JPH07104308B2 - Sensor and manufacturing method thereof - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a sensor for detecting atmospheric components such as flammable gas, toxic gas, oxygen and water vapor, and a method for producing the same. In particular, the present invention relates to a sensor in which an inner heating element as a heater is used as a support for the sensor, and a manufacturing method thereof.

[Prior Art] A sensor used to detect an atmospheric component is basically 2
There are seed shapes. In the first, the atmosphere-sensitive material is sintered in a lump and the heater and the electrode are attached. In the second type, an atmosphere-sensitive substance is supported on an insulating substrate, and a heater and electrodes are attached to this. Each of them has a complicated structure and imposes restrictions on mass productivity, miniaturization of the sensor, heat capacity of the sensor, and the like.

These restrictions are overcome if the heater is used as a support for the sensor and a layered atmosphere-sensitive substance can be supported on the heater. That is, it is not necessary to connect a heater or an electrode to the massive sintered body. In addition, the insulating substrate is unnecessary. A heater provided on an insulating substrate, usually a vapor deposition film such as Pt or a printing film,
No need for a lead to connect the device to the outside. Miniaturize these sensors and reduce their heat capacity. Further, since the sensor does not have a sintered body of an atmosphere-sensitive substance or an insulating base, the heater as a support of the sensor is sufficient to support an extremely small weight.

SUMMARY OF THE INVENTION An object of the present invention is to provide a sensor with low power consumption and a manufacturing method thereof.

[Configuration of Invention] In the present invention, a noble metal such as Pt or Pd-Ir alloy, or Fe-
A heat resistant insulating coating is applied to the surface of a base metal such as a Cr-Al alloy or a Ni-Cr alloy to obtain a metal heating element. Metal heating element has a diameter of 10 ~
80μ metal wire. Such a coating is a plasma CV
It can be provided by D, sputtering, ion plating, vapor deposition, CVD, etc., and the film thickness is 50A to 10μ.
And Choosing the manufacturing conditions for the coating makes it possible to easily obtain a coating that is dense and strongly bonded to the metal. Then, a thin film of an atmosphere sensitive material layer, preferably a thin film having a film thickness of 100 A to 5 μ, is provided on the coating to form a sensor.

Then, both ends of the metal heating element are directly connected to an external terminal such as a stem by welding or the like. The external terminal may have any shape as long as it is a terminal for supporting a metal heating element in addition to the stem shown in the embodiment. It is one of the features of the present invention that the metal heating element is directly connected to the external terminal instead of connecting the metal heating element to the external terminal using the lead wire. This is because the metal heating element with a wire diameter (diameter) of 10 to 80 μ has almost the same thickness as the lead wire, and it is difficult to connect the lead wire to the metal heating element itself. This is because there is no point in interposing a lead wire with the external terminal.

The atmosphere-sensitive material and the metal heating element are separated by the insulating coating, so that they can be separated from each other. Moreover, most of the atmosphere-sensitive substances are metal oxides, and the bonding strength to the metal 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. Further, in general, when the base metal heating element is brought into direct contact with the atmosphere-sensitive substance, there is a problem that the atmosphere-sensitive substance is poisoned or deteriorated by the base metal. However, if the surface of the base metal heating element is coated with a heat resistant insulating material, such a problem can be solved.

Next, the shape of this sensor is determined by the metal heating element itself,
It can be very small. As a result, the heating element is sufficient to support the weight of its own weight, the sensor is downsized, and the heat capacity is reduced.

The manufacture of such a sensor is generally performed as follows.

1) A heat-resistant insulating coating is applied to the surface of a metal heating element made of a metal wire having a diameter of 10 to 80 μm, leaving an exposed portion. The heat resistant insulation coating should have a film thickness of 50A to 10μ.

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

3) Connect electrodes to the atmosphere sensitive material layer. The electrodes may be attached before or after the atmosphere sensitive material layer is provided.

4) Connect a heating element or electrode to an external terminal such as a stem to enable external connection. Both ends of the heating element are directly connected to the external terminals.

A complex part of these steps is the attachment of the electrode and its connection to the stem. However, the need for these steps does not change even with a conventional sensor, for example, a sensor provided with a film-like atmosphere-sensitive substance on an insulating substrate. All other processes are simple, can be handled uniformly, and are highly productive.

[Example] Structure of sensor A basic example is shown in Figs. 1 to 3. In FIG. 1, (2) is a sensor, and (4) is a housing, which is covered with a cover (not shown) from above to protect the sensor from explosion. (6) is a heater stem fixed to the housing, and (8) is an electrode stem similarly fixed to the housing. Reference numeral (10) is a sensor body, in which an atmosphere sensitive material layer (20) is supported on the surface of a metal heating element (14) coated with a heat-resistant insulating coating, and the sensitive material layer (20) has a pair of electrodes (24), (2
6) is connected. The sensor body (10) is housed in the hollow portion of the housing (4).

Turning to FIGS. 2 and 3, (14) shows Pt, Ir, Pd80-Ir2.
Noble metals such as 0, Pt-ZGS (Pt crystal grain boundaries having ZrO ₂ particles precipitated) and base metals such as W, Fe-Cr-Al, and Ni-Cr. The heating element (14) is made of precious metal,
Although it may be a base metal, it is preferable that it has high resistance to atmosphere such as heat resistance and oxidation resistance, heat resistance and reduction resistance, high resistance, and stable resistance value. Among these, a high resistance base metal heating element is preferable, and Kanthal (Fe-Cr-Al alloy of Sweden Gadelius Co., Ltd., Kanthal is a trademark of Gaderius Co.) was used in the examples. Here, the heating element (14) has a wire shape, and its wire diameter may be such that it supports the atmosphere sensitive material layer (20) and can connect the electrodes (24) and (26).
A wire diameter of about 10μ is sufficient, and it should be 80μ or less from the viewpoint of power consumption. Considering the difficulty of wire drawing, 20-80
It is preferably set to μ.

If necessary, cover the heating element (14) with a good conductor such as gold (1
6) is provided. This is because the heating element (14) generates heat uniformly and the heat generated in the vicinity of the stem (6) is not effectively used. That is, the resistance of the portion of the atmosphere-sensitive material layer that cannot be directly used for heating is reduced to reduce the power consumption. The good conductor coating (16) may be provided on the outside of the insulating coating described later. In that case, the heating element (14) and the good conductor coating (16) are connected at an appropriate position. When increasing the resistance value of the heating element (14) is more important than saving power consumption, it is natural that the good conductor coating (16) need not be provided.

Reference numeral (18) is a heat-resistant insulating coating, which is provided on the surface of the heat generating element (14), leaving a connection portion such as welded to the stem (6). The material of the coating (18) is stable to the use atmosphere and does not react with the heating element (14) or the atmosphere sensitive material layer described later. The coating (18) has high adhesion strength to the heating element (14),
A material having a high insulation resistance between the heating element (14) and an atmosphere sensitive material layer described later is used. As the material of the coating (18), a metal oxide such as alumina or silica, a ceramic such as SiC, Si ₃ N ₄ , BN, or the like is used. Of these, preferred are metal oxides such as alumina and silica. It should be noted that the insulating property as used herein means having an insulation resistance sufficiently large with respect to the internal resistance of the atmosphere-sensitive material layer. For example, when SnO ₂ having a low resistance is used as the atmosphere-sensitive material layer, a high resistance TiO It is also possible to use ₂ as the insulating coating (18). Another function of the coating (18) is to shield the heating element (14) from the atmosphere and protect it.

The coating (18) may have any thickness as long as sufficient adhesion strength and insulation are obtained. Preferred thickness is 50A-1
It is 0 μ, and more preferably 100 A to 5 μ.

(20) is an atmosphere sensitive material layer. The material may be determined according to the component to be detected. For example, when detecting a flammable gas or a toxic gas, a metal oxide semiconductor such as SnO ₂ , In ₂ O ₃ or Fe ₂ O ₃ is used. When detecting O ₂ , BaSnO ₃ or
A metal oxide semiconductor such as LaNiO ₃ or NiO is used.
Further, when detecting the temperature in the atmosphere, a ceramic such as MgCr ₂ O ₄ or TiO ₂ is used. These substances physically adsorb water vapor, and humidity can be detected from the electric conductivity of the adsorbed water. In the case of detecting humidity, as is well known, the sensitive material layer (20) is contaminated by dust and oil in the atmosphere, and it is necessary to remove the contamination by heat cleaning the sensitive material layer (20). As another material, a proton conductor such as antimonic acid (H ₂ Sb ₂ O ₆ ) or antimony phosphate (HSbP ₂ O ₈ ) is used. These proton conductors generate an electromotive force due to the difference in H ₂ concentration,
It can be used to detect H ₂ . In this case, if collapsed, one of the electrodes is shielded from the atmosphere, a hydrogen concentration difference is formed between the two electrodes, and an electromotive force is generated. That is, the material of the atmosphere-sensitive material layer (20) may be any material as long as its electrical characteristics change depending on the atmosphere components.

The thickness of the atmosphere sensitive material layer (20) may be in a range that can be supported by the heating element (14), and for example, the sensitive material layer (20) is formed by vacuum deposition, sputtering, or the like, and has a thickness of 100A to 5A.
Let μ. The atmosphere-sensitive material layer (20) itself is already known and can be freely changed within the range of known technology.

(24) and (26) are electrodes, and here, a gold wire having a wire diameter of about 20 μ is used. The electrodes (24) and (26) are connected to the sensitive material layer (20) by a fritless gold paste (28) and fixed to the stem (8) by welding. Electrodes (24), (26)
Is formed on the insulating layer (18) and then the sensitive material layer (20)
May be provided.

Moving to FIG. 4 (d), (32) is a cover, and (34)
Is a ventilation hole made of wire mesh, and is fixed to the housing (4) to complete the sensor (2).

The structure of such a sensor can be variously modified.
The sensor (52) in FIG. 5 eliminates the good conductor coating (16) of gold, and emphasizes higher resistance of the heater than saving power consumption. Further, in this sensor (52), a gold film electrode (30) is made on the insulating coating (18) by vapor deposition or the like, and the gold film electrode (30) is connected to the electrodes (24) and (26). This is intended to improve the connection between the atmosphere sensitive material layer (20) and the electrodes.

In the sensor (62) of FIG. 6, the heating element (14) is also used as an electrode, the insulating coating (18) is partially removed below the sensitive material layer (20), and the sensitive material layer (20) is used as an electrode ( 24) and the heating element (14).

In the sensor (72) of the comparative example shown in FIGS. 7 and 8, a plate-shaped heating element (15) is used, and a heat-resistant insulating coating (19) is applied.
An atmosphere-sensitive material layer (21) is provided on it by printing or the like. Further, the plate-shaped heat generating element (15) has a reduced area in the middle to reduce concentrated heat generation in the central portion and heat loss due to heat conduction. That is, the heat generating element (15) is provided with two constricted portions (76) in the middle to reduce the loss due to heat conduction. Further, the amount of heat generated in this portion is increased to uniformly heat the central portion (74). Further, the area outside the constricted portion (76) is increased to suppress heat generation in this portion.

Manufacturing of Sensor A method of manufacturing the sensor will be described with reference to FIG. Of course, this is only one example of the manufacturing method, and does not exclude other manufacturing methods. A wire (14) having an appropriate wire diameter is prepared, and gold paste is printed or gold is vapor-deposited at predetermined intervals to provide a good conductor coating (16) (FIGS. 3a and 3b).

Then, the heat resistant insulating coating (18) is provided by leaving the position corresponding to the welded portion on the stem (6) by masking or the like (Fig. 3c). The most preferable method for forming the coating (18) is plasma CVD, sputtering, or ion plating. In the case of plasma CVD, an organic compound such as aluminum alkoxide is injected into plasma such as Ar and sprayed on the wire (14) to complete the coating. In the case of sputtering, for example, the film is formed by reactive sputtering of aluminum in a low oxygen partial pressure. The same applies to ion plating. Insulating coating (1
8) the oxidation or the vapor-deposited film of aluminum, alumina sol coating and sintering or aluminum isopropoxide _{Al (O-CH- (CH 3} ) , and ₂₎ can be provided in ₃ thermal decomposition.

The adhesion strength and insulation strength of the coating are almost the same in plasma CVD, sputtering, and ion plating, followed by vapor deposition, and lower in sol firing. Pyrolysis of organic compounds such as isopropoxide is the simplest method in the laboratory, but it has the lowest adhesion strength and insulation strength. The problem of baking the sol and thermal decomposition of organic compounds such as isopropoxide is that a large number of pinholes remain in the film. Therefore, sol coating and baking, or thermal decomposition of organic compounds is repeated 3 to 10 times. Filling the holes improves the adhesion strength and the insulation 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) 1 MΩ or more. However, in the case of alumina sol, it was necessary to perform coating and firing about 3 to 5 times. Further, when impregnating aluminum with isopropoxide and thermally decomposing it to form an alumina film, it was necessary to repeat impregnation and firing about 7 to 10 times.

For the material of the insulating coating, use metal oxides such as alumina and silica, and use SiC and S when used in a neutral atmosphere.
i ₃ N ₄ , BN, TiO, etc. can also be used. Although alumina has been described in the above example, if alumina sol is replaced with silica sol and aluminum isopropoxide is replaced with tetraethyl silicate or the like, the same operation can be performed.

When plasma CVD is used, sufficient insulation strength and adhesion strength were obtained even with 50 A alumina coating. Therefore, the coating thickness is preferably 50 A or more, more preferably 100 A 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 performed by coating a resin such as nylon at a position where the coating is unnecessary to prevent the adhesion of the film, 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 a tourist is allowed to remove the resist, followed by etching. In the case of alumina, HF (room temperature etching) or warm phosphoric acid is preferable as the etching solution. Also in the case of silica, room temperature HF is preferable.

The atmosphere sensitive material layer (20) is provided by vapor deposition, sputtering, powder coating or printing, or depping (FIG. 3d). Further, materials which 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 electrodes (24) and (26) are connected (Fig. 3e) and housed in the housing (4) to complete the sensor (2). The housing will be described with reference to FIG. In the figure, (80) is a series of lead frames, and 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 one shown in FIG. 4 (a). The heating element (14) provided with the sensitive material layer (20) is fixed to this by welding or the like, and then the electrode is attached (Fig. 4b). The electrodes (24) and (26) are attached using, for example, a gold paste (28) and heat-treated at about 600 to 800 ° C. to solidify the paste. Also stem (8)
The electrodes (24) and (26) are connected to, for example, by welding. After welding the heating element (14) to the stem (6), the sensitive material layer (20)
May be formed. Alternatively, the electrodes (24) and (26) may be attached to the heating element (14) and then attached to the stem.

After these operations, the upper cover (32) provided with the vent hole (34) was welded to the housing (4) (Fig. 4c), the excess part of the lead frame was cut, the stem was bent, and the sensor (2) is completed (Fig. 4d). These steps can be performed almost automatically except for setting the electrodes (24) and (26), and a sensor having uniform characteristics can be obtained and mass production is also excellent.

Ancillary circuit The problem with these sensors is that the resistance of the heating element (14) is low. That is, the formation of the atmosphere sensitive material layer (20),
Its characteristics are well known as thin film type and thick film type sensors,
The problem concentrates on the resistance value of the heating element. The operating temperature of the sensor is often about 300 to 400 ° C. for the gas sensor and about 300 ° C. for heat cleaning of the humidity sensor. For proton conductors, the operating temperature is room temperature to 200 ° C
The temperature is high, and when used at room temperature, it is common to perform heat cleaning at about 300 ° C. Stem (6),
The heater characteristics are shown in Table 1 for the case where a wire-shaped heating element is used with an interval between (6) of 2 mm.

If the length of the heating element (14) is unnecessarily increased, the resistance value of the heater can be increased. However, this complicates the structure of the sensor. Next, the condition for obtaining a power of 80 mW with a resistance of 3Ω is about 500 mV and 170 mA. This makes it difficult to stabilize the power supply due to the low voltage. Also commonly used 5V
When the voltage is reduced from a power supply of about 0.5V to 0.5V, the voltage drop in the stabilized power supply is large, leading to power loss and upsizing of the power supply. Furthermore, the required current is as large as 100 to 200 mA, and the capacity of the power supply increases more and more.

An auxiliary circuit considering this point is shown in FIG. The sensor shown in the figure uses the two electrodes (24) and (26) shown in FIG.
(Eb) is a stabilized power supply of about 5V, and its output (Vcc) is used as the power supply for each part of the circuit. (R ₁ ) is a protective resistance of about 10Ω,
(Tr ₁ ) is a transistor, (C ₁ ) is a capacitor of about 100 μF, (Tr ₂ ) is a switch such as a transistor, and (80) is 1
An oscillator circuit that generates a pulse with a duty ratio of about 1/100 at a frequency of about KHz, (R1) is a load resistance of about 100 KΩ. (C ₂ ) is a capacitor for smoothing the transfer force of the capacitor (C ₁ ), (D ₁ ) is a Zener diode for generating a reference potential,
(A ₁ ) is an error amplifier.

The operation of this circuit is shown in FIG. The output of the power supply (Eb) is
Via the protection resistor and the transistor (Tr ₁ ) the capacitor (C
₁ ) is charged. The voltage of the capacitor (C ₁₎ is taken out by the capacitor (C _2), as compared to the reference potential, the transistor (Tr ₁₎ is controlled, always the voltage of the capacitor (C ₁₎ is kept constant. When the transistor (Tr ₂ ) is turned on, the heater (14) is energized in a pulsed manner to heat the sensor. In this case, since the capacitor (C ₁ ) is used, the load of the power supply (Eb) is almost constant, and the load current is 5V, 80mW to 20mA. That is, the load current is small and the load on the power source (Eb) is small. The sensor (2) is heated in a pulse manner, but the pulse is about 1 KHz, and heating is performed at intervals sufficiently shorter than the thermal time constant of the sensor (about 100 msec). Therefore, the load current of the power supply is small, the power loss due to the voltage drop is small, and the sensor temperature is kept constant. In preparation for the capacitance of the capacitor (C ₁ ) changing over time, the time constant between the capacitor and the resistor (14) is made sufficiently longer than the ON time of one pulse. In this example,
Capacitor capacity is 100μF, resistance is 3Ω, time constant is 3
It will be about 00 μsec. On the other hand, the pulse width is about 10 μsec,
For the duration of the pulse, the output of the capacitor (C ₁ ) is constant regardless of its capacitance. The preferable circuit conditions are that the on-off frequency of the transistor (Tr ₂ ) is 5 times or more the thermal time constant of the sensor, and the capacity of the capacitor (C ₁ ) is 5 times or more the pulse width as the time constant with the heater (14). is there. The pulse width of the transistor (Tr ₂₎ is turned on - automatically determined from the duty ratio required heating off frequency. Here, the error amplifier (A ₁ ) does not have to be provided, and its input may be a smoothed voltage to the heating element (14). Also, the two transistors (Tr ₁ ) and (Tr ₂ ) can be replaced with appropriate switches, and the transistor (Tr ₁ ) does not have to be provided.

Next, a load resistance (R1) is connected to the atmosphere sensitive material layer (20) and detection is performed from its output (Vout). In the case of the humidity sensor, the heater is not always used, and the heater may be energized when performing heat cleaning. Further, in the case of a sensor using an electromotive force such as a proton conductor, the electromotive force of the atmosphere sensitive material layer (20) may be measured.

Fig. 10 shows a sensor (62) that also uses the heating element (14) as an electrode.
Shows the circuit to. In this sensor, the voltage applied to the atmosphere sensitive material layer (20) is taken out from the heater voltage. Therefore, the sampling circuit (82) is operated by the pulse synchronized with the turning on of the transistor (Tr ₂ ) to remove the noise caused by turning the power on and off. Such a sampling circuit is well known, and may be an integrating circuit using a simple capacitor and resistor.

Sensor characteristics The sensor characteristics will be described by taking a gas sensor using SnO ₂ as an example. An alumina coating (18) having a thickness of about 1 μm was formed on a linear 40 μm (diameter) Fe—Cr—Al alloy (14) by plasma CVD. SnO ₂ film (SnO ₂ 97wt%, catalyst PdO 3wt%)
Was sputtered to form an atmosphere sensitive material layer (20) having a thickness of about 5000A. Wire diameter 20 using gold paste (28)
A sensor was completed by attaching μ electrodes (24) and (26).

The resistance value of the heating element (14) at room temperature was 3.3Ω, the heating power to 300 ° C was 100 mW, and the thermal time constant was about 100 msec. If the wire diameter of the heating element (14) and electrode (24) is made smaller,
It is obvious that the power consumption, heat capacity, thermal time constant, and resistance value of the heater can be further improved. The insulation resistance between the electrode and the heating element was about 10 MΩ, and the heating element (14) was energized to allow the sensor to undergo 100 thermal cycles between room temperature and 800 ° C, but the insulation resistance did not change.

Note that Fe-Cr-Al alloy and other base metal alloy wires have an S content of approximately 1000 ppm.
It is gradually corroded under O ₂ and H ₂ S. However, when the alumina coating was applied, the alloy wire (14) was shielded from the atmosphere and corrosion was prevented. Further, the adhesion strength of the SnO ₂ film to the metal surface is low, and the film is peeled off by the stress between the electrodes (24) and (26) and the SnO ₂ film as it is. However, applying an alumina coating improves the adhesive strength and prevents peeling of the film.

If necessary, various additives may be added to the SnO ₂ film, and the surface thereof may be covered with an appropriate oxidation catalyst to remove the interfering gas by oxidation.

1000ppm in air, using an atmosphere of 20 ° C and 65% relative humidity
The resistance values in ethanol, CO, H ₂ and isobutane were measured. Isobutane represents a flammable gas. The response characteristics to ethanol and CO at 300 ° C are
Shown in Figure 2. Table 2 shows the resistance value in each atmosphere at 300 ° C, and Table 3 shows the resistance value at 400 ° C. Table 2 Sensor characteristics 300 ℃ Atmosphere resistance value (Ω) 2.4M ethanol in air 40 K CO 200 K H ₂ 350 K Table 3 Sensor characteristics 400 ℃ Atmosphere resistance value (Ω) 1.2M ethanol 50 K Isobutane 400 K H ₂ 300 K Supplement Generally, when a base metal heating element (14) is used, the atmosphere-sensitive material layer (20) may be poisoned due to the reaction between the base metal component in the heating element and the atmosphere-sensitive material layer (20). However, in the present invention, the atmosphere-sensitive substance layer (20) and the reaction (14) are separated by the heat-resistant insulating coating (18), and there is no risk of poisoning of the atmosphere-sensitive substance layer (20).

[Advantages of the Invention] In the present invention, a sensor in which a heater is used as a support for a sensor, and an atmosphere-sensitive material layer is supported on the heater, and a method for manufacturing the sensor are obtained. Such sensors are 1) small and
2) Heat capacity is small, 3) Thermal time constant is short, 4) Power consumption is reduced, and 5) Manufacture is easy.

[Brief description of drawings]

FIG. 1 is a front view of the sensor of the embodiment. FIG. 2 is a sectional view showing the sensor body in the embodiment. FIGS. 3A to 3E are perspective views showing manufacturing steps of the sensor of the example. FIGS. 4A to 4D are front views showing the process of assembling the sensor according to the embodiment. FIG. 5 is a cross-sectional view showing a sensor body in a modified example. FIG. 6 is a cross-sectional view showing a sensor body in still another modification. FIG. 7 is a front view of a main part of a conventional sensor. FIG. 8 is a sectional view taken along line VIII-VIII in FIG. 7. FIG. 9 is a circuit diagram of an auxiliary circuit suitable for the sensor of the embodiment. FIG. 10 is a circuit diagram of another auxiliary circuit. FIG. 11 is a characteristic diagram of the auxiliary circuits of FIGS. 9 and 10. FIG. 12 is a characteristic diagram showing gas sensitivity characteristics of the sensor of the example.

 ─────────────────────────────────────────────────── --Continued from the front page (56) Reference JP-A-55-160842 (JP, A) JP-A-48-63786 (JP, A) JP-A-53-96895 (JP, A) JP-A-58- 102144 (JP, A)

Claims (9)

[Claims] 1. A metal heating element made of a metal wire having a diameter of 10 to 80 μ is coated with a heat-resistant insulating coating having a thickness of 50 A to 10 μ, and a thin film of an atmosphere sensitive material layer is provided on the coating to heat the metal. A sensor characterized in that both ends of the body are directly connected to external terminals, and at least one electrode is connected to the atmosphere sensitive material layer. 2. The sensor according to claim 1, wherein a part of the metal heating element is provided with a conductive coating. 3. The sensor according to claim 1, wherein the thickness of the atmosphere sensitive material layer is 100 A to 5 μm. 4. A step of applying a heat-resistant insulating coating having a thickness of 50 A to 10 μ on the surface of a metal heating element made of a metal wire having a diameter of 10 to 80 μ, leaving an exposed portion, and a thin film atmosphere-sensitive substance on the coating. A step of providing a layer, at least one for detecting the characteristics of the atmosphere-sensitive material layer
A method of manufacturing a sensor, comprising: a step of providing individual electrodes; and a step of specially connecting both ends of a metal heating element to external terminals. 5. The method for manufacturing a sensor according to claim 4, wherein a heat resistant insulating coating is provided by plasma CVD. 6. A method of manufacturing a sensor according to claim 4, wherein a heat resistant insulating coating is provided by sputtering. 7. The method of manufacturing a sensor according to claim 4, wherein a heat resistant insulating coating is provided by ion plating. 8. The method for manufacturing a sensor according to claim 4, wherein a heat-resistant insulating coating is provided by applying and baking the sol-like substance. 9. The method of manufacturing a sensor according to claim 4, wherein a part of the metal heating element is provided with a conductive coating, and then the surface of the heating element is provided with a heat-resistant insulating coating. Manufacturing method of a sensor.