Semiconductor gas sensor

Abstract

To provide an electrode and an electrode chip, capable of improving sensitivity of electrochemical measurement.SOLUTION: A gas sensor 1 is provided, comprising an electrode layer 3 formed on an insulative substrate 2, a rugged structure layer 4 formed on and across the substrate 2 and the electrode layer 3, and a gas sensing layer 5 made of an oxide semiconductor formed on the rugged structure layer 4. The rugged structure layer 4 has a porous structure. The gas sensing layer 5 has a porous structure originating from the porous structure of the rugged structure layer 4.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a semiconductor gas sensor. [Background technology]

[0002] BACKGROUND ART Conventionally, semiconductor gas sensors having a gas detection layer made of an oxide semiconductor are known (see, for example, Patent Document 1).

[0003] This type of semiconductor gas sensor is used by heating the gas sensing layer to a temperature of several hundred degrees, causing the oxygen adsorbed on the surface of the gas sensing layer to take away electrons in the gas sensing layer, making it difficult for electricity to flow through the gas sensing layer. When the gas sensing layer is exposed to a reducing gas such as acetone or carbon monoxide in this state, the reducing gas reacts with the oxygen on the surface of the gas sensing layer, returning the electrons captured by the adsorbed oxygen to the gas sensing layer, making it easier for electricity to flow through the gas sensing layer. Semiconductor gas sensors can detect gas by measuring changes in the electrical resistance of the gas sensing layer.

[0004] In conventional gas sensors, the surface area of ​​the gas sensing layer is increased by forming the gas sensing layer from an aggregate of many columnar crystals, thereby improving the sensor sensitivity and gas selectivity. However, in order to increase the surface area of ​​the gas sensing layer, conventional gas sensors require that the oxide semiconductor constituting the gas sensing layer be formed into columnar crystals, which places limitations on the types of oxide semiconductor that can be formed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5240767 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a semiconductor gas sensor that can increase the surface area of ​​the gas sensing layer, regardless of the type of oxide semiconductor in the gas sensing layer, thereby improving the sensor sensitivity and gas selectivity. [Means for solving the problem]

[0007] The semiconductor gas sensor of the present invention comprises an electrode layer formed on an insulating substrate, a concave-convex structure layer formed across the substrate and the electrode layer, and a gas detection layer made of an oxide semiconductor formed on the concave-convex structure layer, wherein the concave-convex structure layer has a porous structure, and the gas detection layer has a porous structure resulting from the porous structure of the concave-convex structure layer.

[0008] In the semiconductor gas sensor of the present invention, the concave-convex structure layer may be made of, for example, an insulating material.

[0009] The concave-convex structure layer may be made of, for example, an insulating metal oxide.

[0010] The concave-convex structure layer may be formed of an insulating aluminum compound layer obtained by making an alumina layer porous by hot water treatment, for example.

[0011] The gas sensing layer may be formed of, for example, tungsten trioxide to which an impurity has been added and which is biased toward a negative charge. More specifically, the gas sensing layer may be formed of tungsten trioxide to which nickel has been added. The impurity added to tungsten trioxide (hereinafter also referred to simply as tungsten oxide) may be any element having a valence of five or less, and may be, in addition to nickel (Ni), for example, silicon (Si), indium (In), aluminum (Al), or two or more elements. The oxide semiconductor forming the gas sensing layer may be a metal oxide other than tungsten trioxide, such as tin dioxide or titanium dioxide, or may be an oxide semiconductor to which an impurity has been added. [Effects of the Invention]

[0012] The semiconductor gas sensor of the present invention can increase the surface area of ​​the gas sensing layer regardless of the type or crystal structure of the oxide semiconductor of the gas sensing layer. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic plan view showing an embodiment of a semiconductor gas sensor; [Figure 2] FIG. 2 is a schematic exploded perspective view showing the embodiment. [Figure 3] FIG. 2 is a schematic cross-sectional view corresponding to the position AA in FIG. 1. [Figure 4] 5A to 5C are schematic cross-sectional views for explaining an example of a manufacturing process of the embodiment. [Figure 5] 1 is a scanning electron microscope image showing a fracture surface of a concave-convex structure layer. [Figure 6] 1 is a scanning electron microscope image of the surface of a concave-convex structure layer. [Figure 7] 1 is a scanning electron microscope image of the surface of the gas sensing layer of the same embodiment. [Figure 8] 10 is a graph showing the results of using the gas sensor of the example and a conventional gas sensor to detect acetone. [Figure 9] 10 is a graph showing the response characteristics of the gas sensor of the example to acetone. [Figure 10] 10 is a graph showing the response characteristics of the gas sensor of the example to ethanol. [Figure 11] 10 is a graph showing the response characteristics of a gas sensor of a comparative example to acetone. [Figure 12] 10 is a graph showing the response characteristics of a gas sensor of a comparative example to ethanol. [Figure 13] 1 is a graph showing the response characteristics of the gas sensor of Reference Example 1 to acetone. [Figure 14] 1 is a graph showing the response characteristics of the gas sensor of Reference Example 1 to ethanol. [Figure 15]10 is a graph showing the response characteristics of the gas sensor of Reference Example 2 to acetone. [Figure 16] 10 is a graph showing the response characteristics of the gas sensor of Reference Example 2 to ethanol. [Figure 17] 10 is a graph showing the response characteristics of the gas sensor of Reference Example 3 to acetone. [Figure 18] 10 is a graph showing the response characteristics of the gas sensor of Reference Example 3 to ethanol. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment of a semiconductor gas sensor of the present invention will be described with reference to the drawings. Fig. 1 is a schematic plan view showing one embodiment. Fig. 2 is a schematic exploded perspective view showing the same embodiment. Fig. 3 is a schematic cross-sectional view corresponding to the position AA in Fig. 1.

[0015] 1 and 2, the semiconductor gas sensor 1 of this embodiment includes an insulating substrate 2, an electrode layer 3 formed on the substrate 2, a concave-convex structure layer 4 formed across the substrate 2 and the electrode layer 3, and a gas detection layer 5 made of an oxide semiconductor formed on the concave-convex structure layer 4. The gas sensor 1 is a so-called substrate-type gas sensor.

[0016] The insulating substrate 2 is made of an insulating material such as glass, quartz, ceramics, etc. The size, shape, etc. of the substrate 2 are not particularly limited.

[0017] The electrode layer 3 detects changes in the electrical resistance of the gas sensing layer 5 and includes a pair of interdigital electrode layers 3a and 3b. The interdigital electrode layers 3a and 3b can be formed, for example, by a platinum (Pt) layer deposited on the substrate 2 by sputtering using a metal mask with openings corresponding to the electrode layer formation areas. However, the shape of the electrode layer 3 is not limited to this and can be any shape, such as a parallel plate type or a spiral type. The material of the electrode layer 3 is also not particularly limited. For example, in addition to platinum, gold, silver, titanium, nickel, aluminum, ruthenium, tantalum, titanium, copper, platinum, niobium, zirconium, alloys of these elements, alloys of these elements with carbon, or elemental carbon can be used. The electrode layer 3 can be a single-layer film or a multilayer film formed by stacking multiple films.

[0018] As shown in Fig. 3, the concave-convex structure layer 4 is formed across the substrate 2 and the electrode layer 3. The concave-convex structure layer 4 is made of an insulating metal oxide having a porous structure with numerous base pores 4a. In this embodiment, the concave-convex structure layer 4 is made of an aluminum compound layer obtained by making an alumina layer porous by hot water treatment. In this embodiment, the concave-convex structure layer 4 is formed on the upper surface of the substrate 2, covering the areas where the comb teeth of the comb-shaped electrode layers 3a and 3b are formed.

[0019] Such a concave-convex structure layer 4 can be formed, for example, by depositing a film of amorphous alumina to a thickness of about 30 nm on the substrate 2 after the electrode layer 3 has been formed thereon by atomic layer deposition (ALD) or physical vapor deposition (PVD), and then immersing the substrate 2 in hot water at about 75 to 85°C for several minutes to several tens of minutes. The porous aluminum compound layer formed by this hot water treatment has a thickness (height) of, for example, about 140 to 150 nm. In this way, the concave-convex structure layer 4 having a porous structure can be formed simply by performing the extremely simple process of hot water treatment, thereby reducing manufacturing costs.

[0020] Some of the base pores 4a of the rugged-structure layer 4 open to the surface of the rugged-structure layer 4 and reach the electrode layer 3. The gas sensing layer 5, which will be described later, is electrically connected to the electrode layer 3 via the base pores 4a.

[0021] The porous concave-convex-structure layer 4 is not limited to an aluminum compound layer made porous by hot water treatment, and may be formed of other insulating metal oxides. The concave-convex-structure layer 4 may also be formed of an insulating material other than a metal oxide, such as mesoporous silica.

[0022] The gas sensing layer 5 is formed on the concave-convex structure layer 4, and has a porous structure (numerous sensing layer pores 5a) resulting from the porous structure (numerous base pores 4a) of the concave-convex structure layer 4. The gas sensing layer 5 having such a porous structure can be formed by stacking an oxide semiconductor on the concave-convex structure layer 4. In this embodiment, tungsten trioxide (WO3, hereinafter also simply referred to as tungsten oxide) is used as the material for the gas sensing layer 5.

[0023] The material of the gas detection layer 5 is not limited to tungsten oxide, but may be other oxide semiconductors such as tin dioxide, titanium dioxide, zinc oxide, indium oxide, ITO (indium tin oxide), etc., or may be doped (added) with an impurity element.

[0024] The porous structure of the gas sensing layer 5 depends on the porous structure of the concave-convex structure layer 4, and has a thickness (film thickness) of, for example, about 20 to 1000 nm. In addition, by changing the film thickness of the gas sensing layer 5, it is possible to control the porous structure of the gas sensing layer 5 (such as the opening shape, opening width, and pore depth of the sensing layer pores 5a). This makes it possible to form a gas sensor 1 equipped with a gas sensing layer 5 having a porous structure suited to the application.

[0025] The gas sensing layer 5 is preferably manufactured by vapor deposition, since this allows for highly accurate control of the formation area and film thickness. In this embodiment, the formation area of ​​the gas sensing layer 5 is the same as the formation area of ​​the concave-convex structure layer 4. Here, the vapor deposition method may be a so-called physical vapor deposition (PVD) method such as sputtering, vacuum deposition, reactive plasma deposition, or ion plating, or a so-called chemical vapor deposition (CVD) method. However, the manufacturing method of each layer is not limited to vapor deposition, and may also be a printing method such as screen printing or inkjet printing.

[0026] An adhesive layer may be formed on the surface of the substrate 2 to prevent peeling between the substrate 2 and the electrode layer 3. The material for such an adhesive layer may be any material that has good adhesion between the substrate 2 and the electrode layer 3, and examples of such an adhesive layer include chromium, titanium, and tungsten. An adhesive layer may be formed on the surface of the substrate 2 to prevent peeling between the substrate 2 and the concave-convex structure layer 4. Such an adhesive layer may be a surface treatment layer formed by performing a surface treatment on the surface of the substrate 2 that can improve adhesion to the concave-convex structure layer 4. Examples of such surface treatments include plasma treatment, corona treatment, flame treatment, etching treatment, steam treatment, and ion beam treatment.

[0027] The gas sensor 1 has a gas sensing layer 5 with a porous structure, which allows the surface area of ​​the gas sensing layer 5 to be significantly increased compared to a flat surface, thereby improving the sensor sensitivity (detection sensitivity). Furthermore, the gas sensing layer 5 has sensing layer pores 5a with a porous structure, which allows gas components to come into contact with the gas sensing layer 5 within the sensing layer pores 5a, while preventing impurities larger than the opening width of the sensing layer pores 5a on the surface of the gas sensing layer 5 from entering the sensing layer pores 5a. This reduces the area over which impurities come into contact with the gas sensing layer 5, thereby improving selective sensitivity to gas components.

[0028] Furthermore, since the porous structure of the gas sensing layer 5 (sensing layer pores 5a) is derived from the porous structure (base pores 4a) of the underlying concave-convex-structure layer 4, the gas sensing layer 5 having a porous structure can be easily and reliably formed by stacking an oxide semiconductor material on the concave-convex-structure layer 4. In other words, the gas sensor 1 forms the gas sensing layer 5 having a porous structure even if the oxide semiconductor layer forming the gas sensing layer 5 does not have a specific crystal structure that increases the surface area, such as a columnar crystal. That is, the gas sensor 1 can increase the surface area of ​​the gas sensing layer 5 regardless of the type or crystal structure of the oxide semiconductor of the gas sensing layer 5, thereby improving the sensor sensitivity and gas selectivity.

[0029] Furthermore, it is possible to control the porous structure (such as the opening shape, opening width, and pore depth of the sensing layer pores 5a) of the gas sensing layer 5 by changing the film thickness of the gas sensing layer 5. This makes it possible to form a gas sensor 1 equipped with a gas sensing layer 5 having a porous structure suited to the application.

[0030] Next, a fabrication example of the gas sensor 1 will be described with reference to FIG. 4. An electrode layer 3 having a pair of comb-shaped electrode layers 3a, 3b was formed by sputtering on an insulating substrate 2 made of glass and having a thickness of about 10 mm (see FIG. 4(1)). For example, the electrode layer 3 is formed of a platinum layer having a thickness of about 150 nm. The comb-shaped electrode layers 3a, 3b have a line width of 150 μm where the comb-shaped portions are alternately arranged, and the comb-shaped electrode layers 3a, 3b are arranged in parallel and alternately at a pitch of 300 μm (150 μm intervals).

[0031] Next, using a metal mask having an opening pattern corresponding to the formation regions of the comb-teeth electrode portions of the comb-shaped electrode layers 3a and 3b, an alumina layer 6 having a thickness of about 30 nm was formed as a metal oxide film for forming the concave-convex structure layer 4 (see FIG. 4(2)). The thickness of the alumina layer 6 may be greater or less than 30 nm.

[0032] The substrate 2 on which the electrode layer 3 and the alumina layer 6 were formed was immersed in warm water at about 75 to 85°C for about 7 minutes to make the alumina layer 6 porous, thereby forming a concave-convex structure layer 4 having a large number of base pores 4a (porous structure).The substrate 2 was then dried. The porous concave-convex structure layer 4 had a thickness of about 200 to 300 nm (see Figure 4(3)).

[0033] FIG. 5 is a scanning electron microscope image showing a fracture surface of the concave-convex-structure layer 4. FIG. 6 is a scanning electron microscope image of the surface of the concave-convex-structure layer 4. As can be seen from FIGS. 5 and 6, the concave-convex-structure layer 4, which is made of an insulating aluminum compound layer formed by making the alumina layer 6 porous through hot water treatment, has a large number of base pores 4a formed therein. The surface of the concave-convex-structure layer 4 has an uneven shape. Some of the base pores 4a in the concave-convex-structure layer 4 open to the surface of the concave-convex-structure layer 4 and reach the substrate 2. Although not shown in FIGS. 5 and 6, some of the base pores 4a on the electrode layer 3 reach the electrode layer 3.

[0034] Next, an oxide semiconductor material was deposited on the concave-convex structure layer 4 by reactive plasma deposition using a metal mask with an opening pattern corresponding to the formation region of the concave-convex structure layer 4 (the formation region of the alumina layer 6), thereby forming a gas sensing layer 5 with numerous sensing layer pores 5a (porous structure). The gas sensing layer 5 is electrically connected to the electrode layer 3 through the base pores 4a. Here, a 100-nm-thick film of tungsten oxide (WO3) doped with 0.5 at% (atomic percent) indium (In) was used as the oxide semiconductor material (see Figure 4(4)). The gas sensing layer 5 was then sintered.

[0035] In this way, by forming the metal oxide film for forming the uneven structure layer 4 and the gas sensing layer 5 by a vapor deposition method (here, reactive plasma vapor deposition method) using a metal mask with an opening pattern, patterning by etching or lift-off after deposition of each layer is not required, thereby reducing manufacturing costs.

[0036] Fig. 7 is a scanning electron microscope image of the surface of the porous gas sensing layer 5 in the gas sensor 1 according to one embodiment. As can be seen from Fig. 7, a porous structure (sensing layer pores 5a) is formed on the surface of the gas sensing layer 5 due to the porous structure of the relief-structure layer 4. This increases the surface area of ​​the gas sensing layer 5, improving the sensor sensitivity.

[0037] The thickness of the gas sensing layer 5 is not particularly limited, but is preferably 50 nm or more and 1000 nm or less. If the thickness of the gas sensing layer 5 is thinner than 50 nm, the gas sensing layer 5 will have high resistance and the measurement sensitivity will decrease. If the thickness of the gas sensing layer 5 is thicker than 1000 nm, when the gas sensing layer 5 is formed by a vapor deposition method (e.g., reactive plasma vapor deposition), it will take a long time to form the gas sensing layer 5, resulting in a decrease in production efficiency.

[0038] It should be noted that the manufacturing cost can be reduced by providing regions for a plurality of gas sensors 1 on one substrate 2, forming a plurality of gas sensors 1 at the same time, and then separating each gas sensor 1 into individual pieces.

[0039] Next, an example of a measurement result using the gas sensor 1 will be described.

[0040] The gas sensor 1 used in this example had a gas sensing layer 5 made of tungsten oxide containing 0.5 at % indium, and was manufactured using the manufacturing process described with reference to FIG. 4. The measurement gas had an acetone concentration of 25 to 1000 ppb (parts per billion). A conventional gas sensor was used as a comparative example. The gas sensor 1 was heated to, for example, 300°C, and the sensor resistance (R air ) and the sensor resistance value (R gas ) and measure the sensitivity (=R air / R gas ) was sought.

[0041] FIG. 8 is a graph showing the results of using the gas sensor of one example and a conventional gas sensor to detect acetone. In FIG. 8, the vertical axis represents sensitivity (arbitrary units), and the horizontal axis represents the acetone concentration of the measured gas. As can be seen from FIG. 8, gas sensor 1 of the example (see "Example") achieved measurement sensitivity that was approximately 10 times higher than that of the conventional gas sensor (see "Conventional Sensor") (see the measurement result for an acetone concentration of 1000 ppb). Furthermore, gas sensor 1 of the example achieved a sensitivity of approximately 8 for an acetone concentration of 500 ppb, demonstrating high detection sensitivity for acetone. Furthermore, gas sensor 1 of Example 1 was also able to detect acetone at a concentration of 25 ppb, demonstrating high detection sensitivity for acetone.

[0042] It is known that the acetone concentration in the breath of diabetic patients is elevated, and attempts have been made to detect this elevated acetone concentration using a gas sensor to enable the diagnosis of diabetes. In this diabetes diagnosis, the gas sensor is required to be able to detect acetone at low concentrations of about 500 to 1000 ppb and to be selective for components other than acetone (especially ethanol) contained in the breath.

[0043] The detection sensitivity of the gas sensor 1 of the above example to acetone and ethanol was verified. Figures 9 and 10 are graphs showing the response characteristics of the gas sensor 1 of the example to acetone and ethanol. Measurement gases used were those with an acetone concentration of 1000 ppb (1 ppm) and an ethanol concentration of 1000 ppb. In each of the graphs of Figures 9 and 10, the horizontal axis represents relative time (seconds) and the vertical axis represents sensitivity (arbitrary units).

[0044] 9, the gas sensor 1 of the example had a detection peak of about 24.0 for acetone at a concentration of 1000 ppb, and a detection peak of about 25.0 for ethanol at a concentration of 1000 ppb. These results demonstrate that the gas sensor 1 of the example, which has a gas sensing layer 5 made of indium-doped tungsten oxide, exhibits high detection sensitivity for both acetone and ethanol.

[0045] Next, we will explain the results of verifying the effect of forming the gas sensing layer 5 on the concave-convex structure layer 4. As a comparative gas sensor, a sensor was fabricated in which, in the manufacturing process described with reference to FIG. 4, (1) after forming the electrode layer 3 on the substrate 2, (2) the step of forming the alumina layer 6 and (3) the hot water treatment step were omitted, and (4) the gas sensing layer 5 was formed on the substrate 2 and the electrode layer 3. The detection sensitivity of the comparative gas sensor to acetone and ethanol was verified.

[0046] 11 and 12 are graphs showing the response characteristics of the gas sensor of the comparative example to acetone and ethanol. The measurement conditions were the same as those used to measure the response characteristics of the gas sensor 1 of the example shown in FIGS. 9 and 10.

[0047] As shown in Fig. 11, the gas sensor of the comparative example had a detection peak of about 12.5 for acetone at a concentration of 1000 ppb. Also, as shown in Fig. 12, the gas sensor of the comparative example had a detection peak of about 18.7 for ethanol at a concentration of 1000 ppb. Compared with the response characteristics of gas sensor 1 of the example shown in Figs. 9 and 10, it was found that gas sensor 1 of the example had higher detection sensitivity for both acetone and ethanol than the gas sensor of the comparative example.

[0048] Next, the results of verifying the types of impurities added to tungsten oxide will be described. As gas sensors for verification, three types of gas sensors, Reference Examples 1 to 3, were fabricated, each having the same structure as the gas sensor of the comparative example, but with different impurities added to the gas sensing layer (tungsten oxide). The impurities added to the tungsten oxide were 0.5 at% nickel (Reference Example 1), 0.5 at% silicon (Reference Example 2), and 0.5 at% aluminum (Reference Example 3).

[0049] 13 and 14 are graphs showing the response characteristics to acetone and ethanol of the gas sensor of Reference Example 1, which has a gas sensing layer made of tungsten oxide with nickel added. FIGS. 15 and 16 are graphs showing the response characteristics to acetone and ethanol of the gas sensor of Reference Example 2, which has a gas sensing layer made of tungsten oxide with silicon added. FIGS. 17 and 18 are graphs showing the response characteristics to acetone and ethanol of the gas sensor of Reference Example 3, which has a gas sensing layer made of tungsten oxide with aluminum added. The measurement conditions were the same as those used to measure the response characteristics of gas sensor 1 of the example shown in FIGS. 9 and 10. In each of the graphs in FIGS. 13 to 18, the horizontal axis represents relative time (seconds) and the vertical axis represents sensitivity (arbitrary units).

[0050] As shown in Figure 13, the gas sensor of Reference Example 1, which has a gas sensing layer made of tungsten oxide and nickel added, has a detection peak of about 3.9 for acetone at a concentration of 1000 ppb, indicating very high detection sensitivity for acetone. On the other hand, as shown in Figure 14, the gas sensor of Reference Example 1 has a detection peak of about 2.3 for ethanol at a concentration of 1000 ppb, which is roughly half the detection sensitivity for acetone, indicating a difference in detection sensitivity between acetone and ethanol.

[0051] This result indicates that the gas sensor 1 having nickel-added tungsten oxide as the gas sensing layer 5 formed on the concave-convex structure layer 4 is likely to have a difference in detection sensitivity to acetone and ethanol.

[0052] As shown in Fig. 15, the gas sensor of Reference Example 2, which has a gas sensing layer 5 made of tungsten oxide and silicon added, had a detection peak of about 4.7 for acetone at a concentration of 1000 ppb. On the other hand, as shown in Fig. 16, the gas sensor of Reference Example 2 had a detection peak of about 3.7 for ethanol at a concentration of 1000 ppb. The gas sensor of Reference Example 2 showed a difference in detection sensitivity for acetone and ethanol.

[0053] As shown in Figures 17 and 18, the gas sensor of Reference Example 3, which has a gas sensing layer made of tungsten oxide with aluminum added, had detection peaks of about 3.0 for both acetone at a concentration of 1000 ppb and ethanol at a concentration of 1000 ppb, and the detection sensitivity for acetone and ethanol was almost the same.

[0054] As described above, it was found that gas sensors having a gas sensing layer of tungsten oxide (WO3) doped with nickel or silicon exhibit better detection sensitivity to acetone than gas sensors having tungsten oxide doped with aluminum. It was also found that gas sensors having a gas sensing layer made of tungsten oxide doped with nickel exhibit a large difference in detection sensitivity to acetone and ethanol.

[0055] The present invention is not limited to the above-described embodiment and can be embodied in various forms. For example, the porous uneven-structure layer 4 formed on the insulating substrate 2 may have a structure that results in a porous structure in the gas sensing layer 5. Such an uneven-structure layer may be, for example, a porous film of titanium oxide, tin oxide, magnesium oxide, or the like; a porous metal oxide containing multiple metal elements; or a porous layer formed by bonding numerous microparticles made of an insulating metal oxide. The porous uneven-structure layer 4 may be any layer that allows electrical connection between the gas sensing layer 5 formed on the uneven-structure layer 4 and the electrode layer 3 below the uneven-structure layer 4 via pores.

[0056] Such a concave-convex-structure layer 4 may be formed as a porous structure by, for example, performing a process (such as etching) to form a large number of base pores 4a in a film (e.g., a film made of an insulating material) formed across the substrate 2 and the electrode layer 3. The large number of base pores 4a in the concave-convex-structure layer 4 may be formed irregularly or regularly. This also applies to the above-described embodiment described with reference to FIGS. 1 to 3. It is not necessary for all of the base pores 4a opening on the upper surface of the concave-convex-structure layer 4 to reach the lower surface of the concave-convex-structure layer 4. That is, the concave-convex-structure layer 4 may be configured such that at least some of the base pores 4a reach the lower surface of the concave-convex-structure layer 4, allowing electrical connection between the upper gas sensing layer 5 and the lower electrode layer 3. [Explanation of symbols]

[0057] 1 Gas sensor 2 boards 3 electrode layer 3a,3b comb-shaped electrode layer 4 Concave and convex structure layer 4a Base pores 5 Gas sensing layer 5a Sensing layer pores 6 alumina layer

Claims

1. an electrode layer formed on an insulating substrate; a concave-convex structure layer formed across the substrate and the electrode layer; a gas detection layer made of an oxide semiconductor formed on the concave-convex structure layer, the concave-convex structure layer has a large number of base pores, the gas sensing layer has a large number of sensing layer pores formed due to the large number of base pores, and is electrically connected to the electrode layer via the base pores; Semiconductor gas sensor.

2. the concave-convex structure layer is formed of an insulating material; 2. The semiconductor gas sensor according to claim 1.

3. the concave-convex structure layer is formed of an insulating metal oxide; 2. The semiconductor gas sensor according to claim 1.

4. the concave-convex structure layer is formed of an insulating aluminum compound layer obtained by making an alumina layer porous by hot water treatment; 2. The semiconductor gas sensor according to claim 1.

5. The gas sensing layer is formed of tungsten trioxide to which an impurity is added and which is biased to a negative charge.

5. The semiconductor gas sensor according to claim 1.

6. The gas sensing layer is formed of nickel-added tungsten trioxide.

5. The semiconductor gas sensor according to claim 1.

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