JPS63109358A - Sensor and its preparation - Google Patents

Abstract

PURPOSE:To miniaturize a sensor, by a method wherein heat resistant insulating coating is applied to the surface of a metal heat generator and an atmosphere responsive substance layer is provided on said coating and at least one electrode is connected to said layer. CONSTITUTION:A sensor main body 10 is constituted by supporting an atmosphere responsive substance layer 20 by the surface of a metal heat generator 14 to which heat resistant insulating coating 18 is applied and connecting a pair of electrodes 24, 26 to said substance layer 20. As the material quality of the heat generator 14, both of a noble metal and a base metal are used but one having not only high durability against an atmosphere such as heat resistance and oxidation resistance or heat resistance and reduction resistance but also high resistance and stable in a resistance value is pref. As the material quality of the coating 18, metal oxide such as alumina is pref. The material quality of the substance layer 20 may be determined corresponding to a component to be detected and, for example, when combustible gas is detected, a metal oxide semiconductor composed of SnO2 is used. The electrodes 24, 26 are connected to the substance layer 20 by a fritless gold paste 28. By this method, the sensor main body can be miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a sensor for detecting atmospheric components such as flammable gas, toxic gas, oxygen, water vapor, etc., and a method for manufacturing the sensor. The present invention particularly relates to a sensor in which a metal heating element as a heater is used as a support for the sensor, and a method for manufacturing the same.

[Prior art] There are basically two types of sensors used to detect atmospheric components.
There is a seed shape. In the first one, the atmosphere sensitive material is sintered into a mass and a heater and electrodes are attached. In the second one, an insulating substrate supports an atmosphere sensitive material, to which a heater and electrodes are attached. All of them have complex structures, which impose restrictions on mass production, miniaturization of the sensor, and heat capacity of the sensor.

These restrictions can be overcome if a heater can be used as a support for the sensor and a layered atmosphere-sensitive material can be supported on the heater. That is, it becomes unnecessary to connect a heater or an electrode to the bulk sintered body. Furthermore, an insulating substrate is not required. There is no need for a lead to connect the heater provided on the insulating substrate, usually a vapor deposited film or printed film such as PT, to the outside. These reduce the size of the sensor and reduce its heat capacity. In addition, the sensor does not have a sintered body of atmosphere-sensitive material or an insulating substrate.
The heater serving as a support for the sensor only needs to be able to support a very small weight.

[Problems of the Invention] An object of the present invention is to provide a sensor in which a heater is used as a support for the sensor and an atmosphere sensitive material layer is supported on the heater, and a method for manufacturing the same.

Structure of ER Light In the present invention, a heat-resistant insulating coating is applied to the surface of a noble metal such as PT or Pd-Ir alloy, or a base metal such as Fe-Cr-A1 alloy or Ni-Cr alloy, to form a metal heating element. Such coating is done by plasma CVD.

It can be provided by sputtering, ion plating, vapor deposition, or CVD, or by coating and baking a sol-like substance such as alumina sol.

By selecting the manufacturing conditions for the coating, it is easy to obtain a dense coating that is firmly bonded to the metal. A sensor can then be formed by providing an atmosphere sensitive material layer on the coating.

The atmosphere-sensitive substance and the metal heating element are separated by an insulating coating, and can be separated from each other. Furthermore, many atmosphere-sensitive substances are metal oxides, and their bond strength to metals is low.

However, the insulating coating is usually made of ceramic, and there is almost no possibility that the atmosphere-sensitive material will fall off or peel off.

The shape of this sensor is then determined by the metal heating element itself,
It can be made extremely small. As a result, the heating element is large enough to support its own weight, and the sensor becomes smaller and its heat capacity decreases.

The production of such senna is generally carried out as follows.

l) Apply a heat-resistant insulating coating to the surface of the metal heating element, leaving an exposed portion.

2) Providing an atmosphere sensitive material layer on the coating.

3) Connecting electrodes to the atmosphere sensitive material layer. Note that the electrodes may be attached before or after providing the atmosphere sensitive material layer.

4) Connect the heating element and electrodes to the stem to enable connection with the outside.

The more complex of these steps is the attachment of the electrodes and their connection to the stem. However, these steps are still necessary even for conventional sensors, such as those in which a film-like atmosphere-sensitive material is provided on an insulating substrate. All other processes are simple, can be handled uniformly, and are highly suitable for mass production.

[Example] Sensor structure FIGS. 1 to 3 show basic examples. In FIG. 1, (2) is a sensor, and (4) is a housing, which is covered from above with a cover (not shown) to provide explosion protection and protection for the sensor. (6) is a heater stem fixed to the housing, and (8) is an electrode stem also fixed to the housing. (10) is the sensor body, which has an atmosphere sensitive material layer (20
), and a pair of electrodes (24) are supported on the sensitive material layer (20).
), (26) are connected. The sensor body (10) is
It is accommodated in the hollow part of the housing (4).

Moving on to Figures 2 and 3, (14) is Pt1Ir.

Noble metals such as Pd8O-1r20, Pt-ZGS (ZrO* particles precipitated at the grain boundaries of Pt), W, F
It is a metal heating element made of base metal such as e-Cr-Al, Ni-Cr, etc. The material of the heating element (14) may be a noble metal or a base metal, but it is preferably one that has high durability against the atmosphere such as heat resistance, oxidation resistance, heat resistance and reduction resistance, high resistance, and stable resistance value. Among these, a high-resistance base metal heating element is preferred, and Kanthal (an Fe-0r-A1 alloy manufactured by Gadelius, Sweden; Kanthal is a trademark of Gabrius) was used in the examples. The heating element (14) is wire-shaped here,
The wire diameter supports the atmosphere sensitive material layer (20) and the electrode (
24) and (26) can be connected. Specifically, a wire diameter of about 10 μm is sufficient, but in consideration of the difficulty of wire drawing, a diameter of about 20 to 80 μm is preferable.

The heating element (14) may be coated with a good conductor such as gold (
16). This is because the heating element (14) generates heat in a negative manner, and the heat generated near the stem (6) is not utilized effectively. That is, the resistance of the portions that cannot be directly used for heating the atmosphere sensitive material layer is reduced, thereby reducing power consumption. Incidentally, the good conductor coating (16) may be provided outside the insulation coating, which will be described later.

In that case, the heating element (14) and the good conductor coating (16) are connected at an appropriate position. The heating element (
If it is more important to increase the resistance value of 14),
Naturally, it is not necessary to provide a good conductor coating (16).

(18) is a heat-resistant insulating coating, which is provided on the surface of the heating element (14), leaving a connection part such as welded to the stem (6). The coating (18) is made of a material that is stable in the atmosphere in which it is used and does not react with the heating element (14) or the atmosphere-sensitive material layer described below. The coating (18) has a high adhesion strength to the heating element (14) and has a high insulation resistance between the heating element (14) and the atmosphere sensitive material layer described below. Materials for the ff1 (18) include metal oxides such as alumina and silica, S
r Cs S 13N4. A ceramic such as BNs is used. Among these, metal oxides such as alumina and silica are preferred. Note that insulating property here means that the insulation resistance is sufficiently large compared to the internal resistance of the atmosphere sensitive material layer. For example, when using low resistance 5nOy as the atmosphere sensitive material layer, high resistance Tidy is used. It is also possible to use it as an insulating coating (18). Another function of the covering (18) is to shield and protect the heating element (14) from the atmosphere.

Any thickness of the coating (18) can be used as long as sufficient adhesion strength and insulation properties are obtained. The preferred thickness is 50
A-10μ, more preferably 100A to 5μ.

(20) is an atmosphere sensitive material layer. The material may be determined depending on the component to be detected; for example, when detecting flammable gas or toxic gas, a metal oxide semiconductor such as 5nOa, In2O3, or FetO+ is used. Also, when detecting O7, BaSnO3, LaN1ps, some N)
uses a metal oxide semiconductor such as NiO. In addition, when detecting the humidity in the atmosphere, MgCr, O, or TiO2
Use ceramics such as These devices physically adsorb water vapor and can detect humidity from the electrical conductivity of the adsorbed water. In the case of humidity detection, as is well known, the sensitive material layer (20) is contaminated by dust and oil in the atmosphere, and the sensitive material layer (20) is contaminated by dust and oil in the atmosphere.
0) to remove contamination (necessary).Other materials include antimonic acid (Hts bt
A proton conductor such as o e) or antimony phosphate (H8bPffiO,) is used. These proton conductors generate an electromotive force due to the difference in concentration of H6, and can be used for Ht detection. In this case, for example, one of the electrodes is isolated from the atmosphere, and a difference in hydrogen concentration is created between the two electrodes to generate an electromotive force.

That is, the material of the atmosphere sensitive material layer (20) may be any material whose electrical characteristics change depending on the atmospheric components.

The thickness of the atmosphere sensitive material layer (20) may be within a range that can support the heating element (14). For example, the sensitive material layer (20
) is formed by vacuum evaporation, sputtering, etc.
The preferred thickness is 100A to 5μ, and in the case of powder coating or dipping, the thickness is preferably 1μ to 50μ. Note that the atmosphere sensitive material layer (20) itself is already well known and can be freely modified within the range of known techniques.

(24) and (26) are electrodes, and here gold wires with a wire diameter of about 20 μm are used. The electrodes (24), (26) are covered with a layer of sensitive material (20) by fritless gold paste (28).
) and fixed to the stem (8) by welding. The electrodes (24), (26) may be formed on the insulating layer (18) and then provided with the sensitive material layer (20).

Moving to FIG. 4(d), (32) is a cover, and (3
4) is a ventilation hole made of wire mesh, which is fixed to the housing (4) to complete the sensor (2).

The structure of such a sensor can be modified in various ways.

The sensor (52) shown in FIG. 5 eliminates the gold conductor coating (16) and emphasizes increasing the resistance of the heater rather than reducing power consumption. Further, in this sensor (52), a gold film-like electrode (30) is provided on the insulating coating (18) by vapor deposition or the like, and this is used as the electrode (24).

(26). This is intended to improve the connection between the atmosphere sensitive material layer (20) and the electrodes.

In the sensor (62) shown in FIG. 6, the heating element (14) also serves as an electrode, and the insulating coating (18) is placed under the sensitive material layer (20).
), the sensitive material layer (20) is connected to the electrode (24) and the heating element (14).

Furthermore, in the sensor (72) shown in FIGS. 7 and 8, a plate-shaped heating element (15) is used, a heat-resistant insulating coating (I9) is applied, and an atmosphere-sensitive material layer (21) is applied by printing or the like on top of the heat-resistant insulating coating (I9). It is set up. Furthermore, the area of the plate-shaped heating element (15) is reduced in the middle, thereby reducing concentrated heat generation in the center and heat loss due to heat conduction. That is, the heating element (15) is provided with two constrictions (76) in the middle to reduce loss due to heat conduction. Further, the amount of heat generated in this portion is increased to uniformly heat the center portion (74).

Furthermore, the outer area of the constricted portion (76) is increased to suppress heat generation in this portion.

sensor manufacturing A method for manufacturing the sensor will be explained based on FIG.

Of course, this is only one example of the manufacturing method and does not exclude other manufacturing methods. A wire (14) of an appropriate diameter is prepared, gold paste is printed or gold is deposited at predetermined intervals, and a good conductor coating (16) is provided (FIGS. 3a and 3b).

Next, the position corresponding to the welded part to the stem (6) is left by masking etc., and a heat-resistant insulating coating (18) is provided (
Figure 3C). The most preferred methods for forming the coating (18) are plasma CVD, sputtering, and ion plating. In the case of plasma CVD, for example, an organic compound such as aluminum alkoxide is injected into plasma such as Ar, and then sprayed onto the wire (14) to complete the coating. In the case of sputtering, the coating is provided, for example, by reactive sputtering of aluminum in a low oxygen partial pressure. The same applies to ion plating. The insulating coating (18) can be provided by oxidizing a deposited aluminum film, applying and sintering alumina sol, or thermally decomposing aluminum isopropoxide AI(0-CH-(CH3)t)a.

The adhesion strength and insulation strength of the coating are determined by plasma CVD.

Sputtering and ion plating are almost equivalent,
Vapor deposition is next, followed by sol calcination, which is lower. Thermal decomposition of organic compounds such as isopropoxide is the simplest method in the laboratory, but it has the lowest adhesive strength and dielectric strength. The problem with sol firing and thermal decomposition of organic compounds such as isoproboxide is that many pinholes remain in the film, and the pinholes must be removed by repeating sol application and firing or thermal decomposition of the organic compound 3 to 10 times. Filling improves adhesion and dielectric strength. For example, in the case of plasma CVD, an alumina film of 50 A is sufficient to make the resistance between the electrode (24) and the heating element (14) more than IMΩ. However, in the case of alumina sol, it was necessary to perform coating and firing about 3 to 5 times. Further, when impregnating aluminum isopropoxide and thermally decomposing it to form an alumina film, it was necessary to repeat the impregnation and firing about 7 to 10 times.

For example, metal oxides such as alumina and silica are used as the material of the insulating coating, and when used in a neutral atmosphere, 5iC
1SisN+, BNSTiC, etc. may also be used. Although the above example has been explained using alumina, the same effect can be achieved by replacing alumina sol with silica sol and replacing aluminum isopropoxide with tetraethyl silicate or the like.

When plasma CVD was used, sufficient insulation strength and adhesion strength were obtained even with a 50A alumina coating. Therefore, the thickness of the coating is preferably 50. A or more, preferably 10
Must be 0A or more. The upper limit of the coating thickness has no essential meaning, and is preferably 10 μm or less, more preferably 5 μm or less.

Masking of the coating (18) is carried out by coating resin such as nylon on positions where coating is not required to prevent the film from adhering, or by partially etching the adhered film. For example, in the case of etching an alumina film, a photoresist is applied after the film is formed, and the resist is removed by exposure to light, followed by etching. In the case of alumina, HF is used as the etching solution.
(room temperature etching) and warm phosphoric acid are preferred. Also in the case of silica, HF at room temperature is preferred.

The atmosphere sensitive material layer (20) is formed by vapor deposition, sputtering,
Provided by powder coating, printing, or depping (
Figure 3 d). Also, materials that are converted into these substances by thermal decomposition or the like may be decomposed on the coating (18).

After providing the sensitive material layer (20), the electrode (24).

(26) is connected (Fig. 3e) and housed in the housing (4) to complete the sensor (2). The housing will be explained with reference to FIG. In the figure, (80) is a series of lead frames, on which stems (6) and (8) are provided in advance. The housing (4) is fixed to the lead frame (80) by welding or the like to obtain the structure shown in FIG. 4(a).

A heating element (14) provided with a sensitive material layer (20) is fixed to this by welding or the like, and then electrodes are attached (FIG. 4b).

The electrodes (24) and (26) are attached using, for example, gold paste (28), and the paste is solidified by heat treatment at about 600 to 800°C. Also, the stem (8) has an electrode (
24) and (26) are connected by welding or the like. Note that the heating element (1
After welding 4) to the stem (6), the sensitive material layer (20)
Alternatively, the electrodes (24) and (26) may be attached to the stem after being attached to the heating element (14).

After these operations, the upper cover (32) with the ventilation hole (34) is welded to the housing (4) (Fig. 4C), the excess part of the lead frame is cut, the stem is bent, and the sensor ( Complete 2) (Figure 4 d). These steps, except for setting the electrodes (24) and (26), can be carried out almost automatically, and a sensor with uniform characteristics can be obtained, as well as being highly suitable for mass production.

Auxiliary circuits The problem with these sensors is the resistance of the heating element (14).
□The resistance value is at a low point. That is, the formation of the atmosphere sensitive material layer (20) and its characteristics are well known for thin-film and thick-film sensors, and the problem centers on the resistance value of the heating element. The operating temperature of the sensor is 3 in the case of a gas sensor.
The temperature is often around 00 to 400°C, and even in the case of heat cleaning of humidity sensors, it is often around 300'C. In the case of proton conductors, the operating temperature is often from room temperature to about 200°C, and when used at room temperature, heat cleaning is usually performed at about 300°C. Table 1 shows the heater characteristics when the distance between the stems (6) was 2 mm and a wire-shaped heating element was used.

Table l Heater characteristics * Material and wire diameter (μ) Resistance value (Ω) Power (mW) Pd
-Ir 20μ 3 80 (without gold coating) Pd-Ir 20μ 2 50 (with gold coating) Pt 10μ 3 60Fe-
Or-A1 40μ 3.3 100* The resistance value indicates the resistance value at room temperature, and the power indicates the power required for heating to 300°C. Pd-Ir is an alloy of Pd80wt% and Ir20wt%, Fe-Cr -The Al alloy is Kanthal from Gabrius, and its composition is approximately Fe70wt%, Cr25wt%, A
15 wt%, and electrodes (24) and (26) are both gold wires with a wire diameter of 20μ.

If the length of the heating element (14) is increased unnecessarily, the resistance value of the heater can be increased. However, this complicates the structure of the sensor. Next, the conditions for obtaining 80 mW of power with a 3Ω resistor are approximately 500 mV and 170 mA. This makes it difficult to stabilize the power supply due to the low voltage. Further, if the voltage is lowered from a normally used power supply of about 5V to 0.5V, the voltage drop in the stabilized power supply will be large, leading to power loss and an increase in the size of the power supply. Furthermore, the required current is 100~
The power supply capacity is as large as 200mA, and the capacity of the power supply will continue to increase.

FIG. 9 shows an auxiliary circuit that takes this point into consideration. The sensor in the figure uses the two 1i poles (24) and (26) in Figure 1, and (Eb) is a stabilized power supply of about 5V, and its output (
Vcc) is used as the power source for each part of the circuit. (R1) is lOΩ
protection resistance, ('rr+) is the transistor, (C1
) is a capacitor of about 100μF, (Trt) is a switch such as a transistor, (80) is an oscillation circuit that generates a pulse with a duty ratio of about 1/100 at a frequency of about IKHz, and (R1) is a load resistance of about 100KΩ. .

(C2) is a capacitor (a capacitor for smoothing the output of Cυ, (Dl) is a Zener diode for generating reference potential, (
A+) is an error amplifier.

The operation of this circuit is shown in FIG. The output of the power supply (E'b) is charged to the capacitor (C1) via the protection resistor and the transistor (Try). The voltage of the capacitor (CI) is taken out by the capacitor (C2), and compared with a reference potential, the transistor (Trt) is controlled and the voltage of the capacitor (C8) is always kept constant. When the transistor (Trt) is turned on, the heater (14) is energized in a pulsed manner to heat the sensor. In this case, since the capacitor (C1) is used, the load on the power supply (Eb) is almost constant, and the load current ranges from 5V180mW to 2
It becomes about 0mA. In other words, the load current is small and the power supply (Eb
) is less of a burden. The sensor (2) is heated in pulses, and the pulses are approximately IKHz, and the heating is performed at sufficiently shorter intervals than the thermal time constant (approximately 100 msec) of the sensor. Therefore, the load current of the power supply is small, power loss due to voltage drop is small, and sensor temperature is kept constant. In preparation for the capacitance of the capacitor (C8) changing over time, the time constant between the capacitor and the resistor (14) is set to 1.
The on-time of the pulse should be sufficiently longer than the on-time of the second pulse. In this example, the capacitance of the capacitor is 100 μF, the resistance is 3Ω, and the time constant is about 300 μsec. On the other hand, the width of the pulse is 10
μ5ea is 1 degree, and the duration of the pulse is a capacitor (C
, ) is constant regardless of its capacity. The preferred circuit conditions are that the on-off frequency of the transistor (Trt) is at least 5 times the thermal time constant of the sensor, and the capacitor (C2)
The capacity of the heater (14) is at least 5 times the pulse width in terms of time constant. The pulse width of the transistor (Trt) is automatically determined from the on-off frequency and the duty ratio required for heating. Here, the error amplifier (A1) may not be provided, and its input may be a smoothed voltage applied to the heating element (14). There are also two transistors (Trυ, (Try)
can be replaced with an appropriate switch, and the transistor (Try) may not be provided.

Next, a load resistor (R1) is connected to the atmosphere sensitive material layer (20), and detection is performed from its output (Vout). Note that in the case of a humidity sensor, the heater is not normally used, and the heater may be energized when heat cleaning is performed. Furthermore, in a sensor that uses an electromotive force such as a proton conductor, the electromotive force of the atmosphere sensitive material layer (20) may be measured.

Figure 1O shows a sensor (14) that also serves as an electrode.
62) is shown. In this sensor, the voltage applied to the atmosphere sensitive material layer (20) is derived from the heater voltage.

Therefore, the sampling circuit (82) is operated with a pulse synchronized with the turning on of the transistor (Trt) to remove noise caused by turning on and off the power supply.

Such sampling circuits are well known, and may also be simple integration circuits using capacitors and resistors.

Sensor characteristics SnO! The sensor characteristics will be explained using a gas sensor as an example. Fe-Cr-A1 alloy with a wire diameter of 40μ (diameter) (
14) was coated with an alumina coating (18) having a thickness of about 1M by plasma CVD. This is coated with a 5nOt film (SnO
An atmosphere-sensitive material layer (20%
). Electrodes (24) and (26) with a wire diameter of 20 μm were attached using gold paste (28) to complete the sensor.

The resistance value of the heating element (14) at room temperature is 3.3Ω, 300℃
Heating power is 100mW, thermal time constant is 100m5ec
It was about. It is clear that by making the wire diameters of the heating element (14), electrodes (24), etc. smaller, the power consumption, heat shield, thermal time constant, and resistance value of the heater can be further improved. In addition, the insulation resistance between the electrode and the heating element was approximately IOMΩ, and the insulation resistance did not change even though the heating element (14) was energized and the sensor was subjected to thermal cycles between room temperature and 800°C 100 times. .

Note that base metal alloy wire such as Fe-0r-A1 alloy is 1100
Under SO3, H, and S of about 0 pp, it corrodes gradually.

However, when the alumina coating was applied, the alloy wire (14) was isolated from the atmosphere and corrosion was prevented.

Furthermore, the adhesion strength of the S n O film to the metal surface is low;
If left as is, the film will peel off due to stress between the electrodes (24)', (26) and the SnO film. However, applying an alumina coating improves adhesion strength and prevents peeling of the film.

Furthermore, various additives may be added to the Sn0w film as necessary, and the surface thereof may be coated with a suitable oxidation catalyst to remove interfering gases by oxidation.

11 each in air using an atmosphere of 20°C and 65% relative humidity.
The resistance values were measured in 000 pp of ethanol, CO, H2, and isobutane. Isobutane is a representative flammable gas. Figure 12 shows the response characteristics to ethanol, CO, etc. at 300°C. Table 2 also shows 300℃
Table 3 shows the resistance values at 400° C. in each atmosphere.

2.4M ethanol in air 40K CO200K H, 350 Table 3 Sensor characteristics 400℃ In air 1.2M ethanol 50 and isobutane 400K) There is a possibility that the atmosphere sensitive material layer (20) may be poisoned due to the reaction between the base metal component and the atmosphere sensitive material layer (20).

However, in the present invention, the atmosphere sensitive material layer (20) and the reaction (
14) is separated by a heat-resistant insulating coating (18), and there is no risk of poisoning the atmosphere 1 relaxing material layer (20).

[Effects of the Invention] The present invention provides a sensor in which a heater is used as a support for the sensor and an atmosphere sensitive material layer is supported on the heater, and a method for manufacturing the same. Such a sensor is: l) small;
2) It has a small heat capacity, 3) It has a short thermal time constant, 4) It consumes less power, and 5) It is easy to manufacture.

[Brief explanation of the drawing]

FIG. 1 is a front view of the sensor of the example. FIG. 2 is a sectional view showing the sensor body in the example. FIGS. 3(a) to 3(e) are perspective views showing the manufacturing process of the sensor of the example. FIGS. 4(a) to 4(d) are front views showing the assembly process of the sensor of the example. FIG. 5 is a sectional view showing a sensor main body in a modified example. FIG. 6 is a sectional view showing the sensor body in a further modified example of the pond. FIG. 7 is a front view of main parts of a sensor according to another embodiment. FIG. 8 is a sectional view in the direction ■-■ of FIG. 7. FIG. 9 is a circuit diagram of an auxiliary circuit suitable for the sensor of the embodiment. FIG. 1θ is a circuit diagram of another auxiliary circuit. FIG. 11 is a characteristic diagram of the ancillary circuit shown in FIGS. 9 and 10. FIG. 12 is a characteristic diagram showing the gas sensitivity characteristics of the sensor of the example.

Claims (11)

[Claims] (1) In addition to applying a heat-resistant insulating coating to the surface of the metal heating element,
A sensor characterized in that an atmosphere-sensitive material layer is provided on the coating, and at least one electrode is connected to the atmosphere-sensitive material layer. (2) The sensor according to claim 1, wherein a metal heating element is used as a support for the atmosphere sensitive material layer. (3) The sensor according to claim 1, wherein the metal heating element is a metal wire. (4) In the sensor according to claim 1, A sensor characterized in that the metal heating element is a metal plate. (5) The sensor according to claim 1, wherein a part of the metal heating element is coated with a conductive coating. (6) A step of applying a heat-resistant insulating coating to the surface of the metal heating element leaving an exposed part, a step of providing an atmosphere sensitive material layer on the coating, and at least one electrode for detecting the characteristics of the atmosphere sensitive material layer. A method for manufacturing a sensor, comprising the steps of: providing a metal heating element; and connecting an exposed portion of a metal heating element to a stem. (7) The method for manufacturing a sensor according to claim 6, characterized in that the heat-resistant insulating coating is provided by plasma CVD. (8) The method for manufacturing a sensor according to claim 6, characterized in that the heat-resistant insulating coating is provided by sputtering. (9) The method for manufacturing a sensor according to claim 6, characterized in that the heat-resistant insulating coating is provided by ion plating. (10) A method for manufacturing a sensor according to claim 6, characterized in that a heat-resistant insulating coating is provided by applying a sol-like substance and firing. (11) The method for manufacturing a sensor according to claim 6, characterized in that a part of the metal heating element is coated with a conductive coating, and then a heat-resistant insulating coating is coated on the surface of the heating element. manufacturing method.