of the gas detecting element 1 is obtained while maintaining the temperature at a predetermined temperature, the concentration of the combustible gas in contact with the gas detecting element 1 can be measured.

When such switching control is performed, when the predetermined temperature is 500 ° C., the power consumption of the gas detection element 1 is 2
It can be set to an extremely low value of 50 μW. For example, when two single batteries are arranged in series and drive power is supplied, a configuration capable of gas detection for about 5 years can be obtained.

[0014]

【Example】

<1> The response characteristics when gas is detected by the gas detection element 1 are shown by the solid line in FIG. The broken line in the figure is the response characteristic when gas is detected by the conventional gas detecting element manufactured in the same process as described above.
It has a spherical shape of approximately 550 μm, and the distance d4 from the coil portion 2a of the platinum coil wire 2 to the outer surface of the sensitive portion 3 is 145 μm.
m. From FIG. 3, the gas detection element 1 of the present invention is shown.
It can be seen that indicates a stable output with quick response to each flammable gas.

<2> Next, the outer diameter of the platinum coil wire 2 of the gas detecting element 1 and the outer diameter of the sensitive portion 3 are variously changed to change the outer diameter of the platinum coil wire 2 to the sensitive portion. When the relationship between the distance d4 to the outer surface of No. 3 and the response speed of the gas detecting element was examined, the results are shown in Table 1. The numerical values in the table are specific response speeds where the response speed of the conventional gas detection element is 1.

[0016]

[Table 1]

From Table 1, both the outer diameter of the platinum coil wire 2 and the distance d4 from the outer diameter of the platinum coil wire 2 to the outer surface of the sensitive portion 3 are totally the gas detecting element 1
It is found that a configuration in which is smaller is preferable, and that it is greatly useful for improving the response speed. For example, the distance d4 = 50 μ
m, coil outer diameter d1 = 145 μm, conventional one (distance d4 = 145 μm, coil outer diameter d1 = 260 μm
The response speed of 10 times that of here,
Considering the response speed of the gas detection element, the gas detection output is obtained mainly based on the reaction between the detection gas in the vicinity of the platinum coil wire 2 and the semiconductor. It can be said that it depends on the time from when it reaches the vicinity of the platinum coil wire 2. Further, since the detection gas diffuses through the sensitive section 3 and reaches the vicinity of the platinum coil wire 2, a stable output can be obtained only under a condition (a concentration equilibrium state) in which a uniform reaction occurs in the gas detection element. It can be said that this occurs, that is, the response speed depends on the thickness of the sensitive part that greatly contributes to the diffusion time of the detection gas. Since the gas detecting element of the present invention has a small volume and a thin sensing portion, the time required for the detected gas concentration reaching the inside of the gas detecting element (particularly in the vicinity of the platinum coil wire) to reach an equilibrium concentration can be short, Since the conventional gas detection element has a large volume, it takes a long time for the gas detection output to become constant, which allows the response speed to be increased. In the present invention, the reason why the distance d4 from the coil portion 2a to the outer surface of the sensitive portion 3 is 50 μm or less is that the response speed is 10 times or more the response speed of the conventional gas detection element. In consideration of the minimum condition, the situation includes the situation where the platinum coil wire 2 is exposed on the outer surface of the sensitive section 3 (the average distance is 0 μm).

<3> In addition, the relationship between the average secondary particle diameter of the semiconductor containing tin oxide as the main constituent of the sensitive part 3 and the temporal stability of the gas sensitivity (output) of the gas detection element is investigated. After a while, it became like Figure 4. From FIG. 4, it is considered that the smaller the average secondary particle diameter of the particles forming the sensitive part 3 is, the better the adhesion between the particles and the platinum coil wire is, and the long-term stability is obtained. 3 to 0.8 μm
Within the range, it is practically preferable since the particles have both ease of production, output stability, and sufficient response speed.

<4> Further, a poisoning test was conducted on the sensitive part 3 when the gas detecting element detects a combustible gas. First, when the change in gas sensitivity (output) when the gas detection element was poisoned with hexamethyldisiloxane was measured under the gas detection conditions of the previous embodiment, the results of FIG. It became so. From FIG.
It has been found that this gas detection element has a strong resistance to poisoning by hexamethyldisiloxane. Next, each gas detection element was exposed to high-concentration hydrogen gas, and changes in the output characteristics of the gas detection element before and after the exposure were examined. It should be noted that Table 3 also shows the results of similarly examining the change in the output characteristics of the above-described conventional gas detection element.

[0020]

[Table 2]

[0021]

[Table 3]

From Table 2, it was found that the gas detecting element of the present invention has characteristics that it is less likely to deteriorate even with a high-concentration gas and a stable output is easily obtained. This is because the response speed is fast and the gas detection element itself is set to be kept at a high temperature for a short time, which synergistically acts.

[Other Embodiments] In the previous embodiment, the platinum coil wire 2 was used as the noble metal wire coil, but instead of this, a platinum rhodium alloy wire, zirconium-stabilized platinum wire, or other resistance value associated with gas detection is used. Any coil of noble metal wire that can detect changes may be used. Further, the distance d4 from the coil portion to the outer surface of the sensitive portion is expressed by the equation 1 with the minor axis dimension of the outer diameter of the sensitive portion 3 being d3 and the diameter of the coil portion 2a being d1.

[0024]

## EQU1 ## d4 = (d3-d1) / 2

[Brief description of drawings]

FIG. 1 is a partial cross-sectional perspective view of a gas detection element according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a gas detection device.

FIG. 3 is a graph showing an example (response speed test) of the present invention.

FIG. 4 is a graph showing an example (stability over time) of the present invention.

FIG. 5 is a graph showing an example (poisoning stability) of the present invention.

[Explanation of symbols]

 2 noble metal wire coil 2a coil part 3 sensitive part 4 power supply part 6 circuit switching means 7 control device d2 major axis d3 minor axis

Claims (6)

[Claims] 1. A hot-wire type semiconductor gas detecting element, comprising a sensitive part formed of a semiconductor containing tin oxide as a main component, covering the noble metal wire coil, wherein the sensitive part has a major axis of a minor axis. 1.5 times or less and the volume is 6.5 × 1
A hot-wire semiconductor gas detector which is formed to have a size of 0 ^-5 mm ³ or more and 8.2 × 10 ^-3 mm ³ or less, and a distance from the coil portion of the precious metal wire coil to the outer surface of the sensitive portion is 50 μm or less. element. 2. The average secondary particle diameter is 0.3 μm or more and 0.8.
The hot wire semiconductor type gas detection element according to claim 1, wherein the sensitive portion is formed by sintering a semiconductor containing tin oxide having a size of not more than μm as a main component. 3. A hot wire semiconductor gas detecting element is incorporated in a gas detecting circuit, and a voltage supply section for supplying a voltage to the gas detecting circuit is provided to detect the output from the hot wire semiconductor gas detecting element. The gas detection device configured as described above, wherein the gas detector is a hot wire semiconductor type gas detection element.
2. A gas detecting device using the hot-wire semiconductor type gas detecting element of 2 and configured so that power can be supplied to the voltage supply unit by a battery. 4. ON for supplying electric power to the gas detection circuit
State and OF for stopping the power supply to the gas detection circuit
A circuit switching means for alternately switching between the F state and the F state is provided, the duration of the ON state is set to 1 second or less, and the time ratio between the ON state and the OFF state (ON state / OFF state) is 1/10 or less. The gas detection device according to claim 3, further comprising a control device for controlling the gas detection device. 5. An ON circuit for supplying power to the gas detection circuit
State and OF for stopping the power supply to the gas detection circuit
A circuit switching means for alternately switching between the F state and the F state is provided, the duration of the ON state is set to 0.5 seconds or less, and the time ratio between the ON state and the OFF state (ON
5. The gas detection device according to claim 3, further comprising a control device for controlling the (state / OFF state) to 1/40 or less. 6. The gas detection device according to claim 4, wherein the controller is configured to maintain and control the hot-wire semiconductor gas detection element at a set temperature of 350 ° C. or higher and 550 ° C. or lower. apparatus.