JP6810345B2 - Gas sensor and gas detection system - Google Patents

Description

The present invention relates to a gas sensor and a gas detection system.

The gas sensor detects chemical substances contained in the gas. In recent years, the relationship between the chemical substances contained in the exhaled breath and the health condition has been pointed out. For example, the relationship between gastric cancer and the concentration of ammonia in the exhaled breath, and the relationship between asthma and the concentration of nitric oxide in the exhaled breath. Etc. have been pointed out. The concentration of the diagnostic threshold is extremely low, ranging from several tens of ppb to several hundreds of ppb.

According to gas chromatography, it is possible to detect a low concentration of gas. However, the apparatus used for the measurement by gas chromatography is large and takes a long time for detection. It is also possible to detect nitric oxide by the optical chemiluminescence method. However, the device used for measurement by the optical chemiluminescence method is also large. It is also possible to detect nitric oxide by the ion electrode method. However, the life of the sensor used for the measurement by the ion electrode method is short, and it is necessary to replace the consumables for each measurement. As described above, so far, a gas sensor that is small and easy to use and that can detect nitric oxide with high sensitivity at the ppb level has not been developed.

Japanese Unexamined Patent Publication No. 2011-169634

Bae, et al., Nature Nanotechnology, V0l.5,574 (2010) Lee, et al., Adv. Mater. Vol.24, 2320 (2012) Momose, et al., Proceedings of the 11th IEEE Annual International Conference on Nano / Micro Engineered and Molecular Systems (NEMS) 2016 (2016)

An object of the present invention is to provide a gas sensor and a gas detection system capable of detecting a gas such as nitric oxide with high sensitivity.

One aspect of the gas sensor is a detection chamber, a first detection unit that changes the electrical characteristics according to the concentration of at least the first gas in the detection chamber, the first gas in the detection chamber, and the first gas. A second detection unit, which changes the electrical characteristics according to the concentration of the second gas different from the gas of the above, is included. One of the first detection unit and the second detection unit is provided with a semiconductor layer, a graphene film provided above the semiconductor layer, and at least a part of which is in contact with a gas in the detection chamber, and the semiconductor layer and the graphene. A barrier film between the film, a first electrode connected to the graphene film, and a second electrode and a third electrode provided on the surface of the semiconductor layer so as to sandwich a lower portion of the barrier film. Electrodes and are included. The first detection unit or the other of the second detection unit has a metal dichalcogenide film in which at least a part is in contact with a gas in the detection chamber, and a fourth electrode and a fifth electrode connected to the metal dichalcogenide film. Electrodes and are included. The graphene film refers to a film composed of one or more unit layers of graphene.

One aspect of the gas detection system includes the gas sensor and a calculation unit that identifies the concentration of the second gas from the output signals of the first detection unit and the second detection unit.

According to the above-mentioned semiconductor device or the like, since an appropriate first detection unit and a second detection unit are included, gas such as nitric oxide can be detected with high sensitivity.

It is a figure which shows the gas sensor which concerns on 1st Embodiment. It is a top view which shows the 1st detection part. It is a figure which shows the characteristic of graphene. It is sectional drawing which shows the manufacturing method of the 1st detection part in process order. Following FIG. 4A, it is sectional drawing which shows the manufacturing method of the 1st detection part in process order. It is sectional drawing which shows the manufacturing method of the 2nd detection part in process order. It is a figure which shows the gas detection system which concerns on 2nd Embodiment. It is a figure which shows the example of the relationship between a gate voltage and a drain current in a 1st detection part and a 2nd detection part. It is a figure which shows the characteristic of the 1st detection part. It is a figure which shows the change of the drain current in the 1st detection part. It is a figure which shows the relationship between the concentration of nitrogen dioxide, the concentration of nitric oxide, and the rate of change of a drain current in the 1st detection part. It is a figure which shows the relationship between the concentration of nitrogen dioxide, the concentration of nitric oxide, and the rate of change of a drain current in the 2nd detection part. It is a figure which shows the gas detection system which concerns on 3rd Embodiment. It is a figure which shows the change of the drain current in the 1st detection part concerning ammonia and the like. It is a figure which shows the gas detection system which concerns on 4th Embodiment.

Hereinafter, embodiments will be specifically described with reference to the accompanying drawings.

(First Embodiment)
First, the first embodiment will be described. FIG. 1 is a diagram showing a gas sensor according to the first embodiment.

The gas sensor 10 according to the first embodiment includes a detection chamber 11, a first detection unit 100 and a second detection unit 200 provided in the detection chamber 11. FIG. 2 is a plan view showing the first detection unit 100.

In the first detection unit 100, as shown in FIGS. 1 and 2, an element separation region 102 for partitioning an element region is formed on the first conductive type semiconductor substrate 101, and a second conductive type source is formed in the element region. A region 103s and a drain region 103d are formed. For example, the conductive type of the semiconductor substrate 101 is p-type, and the conductive type of the source region 103s and the drain region 103d is n-type. The insulating film 104 is formed on the semiconductor substrate 101. The insulating film 104 is formed with an opening 104s on the source region 103s and an opening 104d on the drain region 103d. A graphene film 111 above the channel region 101a is formed on the insulating film 104. The graphene film 111 comprises one or more unit layers of graphene. The source region 103s and the drain region 103d sandwich the graphene film 111 in a plan view, and the portion between the source region 103s and the drain region 103d of the semiconductor substrate 101 is the channel region 101a. At least a part of the graphene film 111 comes into contact with the gas in the detection chamber 11. The insulating film 104 is an example of a barrier film. The conductive type of the semiconductor substrate 101 may be n-type, and the conductive type of the source region 103s and the drain region 103d may be p-type. In FIG. 1, the element separation region 102 is omitted.

As shown in FIGS. 1 and 2, a metal film 105s in contact with the source region 103s through the opening 104s and a metal film 105d in contact with the drain region 103d through the opening 104d are formed on the insulating film 104. A metal film 105 g in contact with the graphene film 111 is formed on the graphene film 111 above the element separation region 102. The metal film 105g, the metal film 105s, and the metal film 105d are examples of a first electrode, a second electrode, and a third electrode, respectively, and are used as a gate contact electrode, a source contact electrode, and a drain contact electrode.

In the second detection unit 200, as shown in FIG. 1, the insulating film 204 is formed on the semiconductor substrate 201, and the metal dichalcogenide film 211 is formed on the insulating film 204. For example, the conductive type of the semiconductor substrate 201 is p type. A metal film 205s and a metal film 205d in contact with the metal dichalcogenide film 211 are formed on the insulating film 204, and a metal film 205g is formed on the back surface of the semiconductor substrate 201. The metal film 205s, the metal film 205d, and the metal film 205g are examples of a fourth electrode, a fifth electrode, and a sixth electrode, respectively, and are used as a source contact electrode, a drain contact electrode, and a gate contact electrode. For example, the metal dichalcogenide film 211 is a film of molybdenum disulfide (MoS ₂ ).

In the first detection unit 100, the graphene film 111 functions as a gate electrode of the field effect transistor. In general, when a specific gas molecule, such as a molecule of nitrogen dioxide gas, is adsorbed on graphene, charge transfer occurs between this molecule and graphene, and as shown in FIG. 3, the work function of graphene is It changes a lot. Therefore, in the first detection unit 100, the work function of graphene contained in the graphene film 111 changes significantly with the adsorption of the molecules of nitrogen dioxide gas, and the threshold voltage of the field effect transistor also changes significantly. Therefore, the concentration of nitrogen dioxide can be detected with high sensitivity at the ppb level by detecting the change in the drain current while keeping the gate voltage and the drain voltage constant. On the other hand, the above-mentioned change in the work function of graphene does not occur substantially by adsorption of nitric oxide gas molecules. The relationship between the Fermi level and the carrier density n is given by the following equation. Here, v _F is the Fermi velocity, h is Planck's constant, E _{F 0} is the Fermi level before the adsorption of the molecule, and E _F is the Fermi level after the adsorption of the molecule.

In the second detection unit 200, the metal dichalcogenide film 211 functions as a channel of the field effect transistor. In general, when a molecule of a specific gas is adsorbed on a metal dichalcogenide, a charge transfer occurs between this molecule and the metal dichalcogenide, and the electrical resistance of the metal dichalcogenide changes significantly. For example, when a molecule of nitric oxide gas or nitrogen dioxide gas is adsorbed on molybdenum disulfide, the electric resistance of molybdenum disulfide changes significantly. Therefore, in the second detection unit 200, the electric resistance of molybdenum disulfide contained in the metal dichalcogenide film 211 changes significantly with the adsorption of molecules of nitric oxide gas or nitrogen dioxide gas. Therefore, by detecting the change in the drain current while keeping the gate voltage and the drain voltage constant, the total concentration of nitric oxide and nitrogen dioxide can be detected with high sensitivity at the ppb level.

When a gas containing nitric oxide and nitrogen dioxide is supplied from the intake port 31 of the detection chamber 11 and discharged from the exhaust port 32, the concentration of nitrogen dioxide can be specified by using the first detection unit 100. , The total concentration of nitric oxide and nitrogen dioxide can be specified by using the second detection unit 200. Therefore, by reducing the concentration of nitrogen dioxide specified by using the first detection unit 100 from the total concentration of nitric oxide and nitrogen dioxide specified by using the second detection unit 200, the detection chamber 11 The concentration of nitric oxide in it can be specified with high sensitivity. That is, the concentration of nitric oxide, which is extremely effective for diagnosing asthma, can be detected with high sensitivity at the ppb level.

The first detection unit 100 and the second detection unit 200 can be finely manufactured by using a semiconductor process. Therefore, the gas sensor 10 is effective for miniaturization. Further, the first detection unit 100 and the second detection unit 200 are stable in the atmosphere, and the surface can be easily cleaned by heating or the like. Therefore, stable measurement can be performed for a long period of time.

Next, a method of manufacturing the first detection unit 100 will be described. 4A to 4B are cross-sectional views showing the manufacturing method of the first detection unit 100 in the order of steps.

First, as shown in FIG. 4A (a), p-type impurities are ion-implanted into the semiconductor substrate 101 to make the conductive type of the semiconductor substrate 101 p-type, an element separation region is formed, and n-type impurities are placed in the element region. Ion implantation is performed to form the source region 103s and the drain region 103d. Next, the insulating film 104 is formed on the surface of the semiconductor substrate 101. The insulating film 104 can be formed by, for example, thermal oxidation.

Then, as shown in FIG. 4A (b), the graphene film 111 is provided on the insulating film 104. The graphene film 111 can be provided, for example, by growing the graphene film on the growth substrate and transferring it onto the insulating film 104. As the growth substrate, for example, a copper foil or a copper film having a thickness of about 1000 nm formed on a silicon substrate with an oxide film can be used, and the graphene film is formed by a chemical vapor deposition (CVD) method. can do. At the time of transfer, a protective film such as a polymer is used. Such a method is also described in Non-Patent Document 1.

Subsequently, as shown in FIG. 4A (c), the graphene film 111 is patterned. The graphene film 111 can be patterned by, for example, a photolithography technique and an etching technique. Examples of the etching technique include reactive ion etching (RIE) using oxygen plasma.

Next, as shown in FIG. 4B (d), the insulating film 104 is patterned to form the opening 104s and the opening 104d. The insulating film 104 can be patterned by, for example, a photolithography technique and an etching technique.

Then, as shown in FIG. 4B (e), the metal film 105s in contact with the source region 103s through the opening 104s, the metal film 105d in contact with the drain region 103d through the opening 104d, and the graphene film 111 above the element separation region 102. A metal film 105 g is formed. In the formation of the metal film 105s, the metal film 105d and the metal film 105g, for example, a mask is formed to expose the region where they are to be formed, a metal film is formed by a vacuum deposition method, and the mask is formed together with the metal film on the metal film Remove. That is, the metal film 105s, the metal film 105d, and the metal film 105g can be formed by the lift-off method. In the formation of the metal film, for example, a Ti film having a thickness of 5 nm is formed, and an Au film having a thickness of 200 nm is formed on the Ti film. The material of the metal film is not limited to Ti and Au, and other metals may be used. For example, TiN, Ta, TaN, W, WN _x , Mo, Ru, TiSi _x N _y , WSi _x , which have a small diffusion coefficient and are known as materials for barrier films, from the viewpoint of suppressing diffusion into silicon. N _y and WB _x N _y are also suitable (0 <x, y <1). A laminate of films of these materials is also suitable for metal films.

In this way, the first detection unit 100 can be manufactured.

Next, a method of manufacturing the second detection unit 200 will be described. FIG. 5 is a cross-sectional view showing the manufacturing method of the second detection unit 200 in the order of processes. Here, a molybdenum disulfide film is formed as the metal dichalcogenide film 211.

First, as shown in FIG. 5A, the insulating film 204 is formed on the semiconductor substrate 201, and the metal dichalcogenide film 211 is formed on the insulating film 204. The insulating film 204 can be formed by, for example, thermal oxidation. For example, the semiconductor substrate 201 is a silicon substrate, and the insulating film 204 is a silicon oxide film. A silicon substrate on which a silicon oxide film is formed (a silicon substrate with an oxide film) may be prepared. In the formation of the metal dichalcogenide film 211, the semiconductor substrate 201 on which the MoS ₂ powder, the sulfur powder, and the insulating film 204 are formed is placed in a quartz furnace and heated to, for example, about 650 ° C. in a nitrogen atmosphere. As described above, the metal dichalcogenide film 211 can be formed by, for example, a CVD method. Such a method is also described in Non-Patent Document 2.

Next, as shown in FIG. 5B, the metal dichalcogenide film 211 is patterned. The metal dichalcogenide film 211 can be patterned by, for example, a photolithography technique and an etching technique. Examples of the etching technique include RIE using oxygen plasma.

Then, as shown in FIG. 5C, the metal film 205s and the metal film 205d in contact with the metal dichalcogenide film 211 are formed on the insulating film 204. In the formation of the metal film 205s and the metal film 205d, for example, a mask that exposes the region where they are to be formed is formed, the metal film is formed by a vacuum deposition method, and the mask is removed together with the metal film on the mask. That is, the metal film 205s and the metal film 205d can be formed by the lift-off method. In the formation of the metal film, for example, a Ti film having a thickness of 5 nm is formed, and an Au film having a thickness of 200 nm is formed on the Ti film.

Subsequently, as shown in FIG. 5D, 205 g of a metal film is formed on the back surface of the semiconductor substrate 201. In the formation of the metal film 205s and the metal film 205d, for example, a Ti film having a thickness of 5 nm is formed by a vacuum vapor deposition method, and an Au film having a thickness of 200 nm is formed on the Ti film. When the insulating film is present on the back surface of the semiconductor substrate 201, the insulating film is removed by using, for example, buffered hydrofluoric acid before forming the metal film 205 g.

In this way, the second detection unit 200 can be manufactured.

(Second Embodiment)
Next, the second embodiment will be described. A second embodiment relates to a gas detection system including a gas sensor 10. FIG. 6 is a diagram showing a gas detection system according to the second embodiment.

The gas detection system 1 according to the second embodiment includes the gas sensor 10 according to the first embodiment. The gas detection system 1 includes a bias power supply 122 that applies a bias voltage between the metal film 105s and the metal film 105g, a bias power supply 123 that applies a bias voltage between the metal film 105s and the metal film 105d, and a first. A current monitor 121 for detecting the current flowing through the detection unit 100 of the above is included. The gas detection system 1 includes a bias power supply 222 that applies a bias voltage between the metal film 205s and the metal film 205g, a bias power supply 223 that applies a bias voltage between the metal film 205s and the metal film 205d, and a second. A current monitor 221 for detecting the current flowing through the detection unit 200 of the above is included. The current monitor 121 detects the drain current of the first detection unit 100, and the current monitor 221 detects the drain current of the second detection unit 200. The gas detection system 1 includes a calculation unit 12 that specifies the concentration of a specific gas, for example, nitric oxide, in the detection chamber 11 from the output signal of the current monitor 121 and the output signal of the current monitor 221. The gas detection system 1 also includes a heater (heating device) 13 for heating the first detection unit 100 and the second detection unit 200, and a temperature / humidity monitor 14 for detecting the temperature and humidity in the detection chamber 11. A resistance monitor that detects the electrical resistance of the first detection unit 100 may be used instead of the current monitor 121, and a resistance monitor that detects the electrical resistance of the second detection unit 200 may be used instead of the current monitor 221. ..

In the gas detection system 1, for example, the metal film 105s is grounded, the metal film 105g is biased to an arbitrary voltage by the bias power supply 122, and the metal film 105d is biased to an arbitrary voltage by the bias power supply 123. Further, the metal film 205s is grounded, the metal film 205g is biased to an arbitrary voltage by the bias power supply 222, and the metal film 205d is biased to an arbitrary voltage by the bias power supply 223. As the bias voltage of the metal film 105 g, it is preferable to select a voltage at which the drain current changes as steeply as possible. FIG. 7A is a diagram showing an example of the relationship between the gate voltage Vg and the drain current Id in the first detection unit 100. When the characteristics of the first detection unit 100 are as shown in FIG. 7A, the bias voltage by the bias power supply 122 is preferably 900 mV. FIG. 7B is a diagram showing an example of the relationship between the gate voltage Vg and the drain current Id in the second detection unit 200. When the characteristics of the second detection unit 200 are as shown in FIG. 7B, the bias voltage by the bias power supply 222 is preferably about 20V.

The gas to be measured is introduced into the detection chamber 11 from the intake port 31 and discharged from the exhaust port 32. When the gas to be measured is exhaled, it is introduced from the mouth by the force of breathing. When the gas to be measured is the atmosphere, it is introduced by a device such as a pump or a fan. When the gas to be measured contains nitrogen dioxide, the nitrogen dioxide molecules are adsorbed on the graphene film 111 in the first detection unit 100, and the work function of graphene becomes small, as shown in FIG. , The threshold voltage of the field effect transistor rises, and the drain current at the bias voltage (900 mV) is greatly reduced. On the other hand, even if the gas to be measured contains nitric oxide, the drain current does not substantially change according to the concentration of nitric oxide.

FIG. 9 (a) shows the change in the drain current in the first detection unit 100 for various concentrations of nitrogen dioxide (NO ₂ ), and FIG. 9 (b) shows the change in the first detection unit 100 for nitric oxide. The change in drain current is shown. In FIG. 9, "Id0" indicates the magnitude of the drain current at the start of introduction of nitrogen dioxide or nitric oxide, and "Id" indicates the magnitude of the drain current at each time thereafter. As for nitrogen dioxide, as shown in FIG. 9A, the drain current decreases with the passage of time even when the concentration is extremely low, 7 ppb to 200 ppb. Further, the higher the concentration of nitrogen dioxide, the greater the decrease in drain current. On the other hand, with respect to nitric oxide, as shown in FIG. 9B, the drain current hardly changes even when the concentration is 1 ppm (1000 ppb).

FIG. 10 shows an example of the relationship between the concentration of nitrogen dioxide or the concentration of nitric oxide and the rate of change of the drain current at a time when a specific time t has elapsed from the start of gas introduction in the first detection unit 100. Is shown. FIG. 11 shows an example of the relationship between the concentration of nitrogen dioxide or the concentration of nitric oxide and the rate of change of the drain current at the time when time t has elapsed from the start of gas introduction in the second detection unit 200. The calculation unit 12 can obtain the rate of change of the drain current in the first detection unit 100 from the output signal of the current monitor 121, specify the concentration of nitrogen dioxide from the data shown in FIG. 10, and output the output signal of the current monitor 221. The rate of change of the drain current in the second detection unit 200 can be obtained from, and the total concentration of nitrogen dioxide and nitrogen monoxide can be specified from the data shown in FIG. Therefore, the calculation unit 12 can specify the concentration of nitric oxide in the gas to be measured by subtracting the concentration of nitrogen dioxide from the total concentration of nitrogen dioxide and nitric oxide.

The relationship between the concentration and the response shown in FIGS. 10 and 11 changes depending on the measurement conditions and various factors such as environmental factors such as temperature and humidity. Therefore, it is preferable to perform calibration as appropriate. The temperature and humidity in the detection chamber 11 can be specified by the temperature / humidity monitor 14.

It is preferable to control the temperature of the first detection unit 100 and the second detection unit 200 by using the heater 13. By keeping the temperatures of the first detection unit 100 and the second detection unit 200 at a constant temperature higher than room temperature, it is possible to suppress changes in characteristics due to temperature changes. In addition, the influence of humidity can be suppressed by increasing the temperature. By heating the first detection unit 100 and the second detection unit 200 with the heater 13, the chemical substances adsorbed on the surfaces of the graphene film 111 and the metal dichalcogenide film 211 can also be removed. Such removal may be performed after the measurement of the concentration is completed, or may be performed during the measurement of the concentration. The temperature control of the heater 13 may be incorporated in the measurement recipe in advance. The range of temperature control by the heater 13 is, for example, from room temperature to several hundred degrees Celsius. The type of heater 13 is not limited to profit. Light heating with a flash lamp or the like is effective for removing chemical substances. Ultraviolet light may be applied to remove chemicals. In order to stabilize the humidity in the detection chamber 11, it is preferable that a humidity control mechanism capable of dehumidifying and humidifying is provided in front of the intake port 31.

The current monitors 121 and 221 may include, for example, various power supplies, amplifier circuits, sampling circuits, analog-to-digital (AD) converters, data processing computers, and the like. The current monitors 121 and 221 may be integrated.

The material of the metal dichalcogenide film 211 is not particularly limited, and TiS ₂ , ZrS ₂ , HfS ₂ , HfSe ₂ , SnS ₂ , SnSe ₂ , PbS ₂ or PbSe ₂ may be used. The number of unit layers contained in the graphene film 111 is not limited.

The heater 13, the temperature / humidity monitor 14, the humidity control mechanism, and the ultraviolet source can be considered to be included in the gas sensor 10 instead of the gas detection system 1. Further, the gas sensor 10 may include an ultraviolet irradiation device that irradiates the first detection unit 100 and the second detection unit 200 with ultraviolet rays. By irradiating with ultraviolet rays, the chemical substances adsorbed on the first detection unit 100 and the second detection unit 200 can be removed.

(Third Embodiment)
Next, a third embodiment will be described. A third embodiment relates to a gas detection system including a gas sensor different from the gas sensor 10. FIG. 12 is a diagram showing a gas detection system according to a third embodiment.

The gas detection system 2 according to the third embodiment includes a gas sensor 20. Similar to the gas sensor 10 according to the first embodiment, the gas sensor 20 includes a detection chamber 11, a first detection unit 100 and a second detection unit 200 provided in the detection chamber 11. The gas sensor 20 also includes a third detection unit 300 provided in the detection chamber 11. In the third detection unit 300, as shown in FIG. 12, the insulating film 304 is formed on the substrate 301, and the solid electrolyte film 311 is formed on the insulating film 304. A metal film 305s and a metal film 305d in contact with the solid electrolyte film 311 are formed on the insulating film 304. The metal film 305s, the metal film 305d, and the metal film 205g are examples of the seventh electrode and the eighth electrode, respectively, and are used as a source contact electrode and a drain contact electrode. For example, the solid electrolyte membrane 311 is a copper bromide (CuBr) membrane.

In the third detection unit 300, the solid electrolyte membrane 311 functions as a resistance element. In general, when a molecule of a specific gas is adsorbed on a solid electrolyte, charge transfer occurs between this molecule and the solid electrolyte, and the electric resistance of the solid electrolyte changes significantly. For example, when a molecule of ammonia gas is adsorbed on copper bromide, the electric resistance of copper bromide changes significantly. Therefore, in the third detection unit 300, the electric resistance of copper bromide contained in the solid electrolyte membrane 311 changes significantly with the adsorption of the molecules of ammonia gas. Therefore, the concentration of ammonia can be detected with high sensitivity at the ppb level by detecting the change in the current flowing through the third detection unit 300 while keeping the potential difference between the metal film 305s and the metal film 305d constant. Can be done.

In addition, the work function of graphene changes significantly not only by the adsorption of nitrogen dioxide gas but also by the adsorption of ammonia gas. FIG. 13 shows a change in the drain current in the first detection unit 100 regarding ammonia and the like. As shown in FIG. 13, when ammonia (NH ₃ ) is contained, the drain current increases with the passage of time. Even if acetaldehyde (CH ₃ CHO), sulfur dioxide (SO ₂ ) and hydrogen sulfide (H ₂ S) are contained, the drain current hardly changes.

The gas detection system 2 includes a bias power supply 323 that applies a bias voltage between the metal film 305s and the metal film 305d, and a current monitor 321 that detects a current flowing through the third detection unit 300. The calculation unit 12 specifies the concentration of a specific gas, for example, nitrogen monoxide in the detection chamber 11 from the output signal of the current monitor 121, the output signal of the current monitor 221 and the output signal of the current monitor 321. A resistance monitor that detects the electrical resistance of the third detection unit 300 may be used instead of the current monitor 321. In the gas detection system 2, for example, the metal film 305s is grounded, and the metal film 305d is biased to an arbitrary voltage by the bias power supply 323.

The gas detection system 2 is effective for measuring the concentration of nitric oxide when the gas to be measured contains ammonia, for example. From the tendency shown in FIG. 13, the relationship between the concentration and the rate of change of ammonia gas as shown in FIG. 10 can be obtained. Therefore, the calculation unit 12 can obtain the rate of change of the drain current in the first detection unit 100 from the output signal of the current monitor 121, and can specify the total concentration of nitrogen dioxide and ammonia. As described above, the calculation unit 12 can obtain the rate of change of the drain current in the second detection unit 200 from the output signal of the current monitor 221 and specify the total concentration of nitrogen dioxide and nitric oxide. The calculation unit 12 can obtain the rate of change of the current flowing through the third detection unit 300 from the output signal of the current monitor 321 and specify the total concentration of ammonia. Therefore, the calculation unit 12 subtracts the concentration of ammonia from the total concentration of nitrogen dioxide and ammonia to specify the concentration of nitrogen dioxide in the gas to be measured, and nitrogen dioxide from the total concentration of nitrogen dioxide and nitric oxide. The concentration of nitrogen dioxide can be determined by subtracting the concentration of nitrogen dioxide.

The material of the solid electrolyte membrane 311 is not particularly limited.

(Fourth Embodiment)
Next, a fourth embodiment will be described. A fourth embodiment relates to a gas detection system including a gas sensor different from the gas sensors 10 and 20. FIG. 14 is a diagram showing a gas detection system according to a fourth embodiment.

The gas detection system 3 according to the fourth embodiment includes a gas sensor 30. The gas sensor 30 includes a first detection unit 100 and a third detection unit 300, but does not include a second detection unit 200. The gas detection system 3 does not include the current monitor 221 and the bias power supply 222 and the bias power supply 223, and the arithmetic unit 12 determines the specific gas in the detection chamber 11 from the output signal of the current monitor 121 and the output signal of the current monitor 321. For example, the concentration of nitrogen dioxide is specified. Other configurations are the same as in the first embodiment.

The gas detection system 3 is effective for measuring the concentration of nitrogen dioxide, for example. The calculation unit 12 can obtain the rate of change of the drain current in the first detection unit 100 from the output signal of the current monitor 121, and can specify the total concentration of nitrogen dioxide and ammonia. As described above, the calculation unit 12 can obtain the rate of change of the current flowing through the third detection unit 300 from the output signal of the current monitor 321 and specify the total concentration of ammonia. Therefore, the calculation unit 12 can specify the concentration of nitrogen dioxide in the gas to be measured by subtracting the concentration of ammonia from the total concentration of nitrogen dioxide and ammonia.

Hereinafter, various aspects of the present invention will be collectively described as appendices.

(Appendix 1)
Detection room and
A first detection unit that changes the electrical characteristics according to the concentration of at least the first gas in the detection chamber,
A second detection unit that changes the electrical characteristics according to the concentration of the first gas and the second gas different from the first gas in the detection chamber.
Have,
One of the first detection unit or the second detection unit
With the semiconductor layer
A graphene film provided above the semiconductor layer and at least partially in contact with the gas in the detection chamber.
A barrier film between the semiconductor layer and the graphene film,
The first electrode connected to the graphene film and
A second electrode and a third electrode provided on the surface of the semiconductor layer so as to sandwich a lower portion of the barrier film,
A gas sensor characterized by having.

(Appendix 2)
The other of the first detection unit or the second detection unit
A metal dichalcogenide film that is at least partially in contact with the gas in the detection chamber,
A fourth electrode and a fifth electrode connected to the metal dichalcogenide film,
The gas sensor according to Appendix 1, wherein the gas sensor has.

(Appendix 3)
The gas sensor according to Appendix 2, wherein the metal dichalcogenide film is a molybdenum disulfide film.

(Appendix 4)
The other of the first detection unit or the second detection unit
A sixth electrode that controls the potential of the metal dichalcogenide film between the fourth electrode and the fifth electrode, and
An insulating film between the metal dichalcogenide film and the sixth electrode,
The gas sensor according to Appendix 2 or 3, wherein the gas sensor has.

(Appendix 5)
It has a third detection unit that changes its electrical characteristics according to the concentration of a third gas that is different from both the first gas and the second gas in the detection chamber.
The third detection unit is
A solid electrolyte membrane that is at least partially in contact with the gas in the detection chamber,
The seventh electrode and the eighth electrode connected to the solid electrolyte membrane,
The gas sensor according to any one of Appendix 2 to 4, wherein the gas sensor has.

(Appendix 6)
The gas sensor according to Appendix 5, wherein the solid electrolyte membrane is a copper bromide film.

(Appendix 7)
The other of the first detection unit or the second detection unit
A solid electrolyte membrane that is at least partially in contact with the gas in the detection chamber,
The seventh electrode and the eighth electrode connected to the solid electrolyte membrane,
The gas sensor according to Appendix 1, wherein the gas sensor has.

(Appendix 8)
The gas sensor according to Appendix 7, wherein the solid electrolyte membrane is a copper bromide film.

(Appendix 9)
The gas sensor according to any one of Supplementary Provisions 1 to 8, further comprising a heating device for heating the first detection unit and the second detection unit.

(Appendix 10)
The gas sensor according to Appendix 9, wherein the heating device has a lamp.

(Appendix 11)
The gas sensor according to any one of Appendix 1 to 10, wherein the first detection unit and the second detection unit are provided with an ultraviolet irradiation device that irradiates ultraviolet rays.

(Appendix 12)
The gas sensor according to any one of Supplementary notes 1 to 11 and
An arithmetic unit that specifies the concentration of the second gas from the output signals of the first detection unit and the second detection unit, and
A gas detection system characterized by having.

1, 2, 3: Gas detection system 10, 20, 30: Gas sensor 11: Detection room 12: Calculation unit 13: Heater 14: Temperature and humidity monitor 100: First detection unit 111: Graphene film 121: Current monitor 200: No. 2 detection unit 211: Metal dichalcogenide membrane 221: Current monitor 300: Third detection unit 311: Solid electrolyte membrane 321: Current monitor

Claims (6)

Detection room and
A first detection unit that changes the electrical characteristics according to the concentration of at least the first gas in the detection chamber,
A second detection unit that changes the electrical characteristics according to the concentration of the first gas and the second gas different from the first gas in the detection chamber.
Have,
One of the first detection unit or the second detection unit
With the semiconductor layer
A graphene film provided above the semiconductor layer and at least partially in contact with the gas in the detection chamber.
A barrier film between the semiconductor layer and the graphene film,
The first electrode connected to the graphene film and
A second electrode and a third electrode provided on the surface of the semiconductor layer so as to sandwich a lower portion of the barrier film,
Have and
The other of the first detection unit or the second detection unit
A metal dichalcogenide film that is at least partially in contact with the gas in the detection chamber,
A fourth electrode and a fifth electrode connected to the metal dichalcogenide film,
A gas sensor characterized by having. The gas sensor according to claim 1 , wherein the metal dichalcogenide film is a molybdenum disulfide film. The other of the first detection unit or the second detection unit
A sixth electrode that controls the potential of the metal dichalcogenide film between the fourth electrode and the fifth electrode, and
An insulating film between the metal dichalcogenide film and the sixth electrode,
The gas sensor according to claim 1 or 2 , wherein the gas sensor has. It has a third detection unit that changes its electrical characteristics according to the concentration of a third gas that is different from both the first gas and the second gas in the detection chamber.
The third detection unit is
A solid electrolyte membrane that is at least partially in contact with the gas in the detection chamber,
The seventh electrode and the eighth electrode connected to the solid electrolyte membrane,
The gas sensor according to any one of claims 1 to 3 , wherein the gas sensor has. The gas sensor according to claim 4 , wherein the solid electrolyte membrane is a copper bromide membrane. The gas sensor according to any one of claims 1 to 5 .
An arithmetic unit that specifies the concentration of the second gas from the output signals of the first detection unit and the second detection unit, and
A gas detection system characterized by having.

Images