JP4931523B2 - Gas sensor and manufacturing method thereof - Google Patents

Description

  The present invention relates to a gas sensor having an oxide semiconductor thin film as a gas sensing film and a manufacturing method thereof.

  A gas sensor having an oxide semiconductor thin film as a gas sensing film detects the presence of a gas by a change in the electrical resistance value of the thin film that occurs when a gas to be detected comes into contact with the thin film.

  Specifically, the gas is detected based on the following functions. That is, when the gas touches the thin film, the thin film oxidizes the gas. At this time, the thin film is simultaneously reduced. Along with this reaction, electrons are transferred between the gas and the thin film, and the electric resistance value of the thin film changes. Since the change amount of the electric resistance value is specific to the gas type, the gas can be detected by measuring the change amount of the electric resistance value.

  Examples of gases that can be detected by the gas sensor include volatile organic compounds (VOC); flammable gases such as methane; toxic gases such as carbon monoxide and nitrogen oxides; and malodorous gases such as sulfur compounds. Can be mentioned.

  Among the gases, a volatile organic compound (hereinafter also referred to as “VOC”) is an organic compound that easily volatilizes at room temperature, and is known as a typical air pollutant. There are many types of VOCs. In particular, formaldehyde, acetaldehyde, toluene, xylene, ethylbenzene, styrene, and the like are attracting attention as they cause health damage due to long-term exposure. Therefore, the Ministry of Health, Labor and Welfare defines indoor concentration guideline values for each VOC as shown in Table 1 below, and it is desired to control the ventilation system in the building so that the concentration is below the guideline value.

  For example, Patent Document 1 discloses a gas sensor that detects an aromatic VOC (toluene, xylene, ethylbenzene, styrene) among VOCs. Patent Document 1 discloses a semiconductor gas detection element (gas sensor) in which a sensitive layer mainly composed of a metal oxide semiconductor is provided on an insulating substrate provided with a pair of detection electrodes so as to cover the detection electrodes. In addition, there is described a substrate type semiconductor gas detection element in which a catalyst portion for catalyzing a reaction of a gas to be detected is provided in the inter-electrode energization region in the sensitive layer.

  Patent Document 1 exemplifies tungsten oxide as the sensitive layer. Tungsten oxide has aromatic VOC selectivity and is already known to be useful as a gas sensor sensitive film for detecting aromatic VOC (paragraph [0015] of Patent Document 1). Patent Document 1 describes that a catalyst portion containing platinum or palladium is further provided in the inter-electrode energization region, which describes that gas selectivity and detection sensitivity can be further improved (same [0007]. [0010] to [0011] paragraphs).

However, the gas sensor described in Patent Document 1 has room to further improve the VOC detection sensitivity at a low concentration. This is because the guide value is set to a low concentration, and a high detection sensitivity is required at such a low concentration. FIG. 5 of Patent Document 1 shows toluene detection characteristics of a gas sensor using tungsten oxide for the sensitive layer and palladium fine particles for the catalyst layer. This shows that the sensitivity at the guideline value (0.07 ppm) is only 3, and there is room for improving the detection characteristics at low concentrations. The sensitivity is a numerical value calculated as a ratio (Ra / Rg) of the resistance value (Rair) in air and the resistance value (Rgas) in the detection target gas when the gas sensor is operated at 400 ° C. The larger the value, the higher the sensitivity (paragraph [0019]).
JP 2004-294364 A (Claims 1, 6 and 7)

  The main object of the present invention is to provide a gas sensor having an oxide semiconductor thin film as a gas sensing film and having enhanced detection sensitivity for low-concentration VOCs.

  As a result of intensive studies to achieve the above object, the present inventor has found that the above object can be achieved when a thin film containing disk-shaped tungsten oxide particles is used as the oxide semiconductor thin film. It came to complete.

That is, this invention relates to the following gas sensor and its manufacturing method.
1. A gas sensor having a pair of electrodes formed on an insulating substrate, and further comprising an oxide semiconductor thin film formed on the insulating substrate so as to cover the pair of electrodes,
The thin film contains disk-shaped tungsten oxide particles ,
The gas sensor according to claim 1, wherein the disk-shaped tungsten oxide particles have a diameter of 100 to 300 nm and a thickness of 20 to 70 nm .
2 . The gas sensor senses the presence of the target gas by a change in the electric resistance of the thin film that occurs when the detection target gas comes into contact with the thin film gas sensor according to 1.
3 . The pair of electrodes are a pair of comb-shaped electrodes, and are disposed to face each other so that the comb teeth of one comb-shaped electrode and the comb teeth of the other comb-shaped electrode are sandwiched between each other. Item 3. The gas sensor according to Item 1 or 2 , wherein an interval between the other adjacent comb-shaped electrode and the comb teeth is 0.5 to 5 µm.
4 . The gas sensor according to any one of Items 1 to 3 , wherein the thin film is formed by dehydration of H ₂ WO ₄ .
5 . Item 5. The gas sensor according to any one of Items 1 to 4 , which detects an aromatic volatile organic compound.
6 . A method of manufacturing a gas sensor, wherein a pair of electrodes is formed on an insulating substrate, and further includes an oxide semiconductor thin film formed on the insulating substrate so as to cover the pair of electrodes,
(1) Step 1 of forming a pair of electrodes on the insulating substrate,
(2) Step 2 of supplying a liquid containing H ₂ WO ₄ onto the insulating substrate so as to cover the pair of electrodes, and (3) dehydrating the supplied H ₂ WO ₄ to dehydrate the disk-shaped tungsten oxide The manufacturing method characterized by having the process 3 of forming the said thin film containing particle | grains.
7 . Item 7. The manufacturing method according to Item 6 , wherein the disk-shaped tungsten oxide particles have a diameter of 100 to 300 nm and a thickness of 20 to 70 nm.
8 . The manufacturing method according to Item 6 or 7 , wherein the H ₂ WO ₄ -containing liquid is an H ₂ WO ₄ suspension, and the supplied H ₂ WO ₄ suspension is dried and fired in Step 3. .
9 . The _H 2 WO _{4 suspension,} obtained by dispersing the _{(NH 4) 10 W 12 O} 41 · 5H precipitate obtained was neutralized with ₂ O aqueous solution of acid in water and / or organic dispersion medium Item 9. The method according to Item 8 , wherein

Hereinafter, the gas sensor of the present invention and the manufacturing method thereof will be described in detail.

The gas sensor of the present invention has a pair of electrodes formed on an insulating substrate, and further includes an oxide semiconductor thin film formed on the insulating substrate so as to cover the pair of electrodes, It contains disc-shaped tungsten oxide particles. The gas sensor according to the present invention is a gas sensor having an oxide semiconductor thin film as a gas sensing film, and detects the presence of the target gas by a change in electrical resistance value of the thin film generated when the gas to be detected contacts the thin film. To do.

  The gas sensor having the above characteristics includes an oxide semiconductor thin film containing disk-shaped tungsten oxide particles (preferably having a diameter of 100 to 300 nm and a thickness of 20 to 70 nm). Thereby, VOC (especially aromatic VOC) can be detected with high sensitivity even at a low concentration in the vicinity of the concentration guide value defined by the Ministry of Health, Labor and Welfare. In addition to aromatic VOCs, VOCs such as formaldehyde and acetaldehyde can be detected with high sensitivity. In particular, the thin film can be easily obtained by employing the production method of the present invention. By combining such a gas sensor with a ventilator or the like, a highly accurate ventilation system can be constructed.

  Hereinafter, each part of the gas sensor of the present invention will be described. The gas sensor of the present invention is not limited except that the thin film contains the above-described tungsten oxide particles, and in the preferred embodiment, the following fine comb-shaped electrodes are used. A known gas sensor using a semiconductor thin film as a gas sensing film can be used.

≪Insulating substrate≫
The insulating substrate is not limited as long as it has strength and insulating properties as a sensor substrate, and for example, a silicon substrate, an alumina substrate, or the like can be used. When a silicon substrate is used, silicon oxide may be further formed on the substrate.

  The thickness of the insulating substrate is not limited and can be set as appropriate according to the size and characteristics of the sensor.

≪A pair of electrodes≫
The pair of electrodes formed on the insulating substrate is arranged in such a manner that the electrodes do not contact each other. Usually, one electrode and the other electrode may be arranged to face each other. The thin film described later in the gas sensor is coated so as to span such a pair of electrodes. That is, the conductivity between the electrodes is ensured by the thin film. Therefore, if the electric resistance value of the thin film changes, the value of the current passing between the electrodes changes, so that the presence of gas can be detected.

  The material which comprises an electrode will not be limited if it is suitable as an electrode material, For example, gold | metal | money, platinum, palladium, a platinum palladium alloy etc. can be used. The thickness of the electrode is not limited and is usually preferably about 0.1 to 0.5 μm, more preferably about 0.1 to 0.3 μm.

  As the pair of electrodes, it is particularly preferable to use a pair of comb electrodes. The comb-shaped electrode is a comb-shaped electrode having a plurality of comb teeth (so-called electrode elements). In addition, the pair of comb-shaped electrodes are preferably disposed to face each other so that the comb teeth of one comb-shaped electrode and the comb teeth of the other comb-shaped electrode are sandwiched (engaged) with each other.

  This will be described in more detail with reference to the drawings. FIG. 1A is a schematic diagram showing that a pair of comb-shaped electrodes (3a, 3b) are arranged opposite to each other on the insulating substrate 1 in the above-described manner. FIG. 1B is an enlarged view of the comb-shaped electrode, in which a comb tooth 3b extending from the terminal 2b side and a comb tooth 3a extending from the terminal 2a side are sandwiched (white portion). Are comb teeth and terminals).

  The size and number of comb teeth of the comb electrode are not limited, but the sensor sensitivity can be further enhanced when the interval between the comb teeth is narrow. The interval between the comb teeth (line interval: the distance between adjacent comb teeth after opposing arrangement) is preferably about 0.5 to 5 μm, and more preferably about 0.5 to 2 μm. The width (line width) of the comb teeth is not limited, but is preferably set so that the line width and the line spacing of the comb teeth are the same. The length of the comb teeth can be appropriately set according to the size of the sensor, but is preferably about 0.3 to 0.7 mm.

≪Oxide semiconductor thin film≫
The oxide semiconductor thin film is formed on the insulating substrate so as to cover the pair of electrodes. The coating mode is not limited, but from the viewpoint of gas sensing efficiency, it is preferable that the entire electrode is coated as shown in FIG.

In the present invention, the oxide semiconductor thin film contains, in particular, disk-shaped (substantially disk-shaped) tungsten oxide (WO ₃ ) particles. The size of the disk-like particles is not limited, but it is preferable that the diameter is 100 to 300 nm and the thickness is 20 to 70 nm.

  Specifically, it is preferable that the thin film is an aggregate of the disk-shaped tungsten oxide particles and is substantially formed from the disk-shaped tungsten oxide particles. In addition, it can also be set so that the said disk-shaped tungsten oxide particle | grains may be included as a main component and the particle | grains of another form and kind may be further included.

  The form of the tungsten oxide particles is specified by observing the particles with a scanning electron microscope (SEM).

  The thickness of the thin film is not limited, but it is preferably about the same as the thickness of the electrode. That is, when the thickness of the electrode is about 0.1 to 0.5 μm, the thickness of the thin film is preferably about 0.1 to 0.5 μm. Such a thin film is formed on an insulating substrate and covers the electrode in such a manner that the electrode is buried inside the thin film.

≪Other components and sensor operation methods≫
For example, lead wires (4a, 4b) are connected to terminals (for example, 2a, 2b in FIG. 1) connected to the electrodes. The material of the terminal and the lead wire is not particularly limited, and for example, a gold terminal or a gold lead wire can be used.

  Although not shown in FIG. 1, an ohmmeter is connected to the lead wires (4a, 4b). That is, the electrical resistance value between the electrodes (oxide semiconductor thin film) is measured by the resistance meter. When the detection target gas touches the thin film, the electric resistance value of the thin film changes, and the presence of the target gas is detected by detecting the change.

  In addition, since the sensitivity of the gas sensor varies depending on the temperature of the oxide semiconductor thin film, the gas sensor may have a heater for adjusting the gas sensor temperature. The heater is preferably capable of heating at about 600 ° C., and the gas sensor is preferably operated at about 400 to 600 ° C., preferably about 450 to 550 ° C. For example, the heater is installed on the back surface of the insulating substrate.

  The performance of the gas sensor is evaluated by so-called sensitivity. The sensitivity S of the gas sensor of the present invention is calculated from the ratio (Ra / Rg) of the resistance value (Rair) in air and the resistance value (Rgas) in the detection target gas when the gas sensor is driven at 500 ° C. That is, the sensitivity S in this specification is represented by S = Ra / Rg (500 ° C.).

  The gas sensor of the present invention can detect low-concentration aromatic VOCs (toluene, xylene, ethylbenzene, styrene, etc.) with high sensitivity. Specifically, in the preferred embodiment, even low concentration aromatic VOCs at the concentration guideline level are sufficiently detectable. That is, the gas sensor of the present invention is advantageous as a gas sensor for detecting an aromatic VOC, and furthermore, a highly accurate ventilation system can be constructed by linking the gas sensor and the ventilation device.

Manufacturing Method of Gas Sensor The manufacturing method of the gas sensor of the present invention is not limited, but for example, a manufacturing method having the following steps 1 to 3 (a manufacturing method of the present invention) is preferable.
(1) Step 1 of forming a pair of electrodes on the insulating substrate,
(2) Step 2 of supplying a liquid containing H ₂ WO ₄ onto the insulating substrate so as to cover the pair of electrodes, and (3) dehydrating the supplied H ₂ WO ₄ to dehydrate the disk-shaped tungsten oxide Step 3 of forming the thin film containing particles.

The above-mentioned production method is characterized in that, in particular, when forming an oxide semiconductor thin film, a liquid containing H ₂ WO ₄ (tungstic acid) is supplied in a manner to cover the electrode, and then H ₂ WO ₄ is dehydrated. . According to this thin film forming method, a thin film containing tungsten oxide particles having a disk shape (preferably having a diameter of 100 to 300 nm and a thickness of 20 to 70 nm) is easily obtained.

  Hereafter, it demonstrates for every process.

≪Process 1≫
In step 1, a pair of electrodes is formed on the insulating substrate.

  The insulating substrate is as described above.

  As a method for forming the electrode, for example, chemical vapor deposition (CVD), physical vapor deposition (PVD), vapor deposition, sputtering, screen printing, photolithography and the like can be used. In the case of forming a fine comb-shaped electrode, photolithography is particularly preferable. The material, thickness and shape of the electrode are as described above.

≪Process 2≫
In step 2, an H ₂ WO ₄ containing liquid is supplied onto the insulating substrate so as to cover the pair of electrodes.

H ₂ WO _4, for _{example, (NH 4) 10 W 12} O 41 · 5H 2 O aqueous solution was prepared, by neutralizing it with acid, obtained as a precipitate. Although the acid used for neutralization is not limited, For example, nitric acid aqueous solution etc. can be used. _{(NH 4) 10 W 12 O} 41 · 5H 2 concentration of O in the aqueous solution is preferably about 6~10mmol / l. The concentration of the nitric acid aqueous solution is preferably about 3 to 6 mol / l.

During _{neutralization, (NH 4) 10 W 12} O 41 · 5H 2 O-solution and nitric acid aqueous solution previously warmed to about _{70~90 ℃, (NH 4) 10} W 12 O 41 · 5H 2 O of It is preferable to gradually drop the aqueous nitric acid solution into the aqueous solution. The precipitate of H ₂ WO ₄ produced by the dropping is disk-like (preferably having a diameter of about 100 to 300 nm and a thickness of about 20 to 70 nm). When the precipitate is generated, it is preferable to adjust the dropping conditions so that the precipitate having the shape is uniformly generated. Moreover, it is preferable to wash the resulting precipitate with ion-exchanged water or the like after aging overnight (12 hours or more).

The H ₂ WO ₄ -containing liquid is prepared, for example, by dispersing H ₂ WO ₄ in water and / or an organic dispersion medium. In this respect, the H ₂ WO ₄ containing liquid is substantially a suspension.

Examples of the organic dispersion medium include ethylene glycol. When preparing the suspension, it is preferable to stir in the dispersion medium for about 10 days to 2 weeks in order to enhance the dispersibility of H ₂ WO ₄ . By sufficiently increasing the dispersibility of H ₂ WO ₄ , it becomes easy to form a uniform thin film, and further leads to an improvement in sensor sensitivity.

The H ₂ WO ₄ -containing liquid is performed using, for example, a micromanipulator suitable for a small amount of dripping. The supply amount of the liquid is not limited, and is adjusted according to the desired thin film thickness, electrode area, and the like.

≪Process 3≫
Step 3 dehydrates the supplied H ₂ WO ₄ to form an oxide semiconductor thin film containing tungsten oxide particles in a disk shape (preferably having a diameter of 100 to 300 nm and a thickness of 20 to 70 nm). Form.

In order to dehydrate H ₂ WO ₄ , drying and firing are usually performed.

  The drying conditions are not particularly limited, but the drying temperature is preferably about 80 to 120 ° C, more preferably about 90 to 110 ° C. Although drying time can be set according to drying temperature, about 3 to 12 hours are preferable and about 6 to 9 hours are more preferable. The drying atmosphere is not limited, and may usually be in the air.

  The firing conditions are not particularly limited, but the firing temperature is preferably about 400 to 600 ° C, more preferably about 450 to 550 ° C. Although baking time can be set according to baking temperature, about 3 to 6 hours are preferable and about 3 to 4 hours are more preferable. The firing atmosphere is not limited and may usually be in the air.

  Through the above dehydration (drying and baking), an oxide semiconductor thin film containing disk-shaped tungsten oxide particles is formed. The thickness of the thin film is as described above.

As described above, when the H ₂ WO ₄ -containing liquid is supplied to the electrode and dehydrated, the edge portion (peripheral portion) of the supply region tends to rise compared to the center portion. If it demonstrates using a of FIG. 2, the outer periphery of the thin-film part shown by circle | round | yen will be thick compared with a center part. Therefore, when performing the above steps 2 and 3, it is necessary to pay attention to the supply region so that the thin film in the region directly covering the comb electrode has a desired thickness. In addition, it is allowed that the peripheral portion of the supply region inevitably rises within a range that does not affect the sensitivity of the electrode.

  In addition to steps 1 to 3, the steps of connecting a lead wire to the electrode terminal, connecting a resistance meter to the tip of the lead wire, and installing a heater are performed in accordance with a known gas sensor manufacturing method. it can.

  The gas sensor of the present invention includes an oxide semiconductor thin film containing disk-shaped tungsten oxide particles (preferably having a diameter of 100 to 300 nm and a thickness of 20 to 70 nm). Thereby, VOC (especially aromatic VOC) can be detected with high sensitivity even at a low concentration in the vicinity of the concentration guide value defined by the Ministry of Health, Labor and Welfare. In addition to aromatic VOCs, VOCs such as formaldehyde and acetaldehyde can be detected with high sensitivity. In particular, the thin film can be easily obtained by employing the production method of the present invention. By combining such a gas sensor with a ventilator or the like, a highly accurate ventilation system can be constructed.

It is an example which shows the arrangement | positioning aspect of the electrode in the gas sensor of this invention. FIG. 1B is a partially enlarged view of FIG. 1A, and is an example showing an arrangement of comb teeth of a comb-shaped electrode. It is a scanning electron micrograph of the oxide semiconductor thin film formed so as to cover the electrode (WO ₃ film) (SEM image). a is 100 times, b is 1000 times, and c is 50000 times. It is a figure which shows the relationship between the temperature and detection sensitivity of the gas sensor of this invention. It is a figure which shows the relationship between the density | concentration of aromatic VOC in 500 degreeC of the gas sensor of Example 1, and detection sensitivity. It is a figure which shows the relationship between the density | concentration of the aromatic VOC in 500 degreeC of the gas sensor of the comparative example 1, and detection sensitivity.

Explanation of symbols

1 Insulating substrate 2a, 2b Terminal 3a, 3b Electrode (a pair of comb electrodes)
4a, 4b Lead wire

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the examples.

Example 1
≪Preparation of suspension of tungstic acid≫
First, a suspension of tungstic acid (H ₂ WO ₄ ) was prepared by the following procedure.

First _{(NH 4) 10 W 12 O} 41 · 5H 2 O: the 5.012G, by dissolving in ion-exchanged water 200 ml, to obtain an aqueous solution of 8 mM (solution A).

Next, 100 ml of 3N HNO ₃ aqueous solution was kept at 80 ° C. in the flask, and aqueous solution A was added dropwise to neutralize it, thereby obtaining a deep yellow precipitate (H ₂ WO ₄ ).

Next, after aging the precipitate overnight, it was filtered and washed with ion exchange water. Further, the washed precipitate was stirred in water for 2 weeks to prepare a suspension of H ₂ WO ₄ . The suspension was dark yellow and the H ₂ WO ₄ particles were uniformly dispersed.

≪Production of gas sensor≫
This will be described with reference to FIG.

  A 4 mm × 10 mm insulating substrate 1 having a silicon oxide film formed on the surface of a 0.4 mm thick silicon substrate was prepared.

  Gold terminals (2a, 2b) and a pair of gold comb electrodes (3a, 3b) were formed on the insulating substrate 1 by vapor deposition. The thickness of the gold terminal was 0.2 μm. As shown in FIG. 1B, the comb electrodes were arranged so that the opposing comb teeth mesh with each other. The electrode thickness was 0.2 μm. The comb-tooth portion had a line width of 2 μm, a line interval of 2 μm, a comb length of 0.5 mm, and the number of combs (total number of combs) of 50.

  Next, gold lead wires (4a, 4b) were connected to the gold terminal, and a resistance meter (not shown) was connected to the tip of the gold lead wire.

  Next, a small amount of the suspension was dropped with a micromanipulator so as to cover the gold comb electrode. Further, after natural drying, it was calcined in air at 500 ° C. for 3 hours. By firing, the tungstic acid was dehydrated to form a thin film composed of an aggregate of disk-shaped tungsten oxide particles.

  An SEM image of the formed thin film is shown in FIG. FIG. 2a is an overall view of the thin film. FIG. 2b is a 1000 × observation image, and the shape of the comb electrode is slightly observed on the observation surface. The thickness of the thin film was 0.3 μm. FIG. 2c is an observation image of 50000 times. According to FIG. 2c, it can be seen that the thin film is formed of an aggregate of disk-shaped tungsten oxide particles (diameter: 100 to 300 nm, thickness: 20 to 70 nm).

  Through the above, a gas sensor was produced.

  The comb electrodes are referred to as “2-50 electrodes” because both the line width and the line interval are 2 μm and the number of combs is 50.

Example 2
A gas sensor was produced in the same manner as in Example 1 except that the line width and the line interval were 3 μm.

  The comb electrode of the gas sensor of Example 2 is referred to as “3-50 electrode”.

Example 3
A gas sensor was produced in the same manner as in Example 1 except that the line width and the line interval were set to 5 μm.

  The comb electrode of the gas sensor of Example 3 is referred to as “5-50 electrode”.

Comparative Example 1
_{(NH 4)} 10 _W 12 except _{that O} 41 of · 5H ₂ O powder to form a thin film using the tungsten oxide particles spherical obtained by pyrolysis (diameter 100 to 300 nm) at 700 ° C. in the atmosphere A gas sensor was manufactured in the same manner as in Example 1. Specifically, a suspension of tungsten oxide particles is prepared by stirring spherical tungsten oxide particles in water, and the suspension is dropped with a micromanipulator so as to cover the comb-shaped electrode, and dried in air. To form a thin film. The thin film was formed by an aggregate of the spherical tungsten oxide particles, and according to SEM observation, the disk-shaped tungsten oxide particles were not substantially contained.

Test Example 1 (Performance comparison of gas sensors of Examples 1 to 3)
The performance of the gas sensor produced in Examples 1-3 was compared.

  Specifically, the performance was compared using a graph (FIG. 3) showing the relationship between the detection sensitivity (S = Ra / Rg) of 1.5 ppm of xylene and the temperature (° C.).

  FIG. 3 shows that the gas sensor of Example 1 having 2-50 electrodes has the best sensitivity, and the sensitivity decreases as the line spacing increases. It can also be seen that the sensitivity increases as the temperature increases.

Test Example 2 (Performance evaluation of gas sensor of Example 1)
The performance of the gas sensor of Example 1 was examined. Specifically, the relationship between the concentration of aromatic VOC (xylene, toluene, ethylbenzene, styrene) at 500 ° C. and sensitivity was examined. The results are shown in FIG.

  FIG. 4 shows that the sensitivity order at high concentration (1 ppm) is styrene> ethylbenzene> xylene >> toluene, and the sensitivity order at low concentration (0.01 ppm) is xylene> styrene-ethylbenzene-toluene. . The sensitivity of toluene as a whole is the lowest, but the slope of the graph is small, and a sensitivity of S = 3.5 is shown even at a low concentration (0.01 ppm). Xylene is particularly sensitive at low concentrations, exhibiting a sensitivity of S = 6 at 0.01 ppm. Styrene is particularly sensitive at high concentrations and exhibits a high sensitivity of S = 110 at 1 ppm.

  Regarding the sensitivity at the concentration guide value, toluene has a lower sensitivity than other VOCs, but still shows a sensitivity of 6. Since the sensitivity of the conventional gas sensor is about 3 at the toluene concentration guide value, the sensitivity at the concentration guide value is doubled compared to the conventional product.

  All of the three VOCs other than toluene exhibit high sensitivity exceeding 10. From the above results, it can be seen that the gas sensor of the present invention can sufficiently detect the low concentration VOC at the concentration guide value level.

Test Example 3 (Performance Evaluation of Gas Sensor of Comparative Example 1)
The performance of the gas sensor of Comparative Example 1 was examined. Specifically, the relationship between the concentration of the aromatic VOC and the sensitivity was examined in the same manner as in Test Example 2. The results are shown in FIG.

  From FIG. 5, it can be seen that the sensitivity of the low concentration (0.01 ppm) is as low as S = 1 regardless of which gas is the target.

  As for the sensitivity of the concentration guide value, the sensitivity of toluene is as low as S = 1.7. The sensitivity of xylene is as low as S = 4.8, and the sensitivity of styrene is as low as S = 3. The performance of such a gas sensor is equal to or less than that of a conventional product.

  Comparing the results of Test Example 2 and Test Example 3, it can be clearly seen that the gas sensor of Example 1 has high performance. The sensitivity of toluene tends to be low overall, but the sensitivity difference is still about 4 times. Other than toluene, the sensitivity difference is larger, with ethylbenzene being as much as 6 times.

Claims (9)

A gas sensor having a pair of electrodes formed on an insulating substrate, and further comprising an oxide semiconductor thin film formed on the insulating substrate so as to cover the pair of electrodes,
The thin film contains disk-shaped tungsten oxide particles ,
The gas sensor according to claim 1, wherein the disk-shaped tungsten oxide particles have a diameter of 100 to 300 nm and a thickness of 20 to 70 nm . The gas sensor according to claim 1, wherein the gas sensor detects the presence of the target gas by a change in an electric resistance value of the thin film generated when the detection target gas comes into contact with the thin film. The pair of electrodes are a pair of comb-shaped electrodes, and are disposed to face each other so that the comb teeth of one comb-shaped electrode and the comb teeth of the other comb-shaped electrode are sandwiched between each other. The gas sensor according to claim 1 or 2 , wherein the distance between the adjacent adjacent comb-shaped electrodes and the comb teeth is 0.5 to 5 µm. Wherein the thin film _is formed by dehydration of H 2 WO _4, gas sensor according to any one of claims 1-3. The gas sensor according to any one of claims 1 to 4 , which detects an aromatic volatile organic compound. A method of manufacturing a gas sensor, wherein a pair of electrodes is formed on an insulating substrate, and further includes an oxide semiconductor thin film formed on the insulating substrate so as to cover the pair of electrodes,
(1) Step 1 of forming a pair of electrodes on the insulating substrate,
(2) Step 2 of supplying a liquid containing H ₂ WO ₄ onto the insulating substrate so as to cover the pair of electrodes, and (3) dehydrating the supplied H ₂ WO ₄ to dehydrate the disk-shaped tungsten oxide The manufacturing method characterized by having the process 3 of forming the said thin film containing particle | grains. The manufacturing method according to claim 6 , wherein the disk-shaped tungsten oxide particles have a diameter of 100 to 300 nm and a thickness of 20 to 70 nm. The method according to claim 6 or 7 , wherein the H ₂ WO ₄ -containing liquid is an H ₂ WO ₄ suspension, and the supplied H ₂ WO ₄ suspension is dried and fired in the step 3. . The _H 2 WO _{4 suspension,} obtained by dispersing the _{(NH 4) 10 W 12 O} 41 · 5H precipitate obtained was neutralized with ₂ O aqueous solution of acid in water and / or organic dispersion medium The manufacturing method of Claim 8 manufactured.

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