JP3041491B2 - Humidity sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a home air conditioner,
The present invention relates to a humidity sensor used as a humidity detecting unit for environmental control in various industries and agriculture, including a dehumidifier, and more particularly to a humidity sensor using a field effect transistor.

[0002]

2. Description of the Related Art Conventional humidity sensors include those utilizing the expansion and contraction of substances, those utilizing changes in electric resistance, and those utilizing changes in capacitance. As a humidity detecting material, magnesium spinel (MgCr ₂ O) is used.
There are polymer films represented by ceramics such as _4- TiO ₂ ) and hydroxyapatite, solid polymer electrolytes, and dielectric polymers.

On the other hand, there is also known a humidity sensor in which a moisture-sensitive layer using a resin is laminated on a gate insulating layer of a field effect transistor, and a change in capacitance that changes according to humidity is detected. Further, a sensor using silicon oxide or aluminum oxide used as a gate insulating film instead of a resin as the moisture-sensitive layer is also known.

[0004]

Among the above-mentioned conventional humidity sensors, those utilizing the expansion and contraction of a substance have to measure a mechanical variable, have a slow response speed, and have difficulty in hysteresis and accuracy. is there. In the case of using electrical resistance, there is a problem especially in the output characteristics, and even if the linearity is improved, the change in resistance has a logarithmic relationship to the relative humidity on a log scale, so a logarithmic conversion circuit is required .
On the other hand, in the case of using the change in capacitance, since the change in capacitance has a proportional relationship with the relative humidity on a linear scale, there is an advantage that post-processing such as logarithmic conversion is unnecessary. However, the reason why the capacitance type sensor has not become mainstream conventionally is that no excellent moisture-sensitive material has been found, such as high cost, poor weather resistance, low output, and low sensitivity.

[0005] In terms of materials, humidity sensors can be roughly classified into ceramic sintered bodies and polymer films (polymer solid electrolyte, dielectric polymer, etc.). Although the ceramic sintered body sensor is excellent in weather resistance, since it is deteriorated by chemical adsorption of water molecules, a sensor using a regeneration heater is often used. Even if the sensor is said to require no heater, its characteristics deteriorate due to long-term use, and it is necessary to remove adsorbed moisture. On the other hand, polymer materials generally have poor heat resistance, including heat resistance, compared to ceramic sensors, and even when various materials are used, there are problems with any of the properties such as hysteresis, responsiveness, moisture sensitivity, and stability over time. is there.

A field-effect transistor humidity sensor using a resin for the gate insulating layer is not suitable for a DC-driven field-effect transistor because when a DC voltage is applied to the gate electrode, the resin undergoes polarization deterioration. Absent. Further, in a sensor using silicon oxide or aluminum oxide used as a gate insulating film instead of a resin as a moisture sensitive layer, the sensitivity at high humidity is poor, and impurities and ions are easily mixed into the moisture sensitive layer. There were drawbacks.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a humidity sensor which eliminates the above-mentioned conventional drawbacks, and which is small in size, has high performance, and can meet the demands for multiple functions and composites.

[0008]

According to the first aspect of the present invention, a moisture-sensitive body whose capacitance changes due to absorption and desorption of moisture is laminated on a gate insulating film of a field-effect transistor element and is connected to an integral structure. In the humidity sensor, a material obtained by sequentially laminating a metal oxide for the first layer, a semiconductive metal oxide for the second layer, and a moisture-permeable electrode for the third layer, wherein the moisture-permeable electrode of the third layer is There is provided a humidity sensor having a function of a gate of a field-effect transistor element.

According to a second aspect of the present invention, there is provided a humidity sensor in which a moisture-sensitive body whose capacitance changes due to adsorption and desorption of moisture is laminated on a gate insulating film of a field-effect transistor element and integrally connected. The moisture-sensitive body has a metal nitride oxide (MN _X O _Y ) (M is a metal, X and Y are arbitrary numbers) in the first layer, a semiconductor metal oxide in the second layer, and a third layer. Wherein a material formed by sequentially laminating moisture-permeable electrodes is used, and the moisture-permeable electrode of the third layer also functions as a gate of the field-effect transistor element.

According to the third aspect of the present invention, the first layer contains a metal oxide or metal nitride oxide (MN _X O _Y ) (where M is a metal, and X and Y are each an arbitrary number). A material formed by sequentially laminating a semiconductor metal oxide on a layer and a moisture-permeable electrode on a third layer is used as a moisture-sensitive body, and the moisture-permeable electrode functions as a gate electrode on a gate insulating film of the field-effect transistor element. A humidity sensor formed by laminating as described above, wherein the metal oxide or the metal nitride oxide in the moisture-sensitive body is formed by a method capable of adjusting the oxidation number of the metal such as reactive sputtering and CVD. Provided is a humidity sensor characterized in that a stoichiometric ratio as an oxide is satisfied on the side in contact with the gate insulating film, and an oxygen excess composition is provided in a thin portion on the side in contact with the semiconducting metal oxide layer. Is done.

[0011]

In the humidity sensor of the present invention, when a constant voltage is applied to the gate electrode of the field-effect transistor element, a channel is formed on the surface of the semiconductor substrate immediately below the gate insulating film by connecting the source region and the drain region, and the channel is formed. Capacitance is formed between the surfaces of the semiconductor substrate where the channels are formed, with the moisture-sensitive layer and the gate insulating layer interposed therebetween.
When water vapor or moisture is adsorbed to the moisture-sensitive layer of such a humidity sensor in accordance with humidity, the effective area of the electrode constituting the capacitance increases, or the distance between the electrodes substantially decreases, and the electrostatic capacitance decreases. The capacity increases. This change in capacitance can be extracted as a change in the output voltage of the field-effect transistor.

The metal oxide layer is a dielectric moisture-sensitive film having a high dielectric constant, and has a property of reversibly adsorbing moisture in the air at a high response speed. When a voltage is applied, the metal oxide layer has a property of absorbing oxygen and self-repairing even if a defect occurs in the oxide layer. On the other hand,
The semiconducting metal oxide layer plays a role of promoting the absorption and desorption of moisture in the air to the surface of the metal oxide layer, and assisting the moisture sensitivity function of the metal oxide layer.

Further, since the semiconducting metal oxide layer is a layer having semiconductor properties, it has a function of injecting electrons as an electrode for the metal oxide layer and an effect of exerting ionic current and thermal action on the metal oxide layer. Accordingly, the metal oxide layer has a function of promoting a self-repair function of a film defect and improving a dielectric breakdown voltage thereof.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a sectional view showing the structure of a humidity sensor using the field effect transistor of the present invention, and FIG. 2 is an enlarged view of a gate electrode portion of the humidity sensor shown in FIG.

As shown in the drawing, the humidity sensor of the present invention has an n-type source region 12 on a p-type silicon substrate 11.
And a drain region 13 are formed, and a gate insulating film 14 is provided on the surface of the silicon substrate 11 between these two regions. A tantalum oxide film 15 as a metal oxide film is formed on the gate insulating film 14, and a manganese dioxide film 16 as a semiconductor metal oxide film is further formed thereon. The tantalum oxide film 15 and the manganese dioxide film 16 constitute a moisture-sensitive layer that adsorbs water vapor or moisture in the atmosphere. A gate electrode 17 is provided on the surface of the manganese dioxide film 16. A source electrode 19 is provided in the source region 12 by partially removing the field insulating film 18, and a field insulating film 1 is provided in the drain region 13.
8 is partially removed to provide a drain electrode 20.
The surfaces of the source electrode 19 and the drain electrode are covered with a nitride film 21 which is an insulating protective film.

The manganese dioxide film 16 is a very porous film as shown in FIG.
Are in contact with the part a, but are not in contact with the part b.

The gate electrode 17 is formed as a porous film by vapor deposition of a platinum film on the porous manganese dioxide film 16 to constitute a moisture-permeable electrode.

The operation of the humidity sensor using the field-effect transistor according to the present invention thus configured is as follows. First, when this sensor is placed in an atmosphere free of moisture, there is no moisture absorption by the manganese dioxide film 16 formed below the gate electrode 17, so that the effective area of the gate electrode 17 is limited to the manganese dioxide film. Only the contact portion a between the substrate 16 and the tantalum oxide film 15 is reduced, and the size becomes smaller.
Next, when this sensor is placed in an atmosphere where moisture is present, that is, in an atmosphere where the relative humidity (RH) is greater than 0%, the moisture in the atmosphere is reduced to the porous manganese dioxide film 1.
6 and reaches the surface of the tantalum oxide film 15 and is also adsorbed to the non-contact portion b between the manganese dioxide film 16 and the tantalum oxide film 15. As a result, the effective area of the gate electrode 17 increases, but the extent of the increase in the effective area with respect to the non-contact portion b is proportional to the relative humidity in the atmosphere where the sensor is placed. Moreover, this effective area changes quickly and reversibly in response to changes in the relative humidity in the atmosphere.

Here, consider the operation of a MOS field effect transistor (hereinafter referred to as a MOSFET).
In the MOSFET, a capacitor is constituted by the silicon substrate 11 and the gate insulating film 14 interposed between the gate electrodes 17. When V _G becomes the gate voltage is applied to the gate electrode 17, polarization occurs in the gate insulating film 14, the charge on the surface of the silicon substrate 11 between the source region 12 and drain region 13 immediately below the gate insulating film 14 is induced , A channel is formed. The width of the channel formed here varies with the amount of induced charge, and the amount of charge is proportional to the magnitude of the voltage across the capacitor. Therefore, the amount of charge Q in the capacitor is given by the following equation.

Q = C · V Normally, Q is changed in a MOSFET, that is, V (= V _G ) is changed in order to change a channel width, but Q is also changed by changing a capacitance C of a capacitor. It is clear from the above equation that it can be changed. The humidity sensor of the present invention focuses on this point,
The capacitance C varies by humidity while maintaining the V _G constant, whereby it is intended to vary the output of the FET.

Incidentally, the capacitance C of the capacitor is generally expressed by the following equation.

Ε = ε ₀ · εS / d Here, ε is the relative dielectric constant of the insulating film, ε ₀ is the relative dielectric constant of air, S is the electrode area, and d is the distance between the electrodes.

From this equation, it is clear that the capacitance C can be changed by changing any one of the relative permittivity ε of the insulating film, the electrode area S, and the distance d between the electrodes. The objective is achieved by changing the effective area S of the electrode according to the humidity.

Next, how the capacitance C changes in the humidity sensor of the present invention shown in FIG. 1 depending on the relative humidity will be described below.

In the humidity sensor of the present invention shown in FIG. 1, since the inter-electrode insulating layers constituting the capacitor are the gate insulating film 14 and the tantalum oxide film 15, their relative dielectric constants are ε ₁ and ε ₂ , respectively. , And their electrical conductivities are σ ₁ and σ ₂ , respectively. The inter-electrode distance d is the sum of the respective thicknesses of the gate insulating film 14 and the tantalum oxide film 15. Next, the area of the contact portion a between the tantalum oxide film 15 and the manganese dioxide film 16 is Sa, the area b of these non-contact portions is Sb, the ratio of Sb covered with moisture is α, and the relative humidity is RH. When expressed in (%), α and the effective area S of the electrode are represented by Expression 1 and the following expression.

[0027]

(Equation 1) S = Sa + αSb Further, the capacitance C of the capacitor including the gate insulating film 14 and the tantalum oxide film 15 which is a two-layer dielectric is expressed by the following equation (2).

[0028]

(Equation 2) Since the second term of the equation (2) has sufficiently small σ ₁ and σ ₂ , it is approximated by the equation (3).

[0029]

(Equation 3) Equation 4 is obtained from the above equations.

[0030]

(Equation 4) It can be seen from Equation 4 that the capacitance C changes according to the relative humidity RH. Incidentally, the amount of charge stored in the gate insulating film 14 and the tantalum oxide film 15 Qco is represented by the following formula Qco = CV _G, the charge Qch induced in the silicon substrate Equation 5

(Equation 5) As represented by the following equation, Qch is proportional to Qco.

(Equation 6) It is represented as Equation 6 shows that the channel width of the MOSFET changes with the relative humidity RH.
Therefore, it can be seen that the change in the relative humidity can be read from the output change of the MOSFET.

FIG. 3 is a sectional view showing a method of manufacturing the humidity sensor of the present invention shown in FIG. First, as shown in FIG. 3A, a silicon oxide film having a thickness of 5000 A is formed on the surface of a p-type silicon substrate 11 by a thermal oxidation method, and the oxide film is removed while leaving the field insulating film portion 18. A new gate oxide film 15 of about 500 A (angstrom, hereinafter A)
). This gate oxide film 15
As shown in FIG. 3B, tantalum oxide (Ta ₂ O)
₅ ) The film 15 is formed by a plasma CVD method.

The conditions at this time are as follows.

Generation temperature; 350 ° C. reaction gas; mixed gas of tantalum chloride, hydrogen and carbon dioxide (TaCl ₅ —H ₂ —CO ₂ ) pressure; 0.2 Torr power / frequency; 60 W / 13.6 MHz generation rate (film thickness) ); 30A (300A) After the film formation, a heat treatment was performed at 800 ° C in vacuum to improve the film quality.

Next, unnecessary portions of the tantalum oxide film 15 are removed and windows of the gate oxide film 15 are opened, and as shown in FIG.
Drain regions 12 and 13 are formed. Then, a source electrode 19 and a drain electrode 20 are formed by depositing aluminum on the field oxide film 18 including these regions.
After that, as shown in FIG.
The entire structure is covered with a silicon nitride film 21 having a thickness of 2 μm except for the formation part. On the tantalum oxide film 15, a manganese dioxide film 16 is formed by an RF sputtering method. At this time, sputtering is performed under the following conditions to make the film porous.

Substrate temperature: 120 ° C. or less Ar gas pressure: 3 × 10 ⁻² Torr RF power; 1.5 kW Film thickness: 6 μm Then 150 so as not to impair both moisture permeability and conductivity.
A gate electrode 17 is formed by depositing platinum with a thickness of A.

In the first embodiment, the moisture-sensitive layer
Where tantalum oxide is used as the metal oxide
Was described, but as a metal oxide, a group IVa gold
Metals of the Va group, excluding vanadium, aluminum and
Using tungsten or oxides of these alloys
Is also good. In addition, as a semiconductor metal oxide,
The case where a gun is used has been described.
Are tin oxide, nickel oxide, ruthenium oxide, oxide
Any one of bismuth, molybdenum oxide or
A plurality may be included .

In the first embodiment, the metal oxide layer is used as the moisture sensitive layer. However, a metal nitride oxide layer can be used instead of the metal oxide layer. Hereinafter, a second embodiment of the present invention using a metal nitride oxide layer as the moisture sensitive layer will be described.

That is, the metal nitride oxide is MN _X O
_Y (M; metal; N; nitrogen; O; oxygen; X, Y; any number). The metal (M) in this composition is a Group IVa metal, a Group Va metal excluding vanadium, aluminum or tungsten, or an alloy thereof. Here, a TaN _X O _Y film was formed by a plasma CVD method under the following conditions using a metal corresponding to M as tantalum.

Generation temperature; 400 ° C. reaction gas; a mixed gas of tantalum chloride, hydrogen, carbon dioxide and ammonia (TaCl ₅ —H ₂ —CO ₂ —NH ₃ ) pressure; 0.2 Torr power / frequency; 60 W / 13.6 MHz Formation rate (film thickness): 30 A (300 A) In this embodiment, the structure and manufacturing method are the same as those in the first embodiment except that an oxide layer of a metal nitride is used as the moisture-sensitive layer. Is omitted.
Therefore, as a semiconducting metal oxide, man dioxide
Instead of gun, tin oxide, nickel oxide, ruthenium oxide
One of aluminum oxide, bismuth oxide, and molybdenum oxide
One or more than one can be used .

In the second embodiment, the temperature dependence of the dielectric film constituting the moisture sensitive layer is reduced by using a metal nitride oxide layer instead of the metal oxide layer as the moisture sensitive layer. We were able to.

FIG. 4 is a graph showing the temperature dependence of the temperature sensor according to the present invention, wherein the horizontal axis represents the temperature and the vertical axis represents the sensor output. In the figure, a solid line A shows the case of the sensor shown as the second embodiment of the present invention, and a broken line B shows the case of the sensor shown as the first embodiment of the present invention.

As can be seen, the temperature dependency of the sensor is further improved by the second embodiment of the present invention. By lowering the temperature dependence of the sensor, the temperature compensating circuit for obtaining the relative humidity can be simplified or eliminated.

FIG. 5 is a sectional view showing a main part of a humidity sensor according to a third embodiment of the present invention. In this embodiment, the moisture-sensitive layer is the first layer 15 'composed of the metal oxide layer or the metal nitride oxide layer shown in the first and second embodiments.
And the semiconductor metal oxide layer 16 shown in the first and second embodiments. The structure of the first layer 15 'has the following characteristics. That is, this first
The layer 15 ′ film satisfies the stoichiometric ratio as an oxide on the e layer on the side contacting the gate insulating film 14, and has an oxygen excess composition on the f layer on the side contacting the semiconductor metal oxide layer 16. The oxidation number of the metal has been adjusted. For example, when using tantalum oxide TaO ₂ as the first layer 15 ′ film, e
The layer is a p-type semiconductor layer satisfying the stoichiometric ratio TaO ₂ , and the f-layer is a p-type semiconductor layer having an oxygen excess composition TaOn (n> 2.5). It is the e layer that satisfies the stoichiometric ratio that acts as a dielectric in this structure, and f
The layers do not contribute to the capacitance. Therefore, Equation 4 shown above
, The capacity C is represented by the following equation (7).

[0044]

(Equation 7) In the third embodiment of the present invention, d in Expression 7 indicates the thickness of the gate insulating film and the thickness of the e layer.
Incidentally, the f-layer, which is a p-type semiconductor, is a layer that is very active against moisture. When a voltage is applied, the moisture-permeable gate electrode 1
7. When moisture permeating the semiconductive metal oxide layer 16 is adsorbed on the f layer, oxygen ions from H ₂ O diffuse from the f layer toward the e layer, and the thickness of the f layer increases. Conversely, when the water adsorbed on the f-layer is desorbed, the supply of oxygen ions is stopped, the diffusion toward the e-layer gradually decreases, the thickness of the f-layer decreases, and finally, the water adsorbed. It decreases to the state without. In other words, due to the increase in relative humidity,
The thickness of the e-layer will decrease, and the decrease in relative humidity will increase the thickness of the e-layer. Here, d _G ; the thickness of the gate insulating film, de; the thickness of the e layer, β; the ratio of decrease of de due to a change in relative humidity, β is expressed by the following equation 8.

(Equation 8) Since d is represented by the following equation, d = d _G + de−βde, rewriting Equation 4 rewrites C as in the following Equation 9.

[0045]

(Equation 9) Then, Qch is expressed by Expression 10 by Qco and Expression 5.

[0046]

(Equation 10) As described above, according to the third embodiment of the present invention, in addition to the change in the effective area of the electrodes similar to that in the first embodiment, the change in the distance between the electrodes is accompanied, so that the humidity change can be detected with higher sensitivity. be able to.

Also in the third embodiment, the moisture-sensitive layer
Instead of tantalum oxide,
Group IVa metals, Va group metals excluding vanadium, aluminum
Oxidation of tungsten or tungsten or their alloys
An object may be used. In addition, as a semiconductor metal oxide,
Instead of manganese dioxide, tin oxide, nickel oxide, oxide
Ruthenium, bismuth oxide or molybdenum oxide
Any one or more of them may be used .

FIG. 6 shows an apparatus in which a temperature sensor is formed on the same chip as an embodiment of combining the humidity sensor of the present invention. Since the humidity sensor portion has the same structure as the sensor of FIG. 1, each component is denoted by the same reference numeral and description thereof is omitted.
The temperature sensor to be combined is composed of a diode composed of an n-type region 31 formed on the semiconductor substrate 11 and an electrode wiring 32 connected to the n-type region 31 through a window provided in the field insulating film 18. Be composed. The surface of the electrode wiring 32 is covered with the silicon nitride film 21.

The temperature sensor can be manufactured by the same process as that incorporated in the humidity sensor manufacturing process. This is an effect of configuring the humidity sensor with a MOSFET.

[0050]

The humidity sensor according to the present invention described above is small in size, excellent in sensitivity, excellent in weather resistance and stability over time,
In addition, a humidity sensor using a field-effect transistor that can meet the demands for multifunction and composite is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a structure of a humidity sensor using a field-effect transistor of the present invention.

FIG. 2 is an enlarged view of a gate electrode portion of the humidity sensor shown in FIG.

FIG. 3 is a cross-sectional view showing a method of manufacturing the humidity sensor of the present invention shown in FIG.

FIG. 4 is a graph showing the temperature dependence of the temperature sensor of the present invention.

FIG. 5 is a sectional view showing a main part of a humidity sensor according to a third embodiment of the present invention.

FIG. 6 is a sectional view showing an embodiment of combining the humidity sensor of the present invention.

[Explanation of symbols]

 Reference Signs List 11 semiconductor substrate 12 source region 13 drain region 14 gate insulating film 15 tantalum oxide film 16 manganese dioxide film 17 gate electrode 18 field insulating film 19 source electrode 20 drain electrode 21 nitride film 31 n-type region 32 electrode wiring

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 27/00-27/24

Claims (10)

(57) [Claims] 1. A humidity sensor in which a moisture-sensitive body whose capacitance changes due to adsorption and desorption of moisture is laminated on a gate insulating film of a field-effect transistor element and is integrated into an integrated structure. The second layer has a semiconductive metal oxide, and the third layer has
A humidity sensor wherein a material obtained by sequentially laminating a moisture-permeable electrode on a layer is used, and the moisture-permeable electrode of the third layer also functions as a gate of the field-effect transistor element. 2. The metal oxide constituting the moisture-sensitive layer,
2. The humidity sensor according to claim 1, wherein the humidity sensor contains a Group IVa metal, a Group Va metal other than vanadium, an oxide of aluminum or tungsten, or an alloy thereof. 3. The semiconductor metal oxide constituting the moisture-sensitive layer includes one or more of manganese dioxide, tin oxide, nickel oxide, ruthenium oxide, bismuth oxide, and molybdenum oxide. The humidity sensor according to claim 1, wherein: 4. A humidity sensor in which a moisture-sensitive body whose capacitance changes due to adsorption and desorption of moisture is laminated on a gate insulating film of a field-effect transistor element and joined together to form an integral structure. Metal nitride oxide (MN _x O _y ) for layer
(However, M is a metal, X and Y are arbitrary numbers, respectively), second
A material formed by sequentially laminating a semiconductor metal oxide for a layer and a moisture-permeable electrode for a third layer, wherein the moisture-permeable electrode of the third layer also functions as a gate of the field-effect transistor element. A humidity sensor. 5. The metal (M) contained in the metal nitride oxide (MN _x O _y ) constituting the moisture sensitive layer is a group IVa metal, a group Va metal excluding vanadium, aluminum or tungsten. 5. The humidity sensor according to claim 4, wherein the humidity sensor contains one or more of these alloys. 6. The semiconductor metal oxide constituting the moisture-sensitive layer includes one or more of manganese dioxide, tin oxide, nickel oxide, ruthenium oxide, bismuth oxide, and molybdenum oxide. The humidity sensor according to claim 4, wherein: 7. A metal oxide or metal nitride oxide (MN _x O _y ) (M is a metal, X and Y are arbitrary numbers) in a first layer, and a semiconductor metal oxide is formed in a second layer. A material obtained by sequentially laminating a moisture-permeable electrode on the third layer is a moisture-sensitive body, and is laminated on the gate insulating film of the field-effect transistor element so that the moisture-permeable electrode functions as a gate electrode. What is claimed is: 1. A humidity sensor, comprising: reactive sputtering the metal oxide or metal nitride oxide in the moisture-sensitive body;
By making it possible to adjust the oxidation number of a metal such as D, a stoichiometric ratio as an oxide is satisfied on the side in contact with the gate insulating film, and a thin portion on the side in contact with the semiconductive metal oxide layer is formed. A humidity sensor having an oxygen excess composition. 8. The method according to claim 8, wherein the metal oxide constituting the moisture-sensitive body is IV.
8. The humidity sensor according to claim 7, comprising a group a metal, a group Va metal other than vanadium, an oxide of aluminum or tungsten or an alloy thereof. 9. The metal (M) contained in the metal nitride oxide (MN _x O _y ) constituting the moisture-sensitive layer is a group IVa metal, a group Va metal excluding vanadium, aluminum or tungsten. 8. The humidity sensor according to claim 7, further comprising one or more of these alloys. 10. The semiconductor metal oxide constituting the moisture-sensitive layer contains one or more of manganese dioxide, tin oxide, nickel oxide, ruthenium oxide, bismuth oxide, and molybdenum oxide. The humidity sensor according to claim 7, wherein: