JP3498772B2 - Thin film gas sensor 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 thin-film gas sensor and a method for manufacturing the same, and more specifically, by having a proton conductive solid electrolyte vapor deposition layer, the resistance of the electrolyte becomes extremely small, which improves measurement accuracy and reproducibility. A thin-film gas sensor that is excellent, highly reliable, has a simple structure, and can be made extremely small, and its production, which comprises sequentially forming an electrode layer, the electrolyte layer, and an electrode layer on a substrate by using a vapor deposition method. It is about the method.

[0002]

2. Description of the Related Art In recent years, basic research on a solid electrolyte that conducts only specific ions at high temperature and further development of its application have been vigorously pursued. Among various solid electrolytes, solid electrolytes using oxygen ion conductors have been subjected to basic research for a long time, and also regarding their applications, for example, an O ₂ sensor for controlling an engine of an automobile, and a metal melt casting process. It has been put to practical use as a control oxygen concentration measurement sensor.

On the other hand, research on solid electrolytes showing good proton conductivity at high temperatures was energetically carried out by Iwahara (Nagoya Univ.) And others in the 1980s, and some of Ce or Zr such as SrCeO ₃ and CaZrO ₃ was analyzed. It was clarified that the perovskite type oxide substituted with a trivalent cation exhibits high proton conductivity at high temperature. Taking this opportunity, studies are underway on fuel cells, hydrogen generators, chemical sensors, etc. that use perovskite oxides.

High temperature proton conductive oxide (solid electrolyte)
As a chemical sensor using, a gas (for example, hydrogen or water vapor) sensor mainly utilizing the electromotive force of the concentration cell has been studied. These sensors have attracted attention as sensors for controlling the hydrogen concentration in molten metal that causes hydrogen embrittlement of metals. For example, elements manufactured by the sintering method (a cylinder with one end closed (cup) Type) electrolyte element], a concentration cell type (electromotive force type) hydrogen concentration sensor for detecting the hydrogen concentration in molten aluminum has been put to practical use.

A limiting current type hydrogen concentration sensor has also been studied, for example, in Japanese Patent Laid-Open No. 62-269054.
An anode electrode is provided on one surface of the proton-conducting solid electrolyte (sintered body), and a cathode electrode is provided on the other surface, and a cap with a small hole is provided over the anode electrode to form a gap between the anode electrode and the cap. There has been proposed a sensor element provided with and covered with.

[0006]

As described above, the gas sensor using an ionic conductor is roughly classified into a concentration cell type and a limiting current type, but both types have their respective characteristics. That is, while the concentration battery type gas sensor can measure a minute amount of gas concentration with high accuracy, the output has no linearity, and therefore an output correction circuit is required. On the other hand, the limiting current sensor can output the concentration linearly with respect to the gas concentration, and thus can measure the concentration in a wide range. Further, the structure is simple without requiring the reference electrode required in the concentration battery type sensor. From this fact, the limiting current type sensor is convenient when a wide range of concentration measurement is required.

By the way, the proton-conducting oxides reported so far have an oxygen-conducting oxide (8 mo
It is 1 to 3 orders of magnitude smaller than (l /% YSZ), and the electrolyte resistance is very large. Therefore, when the high temperature proton conductive oxide is applied to the limiting current type sensor, a large current cannot flow due to the large total resistance, the S / N ratio is small and the accuracy is low, and the electrolyte occupies the total resistance. There is a problem that the ratio of resistance is large and it is impossible to measure the concentration in a wide range. For this reason, the size of the gas diffusion hole had to be changed according to the concentration of the gas to be measured, so one diffusion control body (for limiting the amount of gas to be measured that reaches the sensor element) was used. In order to realize a limiting current type sensor capable of measuring concentration over a wide range, reduction of electrolyte resistance has been a major issue.

As a method of reducing the resistance of the proton conductor, for example, a method of reducing the resistance (improving the conductivity) by thinning the electrolyte can be considered. However, since the proton conducting function has been obtained only by the sintering method, and it is difficult to form a thin film having a thickness of, for example, several tens of μm by the sintering method, an extremely thin proton conducting solid electrolyte has not been obtained so far. . Further, since the protons move inside the crystal grains of the solid electrolyte, the grain boundary interposed between the grains in the sintered body obtained by the sintering method increases the overall resistance.

Further, the conventional limiting current type sensor using the proton conductive solid electrolyte can detect only hydrogen. Usually, water vapor (water), hydrocarbon (HC) gas, carbon monoxide (CO), and hydrogen (H ₂ ) are present in the reducing atmosphere where these sensors are frequently used. However, measuring the concentrations of hydrogen and water vapor (water) at the same time, and further measuring the concentrations of carbon monoxide and hydrocarbon gas have hitherto been
There are no reports. Therefore, detailed atmosphere detection and atmosphere control have heretofore been impossible.

Further, since the conventional limiting current type sensor using the proton conductive solid electrolyte uses a sintered body as the solid electrolyte, the heat capacity of the sensor element becomes large, and therefore the sensor element is optimally measured. In order to reach the temperature, it is necessary to provide an electrolyte heating device that generates a large amount of heat, and
There was also a possibility that the temperature rise of the sensor element was poor and that the sensor element was unevenly heated. Therefore, conventionally, there has been a problem that the initial operability of the sensor cannot be improved and the sensor cannot be downsized, and sufficient reliability cannot be obtained.

The present invention is to solve the above-mentioned problems of the prior art. In the present invention, a method for forming a proton conductive solid electrolyte membrane having high proton conductivity by reducing the grain boundary resistance of the solid electrolyte was established. Further, the internal resistance of the sensor element was reduced, the measurement range of hydrogen concentration and water vapor concentration was wide, the reproducibility was excellent, and the thin-film gas sensor with high reliability was obtained. Therefore, an object of the present invention is to provide a thin-film gas sensor provided with a dense proton-conducting solid electrolyte thin film, and a method for manufacturing the thin-film gas sensor capable of easily obtaining the proton-conducting solid electrolyte thin film. To provide.

[0012]

By using the PVD method capable of high-energy vapor deposition, the present inventors have reduced the proportion of grain boundary resistance in electrolyte resistance (generally composed of particle resistance and grain boundary resistance). It was found that a proton conductive solid electrolyte thin film having high proton conductivity can be obtained, and by adopting the thin film as a sensor, hydrogen, water vapor,
We have come up with a thin-film gas sensor that can measure the concentrations of carbon monoxide and hydrocarbon gas in a wide range.

That is, the thin-film gas sensor of the present invention comprises a sensor element composed of a porous ceramic substrate, a porous electrode layer, a proton conductive solid electrolyte vapor deposition layer, and a porous electrode layer which are sequentially laminated. It is characterized by

Examples of the proton conductive solid electrolyte include, for example, general formula (1): AB _1-x M _x O _3-y (1) [wherein A is at least one selected from Ca, Ba and Sr. B represents at least one element selected from Zr and Ce, and M represents Yb, Y, Sc,
Zn, Nd, Mg, In, Sm, Dy, Eu, Ho, G
A perovskite-type composite oxide represented by the formula: at least one element selected from d, Tm, Ca, and La, and 0 ≦ x, y ≦ 0.5. Further, the property of the substance is that it is impermeable to gas molecules (for example, it is dense enough to have a density of 90% or more of the theoretical density of oxide), and the grain boundary resistance is half or less of the particle resistance. Is preferred. Reducing the grain boundary resistance is effective in improving the conductivity.

The electrodes may be made of any suitable metallic material, for example Pt, Pd, Rh, Re, Ni, W, F.
It is preferably composed of at least one metal element selected from e, Ag and Au. The size and shape of the electrode are appropriately selected according to the size and shape of the sensor element.

The porous ceramic substrate may be formed of any suitable ceramic material that is refractory and readily available and handleable. The gas permeability of the porous ceramic substrate is 0.05 to 0.5 mL · mm / atm · min ·
Those of cm ² are preferred. The size and shape of the porous ceramic substrate are determined within a range where the target sensor element can be obtained. Porous alumina substrates are especially preferred.

In order to operate the sensor element preferably,
Heating means (for example, a heater) for heating the sensor element
Should be provided at an appropriate position. If the heating unit provided with heating means such as a heater is provided on the side of the porous ceramic substrate where the sensor element unit is provided or on the opposite side, the sensor element may be heated easily and efficiently.

The thin film gas sensor of the present invention may be of the concentration cell type or the limiting current type,
The thin film limiting current type gas sensor is preferable because it has a simple structure and can measure concentration over a wide range. As means for limiting the flow of the gas to be measured into the sensor element, a conventional means in a limiting current type oxygen concentration sensor, for example, (a) a method of coating the sensor element with a gas diffusion rate controlling layer using a porous ceramic, ( b) Various methods may be used such as providing a gap on the sensor element and covering the sensor element with a cap having a small hole.

The proton conductive solid electrolyte layer in the thin film gas sensor of the present invention needs to be formed by a vapor deposition method such as sputtering, but the porous electrode layer is formed by another method such as a printing method. You may. When a porous electrode layer, a proton conductive solid electrolyte layer, and a porous electrode layer are sequentially laminated on a porous ceramic substrate by a vapor deposition method, a sensor element can be obtained with extremely high production efficiency. When the sensor element is incorporated by a conventional method (for example, a method commonly used in the field of limiting current type oxygen concentration sensor), the thin film gas sensor of the present invention can be manufactured.

[0020]

[Function] Since a proton conductive solid electrolyte thin film having high conductivity and good proton conductivity can be easily obtained, it is possible to form a small sensor element in which a gas detection part and a heating part are integrated. became. Therefore, the power consumption of the sensor can be reduced and the starting time can be shortened. Since this sensor aims to reduce the internal resistance, it is possible to measure a wide range of hydrogen concentration from 0% to several tens of% with the same diffusion control body. Further, it has become possible to measure the carbon monoxide concentration and the hydrocarbon gas concentration. Furthermore, by changing the voltage applied to the sensor, not only hydrogen but also water vapor concentration can be detected. Further, in the obtained proton conductive thin film, the contribution of the grain boundary resistance was small, so that the influence of impurities existing in the grain boundary was reduced, the characteristics were stable, and the reliability was improved.

[0021]

EXAMPLES The present invention will now be described in more detail based on examples. Example 1: In order to prepare a proton conductor electrolyte sample, a sintered body sample and a thin film sample were manufactured by the following manufacturing procedures, and film forming conditions and crystallinity, composition, conductivity characteristics of the manufactured sample, etc. It was investigated.

A. Manufacture of sample Sintered body sample Fig. 1 shows a flowchart of a procedure for manufacturing a sintered body sample.
Proton conductive solid electrolyte (composition ratio: CaZ
r _0.9 In _0.1 O _3-a ) To prepare _a sample, CaO, Z
rO ₂ and In ₂ O ₃ were adjusted to have a molar ratio of 1: 0.9: 0.05 (100.09 g: 110.89 g: 13.88).
Prepared at a rate of 2 g and put it in an alumina pot with agate balls and methanol solution, and use a ball mill to make about 10
Mix by rotating for hours. After the predetermined mixing work was completed, it was dried. Then, the mixed raw material was placed in a container made of alumina porcelain and heated to 1300 ° C. at a heating rate of 350 ° C./h in the atmosphere in a silicon nitride electric furnace and held for 5 hours. Then, the power was turned off and the temperature was lowered to room temperature to complete the calcination of the raw material. The calcined raw material was crushed with an agate to make primary particles. Then, a PVA solution in which 10% of polyvinyl alcohol (PVA) was dissolved in water was added, and the calcined raw material was granulated. Next, the granulated powder was dried at 120 ° C. for 30 minutes to prepare a dry powder. About 1 g of this dry powder was put into a mold having a diameter of 10 mm and pressed at a pressure of 700 to 900 Kg per square centimeter. Then, the molded pellets were heated to 600 ° C. in the atmosphere at a heating rate of 350 ° C./h. After holding at 600 ℃ for 2 hours, the temperature rising speed is 350 ℃ /
The temperature was raised to 1400 ° C. for 10 hours and kept for 10 hours, and then the electric furnace was turned off and cooled in the atmosphere.

Vitreous material was deposited on the surface of the pellets that had been fired. This hinders proton conduction. Therefore, in order to remove the precipitated glassy material, the upper and lower surfaces were scraped off by polishing the surface with polishing powder # 1200 for about 200 μm. After that, the polishing powder # 200 was used for final polishing. Then, etching was performed in a 50% HF solution for 10 hours, ultrasonic cleaning was performed in pure water for about 1 hour, and then cleaning was performed with pure water to deposit fresh particle surfaces. Pt of about 0.5 μm was vapor-deposited on the upper and lower surfaces of the fresh pellet thus deposited to form a 3 mm square electrode. Then, a Pt wire having a diameter of 0.3 μm is bonded onto the Pt electrode,
A resistance measurement / proton conductivity confirmation sample was prepared.

Thin film sample A thin film sample was prepared by placing a commercially available CaZr _0.9 In _0.1 O _3-a on a silicon or porous alumina substrate.
It was performed by using a target and forming a film under the conditions shown in Table 1 below by an RF sputtering device.

[Table 1]

The difference in sputtering conditions and the crystal structure and composition of the film obtained by the subsequent heat treatment were investigated by X-ray diffraction and EPMA. The results are shown in Table 2 below.

[Table 2]

According to the result of X-ray diffraction, all the samples showed an amorphous structure immediately after the film formation. However, by the subsequent heat treatment at 800 [deg.] C., it was confirmed that the material has a perovskite structure and the material has an amorphous structure and does not change in structure. X of sample A1 with perovskite structure
The result of the line diffraction is shown in FIG. FIG. 2A shows an X-ray diffraction diagram of an amorphous structure immediately after film formation (sputtering).
2B shows an X-ray diffraction pattern of the perovskite structure after heat treatment at 800 ° C., and FIG. 2C shows CaZrO ₃ for comparison.
ASTM data (below is a diffraction angle) is shown.

According to the compositional ratio analysis result after the film formation by EPMA, a film almost equivalent to the target composition is obtained in the Ar atmosphere, but the ratio of Zr, Ca, In is found when the film is formed in the Ar + O ₂ atmosphere. It was found that the composition ratio did not reach the predetermined ratio and the composition ratio was displaced. Next, the denseness of the thin film electrolyte sample A1 having the perovskite structure was examined. From the result of X-ray diffraction, the lattice constant of this sample was a = 5.74.
8, b = 8.006, c = 5.590 [Å], and the film composition CaZr _0.84 I obtained from the EPMA results.
The density of the sample was calculated using n _0.12 O _3-a . Where a
Was assumed to be 0.025. As a result, the sample density is 4.
59 g / cm ³ next, CaZr _0.9 In _0.1 O _2.975
Of the theoretical density of 4.67 g / cm ³ (using the ASTM card value for the lattice constant) was 98.4%, indicating that a fairly dense film was formed.

B. Conductivity Measurement A proton conductor was formed into a film on a quartz glass substrate in an Ar atmosphere in a thickness of about 1 μm and heat-treated at 900 ° C., and then four Pt electrodes were taken out to prepare a conductivity measurement sample (thin film) ( Thin film method). The sample was left in an atmosphere of 1% H ₂ + 1% H ₂ O / N _{2 and} the temperature dependence of the conductivity was investigated by the 4-terminal method. In addition, the conductivity of the sample (sintered body) manufactured by the sintering method was also measured and compared with the thin film method. The result is shown in FIG. From the measurement results shown in FIG. 3, it was found that the sample manufactured by the thin film method had a conductivity improved by half to one digit compared to the sample manufactured by the sintering method.

C. Confirmation of Proton Conductivity Whether or not the thin film formed by the thin film method has proton conductivity can be checked by a concentration cell electromotive force test. Therefore, Pt (film thickness of 0.
5 μm) / CaZr _0.9 In _0.1 O _3-a (film thickness 5 μm)
/ Pt (film thickness 0.5 μm) was formed in this order to manufacture a sample having a laminated structure. The electromotive force test was conducted at a sample temperature of 500 ° C and 9
Conducting at 00 ° C., introducing 10% H ₂ + 1% H ₂ O / N ₂ gas as a reference electrode on one surface of the porous alumina substrate,
0.1-20% H ₂ + 1% H as sample gas on the other side
A gas of ₂ O / H ₂ was blown. The results are shown in Fig. 4. The measurement results are at 500 ° C and 900 ° C for H ₂ gas,
An electromotive force close to the theoretical value expressed by the following equation was obtained. However, almost no electromotive force was observed with respect to oxygen gas.

[Equation 1] [E: electromotive force, R: gas constant, F: Faraday constant, P
₁ / P ₂ : partial pressure ratio] From these results, it was confirmed that the manufactured sample effectively operates as a good proton conductor that does not show oxygen ion conductivity in the temperature range of 500 to 900 ° C.

D. Observation of cross section of sample by electron microscope (SEM) and examination of sample resistance by AC impedance method The cross section of the sample manufactured by each of the sintering method and the thin film method was observed by electron microscope (SEM) and compared. . Further, the sensor temperature is 70 by the AC impedance method.
The sample resistance was measured in an atmosphere of 0 ° C. and 1% H ₂ + 0.1% H ₂ O / N ₂ . Measurement is voltage amplitude 5 mV, frequency 10
It was performed at mHz to 10 MHz. The result is
It is shown in FIG. 5 as a −cole plot. FIG. 5 (a) shows a sample manufactured by the sintering method, in which thin film platinum electrodes 2 and 3 (both of which have a thickness of 0) are formed on both sides of a plate-shaped proton conductive sintered body 1 (a thickness of 0.3 mm). .5 μm) is formed. Figure 5
5B is a sectional view of the sensor element, and FIG. 5C is FIG. 5A.
3 shows the measurement results of particles, grain boundaries, and interface resistance of the sensor element of FIG. Figure 6 (a)
Indicates a sample manufactured by the thin film method, and a platinum electrode 5 (film thickness 0.5 μm), a proton conductive thin film 6 (film thickness 5 μm), a platinum electrode 7 (film thickness 0.5 μm) on a plate-shaped alumina substrate 4. )
Are sequentially formed. 6B is a cross-sectional view of the sensor element, and FIG. 6C shows the measurement results of particles, grain boundaries, and interface resistance of the sensor element of FIG. 6B at 700 ° C. by the AC impedance method.

Two arcuate loci were observed in FIG. 5 (c), but only one arcuate locus was observed in FIG. 6 (c). Also, when the hydrogen concentration was 0.5% and 5%, the AC impedance characteristics changed only in the size of the arc on the low frequency side. Here, the AC impedance characteristic of the solid electrolyte is generally represented by the characteristic of the electric circuit shown in FIG.
In FIG. 7, R ₁ is the grain resistance, R ₂ is the grain boundary resistance, and R ₃ is the electrode interface resistance. Since the arc on the low frequency side changed depending on the hydrogen gas concentration, it was found that this arc was the electrode interface resistance caused by the electrode reaction. From this, the resistance of the proton conductive sintered body 1 is
It consists of the sum of particle resistance, grain boundary resistance and interface resistance, and the resistance of the proton conductive thin film 6 is an electrolyte resistance with a small grain boundary resistance (particle resistance and grain boundary resistance combined; mainly particle resistance) and interface. It turned out to consist of the sum of resistance. Figure 5
In (c), I is a particle resistance of 1.6 kΩ (10 MH
z), II indicates grain resistance + grain boundary resistance (grain boundary resistance 20.5 kΩ), and III indicates grain resistance + grain boundary resistance + interface resistance (interface resistance 39.9 kΩ; 10 MHz). Further, in FIG. 6 (c), IV is electrolyte resistance 30Ω (10 MH
z), and V represents electrolyte resistance + interfacial resistance (interfacial resistance 2.2 kΩ; 10 MHz).

Here, the resistivity of the grain boundary resistance and grain resistance of the proton conductive sintered body 1 and the proton conductive thin film 6 were calculated and compared. The low resistivity of the particles of the proton conductive sintered body 1 is 5.3 × 10 ² [Ω / cm], and the resistivity of the grain boundary is 6.8 × 10 ³ [Ω / cm]. The electrolyte resistivity of No. 6 was 6.4 × 10 ² [Ω / cm]. Since the electrolyte resistivity of the proton conductive thin film 6 substantially matches the particle resistivity of the proton conductive sintered body 1, it was found that the contribution of the grain boundary resistance to the electrolyte resistance is small in the proton conductive thin film 6. .

Example 2 A limiting current type sensor was constructed using the proton conductive thin film obtained in Example 1, and it was examined whether or not hydrogen gas concentration measurement was possible. The manufacturing procedure of the sensor element and the sensor structure are shown in FIG. Figure 8 (a)
Shows the manufacturing procedure of the sensor element, and in FIG.
Gas evaporation rate of 0.05 [mL ・ mm / a
tm.min.cm < ² >] porous alumina substrate 8 with a folded (zigzag) platinum heater 9 formed on one surface, and the other surface has an anode 10 (platinum electrode) / proton conductive thin film 11 (composition). A solid electrolyte having _a ratio of CaZr _0.9 In _0.1 O _3-a ) / cathode 12 (platinum electrode) were sequentially laminated to obtain a sensor element of a limiting current type sensor. Platinum lead wire 1
The limiting current type sensor shown in FIG. 8B was configured by incorporating necessary components such as No. 3 and the means for limiting the gas to be measured (not shown) into the sensor element. FIG. 9A is a plan view of the sensor element of the limiting current type sensor shown in FIG. 8B.
Further, FIG. 9B shows a cross-sectional view (a schematic view of a cross-sectional SEM photograph) of the sensor element of FIG. 9A. The obtained solid electrolyte membrane was homogeneous and almost no grain boundaries that were normally observed as voids were observed. That is, although grain boundaries are observed in the conventional sintered sensor having the characteristics shown in FIG. 5A, no grain boundaries are observed in the thin film sensor of the present invention, and it is shown by the AC impedance method. It can be seen that the thin film sensor of the present invention has a smaller resistivity.

The current [mA] -voltage [V] characteristics when the sensor element was heated to 650 ° C. and hydrogen was changed in the range of 0 to 10% under a nitrogen atmosphere were examined. The measurement result is shown in FIG. Furthermore, the relationship between the hydrogen concentration [%] and the output current [mA] when the applied voltage is 0.6 V is shown in FIG.
Shown in. From the measurement result of FIG. 10A, it was found that the saturation current corresponding to the hydrogen concentration was obtained, and the hydrogen concentration can be detected from the current value. Further, from the relationship of FIG. 10B, it was found that the output current [mA] increased in proportion to the hydrogen concentration [%].

Next, the current [mA] -voltage [V] characteristics when H ₂ O was changed from 0 to 20% in a 1% H ₂ / N ₂ atmosphere were examined. The result is shown in FIG. It has been found that the characteristic curve of FIG. 11A shows a larger saturation current when the applied voltage is about 0.9 V or more, unlike the characteristic curve of FIG. 10A under the hydrogen atmosphere described above. Further, it can be seen that this saturation current depends on the water vapor concentration and corresponds to the water vapor concentration. From this, it was found that the saturated current with an applied voltage of less than 0.9 V corresponds to the hydrogen concentration, and the saturated current with an applied voltage higher than that corresponds to the water vapor concentration. Therefore, the hydrogen concentration and the water vapor concentration can be measured separately by using two different saturation currents. Further, FIG. 11 shows the relationship between the hydrogen concentration [%] and the output current [mA] when the applied voltage is 1.5V.
It shows in (b). From the relationship in FIG. 11B, it was found that the output current [mA] increased linearly in proportion to the hydrogen concentration [%].

Next, the detection characteristics of combustible gases other than hydrogen were examined. The _{10% H 2 O / N C} 3 H 8 gas or CO gas under a ₂ atmosphere was varied between 0 to 1%, the current of the sensor at that time - voltage characteristics were measured. The result is shown in FIG.
Shown in (a) and (b). It was found that a saturation current corresponding to each concentration can be obtained for C ₃ H ₈ gas and CO gas. It is considered that this is because hydrogen generated by the direct decomposition of C ₃ H ₈ gas or hydrogen generated by the reaction between C ₃ H ₈ CO and H ₂ O is detected. From this result, it was found that the present sensor is effective not only for detecting hydrogen and water vapor but also for detecting flammable gas such as hydrocarbon gas and carbon monoxide gas.

Example 3 The gas permeability of the porous alumina substrate was changed and the effect of the gas permeability on the limiting current characteristics was investigated. Gas permeability is about 0.01 and 0.0, respectively
5, 0.1, 0.5, 1, 5 [mL · mm / atm · m
in.cm ² ] and using a porous alumina substrate having a plate thickness of 0.3 mm, a limiting current sensor was manufactured in the same manner as in Example 1. The sensor element is heated to 650 ° C and the gas flow rate is 5
[L / min] The limiting current characteristics were measured in an atmosphere of 1% H ₂ O + 1% H ₂ / N ₂ . Then, the saturation current when the applied voltage is 0.6 V is obtained, and the gas permeability of the substrate [m
L · mm / atm · min · cm ² ] and saturation current [m
A] was examined. The results are shown in Fig. 13. From this result, the gas permeability is 0.05 to 0.5 [mL · mm / at
It was found that the saturation current was proportional to the gas permeability in the range of [m · min · cm ² ]. From this, as a hydrogen gas diffusion control substrate, 0.05 to 0.5 [mL · mm / at
It was found that a porous substrate having a gas permeability of [m · min · cm ² ] is desirable.

Example 4: When a substance (impurity) other than the elements constituting the proton conductor (proton conductive thin film) is mixed in during film formation, the proton conductivity is lowered. Therefore, the following study was conducted in order to clarify up to what level of mixing there was no problem. The above-mentioned examination was performed by mixing impurities in the electrolyte membrane in advance and examining the influence by a hydrogen concentration electromotive force test. The sample was manufactured by stacking a platinum electrode / proton conductor thin film / platinum electrode on a porous alumina substrate in this order. The proton-conducting thin film was prepared by using Fe on _a CaZr _0.9 In _0.1 O _3-a target.
A crushed piece of Ni and Cr (several mm square) was placed, and impurities were mixed to form a film. In addition, the amount of impurities mixed is changed by changing the size of the crushed pieces, and by using X-ray intensity ratio by EPMA, Fe, Ni,
It was carried out by preparing so that the analysis value of Cr was near 0, 0.1, 0.5, 1, 2. The results of the hydrogen concentration electromotive force test are shown in Table 3 below. The evaluation was performed by a three-level qualitative evaluation of good [○], normal [△], and bad [x]. From this result, the amount of impurities mixed in the proton conductor is 0.1%.
It was found that if it is within the range, the influence on the proton conductivity is small.

[0039]

[Table 3]

[0040]

The thin-film gas sensor of the present invention comprises a sensor element composed of a porous ceramic substrate, a porous electrode layer, a proton conductive solid electrolyte vapor deposition layer, and a porous electrode layer which are sequentially laminated. Therefore, the structure is simple and the size can be remarkably reduced. Further, since the proton conductive solid electrolyte thin film (deposited layer) has high conductivity and exhibits good proton conductivity, the internal resistance of the sensor element is reduced, and for example, 0
Wide range of application, such as wide range hydrogen concentration measurement from 10 to 10%. Furthermore, by changing the voltage applied to the sensor, it is possible to detect not only hydrogen, carbon monoxide, hydrocarbon gas but also water vapor concentration, and it can be used as a hydrogen sensor, carbon monoxide sensor, hydrocarbon gas sensor and / or water vapor sensor. Is. In addition, since the contribution of the grain boundary resistance to the proton conductive solid electrolyte thin film is small, the influence of impurities existing at the grain boundaries is reduced, so that the characteristics of the sensor element are stable, and the durability and reliability are improved.

In the thin film gas sensor of the present invention, the proton-conducting solid electrolyte is represented by the general formula (1): AB _1-x M _x O _3-y (1) [wherein A is selected from Ca, Ba and Sr. Represents at least one element, B represents at least one element selected from Zr and Ce, and M represents Yb, Y, Sc,
Zn, Nd, Mg, In, Sm, Dy, Eu, Ho, G
d, Tm, Ca, La, which represents at least one element selected from the group, 0 ≦ x, y ≦ 0.5], and is a gas molecule impermeable, When the grain boundary resistance is less than half of the grain resistance, the measurement accuracy and reproducibility are excellent and the reliability is high.

The electrodes are Pt, Pd, Rh, Re, Ni,
When formed of at least one metal element selected from W, Fe, Ag and Au, a porous electrode having good performance can be easily obtained.

The porous ceramic substrate is a porous alumina substrate, and the gas permeability is 0.05 to 0.5 mL.
The thin-film gas sensor of the present invention having a size of mm / atm · min · cm ² is easy to obtain and can easily use the alumina substrate having the preferable properties, and the saturation current and the gas permeability are proportional in the sensor characteristics. , The sensor characteristics are stable.

In the thin-film gas sensor of the present invention, a heating unit is provided on the side of the porous ceramic substrate on which the sensor element section is provided or on the opposite side, and the thin-film limiting current type gas sensor is a gas detection section. Since the heating unit is integrated, the shape of the sensor element can be made very small. Further, since the heating efficiency of the sensor element is good, the power consumption of the sensor can be reduced, and further, since the starting time of the sensor can be shortened, the starting performance of the sensor is good.

The method of manufacturing the thin film gas sensor of the present invention is as follows.
A porous electrode layer, a proton conductive solid electrolyte layer, and a porous electrode layer are sequentially laminated on a porous ceramic substrate by a vapor deposition method to obtain a sensor element, and the sensor element is incorporated. The thin film gas sensor of the present invention having excellent performance can be obtained easily and with high production efficiency.

[Brief description of drawings]

FIG. 1 is a flowchart of an example of a procedure for producing a proton conductive sintered body.

FIG. 2 is a view showing a result of X-ray diffraction of a proton conductive solid electrolyte sample.

FIG. 3 is a diagram showing measurement results of electric conductivity of a thin film sample and a sintered body sample.

FIG. 4 is a diagram showing measurement results of a concentration cell electromotive force test of a thin film sample formed by a thin film method.

FIG. 5 is a diagram showing test results by an AC impedance method for a sample manufactured by a sintering method.

FIG. 6 is a diagram showing test results by an AC impedance method for a sample manufactured by a thin film method.

FIG. 7 is an explanatory diagram of an electric circuit showing AC impedance characteristics of a solid electrolyte.

FIG. 8 is an explanatory diagram showing a manufacturing procedure and a sensor structure of an example of a sensor element according to the present invention.

9A and 9B are a plan view and a sectional view of an example of a sensor element according to the present invention.

FIG. 10 is an explanatory diagram of current-voltage characteristics when the sensor element of the present invention is heated to 650 ° C. and hydrogen is changed in a range of 0 to 10% under a nitrogen atmosphere.

FIG. 11: 1% H ₂ / N of the sensor element according to the present invention
Current when of H ₂ O was changed to 0-20% under ₂ atmosphere - it is an explanatory diagram of the voltage characteristic.

FIG. 12: 10% H ₂ O of the sensor element according to the present invention
/ N ₂ atmosphere in propane (C ₃ H ₈₎ current when a gas or carbon monoxide (CO) gas is changed from 0 to 1% - is an explanatory diagram of the voltage characteristic.

FIG. 13 is a diagram showing the relationship between gas permeability and saturation current of the porous ceramic substrate according to the present invention.

[Explanation of symbols]

1: Proton conductive sintered body 2, 3, 5, 7: Platinum electrode 4, 8: Alumina substrate 6, 11: Proton conductive thin film 9: Platinum heater 10: Anode 12: cathode 13: Platinum lead wire

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-62-144063 (JP, A) JP-A-63-172952 (JP, A) JP-A-63-94145 (JP, A) JP-A-62- 269054 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01N 27/41 G01N 27/409 G01N 27/416 G01N 27/406 JISC file (JOIS)

Claims (5)

(57) [Claims] To 1. A porous ceramic substrate were formed comprising a porous electrode layer, a proton-conducting solid electrolyte deposition layer, the sensor element porous electrode layers are configured by sequentially laminating a thin film
In the formula gas sensor, the proton conductive solid electrolyte vapor deposition layer has the general formula (1): AB _1-x M _x O _3-y (1) [wherein A is selected from Ca, Ba and Sr. At least
Also represents one element, B was selected from Zr and Ce.
Represents at least one element, M is Yb, Y, Sc,
Zn, Nd, Mg, In, Sm, Dy, Eu, Ho, G
at least one selected from d, Tm, Ca, La
Representing an element, 0 ≦ x and y ≦ 0.5. ]]
Of perovskite type complex oxide
Amorphous thin film is processed into perovskite structure
It is a gas molecule impermeable thin film obtained by replacing
And, the grain boundary resistance is less than half of the grain resistance.
Characteristic thin-film gas sensor. 2. The electrode is Pt, Pd, Rh, Re, Ni,
The thin film gas sensor according to claim 1, wherein the thin film gas sensor comprises at least one metal element selected from W, Fe, Ag, and Au. 3. The porous ceramic substrate is a porous alumina substrate, and the gas permeability is 0.05 to 0.5 mL · m.
The thin-film gas sensor according to claim 1, wherein m / atm · min · cm ² . 4. The thin-film gas sensor according to claim 1, wherein a heating portion is provided on the side of the porous ceramic substrate where the sensor element portion is provided or on the opposite side thereof, and the thin-film limiting current type gas sensor. . 5. A sensor element is obtained by sequentially laminating a porous electrode layer, a proton conductive solid electrolyte layer, and a porous electrode layer on a porous ceramic substrate by a vapor deposition method, and incorporating the sensor element. A method of manufacturing a thin film gas sensor.
Thus, the proton conductive solid electrolyte vapor-deposited layer has the following general formula (1): AB _1-x M _x O _3-y (1) [wherein A is at least selected from Ca, Ba and Sr.
Also represents one element, B was selected from Zr and Ce
Represents at least one element, M is Yb, Y, Sc,
Zn, Nd, Mg, In, Sm, Dy, Eu, Ho, G
at least one selected from d, Tm, Ca, La
Representing an element, 0 ≦ x and y ≦ 0.5. ]]
Of perovskite type complex oxide
Amorphous thin film is processed into perovskite structure
It is a gas molecule impermeable thin film obtained by replacing
And, the grain boundary resistance is less than half of the grain resistance.
A method for manufacturing a thin-film gas sensor, which is characterized.