Gas Sensors and Sensor Devices

Abstract

To provide a gas sensor with good response characteristics.SOLUTION: A gas sensor is provided, comprising a gas sensing layer including a first layer containing tin oxide and a second layer formed on the first layer and containing cerium oxide particles, where the surface of the cerium oxide particles being {100} plane.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a gas sensor for detecting gas and a sensor device using the gas sensor. [Background technology]

[0002] Various technologies related to gas sensors for detecting gases have been proposed. Among the various gas sensors, semiconductor gas sensors have advantages in detecting low concentrations of gas, but there is a strong demand for further improvement in response characteristics.

[0003] It is widely known that semiconductor gas sensors use metal oxides as the gas-sensitive layer to detect gases, and the gas is detected by utilizing the change in resistance when the gas-sensitive layer adsorbs the target gas.

[0004] Various materials have been investigated as metal oxides to be used as the gas-sensitive layer. It is widely known that tin oxide (SnO2) is used as the metal oxide (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-53804 Summary of the Invention [Problem to be solved by the invention]

[0006] However, there is room for improvement in the response characteristics when a gas-sensitive layer is formed from a single layer containing tin oxide. In particular, when a gas sensor is used to detect gases contained in biological gases (e.g., exhaled breath or skin gases) that are thought to be related to disease, good response characteristics are desired even in the low concentration range. In consideration of the above circumstances, the present invention aims to provide a gas sensor with good response characteristics and a sensor device using such a gas sensor. [Means for solving the problem]

[0007] [1] A gas sensor according to the present invention comprises a gas-sensitive layer including a first layer containing tin oxide and a second layer formed on the surface of the first layer and containing cerium oxide particles, the surfaces of the cerium oxide particles being {100} planes.

[0008] [2] The gas sensor according to [1], wherein the tin oxide is in the form of a nanosheet.

[0009] [3] A semiconductor gas sensor [1] or [2].

[0010] [4] The gas sensor according to any one of [1] to [3], wherein the cerium oxide particles have a particle size of 10 to 90 nm.

[0011] [5] The gas sensor according to any one of [1] to [4], further comprising a first electrode and a second electrode connected to the gas-sensitive layer at different positions.

[0012] [6] A sensor device according to the present invention comprises a gas sensor according to any one of [1] to [5] and a detection unit that detects the presence of a gas to be detected in accordance with a current flowing between the first electrode and the second electrode. [Effects of the Invention]

[0013] The gas sensor according to the present invention can improve response characteristics, and the sensor device according to the present invention can detect gas with high accuracy. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a scanning electron microscope image of cerium oxide nanocubes (cerium hydroxide raw material) in Example 1, in which the {100} plane is exposed. [Figure 2] 1 is a scanning electron microscope image of cerium oxide nanocubes (cerium nitrate raw material) in Example 2, in which the {100} plane is exposed. [Figure 3] 1 is a transmission electron microscope image of cerium oxide nanocubes (cerium hydroxide raw material) in Example 2, in which the {100} plane is exposed. [Figure 4] 1 is a scanning electron microscope image of cerium oxide regular octahedron particles (cerium hydroxide raw material) in Comparative Example 1, in which the {111} plane is exposed. [Figure 5] 1 is a scanning electron microscope image of cerium oxide regular octahedron particles (cerium nitrate raw material) in Comparative Example 2, in which the {111} plane is exposed. [Figure 6] 1 is a transmission electron microscope image of cerium oxide regular octahedron particles (cerium nitrate raw material) in Comparative Example 2, in which the {111} plane is exposed. [Figure 7] 1 is a scanning electron microscope image of the surface of an alumina substrate (before the formation of tin oxide nanosheets) used in the gas sensors according to Examples and Comparative Examples. [Figure 8] 1 is a scanning electron microscope image of a cross section of an alumina substrate (before the formation of tin oxide nanosheets) used in the gas sensors according to Examples and Comparative Examples. [Figure 9] 1 is a scanning electron microscope image of the surface of an alumina substrate (after forming a tin oxide nanosheet) used in a gas sensor according to an example. [Figure 10] 1 is a scanning electron microscope image of a cross section of an alumina substrate (after forming a tin oxide nanosheet) used in a gas sensor according to an example. [Figure 11] 1 is a scanning electron microscope image of the surface ({100} plane of cerium oxide) of the gas-sensitive layer of the gas sensor according to the example. [Figure 12]1 is a scanning electron microscope image of a cross section of a gas-sensitive layer of a gas sensor according to an example. [Figure 13] 10 is a graph showing the sensor response value of the gas sensor according to Example 2 to acetone as a function of the operating temperature. [Figure 14] 1 is a graph showing changes in resistance value with respect to a plurality of target gases for the gas sensors according to Examples 1 and 2 and Comparative Examples 1 to 3. [Figure 15] 1 is a graph showing changes in sensor response (Ra / Rg) for a plurality of target gases for the gas sensors according to Examples 1 and 2 and Comparative Examples 1 to 3. [Figure 16] 1 is a graph showing changes in sensor response (Ra / Rg) to acetone for the gas sensors according to Examples 1 and 2 and Comparative Examples 1 to 3. DETAILED DESCRIPTION OF THE INVENTION

[0015] The gas sensor according to the present invention is a sensor device for detecting a desired gas, and specifically includes an insulating substrate, an electrode pair (a first electrode and a second electrode), and a gas-sensitive layer.

[0016] The electrode pair is formed on the surface of the substrate. The gas-sensitive layer is connected to the first electrode and the second electrode at different positions. For example, the gas-sensitive layer is provided so as to cover the surface of the electrode pair (the surface opposite the substrate). That is, the gas-sensitive layer is provided over the surfaces of the first electrode and the second electrode and over the surface of the substrate between the first and second electrodes. The substrate is made of any known insulating material (e.g., metal oxide, etc.). Similarly, the first electrode and the second electrode are made of any known conductive material (e.g., Pt, Ir, Pd, Ag, Ni, W, Cu, Al, etc.).

[0017] The gas-sensitive layer according to the present invention includes a first layer and a second layer formed on the surface of the first layer (the surface opposite the substrate). The first layer and the second layer are positioned in this order in the thickness direction as viewed from the substrate. That is, the second layer is positioned on the opposite side of the first layer from the substrate. In the gas-sensitive layer of this embodiment, the surface of the second layer (the surface opposite the first layer) is the surface that directly contacts gas (i.e., adsorbs gas).

[0018] The first layer contains tin oxide (SnO2). Tin oxide is contained in the first layer as a main component, for example, at a content of 70 mass% or more in the first layer, preferably 80 mass% or more, and more preferably 90 mass% or more. The first layer may be entirely made of tin oxide (100 mass%).

[0019] The form of tin oxide is not particularly limited, and may be, for example, a nanosheet or nanoparticle form. However, from the viewpoint of reducing the resistance value of the gas sensor and improving gas selectivity, a configuration using nanosheet-shaped tin oxide for the first layer is preferable. A nanosheet is a two-dimensional nanostructure in the form of a layer with a thickness (average) of, for example, about 1 to 100 nm. The thickness of the nanosheet is the average value of thicknesses measured for several tens (for example, 30) of sheet pieces from transmission electron microscope (TEM) images or scanning electron microscope (SEM) images.

[0020] When nanoparticle-shaped tin oxide is used, the particle diameter (average value) is, for example, 1 to 100 nm. The particle diameter (secondary particle diameter) is the average value of particle diameters measured for any tens of particles (for example, 30 particles) from transmission electron microscope (TEM) images or scanning electron microscope (SEM) images. In the present invention, the particle diameter (and the same applies to the primary particle diameter) is the circle-equivalent diameter of the particle (the diameter of a circle or sphere having the same area, volume, etc. as the particle).

[0021] The thickness of the first layer is not particularly limited and may be, for example, the thickness of a nanosheet or the diameter of a nanoparticle. Note that tin oxide doped with other elements (e.g., Zn, Ti, Ce, Fe, etc.) may also be used for the first layer.

[0022] The second layer contains cerium oxide (CeO2) particles. The cerium oxide particles are contained in the second layer as a main component, for example, at a content of 70 mass% or more, preferably 80 mass% or more, and more preferably 90 mass% or more in the second layer. The entire second layer may be made up of cerium oxide particles (100 mass%).

[0023] The surface of the cerium oxide particles is the {100} plane. In other words, the {100} plane of the cerium oxide particles is exposed. It is preferable that the {100} plane of the cerium oxide is exposed on the surface of the second layer opposite to the first layer. The {100} plane is a group of planes equivalent to the (100) plane.

[0024] The fact that the surfaces of the cerium oxide particles are {100} planes can be confirmed by observing the cerium oxide particles with, for example, a transmission electron microscope (TEM) or a scanning electron microscope (SEM).

[0025] The particle diameter (average value) of the cerium oxide particles is not particularly limited, but is, for example, 100 nm to 500 μm. The particle diameter (secondary particle diameter) is the average value of particle diameters measured for several tens of particles (for example, 30 particles) from transmission electron microscope (TEM) images or scanning electron microscope (SEM) images.

[0026] The average primary particle diameter of the primary particles of the cerium oxide particles is, for example, 3 to 100 nm, and preferably 5 to 20 nm. The average primary particle diameter is the average value of primary particle diameters measured for any several tens (for example, 30) of primary particles from, for example, a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image.

[0027] The primary particles of the cerium oxide particles are preferably cubic (approximately cubic). However, the primary particles of the cerium oxide particles may have other shapes (e.g., spherical). Furthermore, the cerium oxide particles used in the second layer are preferably single crystals.

[0028] The thickness of the second layer is not particularly limited, and may be, for example, approximately the particle diameter of the cerium oxide particles. Note that, as long as the surfaces of the cerium oxide particles maintain the {100} plane, cerium oxide particles doped with other elements (e.g., Zn, Bi, Ni, Fe, etc.) may be used for the second layer.

[0029] The proportion (coverage) of the area covered by the second layer (i.e., the {100} faces of the cerium oxide particles) to the entire surface area of ​​the first layer is, for example, 10% or more, preferably 20% or more, and more preferably 30% or more. The upper limit of the coverage is, for example, 100% or less, preferably 80% or less, more preferably 65% ​​or less, and even more preferably 50% or less. When the proportion of the surface of the first layer covered by the second layer is within the above range, the response characteristics can be improved.

[0030] The coverage is determined, for example, from a transmission electron microscope image or a scanning electron microscope image. Note that a layer other than the second layer (i.e., a layer made of an oxide other than cerium oxide particles with an exposed {100} plane) may be present on the surface of the first layer.

[0031] Furthermore, the second layer does not necessarily have to be formed as a continuous layer on the surface of the first layer. That is, the second layer may be scattered as multiple regions spaced apart from one another on the surface of the first layer. Note that the gas-sensitive layer may also include other layers in addition to the first and second layers.

[0032] The gas sensor according to the present invention can improve response characteristics (sensor response (Ra / Rg)) compared to a configuration in which the gas-sensitive layer is a single layer made of tin oxide, for example. Here, Ra is the resistance of the gas sensor in air, and Rg is the resistance in the gas to be detected (target gas).

[0033] The gas sensor of the present invention has an advantage that it can detect a target gas with high accuracy even when the target gas is in low concentration. For example, it is effective for detecting low-concentration gases (e.g., acetone, acetaldehyde, ethanol, ammonia, allyl mercaptan, etc.) contained in biological gases (e.g., exhaled breath and skin gases) that are thought to be related to diseases.

[0034] The present invention can also be conceived as a sensor device including the gas sensor exemplified above and a detection unit that detects the presence (and concentration) of a target gas to be detected in accordance with the current flowing between the first electrode and the second electrode. The sensor device according to the present invention can detect gas with high accuracy.

[0035] The method for manufacturing a gas sensor according to the present invention employs any of various known techniques. First, a first layer is formed on the surface of a substrate on which a first electrode and a second electrode have been formed. Any known film formation technique (e.g., vapor deposition, sputtering, chemical vapor deposition, liquid phase epitaxy, etc.) is used to form the first layer. When a tin oxide nanosheet is used for the first layer, a liquid phase epitaxy method is used in which the substrate is immersed in a tin oxide precursor solution (e.g., a tin fluoride aqueous solution) to form the tin oxide nanosheet on the substrate.

[0036] Next, a second layer is formed on the surface of the first layer by any known film formation technique (e.g., dispersion dropping, evaporation, sputtering, chemical vapor deposition, liquid phase epitaxy, etc.) using cerium oxide particles with the {100} plane exposed.

[0037] Cerium oxide particles with exposed {100} planes can be produced by any known technique. For example, decanoic acid is added to an aqueous solution containing a precursor of cerium oxide particles (e.g., cerium hydroxide or cerium nitrate) in an amount equal to the moles of the precursor, and the mixture is placed in a batch reactor heated to a predetermined temperature (e.g., around 400°C) and maintained for several minutes to synthesize cerium oxide particles with exposed {100} planes. [Example]

[0038] The present invention will be described in detail below with reference to examples, although the present invention is not limited to these examples.

[0039] [Example 1] The gas sensor according to Example 1 used nanosheet-type tin oxide as the first layer and nanocube-type cerium oxide particles (hereinafter referred to as "cerium oxide nanocubes") as the second layer. Example 1 was manufactured as follows.

[0040] <1> Synthesis of cerium oxide nanocubes Cerium oxide nanocubes with exposed {100} faces were produced as follows: First, an aqueous solution (0.1 M) of cerium hydroxide (Ce(OH)4; manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was prepared, and decanoic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the solution in an amount equal to the number of moles of cerium hydroxide. The solution was then placed in a batch reactor preheated to 400°C and held for 10 minutes to synthesize cerium oxide nanocubes with exposed {100} faces.

[0041] The synthesized cerium oxide nanocubes were then taken out and centrifuged to remove impurities, and then powdered using a freeze dryer.

[0042] <2> Synthesis of tin oxide (SnO2) nanosheets First, a pair of Pt interdigital electrodes were formed on the surface of the alumina substrate using screen printing. A Pt heater electrode, used to heat the sensor, was also formed on the backside of the alumina substrate. Next, the surface of the alumina substrate on which the interdigital electrodes were formed was exposed to vacuum ultraviolet light for 20 minutes to remove any adsorbed organic matter from the surface, transforming it into a hydrophilic surface.

[0043] The tin oxide nanosheets were formed by liquid phase crystal growth. Specifically, the alumina substrate was immersed in a 28 mM tin fluoride solution at 90°C for 30 minutes to form a thin film of tin oxide nanosheets on the surface of the alumina substrate.

[0044] <3> Gas sensor fabrication <2> On the surface of tin oxide nanosheets synthesized on an alumina substrate, <1> The powdered cerium oxide nanocubes synthesized in the previous study were dispersed in distilled water using an ultrasonic cleaner, and the dispersion was then dropped onto the tin oxide nanosheet, after which it was dried, thereby coating (modifying) the surface of the nanosheet with cerium oxide nanocubes that exposed the {100} plane. The fabricated gas sensor is designated CeO2{100}-H.

[0045] [Example 2] In Example 2, similar to Example 1, nanosheet-type tin oxide was used as the first layer and cerium oxide nanocubes were used as the second layer. In the synthesis of the cerium oxide nanocubes, cerium nitrate (Ce(NO3)3; manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of cerium hydroxide, similar to Example 1. The fabricated gas sensor is referred to as CeO2{100}-N.

[0046] [Comparative Example 1] In Comparative Example 1, regular octahedral cerium oxide particles (octahedral nanoparticles) with the {111} plane exposed were used as the second layer of the gas sensor. Comparative Example 1 was the same as Example 1, except that synthesis was performed without adding an equal number of moles of decanoic acid to the aqueous solution (0.1 M) in which cerium hydroxide was dissolved. The fabricated gas sensor is referred to as CeO2{111}-H.

[0047] Comparative Example 2 In Comparative Example 2, cerium oxide regular octahedral particles with exposed {111} planes were used as the second layer of the gas sensor. The cerium oxide regular octahedral particles with exposed {111} planes were the same as those in Comparative Example 1, except that cerium nitrate (Ce(NO3)3; manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of cerium hydroxide. The fabricated gas sensor is referred to as CeO2{111}-N.

[0048] Comparative Example 3 In Comparative Example 3, the gas-sensitive layer was a single layer made of a tin oxide nanosheet.

[0049] The examples and comparative examples were evaluated as follows.

[0050] <1> Cerium oxide nanocubes (Examples 1 and 2) and cerium oxide octahedral particles (Comparative Examples 1 and 2) The cerium oxide nanocubes used in Examples 1 and 2 and the cerium oxide regular octahedral particles used in Comparative Examples 1 and 2 were observed under an electron microscope, and the results are shown in FIGS.

[0051] FIG. 1 is a scanning electron microscope (SEM) image of cerium oxide nanocubes (cerium hydroxide raw material) in Example 1, and FIG. 2 is a scanning electron microscope image of cerium oxide nanocubes (cerium nitrate raw material) in Example 2. As can be seen from FIGS. 1 and 2, the cerium oxide nanocubes in Examples 1 and 2 formed aggregates. In Example 1, the primary particle diameter of the cerium oxide nanocubes constituting the aggregates was approximately 10 nm. In Example 2, the primary particle diameter of the cerium oxide nanocubes constituting the aggregates was approximately 20 to 50 nm. That is, the average primary particle diameter of the cerium oxide nanocubes in Examples 1 and 2 was within the range of 3 to 100 nm.

[0052] Figure 3 is a transmission electron microscope (TEM) image of the cerium oxide nanocubes in Example 2. The TEM image in Figure 3 confirms that the cerium oxide nanocubes in Example 2 have a cubic shape (i.e., cube-like) with a lattice fringe spacing of 0.27 nm and are single crystals with the {100} plane exposed.

[0053] FIG. 4 is a scanning electron microscope image of the cerium oxide regular octahedron particles (cerium hydroxide raw material) in Comparative Example 1, and FIG. 5 is a scanning electron microscope image of the cerium oxide regular octahedron particles (cerium nitrate raw material) in Comparative Example 2.

[0054] As can be seen from Fig. 4, the cerium oxide regular octahedral particles according to Comparative Example 1 formed aggregates. The primary particle diameter of the cerium oxide regular octahedral particles constituting the aggregates in Comparative Example 1 was about 10 nm. On the other hand, in Comparative Example 2, aggregates made up of polyhedral particles and large regular octahedral particles were observed. The size of the regular octahedral particles was about 50 to several hundred nm.

[0055] Fig. 6 is a transmission electron microscope image of the cerium oxide regular octahedral particles (cerium nitrate raw material) in Comparative Example 2. It was confirmed from the TEM image in Fig. 6 that the particles in Comparative Example 2 had a regular octahedral shape with a lattice fringe spacing of 0.32 nm and were single crystals with the {111} plane exposed.

[0056] <2> Tin oxide nanosheets 7 and 8 are scanning electron microscope images of the alumina substrate (before the formation of tin oxide nanosheets) used in the gas sensors according to each example and each comparative example. Fig. 7 is a scanning electron microscope image of the surface of the alumina substrate, and Fig. 8 is a scanning electron microscope image of the cross section of the alumina substrate. As can be seen from Figs. 7 and 8, the alumina substrate is composed of alumina particles with a particle size of several μm, and irregularities of about 100 nm were confirmed at the grain boundaries.

[0057] 9 and 10 are scanning electron microscope images of the alumina substrate (after the formation of tin oxide nanosheets) used in the gas sensor of Example 2. Fig. 9 is a scanning electron microscope image of the surface of the alumina substrate, and Fig. 10 is a scanning electron microscope image of the cross section of the alumina substrate. As can be seen from Figs. 9 and 10, tin oxide nanosheets were observed to be precipitated and scattered on the surface of the alumina substrate.

[0058] <3> Gas-sensitive layer 11 and 12 are scanning electron microscope images of the gas-sensitive layer of the gas sensor according to Example 2. FIG. 11 is a scanning electron microscope image of the outermost surface (the {100} plane of cerium oxide) of the gas-sensitive layer, and FIG. 12 is a scanning electron microscope image of a cross section of the gas-sensitive layer. From FIGS. 11 and 12, it was confirmed that the surface of the tin oxide nanosheet in the gas-sensitive layer was covered with cerium oxide nanocubes of about several tens of nanometers in size. The cerium oxide nanocubes were scattered on the surface of the tin oxide nanosheet. The coverage of the cerium oxide nanocubes on the surface of the tin oxide nanosheet was about 50%.

[0059] <4> Gas Sensor The gas sensor (made of cerium nitrate) according to Example 2 was evaluated for its sensor response (Ra / Rg) to 20 ppm acetone when the operating temperature was varied in the range of 200 to 600°C. The results are shown in Figure 13. Ra was measured using dry air (nitrogen:oxygen = 80:20). The operating temperature was varied to 200°C, 300°C, 400°C, 500°C, 550°C, and 600°C. As can be seen from Figure 13, the sensor response (Ra / Rg) was highest (14.8) when the operating temperature was 550°C.

[0060] Resistance values ​​were measured for the gas sensors according to Examples 1 and 2 and Comparative Examples 1 to 3. The results are shown in Figure 14. The temperature of the gas sensor was controlled to 550°C, and resistance values ​​were measured using a sensor evaluation module while the target gas was flowing. As the target gas, several gases contained in exhaled breath components that are thought to be related to diseases were selected. Specifically, (a) acetone, (b) acetaldehyde, (c) ethanol, (d) ammonia, and (e) allyl mercaptan were used. The gas flow rate was controlled using a multi-component gas mixer (MU-3616, manufactured by Horiba, Ltd.), and the total flow rate was 100 cm3. 3 min -1 was set to.

[0061] As shown in Figure 14, in Examples 1 and 2 and Comparative Examples 1 and 2, in which a first layer made of an oxide nanosheet as a gas-sensitive layer is coated with a second layer made of cerium oxide, it was confirmed that the resistance value was higher than that of Comparative Example 3, in which a single layer made of an oxide nanosheet was used as a gas-sensitive layer, regardless of the target gas.

[0062] Next, the sensor response (Ra / Rg) was evaluated when the concentration of each target gas was changed for the gas sensors according to Examples 1 and 2 and Comparative Examples 1 to 3. The results are shown in Fig. 15. Note that Ra was measured using dry air (nitrogen:oxygen = 80:20).

[0063] 15, Examples 1 and 2 had better sensor responses (Ra / Rg) for all target gases than Comparative Examples 1 to 3, and it was confirmed that the sensor responses (Ra / Rg) improved with increasing concentration. Although Examples 1 and 2 had higher resistance values ​​than Comparative Example 3, the sensor responses (Ra / Rg) exceeded that of Comparative Example 3.

[0064] For all target gases, Examples 1 and 2, in which the {100} plane of cerium oxide was exposed, showed a significantly improved sensor response (Ra / Rg) compared to Comparative Example 3. In contrast, Comparative Examples 1 and 2, in which the {111} plane of cerium oxide was exposed, showed a lower sensor response (Ra / Rg) compared to Comparative Example 3.

[0065] When the sensor response (Ra / Rg) at 20 ppm for each target gas was confirmed, (a) for acetone, Example 1 was approximately 6.8 times (15 / 2.2) greater than Comparative Example 3, and Example 2 was approximately 5.9 times (13 / 2.2) greater than Comparative Example 3.

[0066] (b) With regard to acetaldehyde, Example 1 was about 3.2 times that of Comparative Example 3 (8.1 / 2.5), and Example 2 was about 3.6 times that of Comparative Example 3 (8.9 / 2.5).

[0067] (c) In the case of ethanol, Example 1 was about 2.8 times that of Comparative Example 3 (22 / 7.8), and Example 2 was about 3.5 times that of Comparative Example 3 (27 / 7.8).

[0068] (d) With respect to ammonia, Example 1 was approximately 1.4 times that of Comparative Example 3 (4.2 / 3.1), and Example 2 was approximately 1.6 times that of Comparative Example 3 (5.0 / 3.1).

[0069] (e) With regard to allyl mercaptan, the ratio of Example 1 to Comparative Example 3 was about 10.3 times (33 / 3.2), and the ratio of Example 2 to Comparative Example 3 was about 7.5 times (23.9 / 3.2).

[0070] For acetone, which showed a particularly good sensor response (Ra / Rg) in Figure 15, the sensor response (Ra / Rg) at even lower concentrations was evaluated. The results are shown in Figure 16. Focusing on the sensor response (Ra / Rg) at 300 ppb, Comparative Examples 1 to 3 were 1.06 or less, showing almost no response. In contrast, Example 2 had a value of 1.37, and Example 1 had a value of 1.24.

[0071] From the above, it was confirmed that the gas sensor according to the present invention can achieve a high response even to gases with low concentrations of several hundred ppb. In particular, acetone has been reported to be correlated with diabetes, and there is a need to detect low concentrations of acetone in exhaled gases and skin gases. Therefore, the gas sensor according to the present invention is considered to be effective for diabetes screening by detecting low concentrations of acetone.

Claims

1. a first layer comprising tin oxide; a gas-sensitive layer including a second layer formed on a surface of the first layer and including cerium oxide particles; The surface of the cerium oxide particles is a {100} plane. Gas sensor.

2. The tin oxide is in the form of nanosheets. The gas sensor of claim 1.

3. It is a semiconductor gas sensor The gas sensor of claim 1.

4. The average primary particle size of the cerium oxide particles is 3 to 100 nm. The gas sensor of claim 1.

5. The gas-sensitive layer is connected to a first electrode and a second electrode at different positions. The gas sensor of claim 1.

6. The gas sensor of claim 5; a detection unit that detects the presence of a gas to be detected in response to a current flowing between the first electrode and the second electrode. Sensor device.

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