JPS58221154A - Gas sensor element - Google Patents

Abstract

PURPOSE:To measure a gas to be detected with high sensitivity, by providing a lessening and covering layer for decomposing interference gases other than the gas to be detected on a gas permeable electrode film layer which is formed on a gas sensitive material layer made of metallic oxides. CONSTITUTION:A gas sensitive material layer 3 has high sensitivity to alcohol at the time when CH4, C2H6, H2 etc. are measured by the layer 3 consisting of a metallic oxide semiconductor such as SnO2, Fe2O3, ZnO2. Thereupon, a covering layer 1 for eliminating interference gases to decompose alcohol or accelerate the decomposition of alcohol is formed by LaNiO3 on a gas permeable electrode film layer 2 such as Pt which is formed on the layer 3. C2H5OH is decomposed to CO2 and H2O by the layer 1 and CH4 is permeated from the electrode 2 to the layer 3. Hereby, the gas to be detected is detected accurately. Further, an element heating heater 6 is provided on the opposite side of the electrode 4 of a substrate 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas sensor element for city gas and propane gas, and is particularly suitable for reducing the influence of gases other than the target gas to be detected (interfering gases). The present invention relates to a gas sensor element.

There are 5 gas sensors in the US or under development.
n02. There are sintered sensors using metal oxide semiconductors such as F820s and 2nO. However, these gas sensors have strong responsiveness to gases or vapors other than CH4 and H2, which are components of city gas, such as alcohol vapor (hereinafter simply referred to as alcohol). For this reason,
When these gas sensors are used in gas leak alarms,
Regardless of whether or not there is a gas leak, there is a drawback that just by touching alcohol that is used in daily life such as cooking or drinking, it will be detected as if gas were detected.

The purpose of the present invention is to reduce the influence of interfering gas other than the purpose of inspection and inspection by eliminating the above-mentioned work.
An object of the present invention is to provide a gas sensor system that does not cause false detection. For example, for the detection of CH4 or propane gas using a 5n02 sensor, a centimeter sensor with suppressed alcohol sensitivity or, if necessary, the sensitivity of FH2 may be provided.

The gas sensor element of the present invention for the above purpose is characterized by: a gas-sensitive material layer made of metal oxide F; a gas-permeable upper electrode film layer on the upper surface side of the gas-sensitive material layer; a lower electrode film layer between the material layer and the lower substrate; The main feature is that an interfering gas reducing layer, which is a metal oxide twJ process 9, which is effective in promoting W#, is provided over the gas-sensitive material layer.

The principle of the present invention will be described below.

Conventionally m5no2. When metal oxide semiconductors such as F82os#l and 2nO come into contact with city gas components such as CH4 and H2, their conductivity changes and resistance changes.)
A method is known in which the above-mentioned gas components are detected using this method.

However, the biggest drawback of these materials is that they also respond to gases other than those mentioned above, and are particularly sensitive to alcohol.

Table 1 Gas response characteristics of various thick film gas sensors, e.g.
The values shown in Table 1 are those of the present inventors.

These values were clarified in a series of studies that led to the achievement of the present invention, and these values were obtained by prototyping thick film gas sensors using various metal oxide semiconductors (powders) and measuring their gas response. These are the values investigated for characteristics.

#! As is clear from Table 1, this woodcutter's gas-sensitive material is sensitive to multiple types of gases at the same time, especially A, 3.

Most sensors showed strong sensitivity to lucor.

Therefore, for example, when using a 5n02 element to detect (1HJ + H2), alcohol is also more sensitive.

This may be extremely inconvenient from the viewpoint of the intended use of the gas sensor, but since this property is an essential property of the material, several improvements have been made over the years. However, sufficient effects have not yet been seen.

For example, as a conventional improvement method, 5n02 base material 1c
There is a method of adding a small amount of Pt+Pd additives and utilizing the catalytic effect to increase the sensitivity of a certain type of gas, for example, propane gas. However, this method does not remove interfering gases, such as alcohol, that coexist with the gases that come into contact with the gas-sensitive material, so their effects still remain.

Applying the principles of the present invention, a method is provided which attempts to fundamentally eliminate this unreasonable irrationality.

FIG.

FIG. 1 is an enlarged schematic cross-sectional view of a laminated portion of a gas sensor of the present invention for each table example. A typical example of this is:

This is an example in which 5NO2 was used as a gas-sensitive material and the present invention was applied to remove the influence of alcohol. Hereinafter, this will be referred to as a laminated sensan sandwich type senna.

In FIG. 1 (al), numeral 1 is an interfering gas reduction coating layer or a thick film of Nj05. 2 is a gas permeable upper electrode film layer of this sandwich type gas sensor, and P
63, which is a base metal of t, is a gas-sensitive material layer made of a 5noz V gas-sensitive material. 4 is a lower electrode film layer of a sandwich type gas sensor, which is made of a thick film.

5 is an alumina substrate for supporting the above thick film.

FIG. 1 (bl is a cross-sectional view of a conventionally devised sandwich type prior to the present invention; 1 is a cross-sectional view for reference and comparison to clearly explain the parts of the present invention;
4.5 indicate the same elements as the same reference numerals in FIG. 1 (aJ), respectively.

The principle of the present invention will be explained below using FIG. 1(a) and (bl Y).

An example will be described in which alcohol is mixed as a gas that interferes with detection in a case where the target gas for detection is CH& gas.

First, in the conventionally devised solution shown in Figure 1 (bl), I CH4 gas and alcohol are
It passes through the two gas-permeable upper electrode film layers and reaches the gas-sensitive material layer 3, which is 5n02 layer 9. Here, 5n02 is C
Since it has a strong response sensitivity to H4 gas erial alcohol, as shown in Table 1, C at a concentration of 11000pp.
The resistance change force Z is 114% for H4 and 189% for alcohol, which is about 6.4 times larger than that of alcohol.

1 (al), which is based on the present invention, is different from the above-mentioned FIG. The main point is that the interfering gas reducing coating layer 1 is coated with a thick layer of LaN10°, which is a metal oxide having a reducing effect.Here, the properties of LaN1Os must be briefly described.

10g of LaN decomposes into alcohol and other gases.

For example CHa * C2H6, C5Ha, CO#
It has the property of being t-resolved, such as H2. For this reason, if C
If Ha and alcohol are simultaneously present in the element according to the invention shown in FIG.
The aNiO3 film is ultimately decomposed as follows.

C2H50H+12→2C02+3H20 Here, the alcohol is completely combined with CO2 and H20t as shown in the chemical formula above.
Whether or not it is completely decomposed depends on the temperature of the element * La
It varies depending on the thickness of the NiO3 film, the concentration of alcohol, etc. However, when used as a normal city gas senna, it is practically sufficient to prevent interference with alcohol concentrations up to 11,000 pp. In this case, the thickness of the LaNiOs film is experimentally determined to be 30~1
The 00μ effect sufficiently works as described above.

On the other hand, when CHa gas touches the surface of the device of the present invention, shown in FIG. 5nO
The gas-sensitive material layer 3 consisting of z is reached.

7. At this time, the electrical resistance of the gas-sensitive material layer made of 5n02 in the single element decreases due to the action of CH4.

Figure 2 shows that in the gas sensor element of the present invention, when CH4 alcohol touches and acts on the surface of the element, whether alcohol is not felt, or why only CH4 is sensitive. FIG. 2 is a conceptual diagram for explaining the components.The reference numerals of parts shown in FIG. 1 are the same as those in FIG.

As seen in FIG. 2, another feature of the device of the present invention lies in the position and structure of application of the LaNiO3 coating layer 1, which is an interfering gas reducing coating layer. That is, it is characterized by being located further on the upper surface side of the gas permeable Upper Toden & Membrane layer 2,
This is because the lead wires are in contact with only one side (lower part). Therefore, the interfering gas decomposes in the interfering gas reduction coating layer 1 due to chemical or other action, and at this time, an electronic transfer relationship occurs between the coating layer 1 and the interfering residue, and if the coating layer 1 Even if the conductivity of the element changes, this is not completely measured as a change in the conductivity of the element.

That is, the structure of the element is such that the resistance change of 5n02 of the gas-sensitive material layer 3 and the resistance change of LaN10s of the coating layer 1 are completely independent of each other.

This is an improvement method based on an originality that is fundamentally different from conventional improvement methods. That is, in the past, other metal oxides having a catalytic effect were coated on the inside or directly on the surface of the scum-sensitive material, for example 5n02, 7f5. Or, 8102 etc. are held in stock. In this case, since the interface element has the effect of decomposing the interfering gas, this effect can be taken out as a change in the electrical resistance of the YX element.

The disadvantage of the present invention is the decomposition layer (interfering gas reduction coating layer) that decomposes interfering gases, FC, and even alcohol.

There is a possibility that the detection layer (gas-sensitive material layer) for detecting the gas to be detected, for example, CH4, has a laminated structure in which it is a separate and independent layer. As a material for the interference gas decomposition layer Kf, a metal oxide, such as LaNiOs, which is effective in decomposing interference gases other than the gas to be detected and eliminated, is used.
, S, 102, etc.

In this way, in the gas sensor element of the present invention, gases other than those to be detected are decomposed by the first interfering gas reduction coating layer from the upper surface thereof, and the intermediate layer, which is the gas-sensitive material layer, is The feature is that it is suppressed to the point where it cannot be reached.

For this reason, as seen on the representative side above, I CH4V
In contrast to alcohol, which interferes with detection, it is possible to avoid detection of alcohol.

According to the present invention based on such a principle, various gases can be selectively detected by utilizing the property of the decomposition action of metal oxides on various gases, not limited to the above-mentioned representative examples.

Regarding the metal oxide coating method and the structure of the coating layer, which are the characteristics of the present invention, as described in the explanation of the principle above, it is necessary that the coating layer does not touch the electrode at least partially. Ru.

However, in reality, this principle can be used to achieve the purpose even if it is not followed in the following cases. For example, referring to FIG. 3, even if the coating layer touches both ends of the electrode, if the resistance value R1 through the laminated layer and the resistance value R2 through the gas-sensitive material layer are sufficiently high (R, >> R2). good. That is, even if the coating layer comes into contact with the interfering gas and its resistance value R1 decreases by a small amount α,
If the resistance value R1-α of the conduction path via the gas-sensitive material layer is sufficiently small, it will not be adversely affected as a result.

In the present invention, materials that can be used for the gas-sensitive material layer include:
Sn021 Fe used in conventional gas sensors
Examples include metal oxides such as 20 B -2nO.

Materials that can be used for the interfering gas reduction coating layer in the present invention include b Cr20 s -T 1021 M no
2, F e 20s.

N10. CuO, Zn0m8nO2*'l'H2O3,
Metal oxides such as WOasLBN105 can be mentioned, and these can be used singly or in combination, and the type thereof can be selected depending on the target interfering gas.

In addition, in the laminate of the gas sensor element of the present invention, 11
.

The materials used in conventional gas sensors, such as the upper electrode film layer, lower electrode film layer, and substrate, are
It can be used as a material for

The present invention will be explained in more detail below with reference to one drawing per example.

Example 1 This example is a sandwich type gas sensor element in which the gas-sensitive material layer is a 5n02 thick film.

This example is an example in which the sensitivity ratio of I CH4 to alcohol (vapor) in the 5n02 gas-sensitive layer was improved, and thick film technology was used to fabricate the device.

1) Preparation of 81102 paste First, in order to obtain 5y102 paste to be used for the gas-sensitive material layer, 5no2 powder was prepared in the first step.

Concentrated HNOM was added to Golden Cormorant Tin (99.99% Sn) to produce white stannic acid. Decant this.

The sample was thoroughly washed with water to remove excess HNOs. On this occasion,
It was washed with water until the pH of the washing liquid became approximately 6.5 to 8.

Next, this white precipitate of stannic acid was washed with an air purifier for 12 minutes.

After evaporating to dryness at a temperature of 120°C in the air, the lumps were slightly broken in a mortar, and the mass was left in the air at a temperature of 700°C for 2 hours (hereinafter referred to as h).
is an abbreviation for time) One side was grilled.

In this process, in order to mix 1 layer tx of Pd powder into the obtained 7t8nO2 powder, a corresponding amount of PdCA2 is added.
After adding an aqueous solution of and mixing with a Raikai machine for about 6 hours, the mixture was heated in air at a temperature of 600° C. for 1 hour.

Due to this heating, PdCβ2 was decomposed into 10C and 2t of Pd, and fine Pd powder was uniformly dispersed on the surface of the 5n02 powder. A raw material powder of 5n02, which is a sensitive waste material containing 1% Pd, was obtained.

Next, take 10 g of this raw material powder, add 6 aaa of organic vehicle consisting of ethyl cellulose and α-terpineol to it, and add J -Pd -Jl-'['i
Add about 10 wt% of crystallized glass powder consisting of
The paste was kneaded for 1 hour using a Raikai machine to prepare a paste for gas-sensitive materials having a percentage of 5n02.

If) Construction of S102 thick film sandwich type sensor 6 Next,
Using this paste, a thick film sandwich-type gas sensor having 5n02 as a gas-sensitive material layer was fabricated using a thick film technique, as shown in the partially cutaway perspective view of FIG. In FIG. 4, the symbol 2 indicates the thick Pt upper electrode film layer.
The gas-sensitive material layer is made of SHOzz, and the lower electrode film layer is made of Pt, a 4Vi thick film. In addition, 5 is an alumina substrate that supports these films, and 6' is a heater terminal of a Pt heater for heating the element, which is attached to the back side of this alumina substrate using thick film technology (the heater part is located below). (not shown). Further, numerals 4' and 4' are lead terminals for the upper and lower electrodes, respectively.

In addition, - of the firing I/i900'C of this thick film waste sensor
<Ruto Prz-t. A printing screen J1325 mesh stainless steel screen was used.

In this way, a thick-film sandwich type gas sensor was fabricated.The response characteristics to various gases in this state were as shown in Section 2.

As can be seen from the values shown in Table 2, the conventional laminated type (sandwich type) alone responds to I CH4 and is also more sensitive to alcohol than it is to CH4.

1111 Formation of Coating Layer Made of LaNiOs Film Next, in order to eliminate the influence of the interfering alcohol mentioned above, a coating layer made of Ladies film was formed on the surface of the upper electrode layer 2 as follows.

Collect the acetate of La processed N1 so that it has the stoichiometric composition ratio of LaNiOs, dissolve it in pure water, concentrate it in an evaporator under reduced pressure, dry it, and heat it in air at 600°C. It was thermally decomposed at a temperature of 2 hours. Next, this was fired in air at a temperature of 1000° C. to obtain a polycrystalline solid having a composition of LaNiOs. This solid material was pulverized for 10 hours using a Laikai machine to obtain a black powder of LaNi0j.

Using this black powder of LaNiOs, a paste was prepared in the same manner as in the case of 5n02 above.

A coating layer of ICLaN40s was formed on the upper electrode film layer of the sandwich type sensor by using the same film thickening method as in the case of 5n02. At this time, the thickness of the coating layer is approximately 20μ
The size of the film surface was made almost the same as the surface of the above-mentioned upper electrode film. This will direct the alcohol vapor to the lower 5n02
This is to prevent direct contact with the unfinished gas-sensitive material layer.

The gas response characteristics of the 5102 thick film sensor element of Example 1 thus obtained were as shown in Table 3.

Table 3 Gas sensor characteristics of Example 1 Here, the reason why the sensitivity of CHa increased from the value in Table 2 above (at 370°C) is unknown, but some of the following examples When the sensitivity of CH4 was suppressed, the sensitivity of CH4 increased.

As can be seen from the comparison of values in Tables 2 and 3, Honjitsu 71
Example KL was able to reduce the alcohol sensitivity to about 1 A or less compared to the conventional one without an interfering gas reducing coating layer.

Example 2 This example relates to making the effect of the present invention more noticeable by changing the thickness of the LaN2O5 film, which is the interference scum reduction coating layer in Example 1.

A 5N02 thick-film sandwich-type gas sensor element of the present invention having a LaNiOs coating layer was prepared by the same method as in Example 1, except that only the thickness of the 5LaN105 coating layer was changed to 30μ, 40μ, and 50μ. Three types of gas sensor elements according to the present invention were manufactured.

The gas response characteristics of these gas sensor elements were as shown in Figure 4. This measured value indicates that the element temperature is 450℃.
, under conditions of a gas concentration of 11,000 pp.

As can be seen from Table 4, according to the present invention, the sensitivity to alcohol can be suppressed to a level that does not pose a problem within a practical range.

Example & This example is for suppressing the H2 sensitivity of a 5n02 thick film sensor.

TlO2 has a relatively strong decomposition effect on H2 gas.
An oxide powder was selected as the material for lamination to reduce the influence of H2 gas. 'I':102 used here is a commercially available powder with a purity of 999% or more.

Using this powder, ellipaste was prepared by the same treatment as in the case of the seed layer in Example 1, and by the same thick film technique.
The enucleated layer was formed. The thickness of the coating layer was 60μ.

The gas response characteristics of the gas sensor element according to the present invention tabulated using this method were as shown in Section 5.

The measurement conditions in this case are an element temperature of approximately 490'C.

The gas concentration is 11,000 pp.

Table 5 Example 4 of gas sensor element response characteristics of Example 3
In this embodiment, ZnO is used as the gas-sensitive material, and Fe2O is used as the material of the laminated layer for reducing the influence of interfering gas made of alcohol.

For ZnO powder, select the most fine powder among general commercially available products.

In the same manner as in Example 1, a conventional sandwich type element with ZnO as the gas-sensitive material layer was fabricated, and Fe2O and paste were used to create a film thickness of approximately 50 μm after firing.
A coating layer of Fezes was formed in the same manner as in Example 1.

The gas response characteristics of the gas sensor element of the present invention obtained were as shown in Table 6.

In this case, the element temperature is 510℃, gas @ degree ti200Q
, 19, PPm.

Table 6 Gas sensor element response characteristics of Eishi 4 As can be seen from Table 6, the conventional 2no gas-sensitive material alone has a strong sensitivity to alcohol, but the F of the present invention has a strong sensitivity to alcohol.
The temperature of the e2O3 ridge layer was measured here [I was able to keep the temperature down to about 1/4 or less.

Example 5 This example is an example in which 5no2 is used as the material for the sensitive material layer and at the same time as the material for the coating layer. In other words, in this case, the
5no2 is used as a detection material for CHa gas, and
5n02 in the nucleation layer covering the upper electrode layer is (H
It is used for the purpose of separating the layers of artificial interfering gases such as alcohol and H2 that interfere with the detection of 4.

・20・ First, in the same manner as in Example 1, a conventional sandwich type S, nO2 gas sensor element without a coating layer was produced. Next, this uncoated sandwich-type element was coated and fired so that the film thickness after firing was about 50 μm. A gas sensor element according to the present invention having a nucleation layer of 5102↓ was fabricated.

The gas response characteristics of this gas sensor element were as shown in Table 7.

The alcohol concentration in this measurement was set at 11,000 pp'2, which is within the safe range.

Table 7 Gas sensor element characteristics of Example 5 In addition to the above examples, sandwich-type sensors similar to the above-mentioned specific examples were fabricated by combining many gas-sensitive materials and coating layer materials (including those without a coating layer). The results of measuring the characteristics of the sample are shown in Section 8.

Table 8・23・ According to the above, the present invention allows various materials to be combined for the gas-sensitive material layer and the interfering gas reduction coating layer, and to be skillfully utilized according to the purpose of use. I can do it. In the present invention, even the same material can be used for detecting a gas to be detected and for decomposing an interfering gas, and this is a unique example of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of a cass sensor element according to the present invention and a conventional one. FIG. 2 is a sectional view showing a laminated structure for explaining the principle of a thick film gas sensor according to the present invention. FIG. 6 #-i is a circuit diagram for explaining the relationship between the resistance value via the coating layer and the resistance value via the sensitive material layer in the present invention. FIG. 4 is a partially cutaway perspective view showing the structure of a multilayer thick film gas sensor in one embodiment of the present invention. 1... Interfering residue reduction coating layer, 2... Upper electrode film layer. 3... Gas-sensitive material layer, 4... Lower electrode film layer, 5...
Alumina substrate, 6... Heater for element heating. TA/CauseUH4C2H50H CH4(2H5-OH λS day

Claims (1)

[Claims] 1. A gas-sensitive material layer made of a metal oxide; a gas-permeable upper electrode film layer on the upper surface side of the gas-sensitive material layer; a layer between the gas-sensitive material layer and the lower substrate; A layered gas sensor element comprising: a lower electrode film layer; A gas sensor X element characterized in that an interfering gas reducing coating layer made of an oxide is provided to cover the gas-sensitive material layer. z, the interfering gas reducing coating layer is cr2o5. 'I
'102゜Mn02r F620s, Ni O, cu
o, 2nO-5nO2a Ta205. The gas sensor element according to claim 1, which comprises one or more selected from the group of metal oxides W05*LaN10s. 8. The gas-sensitive material layer is a thick film layer using 5n02'Y: and the interfering gas reducing coating layer is LaNi0. The repainted layer. Alternatively, the gas sensor element according to claim 1, wherein the thickness M1fC is a waxed layer formed using thin film technology.