JP2002357581A - Humidity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a humidity sensor which is high in responsiveness and maintaining stable performance over a long period, even in a specific atmosphere to be measured such as the inside of an exhaust pipe of an automobile or the like. SOLUTION: The humidity sensor 1 is provided with an insulation substrate 11 consisting of alumina and the like, a detection electrode comprising noble metal such as Pt and Au, and a humidity sensitive layer 13 comprising alumina as a main component and blending a prescribed quantity of titania and tin oxide. The detection electrode may be formed on the upper and lower faces of the humidity sensitive layer as a lower electrode 12 and an upper electrode 14. An interdigital electrode may be formed on the insulation layer. The humidity sensitive layer is a porous body, and its thickness is 100 μm, particularly preferably 50 μm is or smaller. The electrode is preferably a porous body, and preferably has a thickness which does not exceed half of the humidity sensitive layer. A heater 111 and a temperature measuring resistor 112 are provided in the inside of the insulation substrate and arranged directly under the humidity sensitive layer, in the inside of the insulation substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a humidity sensor for detecting the content of water vapor in an atmosphere to be measured by a change in electric resistance of a moisture-sensitive layer. This humidity sensor detects moisture contained in the air atmosphere, and also detects moisture contained in the exhaust pipe of an internal combustion engine of a vehicle, a ship, an airplane, or the like, or detects a fuel electrode, an air electrode, and piping of a fuel cell. It can be used for detecting moisture contained therein.

[0002]

2. Description of the Related Art At present, as a humidity sensor generally used, a resistance change type utilizing an adsorption / desorption reaction of water molecules,
Alternatively, there is a capacitance change formula using a capacitance value change. These humidity sensors, Al ₂ O ₃ system, MgCr ₂ O ₄ -T
iO ₂ system, TiO ₂ -V ₂ O ₅ system, ZrCr ₂ O ₄ -LiZr
Moisture-sensitive materials such as VO ₄ are used, and most of them sense changes in electric resistance.

A humidity sensor using such a ceramic moisture-sensitive material is generally manufactured by a method described in Japanese Patent Publication No. 1-29655. That is,
It is manufactured by forming a lower electrode on an insulating substrate, providing a moisture-sensitive layer formed by pellet molding or the like on the lower electrode, and forming an upper electrode on the upper surface of the moisture-sensitive layer. A humidity sensor having a comb-shaped detection electrode is also known.

[0004]

These conventional humidity sensors can be used without any problem in a normal atmospheric atmosphere or the like. However, as in an exhaust pipe of an automobile or the like, a temperature change is severe, an oxygen concentration is extremely low, and an atmosphere to be measured in which a gas flow velocity, a flow rate, a pressure, and the like change drastically, or a fuel electrode of a fuel cell. In an atmosphere to be measured containing a considerable amount of reducing gas, there are problems such as a decrease in responsiveness. In such an atmosphere to be measured, in addition to sufficient responsiveness and the like, excellent thermal shock resistance and the like are required. However, a conventional humidity sensor having a moisture-sensitive layer made of a pellet molded body, or a general thick film type The humidity sensor cannot accurately detect a change in resistance of the moisture-sensitive layer due to moisture contained in the atmosphere to be measured with high responsiveness, and is not sufficient in terms of strength such as thermal shock resistance.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, in which the temperature changes drastically as in an exhaust pipe of a vehicle.
Even in an atmosphere under measurement where the oxygen concentration is extremely low and the gas flow rate, flow rate, pressure, etc. change drastically,
It is an object of the present invention to provide a humidity sensor having high responsiveness, excellent thermal shock resistance, and the like, and maintaining stable moisture sensitivity for a long period of time.

[0006]

The responsiveness is improved by making the moisture-sensitive layer of the humidity sensor a thin layer having a specific thickness.
Thermal stress can be reduced. In addition, by forming the sensing electrode from a porous material having excellent heat resistance and corrosion resistance, such as Pt or Au, and having a larger average pore diameter than the moisture-sensitive layer, excellent responsiveness and the like can be obtained without impairing the responsiveness. ,
The adhesion strength between the detection electrode and the moisture-sensitive layer can be increased.
With such a humidity sensor, accuracy and responsiveness are high even in a specific measured atmosphere such as in an exhaust pipe of a vehicle,
In addition, it has sufficient thermal shock resistance and the like, and excellent performance of moisture detection is maintained for a long time. The present invention has been made based on such findings.

A humidity sensor according to the present invention is a humidity sensor having an insulating substrate, a sensing electrode, and a moisture-sensitive layer, wherein the moisture-sensitive layer is a porous body and has a thickness of 200 μm or less.

[0008] The insulating material forming the above-mentioned "insulating substrate" is not particularly limited, and ceramics, resins and the like can be used. Among them, ceramics having excellent heat resistance and the like are preferable. As this ceramic, Al ₂ O ₃ , ZrO ₂
Alumina, which has excellent insulating properties and mechanical strength, and is advantageous in terms of cost, is more preferable. The thickness, plane dimensions and the like of the insulating substrate are not particularly limited.
2.0 mm and the dimension in the plane direction is 3 × 10 mm
It can be a rectangular plate having a length of about 8 × 50 mm.

The above-mentioned "sensing electrode" is formed of a material having conductivity, but is composed of Au, Ag, Ru, Rh, Pd,
It is preferable that at least one noble metal of Os, Ir, and Pt is a main component. Among precious metals, Pt
And Au are more preferred. In particular, Pt is most preferable because it is hardly oxidized at high temperatures, does not diffuse into the moisture-sensitive layer, and has a sufficiently high melting point. By forming the detection electrode with Pt, a humidity sensor having more excellent durability can be obtained.

The sensing electrode may be formed using an alloy composed of two or more of these noble metals. For example, a combination of Pt and Rh, which can suppress the volatilization of Pt at a high temperature, is useful. The electrode made of a noble metal may contain other components within a range that does not significantly affect its physical properties. The “main component” means that the noble metal is contained in an amount of 75 parts by mass or more, particularly 85 parts by mass or more, when the detection electrode is 100 parts by mass.

It is preferable that the detection electrode contains a noble metal as a main component and is a porous body. By making the sensing electrode as well as the moisture-sensitive layer a porous body, the gas to be measured can be easily and uniformly diffused in the moisture-sensitive layer and the sensing electrode. Thereby, the responsiveness of the humidity sensor can be further improved. Further, in this humidity sensor, it is preferable that diffusion of the gas to be measured is not limited in the detection electrode, thereby further improving the responsiveness. For this purpose, there are methods such as making the sensing electrode thinner than the moisture-sensitive layer or increasing the gas permeability than the moisture-sensitive layer.

In order to increase the gas permeability of the detection electrode, there is a method of forming the detection electrode from noble metal particles having an average particle size larger than that of the moisture-sensitive material forming the moisture-sensitive layer. Thus, a porous body having a larger average pore diameter than the moisture-sensitive layer can be obtained, and the responsiveness of the humidity sensor can be improved as in the case where the detection electrode is thinned. The average particle size of the particles of the moisture-sensitive material and the noble metal particles, and the average pore size of the moisture-sensitive layer and the detection electrode are the particle sizes obtained by observing each cross section with an electron microscope and reading them on the screen or from a photograph taken. Alternatively, it can be calculated from the pore diameter.

The diffusion of the gas to be measured in the detection electrode is also affected by the material of the electrode. A raw material for forming an electrode may include a glass component and a sintering aid containing an alkaline earth metal element. This is effective in terms of low-temperature firing and electrode stability. However, the glass component and the like hinder the diffusion of the gas to be measured, and the detection electrode is preferably formed mainly of a noble metal that does not contain these components. By specifying the thickness, the average pore diameter, and the material of the detection electrode in this way, it is possible to almost eliminate the influence of the diffusion control of the gas to be measured on the detection electrode. Note that it is preferable to use a compound having excellent thermal stability such as alumina and zirconia as a sintering aid, thereby improving the adhesion between the detection electrode and the insulating substrate and the moisture-sensitive layer and the stability over time. be able to.

The plane shape of the detection electrode is not particularly limited, and may be any one of a circle, an ellipse, a square as shown in FIG. 1, and a comb-shaped electrode as shown in FIG. In addition, since a portion of the electrode that is not in contact with the moisture-sensitive layer does not function as a detection electrode, it is preferable that the moisture-sensitive layer be stacked in contact with the entire surface of the detection electrode. Furthermore, one and the other of the comb-shaped electrodes, or the lower electrode laminated on the lower surface of the moisture-sensitive layer and the upper electrode laminated on the upper surface, need not necessarily be formed of the same noble metal. The process can be simplified, and simultaneous firing is easy.

[0015] The above-mentioned "moisture sensitive layer" is formed of various moisture sensitive materials.
Can be achieved. As this moisture-sensitive material, Al_TwoO_Three
System, Al_TwoO_Three-TiO_Two-SnO_TwoSystem, MgCr_TwoO_Four-T
iO _TwoSystem, TiO_Two-V_TwoO_FiveSystem, ZrCr_TwoO_Four-LiZr
VO_FourSystem, ZnCrO_FourSystem, TiO_Two-SnO_TwoSystem and NA
Ceramic moisture sensitive materials such as SICON
You. Each of the moisture-sensitive materials consisting of a mixture of multiple oxides
The amount ratio of each oxide is not particularly limited, and is generally used.
Can be used as is.

The moisture-sensitive layer is a porous material having a thickness of 20
0 μm or less. If the thickness of the moisture-sensitive layer exceeds 200 μm, the response time at the time of 62.3% response (order constant τ = 1) described in the following example exceeds 2 seconds, and the response becomes low. This thickness is preferably 100 μm or less, particularly preferably 75 μm or less, and more preferably 50 μm or less, and a thin layer having a thickness of 30 μm or less can also be used. The response time at the time of 62.3% response can be sufficiently shortened to 1.5 seconds or less if the thickness of the moisture-sensitive layer is 50 μm or less, and 1.3 seconds or less if the thickness of the moisture-sensitive layer is 30 μm or less. In consideration of prevention of short circuit when electrodes are formed on the upper and lower surfaces of the moisture sensitive layer, sufficient durability in actual use, and ease of manufacturing, the thickness of the moisture sensitive layer is 5 μm or more, especially The thickness is preferably 10 μm or more.

Another effect of thinning the moisture-sensitive layer is that thermal stress can be reduced.
Thermal shock resistance can be improved. The humidity sensor includes an insulating substrate, a sensing electrode, and a moisture-sensitive layer, which are made of different materials and have different coefficients of thermal expansion. Therefore, when each of the other is thicker than the insulating substrate, the thermal stress accompanying the thermal expansion increases, which may cause cracks, defects, or the like, and may cause breakage.

In the present invention, by making the moisture-sensitive layer thinner and making the sensing electrode thinner than the moisture-sensitive layer,
Thermal stress can be sufficiently reduced, and a humidity sensor having more excellent durability can be obtained. The thickness of the moisture-sensitive layer (t _m) and the ratio of the thickness of the detection electrode (t _e) is not particularly limited, a t _m / t _e 1.5~3, and especially 1.8 to 2.2 be able to. Although the thickness of the electrode is not particularly limited, it is not preferable to make the electrode excessively thin in order to sufficiently adhere the entire surface to the moisture-sensitive layer. Further, when the detection electrode is a lower electrode and an upper electrode, the thickness ratio is not limited, but may be approximately the same.

Further, by making both the moisture-sensitive layer and the sensing electrode thin, the resistance value of the moisture-sensitive layer can be greatly reduced. The humidity sensor of the present invention can be used in an exhaust pipe of an automobile, a fuel supply pipe of a fuel cell, or the like, but generally has a lot of electric noise in the atmosphere to be measured. Therefore, in a conventional humidity sensor having a moisture-sensitive layer having a high resistance value, it is necessary to attach a capacitor or the like to the control circuit or provide a filter circuit. However, by making the moisture-sensitive layer and the sensing electrode thin, the resistance value of the moisture-sensitive layer can be reduced to about 1/10 to 1/100 of the conventional value, and a capacitor, a filter circuit and the like become unnecessary.

The humidity sensor of the present invention is provided with an output substrate connected to the electrode for extending the output from the insulating substrate, the sensing electrode, the moisture-sensitive layer, and the moisture-sensitive layer. Although it can be put to practical use, it is preferable that a heater is provided inside the insulating substrate. By periodically heating the humidity sensor by this heater, moisture and other impurities that have entered the interior of the moisture-sensitive layer can be eliminated. As a result, the moisture-sensitive layer is always kept in a clean state, detection accuracy is improved, and excellent output characteristics are stably maintained over a long period of time. In addition, when the humidity is extremely high, the heater can be operated to prevent condensation on the sensor.

Further, in a humidity sensor which detects moisture by a change in resistance of a moisture-sensitive layer, a change in the resistance value of a humidity-sensitive material with respect to the temperature of the atmosphere to be measured, that is, the temperature dependence of the resistance, means that the insulating substrate has It is preferable that a resistance temperature detector is provided inside. This temperature measuring resistor corrects a change in resistance value due to the temperature of the moisture-sensitive material, and can accurately detect humidity without depending on the ambient temperature. In addition, the relative humidity can be detected by the moisture-sensitive material, and the ambient temperature can be measured by the resistance temperature detector, whereby the absolute humidity can be calculated.

It is preferable that the heater and the resistance temperature detector are disposed directly below the moisture-sensitive layer inside the insulating substrate. By disposing the heater directly below the moisture-sensitive layer, it is easy to heat the entire moisture-sensitive layer almost uniformly, and to efficiently remove moisture and other impurities that have entered the moisture-sensitive layer. The power consumption required for heating can be reduced as much as possible. On the other hand, by arranging the RTD directly under the moisture-sensitive layer, the temperature can be measured at almost the same location as the humidity detection without being affected by the heat conduction of the insulating substrate.
The humidity detection accuracy can be further improved.

The humidity sensor of the present invention can be used in an atmosphere having a low oxygen concentration and containing a considerable amount of reducing gas.
Excellent performance is maintained over a long period of time, but a low oxygen concentration means that it is below the detection limit in measurement with ordinary equipment. It means that the reducing gas is contained in a concentration higher than the concentration that provides an equilibrium state.

In the humidity sensor according to the present invention, the moisture-sensitive layer is a thin layer, and the detection electrode is made thinner than the moisture-sensitive layer.
The gas to be measured is easily diffused, and high responsiveness is obtained.
Hereinafter, this will be described in detail. Humidity sensors may have high responsiveness in certain measured atmospheres, such as in the exhaust pipe of automobiles or in the electrodes and pipes of fuel cells, where the temperature changes rapidly, the oxygen concentration is low, or the reducibility is high. is important. The most influential factor for this response is the diffusion of the gas to be measured inside the moisture-sensitive layer and the sensing electrode.
This gas diffusion will be described based on Fick's law based on FIG. 7 which is a schematic diagram relating to gas diffusion in the moisture-sensitive layer.

Considering an elongated simple cubic lattice having a certain unit cross-sectional area, if the diffusion direction is the X direction, the lattice plane 1
The gas diffusion from to the lattice plane 2 is determined by the frequency at which atoms jump to adjacent lattice planes. The crystal plane is b, the number of diffused atoms per unit volume in each of the lattice planes 1 and _{2 is} C ₁ and C ₂ , and the number of atoms per unit area in each of the lattice planes 1 and 2 is n _1. , N ₂
Then, n ₁ = C ₁ b and n ₂ = C ₂ b. The frequency at which these atoms jump to the adjacent lattice plane is f
When there times, the number of atoms to jump from lattice plane 1 to the lattice plane 2 fn ₁ becomes, in a simple cubic lattice, the fn _1/6 due to the possibility of six directions.

Accordingly, the number of atoms (flux) J passing in the X direction on the A plane between the lattice planes 1 and 2 can be expressed by the following equation. J = −fb / 6 * (C ₂ −C ₁ ) If the difference between C ₁ and C ₂ is very small, the concentration gradient can be used to make C ₂ −C ₁ = b * dC / dX. , J = −fb / 6 * b * dC / dX. Here, if ^{D = fb 2/6, J} = -D * dC / dX , and the amount of diffusion is proportional to the concentration gradient.

According to each of the above equations, the amount of diffusion is
It can be adjusted by the type b of the moisture-sensitive material, the compounding ratio when a plurality of moisture-sensitive materials are used, or the constant b that changes depending on the particle size of the moisture-sensitive material. However, when the material or the like of the moisture-sensitive layer is changed in this way, the characteristics of the moisture-sensitive layer greatly change, and it is not easy to provide a humidity sensor having predetermined moisture-sensitive characteristics. On the other hand, the diffusion amount is the distance in the X direction,
That is, it can be adjusted by the thickness of the moisture-sensitive layer. According to the method of adjusting the thickness based on the thickness of the moisture-sensitive layer, the responsiveness can be improved without changing the moisture-sensitive characteristics unlike the humidity sensor of the present invention.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail by way of examples. [1] Structure of Humidity Sensor First Embodiment FIG. 1A is a perspective view showing an example of a humidity sensor 1 of the present invention. (B) is a cross-sectional view taken along AA ′ of (a). (1) Insulating substrate The insulating substrate 11 is made of Al ₂ O ₃ and has a thickness of 1.6 mm.
The width in the plane direction is 4 mm and the length is 45 mm. Immediately below the moisture-sensitive layer inside the insulating substrate, a bent belt-shaped heater 111 made of Pt is disposed at a position about 1/4 from the lower surface in the thickness direction. A bent temperature measuring resistor 112 made of Pt is disposed just below the moisture-sensitive layer inside the insulating substrate at a position about 1/4 from the upper surface in the thickness direction.

(2) Moisture Sensitive Layer, Sensing Electrode, etc. A lower electrode 12 made of Pt is joined to the upper surface on one end in the longitudinal direction of the insulating substrate. Its thickness is 15 μm,
The dimensions in the plane direction are 2 mm in width and 2.5 mm in length. The lower electrode is partially connected to the output lead wire 12.
1 is connected. Further, a predetermined amount of TiO ₂ and Sn are added to Al ₂ O ₃ on the entire surface of the lower electrode and a part of the insulating substrate.
One surface of the moisture-sensitive layer 13 made of a ceramic moisture-sensitive material containing O ₂ is joined. Its thickness is 30 μm,
The dimensions in the plane direction are both 2.5 mm in width and length. Further, an upper electrode 14 made of Pt is joined to the other surface of the moisture-sensitive layer at a position facing the lower electrode. Its thickness is 15μ
m, the dimension in the plane direction is 2 mm in width and 2.5 mm in length. A part of the upper electrode is extended and connected to the output lead wire 141.

The heater is connected to a power supply source, and the resistance temperature detector is connected to a temperature detection circuit. However, the illustration of the power supply source, the temperature detection circuit, and the lead wires connected thereto are omitted. .

Embodiment 2 FIG. 2B is a perspective view showing another example of the humidity sensor 1 of the present invention. (B) is a perspective view showing a comb-shaped electrode formed on an insulating substrate. (C) is a cross-sectional view taken along line AA ′ of (b). In this humidity sensor,
A comb-shaped electrode 15 made of Pt, having a thickness of 15 μm, an outer dimension in a planar direction of width 2 mm, a length of 2.5 mm, and a width of each comb tooth of 100 μm is formed on the upper surface on one end side in the length direction of the insulating substrate 11. Are joined. One end of each electrode is connected to output lead wires 151 and 152. Furthermore, on the entire surface of the comb-shaped electrode and a part of the insulating substrate,
One surface of a moisture-sensitive layer 13 made of a ceramic moisture-sensitive material obtained by mixing predetermined amounts of TiO ₂ and SnO ₂ with Al ₂ O ₃ is joined. Others are the same as the humidity sensor of the first embodiment.

[2] Manufacture of Humidity Sensor Manufacture of the Humidity Sensor of Example 1 (1) Manufacture of an insulating substrate in which a lead wire for output extraction is formed on the surface and a heater and a temperature measuring resistor are disposed inside Alumina A slurry containing powder was prepared, and 400 μm-thick alumina green sheets A, B, C, and D (these were integrally fired to form an insulating substrate 1 by a doctor blade method).
It becomes 1. ) Formed. Thereafter, a paste for the heater containing Pt is screen-printed on one surface of the alumina green sheet A to form a heater pattern [after firing, a connection line (not shown) to the heater 111 and the power supply source]. ] Was formed.

On one surface of the alumina green sheet C, a paste for a temperature measuring resistor containing Pt is screen-printed, and a temperature measuring resistor pattern [after firing, connecting wires to the temperature measuring resistor 112 and the temperature detecting circuit ( (Not shown). ] Was formed. Further, P on the one surface of the alumina green sheet D
The output take-out paste containing t was screen-printed to form an output take-out lead pattern from the moisture-sensitive layer (after firing, the output take-out leads 121 and 141 were formed).

Next, 1) the other surface of the alumina green sheet D having a lead wire pattern for output extraction formed on one surface thereof, and the surface of the alumina green sheet C having the resistance temperature detector pattern formed thereon, 2) the alumina green sheet C , One surface of an alumina green sheet B laminated as an insulating layer for more reliably preventing contact between the heater pattern and the resistance temperature detector pattern, 3) the other surface of the alumina green sheet B, and alumina green The surface of the sheet A on which the heater pattern was formed was brought into contact with each other and pressed to form a laminate. Then, it was maintained at a temperature of 1550 ° C. for 2 hours and baked integrally, thereby producing an insulating substrate in which a heater and a resistance temperature detector were disposed.

Each of the green sheets has such a size that ten insulating substrates can be manufactured, and a heater pattern, a resistance temperature detector pattern, and a lead wire pattern for output extraction are formed for the number of the green sheets. Then, individual unsintered substrates were cut out from the stacked body, and then fired, thereby simultaneously producing ten insulating substrates.

(2) Formation of moisture sensitive layer, sensing electrode, etc. A moisture sensitive layer, sensing electrode, etc. were formed according to the following steps (1) to (3). Formation of Lower Electrode A platinum paste is printed on the surface of the insulating substrate 11 prepared in (1), the thickness is 15 μm, the width in the plane direction is 2 mm,
A lower electrode pattern having a length of 2.5 mm was formed. Then, it dried at 60 degreeC for 1 hour, hold | maintained at 1200 degreeC for 10 minutes, and baked, and the lower electrode 12 was formed.

On the surface of the lower electrode formed by the formation of the moisture-sensitive layer, a paste for a moisture-sensitive layer containing a mixed powder obtained by mixing a predetermined amount of TiO ₂ powder and SnO ₂ powder with Al ₂ O ₃ powder was printed. This was held at 1200 ° C. for 2 hours and fired to form a moisture-sensitive layer 13 having a thickness of 30 μm and a width and a length of 2.5 mm in a plane direction.

A platinum paste was printed on the surface of the moisture-sensitive layer formed in the step of forming the upper electrode, and the thickness in the plane direction was 15 mm, the width in the plane direction was 2 mm, and the length was 2.5 m.
m of upper electrode patterns were formed. At the same time, a pattern for ensuring conduction between the upper electrode and the output lead wire 141 is printed from one side surface of the moisture sensitive layer to the surface of the insulating substrate, and then dried at 60 ° C. for 1 hour, and dried at 1200 ° C. ° C
For 10 minutes and fired to form the upper electrode 14 and the like,
A humidity sensor was manufactured.

Manufacture of the Humidity Sensor of Example 2 A platinum paste was printed on the surface of the insulating substrate manufactured in the same manner as in the manufacture of the humidity sensor of Example 1 to form a comb-shaped electrode pattern. After drying and firing to form a comb-shaped electrode, the same moisture-sensitive layer paste as in the manufacture of the humidity sensor of Example 1 was printed on the surface of the comb-shaped electrode,
A humidity sensor was manufactured in the same manner as in Example 1 except that a moisture-sensitive layer was formed by firing. Thus, two kinds of humidity sensors of the present invention were manufactured. Also, except for a moisture-sensitive layer having a thickness of 400 μm formed by a pellet molding method,
A humidity sensor of Comparative Example 1 was manufactured in the same manner as in Example 1.

[3] Performance Evaluation of Humidity Sensor (1) Evaluation of Initial Characteristics The humidity sensitivity characteristics and the response characteristics of the humidity sensor of the present invention and the comparative humidity sensor manufactured in [2] are measured by a flow dividing method (JIS Z).
8806. (See FIG. 8). This was performed to evaluate how much each characteristic changes depending on the thickness of the moisture-sensitive layer. The evaluation conditions are as follows.

Humidity Sensitivity (Humidity Sensors of Example 1 and Comparative Example 1) Air was used as an evaluation gas at a temperature of 20 ° C. and a relative humidity of 1
The sensor output was measured under the conditions of 0, 20, 40, 60, 80 and 90%. After the sensor was heated to remove dewed water and the resistance was stabilized, the sensor resistance at each humidity was measured and evaluated. The results are shown in FIG.

Response Characteristics (Humidity Sensors of Examples 1, 2 and Comparative Example 1) Air was used as an evaluation gas, the temperature was changed to 20 ° C., and the relative humidity was changed between 20 to 80%, and the sensor output was measured. did.
The sensor was heated to remove the dew condensation water, and after the resistance value was stabilized, the humidity was changed, and the change in the resistance value was measured and evaluated. The results are shown in Table 1, FIG. 4 and FIG. 4 and 5, the vertical axis represents the sensor output value converted into humidity based on the resistance value, and the response characteristics were compared based on the response time at 63.2% response.

[0043]

[Table 1]

According to FIG. 3, the humidity sensor of the first embodiment and the humidity sensor of the comparative example 1 have almost the same humidity sensitivity, but the sensor of the first embodiment can reduce the sensor resistance to about 1/30. I understand. According to Table 1, FIG. 4 and FIG. 5, the response time of the humidity sensors of Examples 1 and 2 is slightly more than 1 second, and has excellent responsiveness. On the other hand, the response time of the humidity sensor of Comparative Example 1 was close to 9 seconds, and it can be seen that the response was significantly poor due to the thick moisture-sensitive layer.

(2) Correlation between Humidity Sensing Layer Thickness and Responsiveness (Example 1) Using the humidity sensor of Example 1, the correlation between the thickness of the moisture sensitive layer and the responsiveness was determined in the same manner as in (1). evaluated. Fig. 6 shows the results.
Shown in According to FIG. 6, the response is improved as the moisture-sensitive layer becomes thinner, and when the thickness of the moisture-sensitive layer is 100 μm or less, the response time becomes 2 seconds or less, indicating that the device has excellent response. As described above, the response is improved as the moisture-sensitive layer becomes thinner. However, if the thickness is excessively thin as described above, a problem such as a short circuit between the upper and lower electrodes occurs. It is preferable to set it.

[0046]

According to the present invention, even if the atmosphere to be measured has a low oxygen concentration, contains a reducing gas, is at a high temperature, or has a large change in gas flow rate, flow rate, etc., the output can be reduced. The humidity sensor is stable and has excellent durability. Further, such a sensor can be obtained by the same material, manufacturing method, and the like as before, without requiring a specific material, device, operation, or the like. The humidity sensor is particularly useful for detecting moisture in a specific atmosphere such as an exhaust pipe of a vehicle or an electrode of a fuel cell.

[Brief description of the drawings]

FIG. 1A is a perspective view schematically showing a humidity sensor in which electrodes are formed on upper and lower surfaces of a moisture-sensitive layer. (B)
FIG. 3A is a cross-sectional view taken along line AA ′ of FIG.

FIG. 2A is a perspective view schematically showing a comb-shaped electrode formed on an insulating substrate. (B) is a perspective view schematically showing a humidity sensor on which a moisture sensitive layer is further laminated.
(C) is a cross-sectional view along AA 'of (b).

FIG. 3 is a graph showing a change in sensor resistance with respect to relative humidity in a case where an embodiment and a conventional example are compared.

FIG. 4 is a graph showing response characteristics represented by humidity-converted sensor output values in comparison between the embodiment and the conventional example.

FIG. 5 is an enlarged graph showing a region where the response time is short in FIG. 4;

FIG. 6 is a graph showing a correlation between a response characteristic represented by a humidity-converted sensor output value and a thickness of a moisture-sensitive layer.

FIG. 7 is an explanatory view schematically showing diffusion of a gas to be measured in a moisture-sensitive layer.

FIG. 8 is a schematic diagram showing an outline of an apparatus used for evaluating initial characteristics and the like of a humidity sensor by a split flow method.

[Explanation of symbols]

1; humidity sensor, 11; insulating substrate, 111; heater, 1
12; RTD, 12; lower electrode, 13; moisture sensitive layer, 1
4; upper electrode, 15; comb-shaped electrode, 121, 141, 15
1, 152; output lead wire connected to each electrode, 2; air cylinder, 31; mass flow (wet), 32; mass flow (dry), 4;
1, first saturation tank, 52; second saturation tank, 6; evaluation tank, 7;
Temperature and humidity tester.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Noboru Ishida 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi Inside Japan Specialty Ceramics Co., Ltd. F term (for reference) 2G046 AA09 BA01 BB02 BC03 BC05 BE03 EA02 EA04 EA08 EA09 EA11 FB02 FE03 FE10 FE19 FE20 FE23 FE31 FE38 FE39 FE44 FE45 FE49 5H027 AA02 KK41 KK51

Claims (8)

[Claims] 1. A humidity sensor comprising an insulating substrate, a sensing electrode, and a moisture-sensitive layer, wherein the moisture-sensitive layer is a porous body and has a thickness of 200 μm or less. 2. The humidity sensor according to claim 1, wherein said moisture-sensitive layer has a thickness of 50 μm or less. 3. The humidity sensor according to claim 1, wherein the detection electrode is made of a porous material containing a noble metal as a main component and having a larger average pore diameter than the moisture-sensitive layer. 4. The sensing electrode comprises a lower electrode and an upper electrode, the lower electrode is laminated on the insulating substrate, and one surface of the moisture-sensitive layer is laminated on the entire surface of the lower electrode. The humidity sensor according to any one of claims 1 to 3, wherein the upper electrode is stacked on a surface of the other surface facing the lower electrode. 5. The planar shape of the detection electrode is comb-shaped,
The humidity sensor according to any one of claims 1 to 3, wherein the detection electrode is laminated on the insulating substrate, and the moisture-sensitive layer is laminated on the entire surface of the detection electrode. 6. The humidity sensor according to claim 1, wherein a heater is provided inside the insulating substrate. 7. The humidity sensor according to claim 1, wherein a temperature measuring resistor is provided inside the insulating substrate. 8. The humidity sensor according to claim 7, wherein the heater and the resistance temperature detector are disposed directly below the moisture-sensitive layer inside the insulating substrate.