Gas sensor, gas sensor system, method for detecting a gas, and method for measuring the concentration of a gas

Abstract

To enable a layer of one type of gas sensing material to detect a plurality of types of gases. [Solution] The gas sensor 10 according to the present invention includes a gate electrode 20, a gate insulating film 21, and a channel layer 22 stacked in this order, and a source electrode 23 and a drain electrode 24 spaced apart so that the channel layer 22 is electrically located therebetween, and the channel layer 22 includes a film 30 made of graphene, a seed layer 31 placed on the surface of the film 30, and a nanostructure array 32 grown from the seed layer 31.

Description

[Technical Field]

[0001] The present invention relates to a gas sensor, a gas sensor system, a method for detecting a gas, and a method for measuring the concentration of a gas. [Background technology]

[0002] Gas sensors capable of detecting multiple types of gases are known. Patent Document 1 discloses this type of gas sensor. The gas sensor described in this document is capable of detecting multiple types of gases by forming multiple gas detection material layers made of different materials on a single semiconductor substrate and measuring changes in the threshold voltage of field-effect transistors that use each of the layers as a gate.

[0003] Furthermore, Non-Patent Document 1 discloses a gas sensor constructed using graphene, which has higher carrier mobility than oxide semiconductor materials used in conventional gas sensors, and molybdenum oxide nanorods, which have a very large surface area. This gas sensor can reduce impedance compared to conventional gas sensors and can adsorb gas molecules over a wide area, thereby realizing a high-speed and very compact gas sensor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2024-071185 [Non-patent literature]

[0005] [Non-Patent Document 1] Toru Sugawara and 10 others, "Carrier-Type Switching with Gas Detection Using a Low-Impedance Hybrid Sensor of 2D Graphene Layer and MoOx Nanorod 3D Network," March 26, 2023, ACS Applied Engineering Materials 2023 Volume 1 Issue 4, pp.1086-1092 Summary of the Invention [Problem to be solved by the invention]

[0006] As described in Patent Document 1, in order to detect multiple types of gases using a conventional gas sensor, it is necessary to prepare multiple types of gas detection material layers made of different materials. However, this increases the manufacturing cost of the gas sensor, so there has been a demand for the development of a gas sensor that can detect multiple types of gases using a single type of gas detection material layer.

[0007] Therefore, one object of the present invention is to provide a gas sensor, a gas sensor system, and a method for detecting gases using such a gas sensor, which can detect multiple types of gases using a single type of gas sensing material layer.

[0008] In addition to detecting gas, it has also been desired to be able to measure the concentration of the detected gas.

[0009] Therefore, another object of the present invention is to provide a method for measuring the concentration of a detected gas using the above gas sensor. [Means for solving the problem]

[0010] A gas sensor according to the present invention includes a gate electrode, a gate insulating film, and a channel layer stacked in this order, and a source electrode and a drain electrode spaced apart so that the channel layer is electrically located therebetween, the channel layer including a film made of graphene, a seed layer disposed on a surface of the film, and a nanostructure array grown from the seed layer.

[0011] A gas sensor system according to the present invention includes the above-described gas sensor, a constant current source that supplies a constant current from the source electrode to the drain electrode, a voltmeter that measures the voltage between the source electrode and the drain electrode, and a variable DC power supply that supplies a plurality of gate voltages, each of which is different from the other, to the gate electrode.

[0012] According to another aspect of the present invention, there is provided a gas sensor system including a plurality of gas sensors arranged in a matrix, a plurality of switches provided corresponding to each of the plurality of gas sensors, a control line and a gate line provided for each row of the matrix, and a source line and a drain line provided for each column of the matrix, wherein each of the plurality of gas sensors includes a gate electrode, a gate insulating film, and a channel layer stacked in that order, and a source electrode and a drain electrode arranged with a space between them so that the channel layer is electrically located therebetween, the channel layer of each of the plurality of gas sensors includes a film made of graphene, a seed layer disposed on a surface of the film, and a nanostructure array grown from the seed layer, and each of the plurality of switches includes a gate electrode connected to the corresponding control line, a source electrode connected to the corresponding source line, and a drain electrode connected to the source electrode of the corresponding gas sensor.

[0013] A method for detecting gas according to the present invention is a method for detecting gas using a gas sensor including a gate electrode, a gate insulating film, and a channel layer stacked in this order, and a source electrode and a drain electrode spaced apart so that the channel layer is electrically located therebetween, wherein the channel layer is configured to change the resistance between the source electrode and the drain electrode depending on the value of a gate voltage applied to the gate electrode and the type of gas to which it is exposed. The method includes a first measurement step of exposing the channel layer to a known gas and measuring the resistance between the source electrode and the drain electrode while applying a gate voltage to the gate electrode, the process being performed multiple times while changing the applied gate voltage, and a storage step of storing information indicating the response characteristics of the resistance value obtained as a result of the first measurement step to the gate voltage, in association with the type of the known gas.

[0014] A method for measuring the concentration of a gas according to the present invention is a method for measuring the concentration of a gas using a gas sensor including a gate electrode, a gate insulating film, and a channel layer stacked in this order, and a source electrode and a drain electrode spaced apart so that the channel layer is electrically located therebetween, the channel layer being configured to change a resistance value between the source electrode and the drain electrode depending on a value of a gate voltage applied to the gate electrode and a type of gas to which the channel layer is exposed, the method comprising: exposing the channel layer to a known gas; and measuring the resistance value between the source electrode and the drain electrode while applying a gate voltage to the gate electrode. The method includes a first measurement step performed multiple times while changing the voltage and the concentration of the known gas; a first determination step for determining, based on the results of the first measurement step, the gate voltage at which the change in the resistance value obtained as a result of the first measurement step relative to the concentration of the known gas is greatest; and a first storage step for storing information indicating the response characteristics of the resistance value obtained as a result of the first measurement step relative to the concentration of the known gas when the gate voltage determined in the first determination step is applied to the gate electrode, in association with the gate voltage determined in the first determination step and the type of the known gas. [Effects of the Invention]

[0015] According to the present invention, since the response characteristics of the channel layer when the gate voltage is changed differ depending on the type of gas, it is possible to identify the type of gas by measuring the characteristics of the channel layer while changing the gate voltage. Therefore, it is possible to provide a gas sensor and a gas sensor system that can detect multiple types of gases using a single type of gas detection material layer. Furthermore, it is possible to detect gases and measure the concentrations of the detected gases using such a gas sensor or gas sensor system. [Brief explanation of the drawings]

[0016] [Figure 1]1 is a schematic perspective view of a gas sensor system 1 according to an embodiment of the present invention. [Figure 2] 1 is an electron microscope photograph showing the growth of nanorods during sintering. [Figure 3] FIG. 1 is a schematic perspective view of a gas sensor system 1 according to a first modified example of the embodiment of the present invention. [Figure 4] 1(a) and 1(b) are diagrams illustrating a process for detecting a gas using the gas sensor system 1. FIG. [Figure 5] 10(a) and 10(b) are diagrams showing measurement results of response characteristics of the gas sensor 10 with respect to the average value of the resistance value R and the reciprocal value of the gate voltage Vg when the gas sensor 10 is exposed to five different types of gases. [Figure 6] 1A is a graph showing the response characteristics of the average value of the difference R0-Rgas between the resistance value R0 and the resistance value Rgas with respect to the value of the gate voltage Vg when the gas sensor 10 is exposed to each of these gases, and FIG. 1B is a graph showing the response characteristics of the average value of the ratio R0 / Rgas between the resistance value R0 and the resistance value Rgas with respect to the value of the gate voltage Vg when the gas sensor 10 is exposed to each of these gases. [Figure 7] 1 is a diagram showing the configuration of a computer 100 that executes gas detection processing using the gas sensor system 1. FIG. [Figure 8] 1 is a diagram showing a process performed by a computer 100 to execute a gas detection process using the gas sensor system 1. FIG. [Figure 9] 1 is a diagram showing a process performed by a computer 100 to execute a gas detection process using the gas sensor system 1. FIG. [Figure 10] FIG. 10 is a diagram showing the process performed by the computer 100 to measure the concentration of a gas identified by the gas detection process. [Figure 11] FIG. 10 is a diagram showing the process performed by the computer 100 to measure the concentration of a gas identified by the gas detection process. [Figure 12] FIG. 10 is a diagram showing the process performed by the computer 100 to measure the concentration of a gas identified by the gas detection process. [Figure 13] FIG. 2 is a diagram showing a gas sensor system 1 according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] 1 is a schematic perspective view of a gas sensor system 1 according to an embodiment of the present invention. As shown in the figure, the gas sensor system 1 includes a gas sensor 10, a variable DC power supply 11, a constant current source 12, a voltmeter 13, and a chamber 14. In addition, although not shown, the gas sensor system 1 also includes a heater for maintaining a constant temperature of the gas sensor 10.

[0018] The gas sensor 10 has a structure similar to that of a field-effect transistor, and is configured to include a gate electrode 20, a gate insulating film 21, a channel layer 22, a source electrode 23, and a drain electrode 24. Of these, the gate electrode 20, the gate insulating film 21, and the channel layer 22 are laminated in this order. The gas sensor 10 is placed in the chamber 14 in a state where the surface of the channel layer 22 (in particular, the surface of each nanostructure constituting the nanostructure array 32 described later) is exposed to the gas introduced into the chamber 14.

[0019] The gate electrode 20 is a conductive well formed by doping the surface of a silicon substrate with P-type impurities. The variable DC power supply 11 serves to supply a plurality of different gate voltages Vg to the gate electrode 20. The gate insulating film 21 is an insulating film formed on the surface of the gate electrode 20 and is made of, for example, silicon oxide.

[0020] The channel layer 22 is a gas sensing material layer disposed on the upper side of the gate insulating film 21, and is configured to change the resistance value between the source electrode 23 and the drain electrode 24 depending on the value of the gate voltage Vg applied to the gate electrode 20 and the type of gas to which it is exposed. As a specific structure for this purpose, the channel layer 22 includes a film 30 made of graphene, a seed layer 31 made of, for example, molybdenum oxide (MoOx), and a nanostructure array 32. In the example of FIG. 1 , the film 30 is disposed on the surface of the gate insulating film 21, and the seed layer 31 is disposed on the surface of the film 30.

[0021] Graphene is a monolayer material in which carbon atoms form a honeycomb-like hexagonal pattern on a plane, with a density of approximately 15,000 cm at room temperature. 2 / V·s. These properties of graphene enable the film 30 to reduce the impedance of the gas sensor 10. The film 30 is formed by forming graphene on the surface of a copper (Cu) surface catalyst substrate by CVD, and then transferring the graphene onto the gate insulating film 21 using a polymethyl methacrylate (PMMA) thin film as a support.

[0022] The seed layer 31 and the nanostructure array 32 are materials that adsorb molecules of the gas to be detected. In this embodiment, the nanostructure array 32 is composed of numerous nanorods grown from the seed layer 31 and has a very large surface area. The seed layer 31 and the nanostructure array 32 are formed by preparing a precursor solution using a magnetic stirrer, spin-coating it onto the film 30 at 1500 to 3500 rpm for 20 to 30 seconds, and then sintering it in air at 673 K for 15 minutes in a preheated electric furnace. After the nanostructure array 32 is formed, the surface of each nanorod may be coated with a catalyst (e.g., metal oxide, noble metal, transition metal) appropriate for the type of gas to be detected. This further increases the adsorption rate of gas molecules onto the surface of each nanorod.

[0023] Figure 2 shows electron microscope images of nanorod growth during sintering. The images are arranged vertically, showing the nanorods grown 3, 5, 10, and 15 minutes after the start of the sintering process. These images demonstrate that the 15-minute sintering process results in the formation of a nanostructure array 32 on the surface of the seed layer 31.

[0024] In this embodiment, an example is described in which the nanostructure array 32 is formed from a large number of nanorods grown from a seed layer 31 made of molybdenum oxide, but the seed layer 31 may be formed from a material other than molybdenum oxide, and the nanostructure array 32 may be formed from a spherical structure or a dendrimer structure. Specific examples of materials for the seed layer 31 include various semiconductor materials such as transition metal oxides (e.g., titanium oxide, vanadium oxide, cobalt oxide, nickel oxide, manganese oxide, iron oxide, and copper oxide), rare earth oxides, and tin oxide.

[0025] Returning to FIG. 1, the source electrode 23 and the drain electrode 24 are electrodes made of a metal material such as gold or titanium, and are disposed with a gap therebetween so that the channel layer 22 is electrically located therebetween. In the example of FIG. 1, the source electrode 23 and the drain electrode 24 are disposed on the surface of the film 30, and a seed layer 31 is disposed between the source electrode 23 and the drain electrode 24. In this case, the source electrode 23 and the drain electrode 24 are formed on the film 30 using photolithography or the like, and then the seed layer 31 and the nanostructure array 32 are formed by the process described above.

[0026] 3 is a schematic perspective view of a gas sensor system 1 according to a first modified example of the embodiment of the present invention. This modified example differs from the gas sensor system 1 according to the present embodiment in that the source electrode 23 and the drain electrode 24 are arranged with a gap between them on the surface of the gate insulating film 21. The seed layer 31 is arranged to bridge between the source electrode 23 and the drain electrode 24. However, in this modified example, the source electrode 23 and the drain electrode 24 are also electrically arranged with a gap between them so that the channel layer 22 is located therebetween. In manufacturing the gas sensor 10 according to this modified example, the source electrode 23 and the drain electrode 24 may be formed on the gate insulating film 21 by photolithography or the like before forming the film 30 by graphene transfer.

[0027] Returning to Fig. 1, the constant current source 12 serves to apply a constant current Id from the source electrode 23 to the drain electrode 24. The voltmeter 13 serves to measure the voltage Vsd between the source electrode 23 and the drain electrode 24.

[0028] 4(a) and 4(b) are diagrams illustrating a process for detecting gas using the gas sensor system 1. These diagrams show the measurement results of the resistance value R between the source electrode 23 and the drain electrode 24 when 725 ppm of 2-propanol (IPA) is introduced into the chamber 14. FIG. 4(a) shows the case where the temperature of the gas sensor 10 is maintained at 200°C, and FIG. 4(b) shows the case where the temperature of the gas sensor 10 is maintained at 300°C. Hereinafter, a method for using the gas sensor system 1 will be described in detail with reference to FIGS. 4(a) and 4(b) as well as FIG. 1.

[0029] The horizontal axis in Figures 4(a) and (b) represents time in seconds. On the other hand, the vertical axis in Figures 4(a) and (b) represents the resistance value R. The resistance value R can be obtained by dividing the voltage Vsd by the current Id, and is expressed in ohms. Furthermore, "on" and "off" shown in Figures 4(a) and (b) correspond to the state in which the gas to be detected (2-propanol in this case) is introduced into the chamber 14 and the state in which it is not introduced, respectively.

[0030] As shown in Figures 4(a) and 4(b), when gas is introduced into the chamber 14 while a constant current Id is flowing from the source electrode 23 to the drain electrode 24, the resistance value R increases. Then, when the gas introduction is stopped, the resistance value R decreases. As can be seen from Figures 4(a) and 4(b), the absolute value of the resistance value R and the difference between the resistance value R when gas is introduced and when gas introduction is stopped vary depending on the value of the gate voltage Vg. In the example of Figures 4(a) and 4(b), the greater the value of the gate voltage Vg, the greater the absolute value of the resistance value R and the difference between the resistance value R when gas is introduced and when gas introduction is stopped.

[0031] As will be explained in detail later with reference to FIGS. 5 and 6, the response characteristics of the absolute value of the resistance R with respect to the gate voltage Vg and the difference between the resistance R when gas is introduced and when gas is stopped differ depending on the type of gas. Therefore, if the response characteristics of the absolute value of the resistance R and the difference between the resistance R when gas is introduced and when gas is stopped with respect to the gate voltage Vg are known, the type of gas being introduced into the chamber 14 can be identified. Based on this principle, the gas sensor system 1 according to this embodiment aims to detect multiple types of gases using only one type of gas detection material layer. This will be explained in more detail below with reference to a specific example. In the following explanation, the resistance R when gas is introduced will be referred to as resistance Rgas, and the resistance R when gas is stopped will be referred to as resistance R0. In the following description, the resistance value Rgas, the reciprocal of the resistance value Rgas, 1 / Rgas, the difference between the resistance value R0 and the resistance value Rgas, R0-Rgas, and the ratio of the resistance value R0 to the resistance value Rgas, R0 / Rgas, will be used to identify the type of gas, and these will be collectively referred to as "indices."

[0032] In the example shown in FIG. 4(b), even if the gate voltage Vg is the same (e.g., 15 V), the resistances Rgas and R0 increase overall as time passes. This is due to the influence of gas remaining in the chamber 14. As can be seen from the absence of such an increase in FIG. 4(a), this influence becomes more pronounced as the temperature of the gas sensor 10 increases. Therefore, when detecting gas, the gas sensor 10 may be measured while maintaining a low temperature (e.g., below 200°C). However, this would result in a lower overall resistance Rgas (i.e., a decrease in the sensitivity of the gas sensor 10). Therefore, it is preferable to stop the gas supply for a sufficient period before starting the gas supply. To reduce the influence of measurement variations, it is preferable to repeat the gas supply and stop supply multiple times (e.g., three times) as shown in the example shown in FIGS. 4(a) and 4(b), measure the resistances Rgas and R0 each time, and obtain the average value as the measurement result. The following description will be given on the assumption that the resistance values ​​Rgas and R0 are measured in this manner.

[0033] 5 and 6 are graphs showing the response characteristics of each index versus the gate voltage Vg when the gas sensor 10 is exposed to five different gases. The five gases are 1-propanol (1PrOH), acetone (ACE), ethanol (EtOH), 2-propanol (IPA), and methanol (MtOH). FIG. 5(a) shows the response characteristics of the resistance value Rgas, FIG. 5(b) shows the response characteristics of the reciprocal of the resistance value Rgas, 1 / Rgas, FIG. 6(a) shows the response characteristics of the difference R0 and the resistance value Rgas, R0-Rgas, and FIG. 6(b) shows the response characteristics of the ratio R0 / Rgas of the resistance value R0 to the resistance value Rgas.

[0034] 5 and 6, it can be seen that the response characteristics of each index with respect to the value of gate voltage Vg often differ depending on the type of gas. Therefore, it can be said that by acquiring these response characteristics, the type of gas introduced into chamber 14 can be identified.

[0035] The gas detection process using the above-described principle can be performed manually, but is preferably performed by computer processing. The computer configuration required for this purpose and the specific processing performed by the computer will be described in detail below.

[0036] 7 is a diagram showing the configuration of a computer 100 that executes gas detection processing using the gas sensor system 1. As shown in the figure, the computer 100 has a configuration in which a CPU (Central Processing Unit) 101, a storage device 102, an input device 103, an output device 104, and a communication device 105 are interconnected via a bus 106.

[0037] The CPU 101 is a device that controls each part of the computer 100 and also reads and executes various programs stored in the storage device 102. The storage device 102 includes a main storage device such as a dynamic random access memory (DRAM) and an auxiliary storage device such as a hard disk, and serves to store various programs for executing the operating system and various applications of the computer 100, as well as data used by these programs. The processes shown in FIGS. 8 to 12, which will be described later, are realized by the CPU 101 executing the programs stored in the storage device 102.

[0038] The input device 103 is a device that receives external input and supplies it to the CPU 101, and is configured to include, for example, a keyboard, a mouse, and a touch panel. The voltmeter 13 shown in FIG. 1 is one type of the input device 103, and serves to supply a voltage Vsd to the CPU 101.

[0039] The output device 104 is a device that outputs the processing results of the CPU 101 to the outside, and is configured to include, for example, a display and a speaker. The variable DC power supply 11 and constant current source 12 shown in FIG. 1 are types of output device 104, and serve to generate a gate voltage Vg and a constant current Id, respectively, in response to instructions from the CPU 101. Although not explicitly shown in FIG. 1, the chamber 14 is provided with a switch for controlling the start and stop of the introduction of gas into the chamber 14, and this switch is also a type of output device 104. The CPU 101 starts or stops the introduction of gas into the chamber 14 by controlling this switch.

[0040] The communication device 105 is a device for communicating with external devices, and transmits and receives data according to instructions from the CPU 101 .

[0041] 8 and 9 are diagrams showing the processes performed by the computer 100 to execute a gas detection process using the gas sensor system 1. The process shown in FIG. 8 is a response characteristic acquisition process for acquiring response characteristics for each gas, and is executed using a known gas before detecting an unknown gas. On the other hand, the process shown in FIG. 9 is a gas detection process for detecting an unknown gas. Each process will be described in detail below.

[0042] 8, the computer 100 uses two variables m and n when executing the response characteristic acquisition process. The variable m is a variable that changes in increments of 1 from a minimum value of 1 to a maximum value of M, and corresponds to the number of values ​​of the gate voltage Vg. In the following, the m-th gate voltage Vg is referred to as the gate voltage Vg m The variable n is a variable that changes in increments of 1 from a minimum value of 1 to a maximum value of N, and corresponds to the number of trials required to find the average value mentioned above.

[0043] The computer 100 starts the response characteristic acquisition process by controlling the constant current source 12 to start supplying a constant current Id to the gas sensor 10 (step S1), and then repeatedly executes the processes of steps S3 to S12 while changing the variable m by 1 (step S2). In step S3, the computer 100 controls the variable DC power supply 11 to obtain the m-th gate voltage Vg m The application of the voltage to the gate electrode 20 is started (step S3).

[0044] In step S4, computer 100 repeatedly executes the processes of steps S5 to S8 while changing variable n by 1 (step S4). Specifically, computer 100 first starts the introduction of a known gas of a predetermined concentration (step S5), and measures resistance value Rgas between source electrode 23 and drain electrode 24 using voltmeter 13 (step S6). Thereafter, computer 100 stops the introduction of the gas (step S7), and again measures resistance value R0 between source electrode 23 and drain electrode 24 using voltmeter 13 (step S8).

[0045] Here, in measuring the resistance values ​​Rgas and R0 in steps S6 and S8, it is preferable to wait a predetermined time after executing steps S5 and S7, respectively, before measuring the voltage Vsd. This is because, as can be seen from Fig. 4, it takes a certain amount of time from the start or stop of gas introduction until the voltage Vsd stabilizes. This also applies to steps S25 and S27 in Fig. 9, steps S46 and S48 in Fig. 10, and steps S65 and S67 in Fig. 12, which will be described later.

[0046] After executing the processes of steps S5 to S8 N times, the computer 100 controls the variable DC power supply 11 to supply the gate voltage Vg to the gate electrode 20. mThe application of R is stopped (step S9), and the average value and standard deviation of N measurements are calculated for each of a plurality of indices (specifically, Rgas, 1 / Rgas, R0-Rgas, and R0 / Rgas; the same applies below) (step S10). The standard deviation is calculated here to determine whether or not there are any abnormal values. The computer 100 determines whether or not there are any abnormal values ​​that are a predetermined multiple (e.g., three times) or more of the standard deviation from the average value among the indices obtained as a result of the N measurements (step S11). If there are any abnormal values, the computer 100 starts the process again from step S3. On the other hand, if there are no abnormal values, the computer 100 stores the value calculated in step S10 in association with the variable m (step S12), and proceeds to the process for the next value of the variable m.

[0047] After the processing of steps S2 to S12 for all variables m is completed, the computer 100 controls the constant current source 12 to stop supplying the constant current Id to the gas sensor 10 (step S13), and uses the values ​​stored in step S11 to obtain an approximate curve of the change in each of the multiple indices relative to the gate voltage Vg (step S14). The obtained approximate curves are then stored in a gas characteristics table in association with the type of gas introduced in step S4 (step S15). The gas characteristics table is a table that stores the response characteristics of each index relative to the gate voltage Vg (specifically, the approximate curves) for each type of gas, and is stored in the storage device 102 shown in FIG. 7.

[0048] By performing the above-described response characteristic acquisition process for all gases to be detected, the response characteristics for all gases are stored in the gas characteristics table. The gas detection process shown in Fig. 9 is performed after the gas characteristics table is in this state.

[0049] 9, many of the processes executed in the gas detection process are the same as those executed in the response characteristic acquisition process. Specifically, the processes in steps S20 to S33 shown in Fig. 9 are the same as the processes in steps S1 to S14 in Fig. 8, except that the gas introduced into chamber 14 in step S24 is an unknown gas rather than a known gas.

[0050] After completing step S33, the computer 100 reads the gas characteristics table from the storage device 102 shown in Fig. 7, and identifies the type of gas introduced in step S24 based on the approximation curves stored therein and the approximation curves calculated in step S33 (step S34). Specifically, for each type of gas stored in the gas characteristics table, the computer 100 calculates the similarity between the multiple approximation curves stored in the gas characteristics table and the multiple approximation curves calculated in step S33, and identifies the gas type with the highest calculated similarity as the type of gas introduced in step S24. This allows the gas sensor 10, which has only one type of gas detection material layer, to identify which of the multiple gases stored in the gas characteristics table the gas introduced in step S24 is.

[0051] As described above, in the gas sensor system 1 according to this embodiment, the response characteristics of the channel layer 22 when the gate voltage Vg is changed (specifically, the response characteristics of Rgas, 1 / Rgas, R0-Rgas, and R0 / Rgas) differ depending on the type of gas. Therefore, by measuring the indices indicating the characteristics of the channel layer 22 (specifically, Rgas, 1 / Rgas, R0-Rgas, and R0 / Rgas) while changing the gate voltage Vg, it is possible to identify the type of gas. Therefore, the gas sensor system 1 according to this embodiment can provide a gas sensor and a gas sensor system that can detect multiple types of gases using a single type of gas detection material layer. Furthermore, it is also possible to detect gases using such a gas sensor or gas sensor system.

[0052] Furthermore, the gas sensor system 1 according to this embodiment also makes it possible to measure the concentration C of the gas detected by the gas detection process. The specific process for this purpose will be described in detail below with reference to FIGS. 10 to 12.

[0053] 10 to 12 are diagrams showing the processes performed by computer 100 to measure the concentration of a gas identified by the gas detection process. The processes shown in Fig. 10 and Fig. 11 are concentration measurement preparation processes for preparing for concentration measurement, and can be performed at the same time as the response characteristic acquisition process shown in Fig. 8. The process shown in Fig. 12 is a concentration measurement process for measuring the concentration of a gas identified by the gas detection process. Each of these processes will be described in detail below.

[0054] 10, the computer 100 uses three variables k, m, and n when executing the concentration measurement preparation process. The variables m and n are the same as the variables m and n used in FIGS. 8 and 9. The variable k is a variable that changes in increments of 1 from a minimum value of 1 to a maximum value of K, and corresponds to the number of samples of gas concentration C. In the following, the kth sample of concentration C is referred to as concentration C. k It may be marked as such.

[0055] After starting the concentration measurement preparation process, the computer 100 controls the constant current source 12 to start supplying a constant current Id to the gas sensor 10 (step S40), and then repeatedly executes the processes of steps S42 to S52 while changing the variable k by 1 (step S41).

[0056] In step S42, the computer 100 repeatedly executes the processes of steps S43 to S52 while changing the variable m by 1 (step S42). In step S43, the computer 100 controls the variable DC power supply 11 to change the m-th gate voltage Vg m The application of the voltage to the gate electrode 20 is started (step S43).

[0057] In step S44, the computer 100 repeatedly executes the processes of steps S45 to S48 while changing the variable n by 1 (step S44). The processes of steps S45 to S48 are executed when the concentration of the known gas introduced into the chamber 14 in step S45 is C k 8. Except for this, the process is the same as steps S5 to S8 in FIG.

[0058] After executing the processes of steps S45 to S48 N times, the computer 100 controls the variable DC power supply 11 to supply the gate voltage Vg to the gate electrode 20. m The application of the voltage is stopped (step S49), and the average value and standard deviation for each of the N measurements are calculated for each of the multiple indices (step S50). Then, computer 100 determines whether or not there is an abnormal value that is a predetermined multiple (e.g., three times) or more of the standard deviation away from the average value among the indices obtained as a result of the N measurements (step S51). If there is an abnormal value, computer 100 starts the process again from step S43. On the other hand, if there is no abnormal value, computer 100 stores the value calculated in step S50 in association with variable m (step S52), and proceeds to the process for the next value of variable m. After the processes of steps S43 to S52 have been completed for all variables m, computer 100 proceeds to the process for the next value of variable k.

[0059] After the processes of steps S42 to S52 are completed for all variables k, the computer 100 controls the constant current source 12 to stop supplying the constant current Id to the gas sensor 10 (step S53).

[0060] Next, as shown in FIG. 11, the computer 100 repeatedly executes the processes of steps S55 to S58 for each of the multiple indices (step S54).

[0061] In step S55, the computer 100 determines m at which the change in the index of interest due to the concentration C is greatest (step S55), and determines whether the range of change in the index of interest due to the concentration C at the determined m is equal to or greater than a predetermined value (step S56). The range of change in the index of interest due to the concentration C is, in short, the sensitivity of the index of interest to the gas concentration C, and the processing of step S56 is equivalent to determining whether the sensitivity is equal to or greater than a predetermined value.

[0062] If it is determined in step S56 that the value is equal to or greater than the predetermined value, the computer 100 calculates an approximate curve of the change in the index of interest relative to the gas concentration at the determined m (step S57), stores the calculated approximate curve in a concentration characteristics table in association with the type of gas, the value of the variable m, and the index of interest (step S58), and moves on to the processing for the next index. The concentration characteristics table stores the gate voltage Vg applied to the gate electrode 20 in association with the combination of the type of gas, the variable m, and the index. m This is a table that stores the response characteristics of the index (specifically, the above-mentioned approximate curve) with respect to the gas concentration C when a gas is applied, and like the gas characteristics table described above, is stored in the storage device 102 shown in Fig. 7. If it is determined in step S56 that the index is not equal to or greater than the predetermined value, the computer 100 skips steps S57 and S58 and moves on to the processing of the next index.

[0063] When the concentration measurement preparation process described above is performed for various types of gas, the concentration characteristics table stores, for each type of gas, the variable m, the index, and an approximate curve showing the change in the index relative to the gas concentration C. Therefore, for example, if the concentration of 1-propanol is to be measured, the variable m, the index, and the approximate curve stored in the concentration characteristics table for 1-propanol are read out, and the gate voltage Vg indicated by the read variable m is calculated. m is applied to the gate electrode 20, the read index is measured, and the measurement result is substituted into the read approximation curve, thereby obtaining the concentration of 1-propanol.

[0064] 12, the computer 100 first acquires the value of the variable m, the index, and the approximate curve stored in the concentration characteristics table in association with the type of gas identified in the gas detection process (step S60). Then, the computer 100 controls the constant current source 12 to start supplying the constant current Id to the gas sensor 10 (step S61). m The application of the voltage to the gate electrode 20 is started (step S62).

[0065] Next, computer 100 repeatedly executes the processes of steps S64 to S67 while changing variable n by 1 (step S63). Specifically, computer 100 first starts introducing the type of gas identified in the gas detection process (step S64), and measures resistance value Rgas between source electrode 23 and drain electrode 24 using voltmeter 13 (step S65). Thereafter, computer 100 stops introducing the gas (step S66), and again measures resistance value R0 between source electrode 23 and drain electrode 24 using voltmeter 13 (step S67).

[0066] After executing the processes of steps S64 to S67 N times, the computer 100 calculates the average value and standard deviation for each of the N times for a plurality of indices (step S68). Then, the computer 100 determines whether or not there is an abnormal value that is a predetermined multiple (e.g., three times) or more of the standard deviation from the average value among the indices acquired as a result of the N times of measurement (step S69). If there is an abnormal value, the computer 100 starts the process again from step S63. On the other hand, if there is no abnormal value, the computer 100 controls the variable DC power supply 11 to increase the gate voltage Vg applied to the gate electrode 20. m The application of the constant current Id to the gas sensor 10 is stopped (step S70), and the constant current source 12 is controlled to stop the supply of the constant current Id to the gas sensor 10 (step S71).

[0067] Thereafter, the computer 100 obtains the value of the index obtained in step S60 from the measurement results obtained this time (step S73). For example, if the index obtained in step S60 is the reciprocal 1 / Rgas of the resistance value Rgas, the computer 100 obtains the reciprocal of the average value of the resistance values ​​Rgas obtained as the measurement result as the "index value." Finally, the computer 100 determines the gas concentration C based on the approximation curve obtained in step S60 and the value obtained in step S73 (step S74), and ends the process.

[0068] As described above, the gas sensor system 1 according to this embodiment also makes it possible to measure the concentration C of the gas detected by the gas detection process.

[0069] 13 is a diagram showing a gas sensor system 1 according to a second embodiment of the present invention. As shown in the figure, the gas sensor system 1 according to this embodiment includes four gas sensors 10-1 to 10-4 arranged in a matrix, switches SW1 to SW4 provided corresponding to the gas sensors 10-1 to 10-4, two control lines C1, C2 and two gate lines G1, G2 provided for each row of the matrix, and two source lines S1, S2 and two drain lines D1, D2 provided for each column of the matrix.

[0070] The gas sensors 10-1 to 10-4 are each similar in configuration to the gas sensor 10 described in the first embodiment. However, the gas sensors 10-1 to 10-4 are configured to have different formation conditions, structures, materials, thicknesses, widths, etc. of the channel layers 22, so that the response characteristics of the channel layers 22 when the gate voltage Vg is changed or when the gas concentration C is changed are different from one another.

[0071] Each of the switches SW1 to SW4 is configured by, for example, a field-effect transistor. In the following description, it is assumed that the switches SW1 to SW4 are field-effect transistors. The gate electrodes of the switches SW1 and SW2 are commonly connected to a control line C1, and the gate electrodes of the switches SW3 and SW4 are commonly connected to a control line C2. The source electrodes of the switches SW1 and SW3 are commonly connected to a source line S1, and the source electrodes of the switches SW2 and SW4 are commonly connected to a source line S2. The drain electrodes of the switches SW1 to SW4 are connected to source electrodes 23 (see FIG. 1; indicated as "S" in FIG. 10) of the gas sensors 10-1 to 10-4, respectively.

[0072] The gate electrodes 20 (see FIG. 1, indicated as "G" in FIG. 10) of the gas sensors 10-1 and 10-2 are commonly connected to a gate line G1. The gate electrodes 20 of the gas sensors 10-3 and 10-4 are commonly connected to a gate line G2. Variable DC power supplies 11 configured to be controllable independently of each other are connected to the gate lines G1 and G2, respectively.

[0073] The drain electrodes 24 (see FIG. 1; indicated as "D" in FIG. 10) of the gas sensors 10-1 and 10-3 are commonly connected to a drain line D1. The drain electrodes 24 of the gas sensors 10-2 and 10-4 are commonly connected to a drain line D2. A constant current source 12 and a voltmeter 13 are connected between the source line S1 and the drain line D1, and between the source line S2 and the drain line D2, respectively. These constant current sources 12 and voltmeters 13 are configured to be capable of being controlled or measured independently of each other.

[0074] When performing a gas detection process using the gas sensor system 1 according to this modification, the computer 100 first activates the control line C1 and deactivates the control line C2. This turns on the switches SW1 and SW2 and turns off the switches SW3 and SW4. Therefore, the source electrode 23 of the gas sensor 10-1 is connected to the source line S1, and the source electrode 23 of the gas sensor 10-2 is connected to the source line S2. Therefore, the computer 100 can identify the type of gas in each of the gas sensors 10-1 and 10-2 by performing the gas detection process shown in FIG. 9 for each of the gas sensors 10-1 and 10-2.

[0075] Next, the computer 100 activates the control line C2 and deactivates the control line C1. This turns on the switches SW3 and SW4 and turns off the switches SW1 and SW2. Therefore, the source electrode 23 of the gas sensor 10-3 is connected to the source line S1, and the source electrode 23 of the gas sensor 10-4 is connected to the source line S2. Therefore, the computer 100 can identify the type of gas in each of the gas sensors 10-3 and 10-4 by executing the gas detection process shown in FIG. 9 for each of the gas sensors 10-3 and 10-4.

[0076] As described above, the gas sensor system 1 according to this embodiment can identify the type of gas using the four gas sensors 10-1 to 10-4, thereby enabling gas detection with higher accuracy than when using only one gas sensor 10. If the type of gas identified as a result of executing the gas detection process differs for each gas sensor 10, the final gas type can be identified by, for example, majority vote.

[0077] Furthermore, according to the gas sensor system 1 of this embodiment, the gas sensors 10-1 to 10-4 are configured so that the response characteristics of the channel layer 22 when the gate voltage Vg is changed are different from one another, and therefore the type of gas can be identified using four different criteria. Therefore, gas can be detected with higher accuracy than when four gas sensors 10 are used, each of which has the same response characteristic of the channel layer 22 when the gate voltage Vg is changed. However, it goes without saying that the gas sensors 10-1 to 10-4 may be configured so that the response characteristics of the channel layer 22 when the gate voltage Vg is changed are the same from one another.

[0078] Although the gas detection process has been described in the present embodiment, it is of course possible to perform a response characteristic acquisition process, a concentration measurement preparation process, and a concentration measurement process using similar processes. When the gas sensors 10-1 to 10-4 have the same configuration, ideally, the contents of the gas characteristic table and concentration characteristic table for each gas sensor 10-1 to 10-4 will be identical, so the response characteristic acquisition process and the concentration measurement preparation process can be performed using any one gas sensor 10. However, in reality, identical characteristics cannot always be reproduced even when the gas sensors are manufactured identically. Therefore, it is preferable to perform the response characteristic acquisition process and the concentration measurement preparation process for each gas sensor 10 and obtain a gas characteristic table and a concentration characteristic table. Furthermore, when the gas sensors 10-1 to 10-4 are configured so that the response characteristics of the channel layer 22 differ from one another when the gate voltage is changed, it is naturally necessary to perform the response characteristic acquisition process and the concentration measurement preparation process for each gas sensor 10 and obtain a gas characteristic table and a concentration characteristic table.

[0079] Furthermore, the gas sensor system 1 according to this embodiment can detect multiple gases constituting a mixed gas individually and measure their respective concentrations. To explain in more detail, when performing such detection and measurement, the multiple gas sensors 10 constituting the gas sensor system 1 are configured to be specialized for detecting and measuring the concentrations of different gases. Specifically, by adjusting the formation conditions, structure, material, thickness, width, etc. of the channel layer 22 of each gas sensor 10, each gas sensor 10 is configured so that when exposed to one or more specialized gases, the indicators change significantly with changes in gate voltage Vg or gas concentration, whereas when exposed to other types of gases, the indicators change little with changes in gate voltage Vg or gas concentration. This allows each gas sensor 10 to perform gas detection processing and concentration measurement processing for different types of gases, thereby enabling the multiple gases constituting a mixed gas to be individually detected and their respective concentrations to be measured.

[0080] Although the present embodiment has been described with reference to an example in which four gas sensors 10-1 to 10-4 are arranged in a matrix, it is of course possible to arrange a smaller or larger number of gas sensors 10 in a matrix. In this case, too, by providing a switch for each gas sensor 10, a control line and a gate line for each row of the matrix, and a source line and a drain line for each column of the matrix, it is possible to identify the type of gas in each of the plurality of gas sensors 10, as described above.

[0081] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and it goes without saying that the present invention can be embodied in various forms without departing from the spirit of the present invention.

[0082] For example, in the above embodiments, the resistance values ​​R0 and Rgas are obtained by repeatedly introducing and stopping the gas into the chamber 14. However, two gas sensors 10 may be placed in the chamber 14, and one of them may be covered in advance to prevent it from being exposed to the gas, so that it can be used as a reference for measuring the resistance value R0. In this way, the resistance values ​​R0 and Rgas can be obtained without repeatedly introducing and stopping the gas into the chamber 14.

[0083] Although the above embodiment identifies the type of gas by determining the similarity of the approximation curve, the type of gas may be identified using machine learning. That is, the correspondence between the gas type and the approximation curve obtained by the response characteristic acquisition process may be learned in advance in a machine learning model, and the approximation curve obtained in the gas detection process may be input to this machine learning model, which may then output the type of gas, thereby identifying the type of gas. [Explanation of symbols]

[0084] 1 Gas sensor system 10 Gas Sensor 11 Variable DC power supply 12 Constant current source 13 Voltmeter 14 chambers 20 gate electrode 21 Gate insulating film 22 Channel Layer 23 Source electrode 24 Drain electrode 30 Film 31 seed layer 32 Nanostructure Array 100 computers 101 CPU 102 Storage device 103 Input Device 104 Output Device 105 Communication equipment Bus 106 C1, C2 control lines D1, D2 drain wires G1, G2 gate lines R is the resistance between the source electrode 23 and the drain electrode 24 R0 Resistance value when gas is stopped R Rgas Resistance value when gas is introduced R S1, S2 source lines

Claims

1. a gate electrode, a gate insulating film, and a channel layer stacked in this order; a source electrode and a drain electrode spaced apart such that the channel layer is electrically located therebetween; The channel layer is a film made of graphene; a seed layer disposed on a surface of the film; a nanostructure array grown from the seed layer. Gas sensor.

2. the film is disposed on a surface of the gate insulating film; the seed layer is disposed between the source electrode and the drain electrode.

2. The gas sensor according to claim 1.

3. the source electrode and the drain electrode are disposed on the surface of the gate insulating film with a gap therebetween; The film is disposed so as to bridge between the source electrode and the drain electrode.

2. The gas sensor according to claim 1.

4. The gas sensor according to any one of claims 1 to 3; a constant current source that supplies a constant current from the source electrode to the drain electrode; a voltmeter for measuring the voltage between the source electrode and the drain electrode; a variable DC power supply configured to be able to supply a plurality of gate voltages different from one another to the gate electrode; A gas sensor system comprising:

5. a plurality of gas sensors arranged in a matrix; a plurality of switches provided corresponding to the plurality of gas sensors; a control line and a gate line provided for each row of the matrix; a source line and a drain line provided for each column of the matrix; A gas sensor system comprising: Each of the plurality of gas sensors includes: a gate electrode, a gate insulating film, and a channel layer stacked in this order; a source electrode and a drain electrode spaced apart such that the channel layer is electrically located therebetween; The channel layer of each of the plurality of gas sensors is a film made of graphene; a seed layer disposed on a surface of the film; a nanostructure array grown from the seed layer; Each of the plurality of switches includes a gate electrode connected to the corresponding control line, a source electrode connected to the corresponding source line, and a drain electrode connected to the source electrode of the corresponding gas sensor. Gas sensor system.

6. a gate electrode, a gate insulating film, and a channel layer stacked in this order; a source electrode and a drain electrode spaced apart such that the channel layer is electrically located therebetween; The channel layer is configured to change a resistance value between the source electrode and the drain electrode depending on a value of a gate voltage applied to the gate electrode and a type of gas to which the channel layer is exposed.

1. A method for detecting a gas using a gas sensor, comprising: a first measurement step of exposing the channel layer to a known gas and measuring a resistance value between the source electrode and the drain electrode while applying a gate voltage to the gate electrode, the first measurement step being performed multiple times while changing the applied gate voltage; a storage step of storing information indicating a response characteristic of the resistance value obtained as a result of the first measurement step to the gate voltage in association with the type of the known gas; A method comprising:

7. a second measurement step of measuring a resistance value between the source electrode and the drain electrode multiple times while changing the gate voltage applied, without exposing the channel layer to the known gas and while applying a gate voltage to the gate electrode; the storing step stores information indicating response characteristics of the resistance value obtained as a result of the first measuring step and the resistance value obtained as a result of the second measuring step to the gate voltage, in association with the type of the known gas; The method of claim 6.

8. the storage step stores, in association with the type of the known gas, a response characteristic of the resistance value obtained as a result of the first measurement step to the gate voltage, a response characteristic of the difference between the resistance value obtained as a result of the first measurement step and the resistance value obtained as a result of the second measurement step to the gate voltage, and a response characteristic of the ratio of the resistance value obtained as a result of the first measurement step and the resistance value obtained as a result of the second measurement step to the gate voltage; The method of claim 7.

9. a gate electrode, a gate insulating film, and a channel layer stacked in this order; a source electrode and a drain electrode spaced apart such that the channel layer is electrically located therebetween; The channel layer is configured to change a resistance value between the source electrode and the drain electrode depending on a value of a gate voltage applied to the gate electrode and a type of gas to which the channel layer is exposed.

1. A method for measuring a concentration of a gas using a gas sensor, comprising: a first measurement step of exposing the channel layer to a known gas and measuring a resistance value between the source electrode and the drain electrode while applying a gate voltage to the gate electrode, the first measurement step being performed multiple times while changing the applied gate voltage and the concentration of the known gas; a first determination step of determining, based on a result of the first measurement step, the gate voltage at which the change in the resistance value obtained as a result of the first measurement step relative to the concentration of the known gas is greatest; a first storage step of storing information indicating a response characteristic of the resistance value obtained as a result of the first measurement step to the concentration of the known gas when the gate voltage determined in the first determination step is applied to the gate electrode, in association with the gate voltage determined in the first determination step and the type of the known gas; A method comprising:

10. a first determination step of determining whether a change in the resistance value obtained as a result of the first measurement step with respect to the concentration of the known gas when the gate voltage determined in the first determination step is applied to the gate electrode is equal to or greater than a predetermined value; the first storing step, when it is determined in the first determining step that the resistance is equal to or greater than a predetermined value, stores information indicating a response characteristic of the resistance value obtained as a result of the first measuring step when the gate voltage determined in the first determining step is applied to the gate electrode, in association with the gate voltage determined in the first determining step and the type of the known gas; 10. The method of claim 9.

11. a second measurement step of measuring a resistance value between the source electrode and the drain electrode multiple times while applying a gate voltage to the gate electrode and without exposing the channel layer to the known gas, while changing the applied gate voltage and the concentration of the known gas; a second determination step of determining, based on a result of the second measurement step, the gate voltage at which an index based on the resistance value obtained as a result of the first measurement step and the resistance value obtained as a result of the second measurement step changes most significantly with respect to the concentration of the known gas; a second storage step of storing information indicating a response characteristic of the indicator to the concentration of the known gas when the gate voltage determined in the second determination step is applied to the gate electrode, in association with the gate voltage determined in the second determination step and the type of the known gas; The method of claim 9 or 10, further comprising:

12. a second determination step of determining whether a range of change in the indicator relative to the concentration of the known gas is equal to or greater than a predetermined value when the gate voltage determined in the second determination step is applied to the gate electrode; the second storing step, when it is determined in the second determining step that the value is equal to or greater than a predetermined value, stores information indicating a response characteristic of the index to the concentration of the known gas when the gate voltage determined in the second determining step is applied to the gate electrode, in association with the gate voltage determined in the second determining step and the type of the known gas; The method of claim 11.

Images