JP3344606B2 - NOx gas sensing element and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material for a NOx gas sensing element and a method for manufacturing the NOx gas sensing element. INDUSTRIAL APPLICABILITY The NOx gas detecting element according to the present invention can be suitably used when measuring the NOx gas concentration in a high-temperature, high-humidity, reducing gas atmosphere, such as in the air and exhaust gas of a vehicle interior or in a flue in a factory. .

[0002]

2. Description of the Related Art Ever since environmental issues were highlighted in the late 1960s, environmental conservation has been called out worldwide.
In particular, regarding the atmospheric environment, SOx and NOx gases in the exhaust gas of automobiles and the exhaust gas from the chimneys of factories etc. are considered to have a large effect on the environment, and the emission and emission of exhaust gases are monitored and reduced. Measurement of gas concentration in the atmosphere such as indoor air and roadside has been performed.

Here, as a method of measuring the NOx gas concentration,
Are known for infrared absorption, chemiluminescence, electrolysis, etc.
Have been. However, these methods increase gas detection accuracy.
Attempts generally require expensive and large equipment
There is a problem. For this reason, oxide semiconductors and solid-state
Degradation, gas detection using materials such as organic semiconductors and piezoelectrics
Inexpensive and small gas detector incorporating elements has been researched a lot
Is being considered by the public. This gas detector
A pair of electrodes is connected to the sensing element, and the element
Measuring the change in electrical resistance that occurs when the material is adsorbed
NOx gas amount is measured by
The greater the change in electrical resistance, the higher the sensitivity of the gas detector.
You. A gas detection element used in such a gas detector and
Then, for example, titanium oxide (Ti
O_Two), Tin oxide (SnO) _Two) And zinc oxide (ZnO)
Using an oxide semiconductor as a material for gas sensing elements
JP-B-3-13854, JP-A-2-12614
No. 6 and US Pat. No. 4,358,950.
Proposed.

However, gas detecting elements using these materials have the following problems. For example, in a gas detection element using titanium oxide, the electric resistance value in the initial state where no NOx gas is present is high, and accordingly, the change in electric resistance due to NOx gas adsorption is reduced and the sensitivity is lowered. Further, in a gas detection element using tin oxide or zinc oxide, sensitivity and responsiveness are liable to deteriorate in a high temperature, high humidity or reducing gas atmosphere, and durability is low. Therefore, it is difficult to stably measure the NOx gas concentration in automobile exhaust gas and flue gas using a gas detection element using an oxide semiconductor such as titanium oxide, tin oxide, or zinc oxide as a material for the gas detection element. there were.

Further, a spinel type crystal structure (Zn ₂ SnO ₄ ) is used as an element using a composite oxide material with consideration for high-temperature stability, for example, zinc stannate (Zn—Sn—O) as a material for a gas detection element. ) Or an oxide semiconductor having a perovskite-type crystal structure (ZnSnO ₃ ) has been reported to exhibit high sensitivity to ethanol gas or NOx gas (Shen Yu-Sheng and Zhang Tian-Shu, Sensor).
s and Actuators B, 12 (1993) 5-9. Proceedings of the 18th Chemical Sensor Research Conference, 5, Vol. 10, Supplement A, 19
94.).

However, a gas sensing element using a material having a spinel-type crystal structure made of only zinc stannate has a high electric resistance in the initial state without NOx gas and a low sensitivity like titanium oxide. There is a problem that it is very difficult to measure a change in electric resistance based on NOx gas adsorption. Further, zinc stannate having a perovskite-type crystal structure is easily deteriorated at a high temperature of 800 ° C. or higher, and has lower durability in a high-temperature, high-humidity, and reducing gas atmosphere than zinc stannate having a spinel-type crystal structure. There is a problem.

Next, a method of fabricating the element is generally described as follows.
The gas detection element for Ox gas is manufactured by a method of pulverizing material powder, forming a paste using a solvent such as PVA (polyvinyl alcohol) or ethylene glycol, applying the paste on an electrode, and baking. I have. However, in such a method of applying and baking a paste, only an element having a large crystal grain and a thick film can be formed. Therefore, the adhesion between the element and the substrate is reduced, and the responsiveness and sensitivity are also reduced. Therefore, it is very difficult to control the engine by instantaneously measuring the NOx concentration in the exhaust gas of an automobile with severe vibration using the sensing element manufactured by such a method.

[0008] Further, in the same manner as described above, a conventional sensing element using zinc stannate having a spinel-type crystal structure as a material for a sensing element is also obtained by pulverizing a raw material powder of zinc stannate having a spinel-type crystal structure into a PVA. It is produced by a method in which a paste is formed by using a solvent such as ethylene glycol or ethylene glycol, and the paste is applied on an electrode and baked, which has the same problems as described above.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and comprises zinc stannate having a spinel type crystal structure having high durability in a high-temperature, high-humidity, reducing gas atmosphere as a main component. In addition, it is possible to provide a highly sensitive NOx gas detecting element having a low electric resistance value in an initial state where no NOx gas is present, and therefore having a large electric resistance change based on NOx gas adsorption, and having a high adhesion to a substrate and a high response. An object of the present invention is to provide a method for manufacturing a NOx gas detection element having high performance and sensitivity.

[0010]

The NOx gas sensing element according to the present invention which solves the above-mentioned problem has zinc stannate (Zn-Sn-O) having a spinel type crystal structure as a main component, and is provided with respect to the zinc stannate. Antimony oxide (Sb ₂ O ₃ )
It is characterized by being added at a rate of 3.0 mol%.

The ratio (mol%) of adding antimony oxide (Sb ₂ O ₃ ) to zinc stannate is as follows: ｛(moles of antimony oxide) / (moles of antimony oxide +
It is a value determined by (molar number of zinc stannate)｝ × 100. In addition, a method of manufacturing a NOx gas detection element according to the present invention that solves the above-mentioned problem includes a thin film forming step of forming a thin film made of a material containing zinc stannate (Zn—Sn—O) as a main component on a substrate by a vapor deposition method. And a heat treatment step of heat-treating the thin film to crystallize it into a spinel-type crystal structure.

In a preferred embodiment of the above-mentioned manufacturing method, the thin film made of a material containing zinc stannate (Zn—Sn—O) as a main component has an antimony oxide (S
b ₂ O ₃₎ is added in a proportion of 0.01~3.0mol%.

[0013]

The NOx gas sensing element of the present invention is mainly composed of zinc stannate having a spinel type crystal structure, and is therefore stable and has high durability in a high-temperature, high-humidity, reducing gas atmosphere. Then, antimony oxide (Sb ₂
O ₃ ) is added at a rate of 0.01 to 3.0 mol%, so that the electrical resistance in the initial state without NOx gas is reduced by about 3 to 4 digits as compared with the case where antimony oxide is not added. be able to.

The addition ratio of antimony oxide is 0.01 mol
When the amount is less than 1%, the effect of lowering the electric resistance in the initial state is small. On the other hand, when the amount is more than 3.0 mol%, the crystallinity of the spinel-type crystal structure is disturbed, and a high-temperature, high-humidity, reducing gas atmosphere is used. Insufficient durability underneath. NO
The reason why the electric resistance in the initial state without x gas is reduced by the addition of antimony oxide is not clear, but can be considered as follows.

That is, zinc stannate having a spinel-type crystal structure and no added antimony oxide is a complete insulator in the first place, and this material has electrical conductivity only because of the metal or oxygen in the crystal lattice. This is considered to cause lattice defects and deviate electrons, which is considered to function as a carrier for electric conduction. When antimony oxide is added to zinc stannate having such a spinel-type crystal structure, for example, zinc (a divalent metal) in the spinel crystal is replaced with antimony (a trivalent metal), whereby the crystal is formed. It is considered that the electron concentration in the inside increases and the electrical conductivity improves.

Next, in the method of manufacturing the NOx gas sensing element of the present invention, first, a thin film made of a material containing zinc stannate (Zn-Sn-O) as a main component is formed on a substrate by a vapor deposition method. The thin film is heat-treated and crystallized into a spinel type crystal structure. For this reason, the NOx gas detection element manufactured by the method of the present invention is a thin film having high adhesion to the substrate, high sensitivity and high responsiveness. In addition, since it is crystallized into a spinel-type crystal structure by heat treatment, it has high durability in a high-temperature, high-humidity, reducing gas atmosphere.

[0017]

The present invention will be specifically described below with reference to examples. (Embodiment 1) NOx according to this embodiment shown in FIGS. 1 and 2
The gas detector has a rectangular parallelepiped shape (1.6 mm x 10 mm x
0.6 mm) alumina substrate (surface roughness: Ra ≒ 0.0
75 μm) 1, a pair of electrodes 2, 2 fixed to the surface of the substrate 1, a NOx gas detection element 3 formed on the surface of the substrate 1 and one end of the electrodes 2, 2, and one end of the substrate 1 And a heater 4 fixed to the back surface on the side.

The pair of electrodes 2, 2 is made of platinum, and the distance between the electrodes 2, 2 is set to 0.2 mm. At one end of each of the electrodes 2, that is, at a portion where the NOx gas detecting element 3 is formed on the surface, two branch portions 2 a protruding in a comb shape are provided on the opposing electrodes. The length of the electrodes has been lengthened to reduce the electrical resistance during measurement. The electrodes 2, 2
Are connected in series to a power supply and a voltmeter (not shown).

The NOx gas detecting element 3 is mainly composed of zinc stannate (Zn-Sn-O) having a spinel type crystal structure, and antimony oxide (Sb ₂ O ₃ ) is used for the zinc stannate.
Is added at a ratio of 1.2 mol%. The thickness of the NOx gas detecting element 3 is 0.5 μm,
The atomic ratio of Zn / Sn is set to 1.8. The heater 4 is made of platinum, and serves to heat the NOx gas detecting element 3 via the substrate 1 to increase the reactivity with the NOx gas. The heater 4 is energized and heated by a heater electrode and a heater power supply (not shown).

The NOx gas detector having the above configuration was manufactured as follows. First, the alumina substrate 1 having the above shape
And a pair of electrodes 2 and 2 are provided on the surface of the substrate 1.
A heater 4 was formed at a predetermined position on the back surface of the substrate 1 by vapor deposition. Then, each target made of zinc oxide, tin oxide and antimony oxide was prepared, and a thin film was formed on the surface of one end of the substrate 1 and the electrodes 2 and 2 by ternary simultaneous sputtering.

Here, the sputtering conditions were set as follows. First, as shown in FIG. 3, the film forming speed of each oxide with respect to the input power is obtained, and based on the film forming speed, the atomic ratio of Zn / Sn is set to a predetermined atomic ratio (1.8 in this embodiment). The input power to each target was determined so that Further, the argon gas pressure is set to 15 × 10 ⁻³ T
orr. Further, a 13.56 MHz high frequency power supply is used as a power supply, and a predetermined film thickness (0.5 μm in this embodiment) is used.
In order to satisfy m), the sputtering time was determined from the film formation rate of each oxide shown in FIG. The atomic ratio of Zn / Sn in the formed thin film was determined and confirmed by high-frequency plasma emission spectroscopy.

After forming a thin film on the surfaces of the substrate 1 and the electrodes 2 and 2 as described above, heat treatment was performed at 1,000 ° C. for 1 hour using an electric heating furnace in an air atmosphere to complete the element. Nox gas detector was completed. In the above embodiment, an alumina substrate was used as the substrate 1.
The material does not change with time in a high-temperature, high-humidity, reducing gas atmosphere, does not react with the NOx gas detection element 3, does not affect the NOx gas detection element 3 for measuring a change in electric resistance, and has a high strength. It is not particularly limited, as long as it is strong against. In addition to the above alumina, steatite, spinel (MgAl ₂ O ₄ ), zirconia and the like can be used. In particular, with respect to alumina, a substrate having small irregularities on the substrate surface is commercially available, and the strength is high, which is more convenient.

Also, as the material of the electrode 2 and the heater 4, in addition to the platinum used in the above embodiment, a material having high electric conductivity such as gold or nickel can be appropriately used. Further, in the above embodiment, a method of forming a thin film on the substrate 1 by sputtering is employed, but a physical vapor deposition method such as vacuum vapor deposition and ion plating, and a chemical vapor deposition method can also be employed.

(Evaluation) With respect to the NOx gas detector of the first embodiment, when 5% of oxygen, 94% of nitrogen, and about 1% of water vapor were introduced, and when NO ₂ gas was introduced while changing in the range of 0 to 60 ppm. The electric resistance was measured. The results are shown in Table 1 and FIG. For comparison, Table 1 and FIG. 4 also show the measurement results of the NOx gas detector of Comparative Example 1 produced in the same manner as in Example 1 except that antimony oxide was not added.

[0025]

[Table 1] As a result, N in Comparative Example 1 to which antimony oxide was not added was used.
The Ox gas detector has a large electric resistance even in the initial state where the NO ₂ concentration is 0 ppm, and shows a change in electric resistance of only about one digit even when the NO ₂ concentration changes. On the other hand, the NOx gas detector of Example 1 to which antimony oxide was added
O ₂ concentration is low electrical resistance value early in the 0 ppm, NO ₂
When the concentration was changed, it was found that a slight change in the concentration caused a change in electric resistance of about four orders of magnitude.

(Relationship between the amount of antimony oxide added and the change in electric resistance) In Example 1, the atomic ratio of Zn / Sn was kept constant at 1.8, and as shown in Table 2, the amount of antimony oxide added was set to 0. The NOx gas detectors of Test Examples 1 to 5 were manufactured by changing the range from 2.9 mol% to 2.9 mol%. For these gas detectors, the electric resistance was measured when 5% oxygen, 94% nitrogen and about 1% water vapor were introduced, and when 0 or 20 ppm of NO ₂ gas was introduced. The results are shown in Table 2 and FIG.

The test example 2 is the same as the example 1 described above.
A sample was prepared under the same conditions as in Example 1 including the reproducibility of the sample, and the characteristics were evaluated. Also, in Test Example 5, a sample was prepared under the same conditions as in Comparative Example 1.

[0028]

[Table 2] From these results, Test Examples 1-4 in which antimony oxide was added
Is higher than that of Test Example 5 in which antimony oxide is not added.
It was found that the electric resistance in the initial state where the _two gases were 0 ppm was reduced by about 3 to 4 digits at the maximum. In Test Example 5 in which antimony oxide was not added, the electrical resistance value changed by only about one digit with respect to the change in the gas concentration when the NO ₂ gas was flown, whereas the test in which antimony oxide was added was not performed. Examples 1 to 4 were found to vary greatly by about 3 to 4 digits.

It should be noted that a small absolute value of the electric resistance value facilitates the fabrication of a gas detector peripheral circuit, and a large change in resistance leads to high sensitivity. Thus, it was found that all of the examples provided good results as gas detectors. In addition, when the reproducibility was examined by comparing Example 1 and Test Example 2, the electric resistance values at the initial stage and when NO ₂ gas was flown showed almost the same values. It is considered that the variation is small.

(Relationship Between the Atomic Ratio of Zn / Sn and the Crystal Structure) In Example 1, the amount of antimony oxide added was kept constant at 1.2 mol%, and as shown in Table 3, Zn / Sn was added.
The NOx gas detectors of Test Examples 6 to 9 were manufactured by changing the atomic ratio of n in the range of 1.4 to 2.0. The substrate 1
And a heat treatment temperature of 800 ° C.

With respect to these gas detectors, the crystal structure of the NOx gas detection element 3 was examined by X-ray diffraction. The result is shown in FIG.

[0032]

[Table 3] As is clear from FIG. 6, the atomic ratio of Zn / Sn is 1.6.
In Test Example 9 which is smaller, tin oxide precipitates, but Zn / Sn
In Test Examples 6 to 8 in which the atomic ratio of is in the range of 1.6 to 2.0, only the spinel crystal structure was obtained. When tin oxide precipitates as in Test Example 9 in which the atomic ratio of Zn / Sn is smaller than 1.6, this tin oxide reacts in a high-temperature, high-humidity, reducing gas atmosphere, and has a sensitivity as a NOx gas detector. Deteriorate responsiveness. Therefore, considering the durability of the NOx gas detector under high temperature, high humidity, and reducing gas atmosphere, Zn
The atomic ratio of / Sn is preferably in the range of 1.6 to 2.0.

(Relationship Between Film Thickness of NOx Gas Sensing Element and Initial Electric Resistance Value and Responsiveness)
As shown in Table 4, the thickness of the Ox gas detection element 3 was set to 0.3 to
The N of Test Examples 10 to 12 was changed by changing the range of 1.0 μm.
An Ox gas detector was made. In addition, when changing the film thickness of the NOx gas detection element 3, it responded by changing the sputtering time.

For these gas detectors, oxygen 5%,
94% nitrogen and introducing about 1% water vapor, NO ₂ gas is 0
The electric resistance at ppm was measured. In addition, the change in electric resistance value when introducing 20 ppm of NO ₂ gas is 90%.
The time to reach (90% response time) was measured to evaluate the responsiveness. The results are shown in Table 4 and FIG. In FIG. 7, the solid line indicates the measurement result of the electric resistance value in the initial state, and the dotted line indicates the evaluation result of the responsiveness.

[0035]

[Table 4] From the above results, as the film thickness of the NOx gas detection element 3 becomes thinner, the electric resistance in the initial state gradually increases,
When the thickness is smaller than 0.3 μm, it is considered that it is very difficult to measure the NO ₂ concentration. This is considered to be because if the thickness of the NOx gas detecting element 3 is small, the film is likely to be divided into islands by the heat treatment, and the electrical conductivity cannot be maintained. Further, as the thickness of the NOx gas detecting element 3 increases, the change in the electric resistance value when the NO ₂ gas flows becomes slow (it takes a long time until the resistance becomes constant). Responsiveness is reduced. For this reason, the thickness of the NOx gas detecting element 3 is 0.3 to 1.
0 μm, more preferably 0.4 to
0.8 μm.

In Test Example 11, the surface and cross-sectional state of the NOx gas detecting element 3 were observed with a high-resolution scanning electron microscope (FE-SEM). FIG. 8A shows the result on the surface of the NOx gas detection element 3 and FIG.
(B) shows each. 8 (a) and 8 (b), by forming a thin film by sputtering, the substrate 1 and the NOx gas detection element 3 have a very good adhesion state, and the film of the NOx gas detection element 3 It was found that the small thickness reflects the unevenness on the surface of the substrate 1 and the unevenness on the surface of the NOx gas detecting element 3 is large.
When the thickness of the NOx gas detecting element 3 is increased, the unevenness of the surface of the NOx gas detecting element 3 reflecting the surface of the substrate 1 is expected to decrease, and the response is expected to decrease. It is significant that the film thickness is small. (Relationship between heat treatment temperature after formation of thin film and crystal structure) In Example 1, as shown in Table 5, the heat treatment temperature after formation of the thin film was changed in the range of 600 to 1000 ° C, and addition of antimony oxide was performed. 1.2mol% or 2.0m
ol%, the NOx gas detectors of Test Examples 13 to 19 were produced.

For these NOx gas detectors, NO
The crystal structure of the x gas detecting element 3 was examined by X-ray diffraction.
The result is shown in FIG.

[0038]

[Table 5] FIG. 9 shows that Test Example 13 was heat-treated at a temperature of 800 ° C. or more.
In the NOx gas detectors of Nos. 1 to 18, the spinel type crystal structure clearly appears, and only the crystallinity improves as the temperature increases, and the crystal form does not change even at a high temperature of 1000 ° C. Was. However, in the NOx gas detector of Test Example 19 heat-treated at a temperature of 600 ° C., a spinel-type crystal structure did not appear and a high temperature (for example, 800
(° C.), it is considered that the electrical characteristics change, and it is considered that the element cannot be put to practical use as a NO ₂ gas detecting element in a high-temperature, high-humidity, reducing gas atmosphere.

Also, due to the difference in the amount of antimony oxide added, the peak height of 2.9 mol% added was lower than that of 1.2 mol%, and the crystallinity of the spinel type crystal structure was poor. It can be seen that it has become. For this reason, the addition amount of antimony oxide is 0.6 to 2.0 mol.
% Is more preferable. (Relationship between Surface Roughness of Substrate and Change in Electrical Resistance) In Example 1 described above, as shown in Table 6, the surface roughness of the substrate 1 and the heat treatment temperature were changed, and the NOx gas detectors of Test Examples 20 to 23 were changed. Was prepared.

For these gas detectors, oxygen 5%
Electric resistance was measured when 94% of nitrogen and about 1% of steam were introduced, and when 0 or 300 ppm of NO ₂ gas was introduced. Table 6 shows the results.

[0041]

[Table 6] As a result, in the NOx gas detectors of Test Examples 21 to 23 in which the surface roughness of the substrate 1 was as large as Ra = 0.30 μm or more, the electrical resistance value was too high to measure. In particular, substrate 1
Test Example 23 having a surface roughness of Ra = 0.69 μm, which is the roughest.
In the NOx gas detector, the electrical resistance value was too high to be measured despite the heat treatment temperature being as low as 600 ° C. and the NOx gas detecting element 3 being as thick as 1.0 μm. Did not.

Here, considering the relationship between the heat treatment temperature and the electrical conductivity of the NOx gas detection element 3, as the heat treatment temperature increases, the film of the NOx gas detection element 3 shrinks and cracks easily occur in the film. It tends to adversely affect the electrical conductivity of the film. And, as the surface roughness of the substrate 1 increases,
Further, as the thickness of the NOx gas detecting element 3 is smaller, the film of the NOx gas detecting element 3 is more likely to be interrupted, so that the above tendency becomes remarkable.

FIGS. 10 to 12 show the results of observing the surface states of the substrate 1 and the NOx gas detecting element 3 with a high-resolution scanning electron microscope (FE-SEM) for the NOx gas detector of Test Example 23. (FIG. 10 shows the surface of the substrate 1, FIG. 11 shows the surface of the NOx gas detecting element 3, and FIG. 12 shows a partially enlarged surface of the NOx gas detecting element 3). Regardless, N
The crack of the film of the Ox gas detecting element 3 is large, and the valley is deep and the film is intermittent.

From the above, when the surface roughness of the substrate 1 is large, the film of the NOx gas detecting element 3 tends to be intermittent,
Since the electric conductivity of the film is adversely affected, it was confirmed that the smaller the surface roughness of the substrate 1, the better.
Specifically, the surface roughness of the substrate 1 is preferably set to Ra = 0.1 μm or less, and more preferably Ra = 0.07.
It is to be 5 μm or less.

(Gas Pressure During Sputtering) In Example 1 and Test Examples 1 to 5, 10 to 12, and 20 to 23, the argon gas pressure during sputtering was 15 × 10 which was one digit higher than that in a normal case. ^-3 Torr.
This is a measure for reducing the density of the formed film, increasing the surface area, increasing the sensitivity of the NOx gas detection element, and improving the response. However, if the heat treatment temperature is 1
When the temperature is as high as 000 ° C., sintering of the NOx gas detection element occurs, so that the argon gas pressure at the time of sputtering is equivalent to a normal value of about 5 × 10 ⁻³ Torr.

Therefore, the gas pressure at the time of sputtering is in the range of 5 × 10 ⁻³ to 15 × 10 ⁻³ Torr,
There is no particular problem as long as the conditions allow formation of the NOx gas detection element.

[0047]

As described in detail above, the NOx gas sensing element of the present invention is mainly composed of zinc stannate having a spinel type crystal structure, and therefore is stable under high temperature, high humidity, and a reducing gas atmosphere. High durability and antimony oxide (Sb ₂ O ₃ ) of 0.01 to 3.0 m with respect to zinc stannate
ol%, the electric resistance in the initial state where there is no NOx gas can be reduced by about 3 to 4 digits as compared with the case where antimony oxide is not added. The change in electric resistance is large and the sensitivity is high.

Further, the NOx gas sensing element manufactured by the manufacturing method of the present invention is a thin film having high adhesion to the substrate, high sensitivity and responsiveness, and is crystallized into a spinel type crystal structure by heat treatment. , High durability under high temperature, high humidity, and reducing gas atmosphere. Therefore, the NOx gas detection element according to the present invention can measure the NOx concentration instantaneously and with high sensitivity even in a high-temperature, high-humidity, or reducing gas atmosphere such as in exhaust gas from automobiles.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a NOx gas detector according to the present embodiment, and is a cross-sectional view taken along line AA of FIG.

FIG. 2 is a cross-sectional view of the NOx gas detector.

FIG. 3 is a line graph showing a sputter deposition rate with respect to an input output to a target.

FIG. 4 is a line graph showing a relationship between a NO ₂ concentration and a change in electric resistance.

FIG. 5 is a line graph showing a relationship between an added amount of antimony oxide and a change in electric resistance.

FIG. 6 is a chart of X-ray diffraction.

FIG. 7 is a line graph showing a relationship between a film thickness of the NOx gas detection element, an electric resistance value, and responsiveness.

8A is an electron micrograph showing a particle structure on a surface of a NOx gas detection element, and FIG. 8B is an electron micrograph showing a particle structure on a cross section of the NOx gas detection element.

FIG. 9 is an X-ray diffraction chart.

FIG. 10 is an electron micrograph showing a particle structure on a surface of a substrate.

FIG. 11 is an electron micrograph showing a particle structure of a cross section of the NOx gas detection element.

FIG. 12 is an electron micrograph showing a particle structure in which a part of the surface of the NOx gas detection element is enlarged.

[Explanation of symbols]

1 is a substrate, 2 is an electrode, 3 is a NOx gas detecting element, and 4 is a heater.

Continuing on the front page (72) Inventor Katsuji Yamashita 41, Chuchu-Yokomichi, Oji-cho, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside of Toyota Central R & D Laboratories Co., Ltd. No. 1 Inside Toyota Central Research Laboratory Co., Ltd. (56) References JP-A-60-4849 (JP, A) JP-A-59-50352 (JP, A) JP-A-7-218460 (JP, A) 3-13854 (JP, A) JP-A-2-126146 (JP, A) JP-A-6-160324 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/12 JICST file (JOIS)

Claims (3)

(57) [Claims] 1. Zinc stannate having a spinel type crystal structure (Zn—Sn—O) as a main component, and 0.01 to 3.0 mol of antimony oxide (Sb ₂ O ₃ ) is added to the zinc stannate.
A NOx gas detection element characterized by being added at a rate of 1%. 2. A thin film forming step of forming a thin film made of a material containing zinc stannate (Zn—Sn—O) as a main component on a substrate by vapor deposition, and heat treating the thin film to form a spinel crystal structure. A method of manufacturing a NOx gas detection element, comprising: 3. A thin film made of a material containing zinc stannate (Zn—Sn—O) as a main component, wherein antimony oxide (Sb ₂ O ₃ ) is contained in the thin film of 0.01 to 3. 0 mol
3. The method for manufacturing a NOx gas detection element according to claim 2, wherein the NOx gas detection element is added at a ratio of 0.1%.