Solid electrolyte assembly, electrochemical element, and limiting current-type gas sensor

Abstract

This solid electrolyte assembly comprises a substrate, a solid electrolyte, a first electrode, and a second electrode. The solid electrolyte has oxide ion conductivity, and the first electrode is located below the solid electrolyte and includes a porous body. The first electrode has only one oxygen diffusion path, which is formed so as to overlap with the substrate and the solid electrolyte. A portion of the oxygen diffusion path that overlaps with the substrate and the solid electrolyte in plan view of the solid electrolyte assembly is cut perpendicularly to the direction of diffusion of oxygen to obtain a cross-section of the first electrode, and at that time, if the smallest cross-sectional area at a site where the area of the cross-section is smallest is Sr and the area of the region where the first electrode and the second electrode overlap in plan view of the solid electrolyte is Sp, then Sr / Sp is at least 1 × 10−7 and no more than 6.9 × 10−4.

Description

Solid electrolyte junction, electrochemical element and limiting current gas sensor

[0001] The present invention relates to a solid electrolyte junction. The present invention also relates to an electrochemical device and a limiting current gas sensor. The solid electrolyte junction of the present invention is used in various fields that utilize its oxide ion conductivity.

[0002] Various oxygen sensors using oxide-ion conductive solid electrolytes are known. These types of oxygen sensors can be broadly divided into electromotive force-based and limiting current-based oxygen sensors. For example, Patent Document 1 describes a limiting current-based gas sensor including an ion-conductive solid electrolyte layer formed on a silicon substrate, a pair of positive and negative porous electrodes formed on the solid electrolyte layer, and a porous membrane formed on the solid electrolyte layer and the pair of positive and negative porous electrodes. This limiting current-based gas sensor uses a porous membrane to limit the amount of oxygen gas absorbed into the solid electrolyte layer, thereby achieving a saturation phenomenon in which the current remains constant even when the voltage applied between the electrodes is increased.

[0003] US2015 / 0377823A1

[0004] However, the limiting current gas sensor described in Patent Document 1 requires a porous membrane separate from the electrodes in order to limit the amount of oxygen gas absorbed by the solid electrolyte layer. This makes the gas sensor described in Patent Document 1 complicated to manufacture. Furthermore, the formation of the porous membrane may require oblique deposition, plasma spraying, or anodizing, which may result in a long lead time for sensor manufacture. Therefore, an object of the present invention is to provide a solid electrolyte assembly useful for limiting current gas sensors that can overcome the various drawbacks of the prior art described above.

[0005] The present invention provides a solid electrolyte junction including a substrate, a solid electrolyte disposed on the substrate, and a first electrode and a second electrode disposed opposite each other with the solid electrolyte interposed therebetween, wherein the solid electrolyte has oxide ion conductivity, and at least a portion of the first electrode is located between the substrate and the solid electrolyte and includes a porous body, and the first electrode has only one oxygen diffusion path formed to overlap with the substrate and the solid electrolyte in a plan view of the solid electrolyte junction, and when a portion of the oxygen diffusion path where the substrate and the solid electrolyte overlap in a plan view of the solid electrolyte junction is cut perpendicularly to the oxygen diffusion direction to obtain a cross section of the first electrode, Sr denotes the minimum cross-sectional area at a portion where the area of ​​the cross section is smallest, and Sp denotes the area of ​​a region where the first electrode and the second electrode overlap in a plan view of the solid electrolyte, and Sr / Sp is 1.0×10 －７ 6.9 x 10 －４ The present invention provides a solid electrolyte junction as follows:

[0006] The present invention also provides a solid electrolyte junction including a substrate, a solid electrolyte disposed on the substrate, and a first electrode and a second electrode disposed opposite each other with the solid electrolyte interposed therebetween, wherein the solid electrolyte has oxide ion conductivity, and at least a portion of the first electrode is located between the substrate and the solid electrolyte and includes a porous body, and the first electrode has a plurality of oxygen diffusion paths formed to overlap with the substrate and the solid electrolyte in a plan view of the solid electrolyte junction, and when a portion of each oxygen diffusion path where the substrate and the solid electrolyte overlap in a plan view of the solid electrolyte junction is cut perpendicularly to the oxygen diffusion direction to obtain a cross section of the first electrode, Sr denotes the minimum cross-sectional area at a portion where the cross section has the smallest area, and ΣSr denotes the sum of the minimum cross-sectional areas Sr of all the oxygen diffusion paths, and when Sp denotes the area of ​​a region where the first electrode and the second electrode overlap in a plan view of the solid electrolyte, ΣSr / Sp is 1.0×10 －７ 6.9 x 10 －４ The present invention provides a solid electrolyte junction as follows:

[0007] The present invention also provides an electrochemical device having the solid electrolyte junction.

[0008] The present invention also provides a limiting current gas sensor having the electrochemical element, wherein the dependency of the current value on the oxygen concentration is linear.

[0009] FIG. 1 is a plan view showing the structure of one embodiment of a solid electrolyte bonded structure of the present invention. FIG. 2 is a cross-sectional view taken along line II-II of the solid electrolyte bonded structure shown in FIG. 1. FIG. 3 is a plan view showing the structure of another embodiment of a solid electrolyte bonded structure of the present invention. FIG. 4 is a cross-sectional view taken along line II-II of the solid electrolyte bonded structure shown in FIG. 3. FIG. 5 is a plan view showing the structure of yet another embodiment of a solid electrolyte bonded structure of the present invention. FIG. 6 is a cross-sectional view taken along line III-III of the solid electrolyte bonded structure shown in FIG. 5. FIG. 7 is a plan view showing the structure of yet another embodiment of a solid electrolyte bonded structure of the present invention. FIG. 8 is a cross-sectional view taken along line IV-IV of the solid electrolyte bonded structure shown in FIG. 7. FIG. 9 is a plan view showing the structure of yet another embodiment of a solid electrolyte bonded structure of the present invention. FIG. 10 is a cross-sectional view taken along line V-V of the solid electrolyte bonded structure shown in FIG. 9. FIG. 11 is a plan view showing the structure of yet another embodiment of a solid electrolyte bonded structure of the present invention. FIG. 12 is a cross-sectional view taken along line VI-VI of the solid electrolyte bonded structure shown in FIG. 11. FIG. 13 is a plan view showing the structure of yet another embodiment of a solid electrolyte bonded structure of the present invention. FIG. 14 is a cross-sectional view of the solid electrolyte assembly shown in FIG. 13 taken along line VII-VII.

[0010] The present invention will be described below based on preferred embodiments with reference to the drawings. Fig. 1 is a plan view showing the structure of one embodiment of a solid electrolyte bonded body of the present invention, and Fig. 2 is a cross-sectional view taken along line II of the solid electrolyte bonded body shown in Fig. 1.

[0011] 1 and 2 includes a substrate 11, a solid electrolyte 12 disposed on the substrate 11, and a first electrode 13 and a second electrode 14 disposed opposite each other with the solid electrolyte 12 interposed therebetween. The solid electrolyte 12 has oxide ion conductivity.

[0012] The first electrode 13 is located below the solid electrolyte 12, is in contact with the substrate 11 and the solid electrolyte 12, and includes a gas-permeable porous body. The first electrode 13 may be entirely made of a gas-permeable porous body. In a plan view of the solid electrolyte assembly 10, the solid electrolyte 12 has a shape extending from the periphery of the second electrode 14. In a plan view of the solid electrolyte assembly 10, the first electrode 13 and the second electrode 14 partially overlap each other. In a plan view of the solid electrolyte assembly 10, the first electrode 13 and the solid electrolyte 12 partially overlap each other. The first electrode 13 has an L-shaped exposed portion 13C exposed to the outside from the solid electrolyte 12. The first electrode 13 has an oxygen diffusion path formed to overlap the substrate 11 and the solid electrolyte 12. In the solid electrolyte joint 10 of this embodiment, the oxygen diffusion path 13A is defined as a region surrounded by a boundary surface B1 where the substrate 11 and the first electrode 13 are in direct contact, a boundary surface B2 between the exposed portion 13C and the solid electrolyte 12, a boundary surface B3 where the first electrode 13 and the solid electrolyte 12 are in direct contact, and a boundary surface B4 where the first electrode 13 and the second electrode 14 overlap in a plan view of the solid electrolyte joint 10. The boundary surface B2 is defined as a region surrounded by a pair of opposing vertical boundary lines B2 Ａ and a pair of opposing horizontal boundary lines B2 Ｂ The second electrode 14 is on the solid electrolyte 12 and is in contact with the solid electrolyte 12. The second electrode 14 may be arranged to extend to a position where it is in contact with the substrate 11.

[0013] The solid electrolyte assembly 10 of this embodiment has only one oxygen diffusion path 13A. When a portion of the oxygen diffusion path 13A where the substrate 11 and the solid electrolyte 12 overlap in a plan view of the solid electrolyte assembly 10 is cut perpendicularly to the oxygen diffusion direction to obtain a cross section of the first electrode 13, the minimum cross-sectional area of ​​the portion where the area of ​​the cross section is smallest is defined as Sr, and the area of ​​the region where the first electrode 13 and the second electrode 14 overlap in a plan view of the solid electrolyte 12 is defined as Sp, and Sr / Sp is 1.0×10 －７ 6.9 x 10 －４ It is preferably equal to or less than 1.0 × 10 －６ Above 6.0 x 10 －４More preferably, it is 5.0 × 10 or less. －５ Above 6.0 x 10 －４ and even more preferably 1.0 × 10 －４ 3.2 x 10 －４ When the solid electrolyte junction 10 satisfies these relationships, it is not necessary to provide a porous film separately from the electrodes, the solid electrolyte junction 10 does not have a complicated structure, and the manufacturing time can be shortened, and further, various electrochemical elements, such as limiting current gas sensors, having the solid electrolyte junction 10 can be obtained.

[0014] In particular, when used as a limiting current gas sensor, the oxygen concentration dependency of the current value is linear, and a limiting current is generated when a voltage of 1.0 V or more, preferably 0.80 V or more, is applied at a low temperature of 600°C, preferably 550°C, and more preferably 500°C. Therefore, oxygen concentration can be measured at low temperatures and low applied voltages, and oxygen degradation of the limiting current gas sensor, particularly oxygen degradation of the solid electrolyte 12, can be suppressed. In other words, it is not necessary to provide a porous film separately from the electrodes, and a limiting current gas sensor without a complicated structure can be provided, which can shorten the manufacturing time and is less susceptible to deterioration of the solid electrolyte 12 and, ultimately, the solid electrolyte assembly 10.

[0015] In the present invention, the limiting current is defined as follows. A voltage is applied to a solid electrolyte junction from 0 V to 1.4 V or higher in increments of 10 mV or less, with a holding time of 0.1 second or more at each step, so that the potential of the upper electrode relative to the lower electrode increases. The measured current values ​​are plotted in an applied voltage-current graph. Here, the increase in the detected current per 30 mV is defined as ΔI, and the increase in applied voltage (30 mV) is defined as ΔV. The value calculated from ΔI / ΔV is defined as the first-order differential of the current, I'. The peak top of the first-order differential of the current after 0.1 V is defined as I'B, and the voltage at this point is defined as VB. The largest voltage value after VB that satisfies I'B / I≧5 is defined as VLC. The peak top of the first-order differential of the current after VLC is defined as I'LC2. A limiting current is defined to be present after VLC when I'B / I'LC2>3 is satisfied. The peak top is the maximum value of the Gaussian function when fitting is performed using a Gaussian function within ±0.1 V in the vicinity of the maximum value within the section.

[0016] In the case of a limiting current gas sensor, particularly a limiting current oxygen gas sensor, the following reactions occur on the cathode and anode sides: Cathode side: O ２ +4e － →20 ２－ Anode side: 2O ２－ →O ２ +4e －

[0017] The value of Sr / Sp is preferably as described above, and the value of Sr is set to 1 μm from the viewpoint of easily obtaining a solid electrolyte assembly 10 that does not require the provision of a porous film separately from the electrodes, does not have a complicated structure, and can be produced in a shorter time. ２ 5000 μm or more ２ Preferably, it is 5 μm or less. ２ 4000 μm or more ２ More preferably, it is 10 μm or less. ２ 3300 μm or more ２ More preferably, it is 20 μm or less. ２ 400 μm or more ２From the same viewpoint, the value of Sp is preferably 1×10 ３ μm ２ 1x10 or more ９ μm ２ Preferably, it is 5×10 or less. ３ μm ２ 1x10 or more ８ μm ２ More preferably, it is 1×10 or less. ４ μm ２ 1x10 or more ７ μm ２ It is even more preferred that:

[0018] In the case shown in Figures 1 and 2, the cross-sectional shape of the oxygen diffusion path 13A along the thickness direction of the first electrode 13 is trapezoidal or rectangular, and the minimum cross-sectional area Sr is constant along the flow path of the oxygen diffusion path 13A. The shape of the minimum cross-sectional area Sr can be measured using a stylus-type step profiler and determined using a known method based on the measurement results. A trapezoidal or rectangular cross-sectional shape along the thickness direction of the first electrode 13 is preferable from the viewpoint of ease of manufacturing when the first electrode 13 is constructed from the materials described below. A trapezoidal or rectangular cross-sectional shape along the thickness direction of the solid electrolyte 12 is advantageous in that it can maintain a large cross-sectional area even when the flow path of the oxygen diffusion path 13A is small, thereby reducing the oxygen diffusion resistance. As a result, oxygen-induced deterioration of the first electrode 13 can be suppressed. When the cross-sectional shape along the thickness direction of the first electrode 13 is trapezoidal, the minimum cross-sectional area Sr can be determined by dividing the first electrode 13 into four triangles and adding up the areas of the triangles. If the shape is a rectangle, the area is determined by subtracting the excess area of ​​two areas that can be approximated as a triangle from the area of ​​the surrounding rectangle.

[0019] The first electrode 13 has a circular portion 13B connected to the oxygen diffusion path 13A in a plan view of the solid electrolyte 12. By having such a circular portion 13B, stress concentration in the laminated structure of the solid electrolyte 12 and the first electrode 13 can be alleviated, thereby achieving the effect of obtaining a solid electrolyte joint 10 with fewer defects. The circular portion 13B of the first electrode 13 may be a quadrilateral, pentagonal, or polygonal portion instead of a circle. In such a case, it is desirable to provide arc-shaped curvatures at the corners in order to achieve the above-mentioned effect. The circular portion 13B of the first electrode 13 may be circular, polygonal, elliptical, or a combination of these shapes.

[0020] The second electrode 14 also has a circular portion 14A in plan view that overlaps with the circular portion 13B, which is part of the oxygen diffusion path 13A of the first electrode 13. This shape is preferable from the viewpoint of ease of manufacturing the first electrode 13 and the second electrode 14, but the portion 14A of the second electrode 14 that overlaps with the circular portion 13B of the first electrode 13 is not necessarily limited to a circular shape.

[0021] The solid electrolyte 12 has a rectangular shape in plan view. This shape is preferable from the viewpoint of ease of manufacture. However, the shape of the solid electrolyte 12 in plan view does not necessarily have to be rectangular, and may be circular, elliptical, or a combination thereof.

[0022] The substrate 11 is made of, for example, silicon (Si), silicon carbide (SiC), gallium nitride (GaN), aluminum nitride (AlN), sapphire, silicon oxide (SiO ２ ), silicon nitride (Si ３ N ４ ), zirconium oxide (ZrO ２ ), aluminum oxide (Al ２ O ３The substrate 11 can be made of a general-purpose substrate material such as silicon. Because of its ease of availability, ease of formation, and chemical stability, the substrate 11 is preferably made of silicon. The thickness of the substrate 11 is not particularly limited, but is generally 50 nm or more and 1000 μm or less. By having the thickness within this range, the rigidity of the substrate can be maintained, making it possible to support the solid electrolyte on the upper surface, while ensuring productivity.

[0023] The type of the solid electrolyte 12 is not particularly limited. Because of its high oxide ion conductivity, the solid electrolyte 12 preferably includes a ceramic containing at least one selected from the group consisting of a composite oxide containing lanthanum and silicon, yttrium-stabilized zirconia, samarium-doped ceria, gadolinium-doped ceria, lanthanum gallate, and yttrium-doped bismuth oxide. These ceramics, i.e., metal oxides, are chemically stable and, as described above, are less likely to react with oxygen when the solid electrolyte assembly 10 is used in a limiting current gas sensor, thereby preventing deterioration of the solid electrolyte 12.

[0024] The thickness of the solid electrolyte 12 is not particularly limited, but is, for example, 1.0 nm to 1000 nm, and can be measured using a stylus profilometer or an electron microscope.

[0025] The first electrode 13 contains a metal oxide and has a porosity ρ ０ The porosity ρ of the first electrode 13 is preferably 1.0% or more and 50% or less, more preferably 5.0% or more and 45% or less, even more preferably 15.0% or more and 40% or less, and even more preferably 20% or more and 30% or less. ０ By setting the porosity ρ of the first electrode 13 within this range, the first electrode 13 can reliably diffuse oxygen molecules or conduct oxide ions through the oxygen diffusion paths 13A. In detail, if the porosity of the oxygen diffusion paths 13A is low, the proportion of pores decreases, and the amount of oxygen actually flowing through the oxygen diffusion paths 13A decreases, causing the solid electrolyte assembly 10 to fail to function as, for example, a limiting current gas sensor. However, if the porosity ρ of the first electrode 13 is low, ０The above-mentioned problems can be avoided by setting the temperature within the above range. As the metal oxide, ceramics such as those exemplified for the solid electrolyte 12 can be used.

[0026] The first electrode 13 has the porosity ρ ０ In order to satisfy the above, the content of the metal oxide is preferably 1.0% by volume or more and 60% by volume or less, and more preferably 2.0% by volume or more and 55% by volume or less.

[0027] In this embodiment, the porosity of the oxygen diffusion path 13A is ρ ０ (%), Sr × ρ ０ / (Sp×100) is 1.0×10 －８ 1.9 x 10 －４ Preferably, it is 2.0 × 10 or less. －７ 1.8 x 10 －４ More preferably, it is 1.0 × 10 or less. －５ 1.5 x 10 －４ More preferably, it is 1.5×10 or less. －５ Above 8.0 x 10 －５ It is even more preferable that the porosity ρ of the oxygen diffusion path 13A of the first electrode 13 is less than 0.05. This allows the first electrode 13 to reliably allow oxygen to flow through the oxygen diffusion path 13A. In detail, if the porosity of the oxygen diffusion path 13A is excessively small, the proportion of pores decreases, and the amount of oxygen actually flowing through the oxygen diffusion path 13A decreases, causing the solid electrolyte assembly 10 to fail to function accurately as, for example, a limiting current gas sensor. In contrast, if the porosity ρ of the oxygen diffusion path 13A of the first electrode 13 is less than 0.05, the porosity ρ of the oxygen diffusion path 13A of the first electrode 13 is less than 0.05. ０ By setting the range as described above, the above-mentioned problems can be avoided.

[0028] For similar reasons, the average pore diameter of the first electrode 13 is preferably 5 nm to 200 nm, more preferably 15 nm to 150 nm, and even more preferably 20 nm to 100 nm. The average pore diameter can be calculated by observing the top surface of the first electrode 13 using a scanning electron microscope and using Image-Pro 10, an image analysis software manufactured by Media Cybernetics. For example, a 2.5 μm x 1.8 μm area is designated at 50,000x magnification, and contrast enhancement or contour line drawing is performed as necessary. Then, the machine learning function is used to select three or more points on each of the voids and electrode portions to binarize the brightness. Select "Diameter, Average" as the measurement item, and perform image analysis to identify the pores and determine the average pore diameter. Porosity can also be calculated in the same manner as the average pore diameter by selecting "Area Ratio (%)" as the measurement item.

[0029] The first electrode 13 preferably contains a precious metal element consisting of at least one of platinum group elements (platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), osmium (Os)), gold (Au), and alloys containing these. In particular, the first electrode 13 is preferably a porous composite of the metal oxide and the precious metal element, particularly a cermet. This improves the heat resistance of the first electrode 13 and makes it less likely to become densified during heating, thereby providing the effect of making it easier to maintain voids. Examples of the alloy include general-purpose alloys such as Pt-Rh, Au-Pt, and Au-Pd.

[0030] The thickness of the first electrode 13 is preferably 10 nm or more and 2000 nm or less, more preferably 20 nm or more and 1600 nm or less, or more preferably 30 nm or more and 1200 nm or less. This makes it possible to realize a first electrode 13 large enough to form the oxygen diffusion path 13A. This thickness can be measured using a stylus profilometer, an electron microscope, or an optical three-dimensional measuring device.

[0031] The second electrode 14 may be made of a general-purpose electrode material, such as a metal electrode or graphite, or, like the first electrode 13, may be made of a porous composite of a metal oxide and a metal, particularly a cermet.

[0032] The thickness of the second electrode 14 is preferably 10 nm to 1000 nm, and more preferably 20 nm to 700 nm. This thickness can be measured using a stylus profilometer, an electron microscope, or an optical three-dimensional measuring device.

[0033] Fig. 3 is a plan view showing the structure of another embodiment of the solid electrolyte joined body of the present invention, and Fig. 4 is a cross-sectional view taken along line II-II of the solid electrolyte joined body shown in Fig. 3. In Fig. 3 and Fig. 4, the same reference numerals are used for components similar to or the same as those in Fig. 1 and Fig. 2.

[0034] The solid electrolyte joint 20 of this embodiment is similar to the solid electrolyte joint 10 of the above embodiment in that it has only one oxygen diffusion path, but differs from the solid electrolyte joint 10 of the above embodiment in that a narrow portion 13D is formed in a part of the oxygen diffusion path 13A of the first electrode 13. Therefore, it is necessary to calculate the minimum cross-sectional area Sr of the oxygen diffusion path 13A at the narrow portion 13D. The L-shaped exposed portion 13C of the first electrode 13 is exposed to the outside from the solid electrolyte 12.

[0035] In this embodiment, when the area of ​​the region where the first electrode 13 and the second electrode 14 overlap is Sp, Sr / Sp is 1.0×10 －７ 6.9 x 10 －４ It is preferably equal to or less than 1.0 × 10 －６ Above 6.0 x 10 －４ When the solid electrolyte junction 20 satisfies the above relationship, it is not necessary to provide a porous film separately from the electrodes, the solid electrolyte junction 20 does not have a complicated structure, and the manufacturing time can be shortened, and further, various electrochemical elements including the solid electrolyte junction 20, such as a limiting current gas sensor, can be obtained.

[0036] Other features and advantages of this embodiment are the same as those of the embodiment shown in FIGS. 1 and 2, and therefore will not be described here.

[0037] Fig. 5 is a plan view showing the structure of a solid electrolyte joint according to still another embodiment of the present invention, and Fig. 6 is a cross-sectional view taken along line III-III of the solid electrolyte joint shown in Fig. 5. In Fig. 5 and Fig. 6, the same reference numerals are used for components similar to or identical to those in Figs. 1 to 4.

[0038] In the solid electrolyte joint 30 of this embodiment, the solid electrolyte 12, the first electrode 13, and the second electrode 14 are all disk-shaped. As shown in Fig. 6 , which is a cross section of the solid electrolyte joint 30, the solid electrolyte joint 30 is similar to the solid electrolyte joint 10 of each of the above-described embodiments in that it has only one oxygen diffusion path. However, the solid electrolyte joint 30 of this embodiment differs from the solid electrolyte joint 10 of each of the above-described embodiments in that there is no portion where the substrate 11 and the solid electrolyte 12 are in direct contact with each other, and the circular portion where the first electrode 13 and the solid electrolyte 12 overlap in a plan view of the solid electrolyte 12 constitutes the oxygen diffusion path 13A in the first electrode 13. Therefore, in this embodiment, the length of the boundary line of the region where the first electrode 13 and the second electrode 14 overlap in a plan view of the solid electrolyte 12 is the circumference of the second electrode 14. Therefore, the minimum cross-sectional area Sr can be expressed as πr × t, where r is the diameter of the second electrode 14 and t is the thickness of the first electrode 13. The boundary line πr is calculated using a microscope as the circumference of a circle that passes through three points on the boundary line. The thickness t is measured using a stylus step gauge.

[0039] In this embodiment, when the area of ​​the region where the first electrode 13 and the second electrode 14 overlap is Sp, Sr / Sp is 1.0×10 －７ 6.9 x 10 －４ It is preferably equal to or less than 1.0 × 10 －６ Above 6.0 x 10 －４ The relationship is as follows. When the solid electrolyte junction 30 satisfies this relationship, it is not necessary to provide a porous film separately from the electrodes, the solid electrolyte junction 30 does not have a complicated structure, and the manufacturing time can be shortened, and various electrochemical elements, such as limiting current gas sensors, that include the solid electrolyte junction 30 can be obtained. Sp was calculated using a microscope as the area of ​​a circle that passes through three points on the boundary line of the overlapping region between the first electrode 13 and the second electrode 14.

[0040] Other features and advantages of this embodiment are the same as those of the embodiment shown in FIGS. 1 and 2, and therefore will not be described here.

[0041] Fig. 7 is a plan view showing the structure of a solid electrolyte bonded body according to still another embodiment of the present invention, and Fig. 8 is a cross-sectional view taken along line IV-IV of the solid electrolyte bonded body shown in Fig. 7. In Fig. 7 and Fig. 8, the same reference numerals are used for components similar to or identical to those in Fig. 1 to Fig. 6.

[0042] The solid electrolyte joined body 40 of this embodiment differs from the solid electrolyte joined body 10 of the above embodiment in that the first electrode 13 has a plurality of oxygen diffusion paths, specifically, four oxygen diffusion paths 13A-1, 13A-2, 13A-3, and 13A-4. Therefore, the minimum cross-sectional area Sr of the oxygen diffusion path 13A at a portion where the cross-sectional area along the thickness direction of the solid electrolyte 12 is minimum is expressed as the sum ΣSr of the minimum cross-sectional areas Sr1, Sr2, Sr3, and 13A-4 of the four oxygen diffusion paths 13A-1, 13A-2, 13A-3, and 13A-4, respectively.

[0043] In this case, the cross-sectional shape along the thickness direction at the position where the minimum cross-sectional area of ​​each oxygen diffusion path is located is trapezoidal or rectangular. When the cross-sectional shape along the thickness direction is rectangular, the minimum cross-sectional area Sr1 of the oxygen diffusion path 13A-1 can be expressed as width w1 x thickness t1. Similarly, the minimum cross-sectional area Sr2 of the oxygen diffusion path 13A-2 can be expressed as width w2 x thickness t2, the minimum cross-sectional area Sr3 of the oxygen diffusion path 13A-3 can be expressed as width w3 x thickness t3, and the minimum cross-sectional area Sr4 of the oxygen diffusion path 13A-4 can be expressed as width w4 x thickness t4. That is, the minimum cross-sectional area ΣSr in this embodiment is Sr1 + Sr2 + Sr3 + Sr4, which is the sum of the minimum cross-sectional areas of the four oxygen diffusion paths. When the cross-sectional shape along the thickness direction is trapezoidal, ΣSr can also be calculated as Sr1 + Sr2 + Sr3 + Sr4, which is the sum of the minimum cross-sectional areas.

[0044] In this embodiment, when the area of ​​the region where the first electrode 13 and the second electrode 14 overlap is Sp, ΣSr / Sp is 1.0×10 －７ 6.9 x 10－４ It is necessary that the density is equal to or less than 1.0×10 －６ Above 6.0 x 10 －４ When the solid electrolyte junction 40 satisfies the above relationship, it is not necessary to provide a porous film separately from the electrodes, the solid electrolyte junction 40 does not have a complicated structure, and the manufacturing time can be shortened, and further, various electrochemical elements including the solid electrolyte junction 40, such as a limiting current gas sensor, can be obtained.

[0045] In this embodiment, the porosity of the oxygen diffusion path is ρ ０ (%), ΣSr×ρ ０ / (Sp×100) is 1.0×10 －８ 1.9 x 10 －４ Preferably, it is 2.0 × 10 or less. －７ 1.8 x 10 －４ It is more preferable that the following holds true. This enables the first electrode 13 to reliably allow oxygen to flow through the oxygen diffusion paths 13A-1, 13A-2, 13A-3, and 13A-4. Regarding this embodiment, the features and advantages when the above conditions are satisfied are the same as those of the embodiment shown in FIGS. 1 and 2, and therefore description thereof will be omitted.

[0046] In this embodiment, the first electrode 13 has four oxygen diffusion paths. However, the present invention can be applied to all cases where the number of oxygen diffusion paths is two or more. In this case, the sum of the minimum cross-sectional areas Sr of the two or more oxygen diffusion paths, ΣSr / Sp, is 1.0×10 －７ 6.9 x 10 －４ The effects of this embodiment can be achieved if the following conditions are met.

[0047] In this embodiment, the exposed portion 13C of the first electrode 13 that is exposed to the outside from the solid electrolyte 12 has an I-shape, but this shape is not particularly limited, and it can have any shape, such as an L-shape, as in the embodiment shown in FIGS. 1 and 2 .

[0048] Other features and advantages of this embodiment are the same as those of the embodiment shown in FIGS. 1 and 2, and therefore will not be described here.

[0049] Figures 9, 11 and 13 are plan views showing the structure of still another embodiment of a solid electrolyte bonded body of the present invention, Figure 10 is a cross-sectional view taken along line V-V of the solid electrolyte bonded body shown in Figure 9, Figure 12 is a cross-sectional view taken along line VI-VI of the solid electrolyte bonded body shown in Figure 11, and Figure 14 is a cross-sectional view taken along line VII-VII of the solid electrolyte bonded body shown in Figure 13. In Figures 9 to 14, the same reference numerals are used for components similar or identical to those in Figures 1 to 8.

[0050] 9 to 14 are similar to the solid electrolyte junction 10 of the embodiment shown in FIG. 1 etc. in that they have only one oxygen diffusion path, but differ from the solid electrolyte junction 10 of the above embodiment in that a substrate 11 containing a heater 15 is formed on a support 11a, and a cavity 11b having a larger area than the solid electrolyte 12 in a plan view is provided below the solid electrolyte 12. The support 11a may be formed integrally with the substrate 11, or may be formed as a separate member. Among these embodiments, the embodiments shown in FIGS. 13 and 14 differ from the embodiments shown in FIGS. 9 to 12 in that, when viewed from above, the support 11a has a through-hole 11c formed in a partial region around the periphery of the region where the solid electrolyte 12 and the second electrode 14 are located, and a part of the first electrode 13 is positioned above the through-hole 11c to suppress heat conduction.

[0051] In the embodiment shown in FIGS. 9 to 14 , when the area of ​​the region where the first electrode 13 and the second electrode 14 overlap is Sp, Sr / Sp is 1.0×10 －７ 6.9 x 10 －４ It is necessary that the density is equal to or less than 1.0×10 －６ Above 6.0 x 10 －４ When the solid electrolyte junction 50 satisfies the above relationship, it is not necessary to provide a porous film separately from the electrodes, the solid electrolyte junction 50 does not have a complicated structure, and the manufacturing time can be shortened, and further, various electrochemical elements including the solid electrolyte junction 50, such as a limiting current gas sensor, can be obtained.

[0052] In the embodiment shown in FIGS. 9 to 14, the substrate 11 is made of silicon oxide (SiO ) because of its ease of formation, ease of stress control, and low thermal conductivity. ２ ), silicon nitride (Si ３ N ４ The substrate 11 is preferably formed by chemical vapor deposition (CVD) or reactive sputtering, and the thickness of the substrate 11 is preferably 0.05 μm or more and 30 μm or less from the viewpoint of suppressing heat conduction.

[0053] 9 to 14, materials such as platinum and silicon are preferably used for the heater 15. From the viewpoint of productivity, the heater 15 is preferably formed by a sputtering method.

[0054] 9 to 14 , by providing a substrate 11 containing a heater 15 on a support 11a having a cavity 11b, heat radiation from the heater 15 to the support 11a can be suppressed, and the solid electrolyte joint 50 can be efficiently heated. Therefore, a limiting current can be generated in the solid electrolyte joint 50 with low power consumption. In particular, in the embodiments shown in FIGS. 13 and 14 , the through-holes 11c are provided in a partial region, so that a limiting current can be generated in the solid electrolyte joint 50 with even lower power consumption.

[0055] In the embodiment shown in FIGS. 9 to 14, the support 11a is made of, for example, silicon (Si), silicon carbide (SiC), gallium nitride (GaN), aluminum nitride (AlN), sapphire, silicon oxide (SiO ２ ), silicon nitride (Si ３ N ４ ), zirconium oxide (ZrO ２ ), aluminum oxide (Al ２ O ３ The substrate may be made of a general-purpose substrate material such as silicon, which is readily available and chemically stable.

[0056] Other features and advantages of the embodiment shown in FIGS. 9 to 14 are similar to those of the embodiment shown in FIGS. 1 and 2, and therefore will not be described further.

[0057] Next, a preferred method for manufacturing a solid electrolyte junction of the present invention will be described using the solid electrolyte junction 10 shown in FIGS. 1 and 2 as an example. First, a first electrode 13 is formed on a substrate 11. In the process of forming the first electrode 13, the substrate 11 is prepared, and the first electrode 13 is formed on one surface of the substrate 11. Various thin film formation methods are used to form the first electrode 13. Specifically, the first electrode 13 can be formed by physical vapor deposition (PVD) methods such as evaporation, sputtering, and ion plating, or chemical vapor deposition (CVD). Of these various methods, sputtering is preferred because it is easy to form the first electrode 13 having a cocontinuous structure in which ion-conductive metal oxides are bonded by platinum or the like, and because it is suitable for mass production.

[0058] When forming the first electrode 13 by sputtering, a target of platinum or the like and a target of an ion-conductive metal oxide are used, thereby forming the first electrode 13 containing platinum or the like and the ion-conductive metal oxide. Furthermore, the porosity of the formed first electrode 13 can be controlled by adjusting the gas pressure during sputtering; for example, increasing the gas pressure can improve the porosity of the first electrode 13. The respective proportions of platinum or the like and the ion-conductive metal oxide in the first electrode 13 can be adjusted by appropriately setting the power supplied to the targets when performing the sputtering method.

[0059] After the first electrode 13 is formed, a step of forming the solid electrolyte 12 is carried out. The solid electrolyte 12 is formed on one of the two surfaces of the first electrode 13 that does not face the substrate 11. As with the formation of the first electrode 13, various thin film formation methods are used to form the solid electrolyte 12. Of the thin film formation methods, it is preferable to use a sputtering method, since it is easy to form the solid electrolyte 12 having the desired composition.

[0060] After the formation of the first electrode 13 and before the formation of the solid electrolyte 12, a firing step of the first electrode 13 may be performed. The firing step of the first electrode 13 is performed to reliably form a co-continuous structure, i.e., a cermet, in the first electrode 13, in which ion-conductive metal oxides are bonded by platinum or the like. From the viewpoint of reliably forming the co-continuous structure, the firing temperature is preferably 300°C or higher and 1300°C or lower, more preferably 500°C or higher and 1000°C or lower, and even more preferably 600°C or higher and 950°C or lower. From the same viewpoint, the firing time at the above firing temperature is preferably 1 minute or higher and 10 hours or lower, more preferably 3 minutes or higher and 5 hours or lower, and even more preferably 10 minutes or higher and 3 hours or lower. The firing atmosphere is not limited, and may be an oxygen-containing atmosphere or a reducing atmosphere. By carrying out the firing step of the electrode layer, if the electrode layer is a layer containing, for example, samarium-doped ceria (hereinafter also referred to as "SDC") and platinum, a layer consisting only of SDC is formed on the surface of the substrate 11 facing the electrode layer. Alternatively, if the substrate 11 is made of silicon, a layer consisting only of SiO ２ A layer is formed.

[0061] The solid electrolyte 12 can be formed by various thin film forming methods, similar to the first electrode 13. Specifically, the solid electrolyte 12 can be formed by physical vapor deposition (PVD) methods such as vapor deposition, sputtering, and ion plating, or chemical vapor deposition (CVD) methods. Sputtering is preferred because of its superior mass productivity.

[0062] It is preferable to perform a firing process on the formed solid electrolyte 12. The firing process for the solid electrolyte 12 can be performed in the same manner as the firing process for the first electrode 13 described above.

[0063] In this manufacturing method, the above-mentioned firing step can also be performed after the formation of the solid electrolyte 12. In this case, the firing step is primarily directed to the solid electrolyte 12, not to the first electrode 13. Therefore, in addition to the firing step primarily directed to the solid electrolyte 12, a firing step directed to the first electrode 13 can be performed after the step of forming the first electrode 13 is completed and before the step of forming the solid electrolyte 12. However, if the first electrode 13 is also sufficiently fired by the firing step primarily directed to the solid electrolyte 12, there is no need to perform a separate firing step directed to the first electrode 13 after the step of forming the first electrode 13 is completed and before the step of forming the solid electrolyte 12.

[0064] After the solid electrolyte 12 is formed, the second electrode 14 is formed by the same method as the first electrode 13. In this case, a firing step can be performed after the step of forming the solid electrolyte 12 is completed, and then a firing step can be performed again after the step of forming the second electrode 14 is completed. From the viewpoint of simplifying the process, it is preferable not to perform the firing step after the step of forming the solid electrolyte 12 is completed, but to perform the firing step after the step of forming the solid electrolyte 12 and after the step of forming the second electrode 14 is completed.

[0065] The above description has been given regarding the method for manufacturing the solid electrolyte junction 10 shown in FIGS. 1 and 2 . However, the solid electrolyte junction 20 shown in FIGS. 3 and 4 , the solid electrolyte junction 30 shown in FIGS. 5 and 6 , and the solid electrolyte junction 40 shown in FIGS. 7 and 8 can be manufactured in the same manner, except for changing the shapes of the masks used when forming the solid electrolyte 12, the first electrode 13, and the second electrode 14.

[0066] Although the present invention has been described above based on the preferred embodiments, the present invention is not limited to the above embodiments.

[0067] In addition to the above-described embodiments, the present invention further discloses the following solid electrolyte junction, electrochemical element, and limiting current gas sensor. [1] A solid electrolyte junction including a substrate, a solid electrolyte disposed on the substrate, and a first electrode and a second electrode disposed opposite each other with the solid electrolyte interposed therebetween, wherein the solid electrolyte has oxide ion conductivity, at least a portion of the first electrode is located between the substrate and the solid electrolyte and includes a porous body, and the first electrode has only one oxygen diffusion path formed to overlap with the substrate and the solid electrolyte in a plan view of the solid electrolyte junction, and when a portion of the oxygen diffusion path where the substrate and the solid electrolyte overlap in a plan view of the solid electrolyte junction is cut perpendicularly to the oxygen diffusion direction to obtain a cross section of the first electrode, Sr denotes the minimum cross-sectional area at a portion where the area of ​​the cross section is smallest, and Sp denotes the area of ​​a region where the first electrode and the second electrode overlap in a plan view of the solid electrolyte, and Sr / Sp is 1.0×10 －７ 6.9 x 10 －４ [2] A solid electrolyte junction comprising: a substrate; a solid electrolyte disposed on the substrate; and a first electrode and a second electrode disposed opposite each other with the solid electrolyte interposed therebetween, wherein the solid electrolyte has oxide ion conductivity, at least a portion of the first electrode is located between the substrate and the solid electrolyte and includes a porous body, the first electrode has a plurality of oxygen diffusion paths formed to overlap with the substrate and the solid electrolyte in a plan view of the solid electrolyte junction, a portion of each oxygen diffusion path where the substrate and the solid electrolyte overlap in a plan view of the solid electrolyte junction is cut perpendicularly to the oxygen diffusion direction to obtain a cross section of the first electrode, Sr is the minimum cross-sectional area at a portion where the cross section has the smallest area, and ΣSr is the sum of the minimum cross-sectional areas Sr of all the oxygen diffusion paths, and Sp is the area of ​​a region where the first electrode and the second electrode overlap in a plan view of the solid electrolyte, where ΣSr / Sp is 1.0×10 －７ 6.9 x 10 －４[3] The solid electrolyte joined body according to [1] or [2], wherein the shape of a cross section of the oxygen diffusion path along the thickness direction at a portion where the minimum cross-sectional area Sr is located is trapezoidal or rectangular. [4] The solid electrolyte joined body according to any one of [1] to [3], wherein the first electrode has a shape including a circular portion or a polygonal portion in a plan view of the solid electrolyte. [5] The solid electrolyte joined body according to any one of [1] to [3], wherein the first electrode contains a metal oxide and has a porosity ρ ０ [6] The solid electrolyte junction according to any one of [1] to [4], wherein the ratio of the metal oxide in the first electrode is 1.0% to 60% by volume. [7] The solid electrolyte junction according to any one of [1] to [6], wherein the first electrode is in contact with the substrate made of silicon.

[0068] [8] The solid electrolyte junction according to any one of [1] to [7], wherein the first electrode has a thickness of 10 nm or more and 2000 nm or less. [9] The solid electrolyte junction according to any one of [1] to [8], wherein the first electrode has an average pore diameter of 5 nm or more and 200 nm or less.

[10] The solid electrolyte junction according to any one of [1] to [9], wherein the first electrode contains at least one of a platinum group element, gold, and an alloy containing these.

[11] The solid electrolyte junction according to any one of [1] to

[10] , wherein the solid electrolyte is a ceramic containing at least one selected from the group consisting of a composite oxide containing lanthanum and silicon, yttrium-stabilized zirconia, samarium-doped ceria, gadolinium-doped ceria, lanthanum gallate, and yttrium-doped bismuth oxide.

[12] An electrochemical device having the solid electrolyte junction according to any one of [1] to

[11] .

[13] A limiting current gas sensor having the electrochemical element according to

[12] , wherein the relationship between the current value and the oxygen concentration is linear.

[14] A limiting current gas sensor in which a limiting current is generated when a voltage of 1.0 V or more is applied to the electrochemical element according to

[12] at 600°C.

[0069] Example 1 In this example, a solid electrolyte junction 10 shown in FIGS. 1 and 2 was fabricated. A silicon substrate 11 with a crystal orientation of <100> and a thickness of 300 μm was prepared. A first electrode 13 with a thickness of 0.850 μm was formed on one surface of this substrate 11 by a sputtering method. The shape of the first electrode 13 was controlled to w=1600 μm using a stencil mask. A 2-inch platinum target and a 4-inch (La) target were used as targets for the sputtering method. ０．７５ Y ０．２５ ) ９．３３ Si ６ O ２６ A target of YLSO was used. Co-sputtering, in which power is supplied to two targets simultaneously, was used to form the film. DC sputtering was used for platinum, and RF sputtering was used for YLSO. The argon gas flow rate was 50 sccm, and the argon pressure was 4 Pa. The power was 90 W and 200 W, respectively, and sputtering was performed at room temperature. The first electrode 13 contained 15 vol% YLSO and 85 vol% platinum.

[0070] Next, a 300 nm thick layer of solid electrolyte 12 was formed on the first electrode 13 by RF sputtering. A 4-inch YLSO target was used as the sputtering target. The argon gas flow rate was 50 sccm, and the argon pressure was 0.5 Pa. The power was 200 W, and sputtering was performed at room temperature. Furthermore, a second electrode 14 made of the same porous composite as the first electrode 13 was formed on the solid electrolyte 12 using the same manufacturing method as the first electrode 13.

[0071] The oxygen diffusion path 13A of the first electrode 13 has a trapezoidal cross-sectional shape along the thickness direction of the first electrode 13, and the minimum cross-sectional area Sr, the area Sp of the region where the first electrode 13 and the second electrode 14 overlap, and the value of Sr / Sp are as shown in Table 1.

[0072] Next, a maximum voltage of 1.5 V was applied to the first electrode 13 and the second electrode 14 of the solid electrolyte joint 10 fabricated as described above, and the occurrence of limiting current was examined at 600°C, 550°C, 500°C, and 450°C in an atmosphere with an oxygen concentration of 100%. The results are shown in Table 1. In the table, "A" indicates that limiting current was clearly generated, "B" indicates that limiting current was observable, and "C" indicates that no observable limiting current was generated.

[0073] Example 2 The minimum cross-sectional area Sr of the oxygen diffusion path 13A of the first electrode 13, the area Sp of the region where the first electrode 13 and the second electrode 14 overlap, and the value of Sr / Sp were changed as shown in Table 1. In addition, a heater 15 layer was provided on one of the two atomically flat surfaces of a 300 μm-thick silicon substrate, on which the first electrode 13 was not formed. Except for these, the solid electrolyte joint 10 was fabricated in the same manner as in Example 1.

[0074] An oxygen gas sensor was fabricated in the same manner as in Example 1, and a maximum voltage of 1.5 V was applied to check whether or not a limiting current was generated in an atmosphere with an oxygen concentration of 100% at temperatures of 600°C, 550°C, 500°C, and 450°C. The results are shown in Table 1.

[0075] Example 3 A solid electrolyte joint 10 was fabricated in the same manner as in Example 1, except that the minimum cross-sectional area Sr of the oxygen diffusion path 13A of the first electrode 13, the area Sp of the region where the first electrode 13 and the second electrode 14 overlap, and the value of Sr / Sp were set as shown in Table 1.

[0076] An oxygen gas sensor was fabricated in the same manner as in Example 1, and a maximum voltage of 1.5 V was applied to check whether or not a limiting current was generated in an atmosphere with an oxygen concentration of 100% at temperatures of 600°C, 550°C, 500°C, and 450°C. The results are shown in Table 1.

[0077] 5 and 6 was produced. The solid electrolyte joint 30 was formed in the same manner as in Example 1, except that the first electrode 13 was formed on the silicon substrate 11 with a larger area than the solid electrolyte 12, and the solid electrolyte 12 and the second electrode 14 were disk-shaped.

[0078] Table 1 shows the diameter r of the second electrode 14, the thickness t of the first electrode 13, the minimum cross-sectional area Sr, the area Sp of the region where the first electrode 13 and the second electrode 14 overlap, and the value of Sr / Sp.

[0079] An oxygen gas sensor was fabricated in the same manner as in Example 1, and a maximum voltage of 1.5 V was applied to check whether or not a limiting current was generated in an atmosphere with an oxygen concentration of 100% at temperatures of 600° C., 550° C., 500° C., and 450° C. The results are shown in Table 1.

[0080] Example 5 A solid electrolyte joint 10 was fabricated in the same manner as in Example 1, except that the minimum cross-sectional area Sr of the oxygen diffusion path 13A of the first electrode 13, the area Sp of the region where the first electrode 13 and the second electrode 14 overlap, and the value of Sr / Sp were set as shown in Table 1, and the ratio of YLSO to Pt in the first electrode was set to 53 vol % YLSO and 47 vol % platinum.

[0081] Table 1 shows the minimum cross-sectional area Sr, the area Sp of the region where the first electrode 13 and the second electrode 14 overlap, and the value of Sr / Sp.

[0082] An oxygen gas sensor was fabricated in the same manner as in Example 1, and a maximum voltage of 1.5 V was applied to check whether or not a limiting current was generated in an atmosphere with an oxygen concentration of 100% at temperatures of 600° C., 550° C., 500° C., and 450° C. The results are shown in Table 1.

[0083] Comparative Example 1 A solid electrolyte joint 30 was fabricated in the same manner as in Example 4, except that the diameter r of the second electrode 14, the thickness t of the first electrode 13, the minimum cross-sectional area Sr, the area Sp of the region where the first electrode 13 and the second electrode 14 overlap, and the value of Sr / Sp were changed as shown in Table 1.

[0084] An oxygen gas sensor was fabricated in the same manner as in Example 1, and a maximum voltage of 2 V was applied to check whether or not a limiting current was generated in an atmosphere with an oxygen concentration of 100% and an atmosphere with an oxygen concentration of 21% at temperatures of 600°C, 550°C, 500°C, and 450°C. The results are shown in Table 1.

[0085]

[0086] In Examples 1 to 5 according to the present invention, the Sr / Sp values ​​were within the range of the present invention, and therefore when these solid electrolyte assemblies were used in oxygen gas sensors, limiting currents were observed at 500°C or higher in all cases, confirming that they could be used as limiting current-type gas sensors. On the other hand, in Comparative Example 1, in which the Sr / Sp value was outside the range of the present invention, no limiting current was observed at the measurement temperature in an atmosphere with an oxygen concentration of 100%, and a limiting current was observed at 1.7 V in an atmosphere with an oxygen concentration of 21%. It was confirmed that the solid electrolyte assemblies could not be used as limiting current-type gas sensors over a wide concentration range.

[0087] Furthermore, in Examples 1 to 5, it was found that since it was not necessary to provide a porous membrane separately from the electrodes, a solid electrolyte junction and, in turn, a limiting current gas sensor could be obtained that did not have a complicated structure and that could be manufactured in a shorter time.

[0088] According to the present invention, there is provided a solid electrolyte assembly that does not have a complicated structure and can be produced in a shorter time.

Claims

1. A solid electrolyte junction comprising: a substrate; a solid electrolyte disposed on the substrate; and a first electrode and a second electrode disposed opposite each other with the solid electrolyte interposed therebetween, wherein the solid electrolyte has oxide ion conductivity; at least a portion of the first electrode is located between the substrate and the solid electrolyte and includes a porous body; in a plan view of the solid electrolyte junction, the first electrode has only one oxygen diffusion path formed to overlap with the substrate and the solid electrolyte; when a portion of the oxygen diffusion path where the substrate and the solid electrolyte overlap in a plan view of the solid electrolyte junction is cut perpendicularly to the oxygen diffusion direction to obtain a cross section of the first electrode, Sr denotes the minimum cross-sectional area at a portion where the area of ​​the cross section is smallest; and Sp denotes the area of ​​a region where the first electrode and the second electrode overlap in a plan view of the solid electrolyte, Sr / Sp is 1.0×10 －７ 6.9 x 10 －４ A solid electrolyte junction, which is as follows:

2. A solid electrolyte junction comprising: a substrate; a solid electrolyte disposed on the substrate; and a first electrode and a second electrode disposed opposite each other with the solid electrolyte interposed therebetween, wherein the solid electrolyte has oxide ion conductivity; at least a portion of the first electrode is located between the substrate and the solid electrolyte and includes a porous body; in a plan view of the solid electrolyte junction, the first electrode has a plurality of oxygen diffusion paths formed to overlap with the substrate and the solid electrolyte; when a portion of each oxygen diffusion path where the substrate and the solid electrolyte overlap in a plan view of the solid electrolyte junction is cut perpendicular to the oxygen diffusion direction to obtain a cross section of the first electrode, Sr denotes the minimum cross-sectional area at a portion where the cross section has the smallest area, and ΣSr denotes the sum of the minimum cross-sectional areas Sr of all the oxygen diffusion paths; and when Sp denotes the area of ​​a region where the first electrode and the second electrode overlap in a plan view of the solid electrolyte, ΣSr / Sp is 1.0×10 －７ 6.9 x 10 －４ A solid electrolyte junction, which is as follows:

3. A solid electrolyte joint according to claim 1 or 2, wherein the cross section of the oxygen diffusion path along the thickness direction at the portion where the minimum cross-sectional area Sr is located is trapezoidal or rectangular.

4. A solid electrolyte joint according to claim 1 or 2, wherein the first electrode has a shape including a circular portion or a polygonal portion in a plan view of the solid electrolyte.

5. The first electrode comprises a metal oxide and has a porosity ρ ０ The solid electrolyte joint according to claim 1 or 2, wherein the ratio of the total surface area to the total surface area is 1.0% or more and 50% or less.

6. The solid electrolyte joint according to claim 5, wherein the ratio of said metal oxide in the first electrode is 1.0% by volume or more and 60% by volume or less.

7. A solid electrolyte junction according to claim 1 or 2, wherein the first electrode is in contact with the substrate made of silicon.

8. The solid electrolyte joint according to claim 1 or 2, wherein the first electrode has a thickness of 10 nm or more and 2000 nm or less.

9. The solid electrolyte joint according to claim 1 or 2, wherein the first electrode has an average pore size of 5 nm or more and 200 nm or less.

10. A solid electrolyte joint according to claim 1 or 2, wherein the first electrode contains at least one of a platinum group element, gold, and an alloy containing these.

11. A solid electrolyte joint according to claim 1 or 2, wherein the solid electrolyte is a ceramic containing at least one selected from the group consisting of a composite oxide containing lanthanum and silicon, yttrium-stabilized zirconia, samarium-doped ceria, gadolinium-doped ceria, lanthanum gallate, and yttrium-doped bismuth oxide.

12. An electrochemical device comprising the solid electrolyte junction according to claim 1 or 2.

13. A limiting current gas sensor comprising the electrochemical element according to claim 12, wherein the relationship between the current value and the oxygen concentration is linear.

14. A limiting current gas sensor in which a limiting current is generated when a voltage of 1.0 V or more is applied to the electrochemical element according to claim 12 at 600°C.