Method for manufacturing a humidity-sensitive material, humidity-sensitive material, and humidity sensor

Abstract

To improve the responsiveness of the resistance value to humidity fluctuations. [Solution] The method for manufacturing a moisture-sensitive material S110 includes: a first step S110-1 in which a first laminate is manufactured by forming a first layer made of graphite on a substrate; a second step S110-2 in which a second laminate is manufactured by forming a second layer made of a plurality of nitrogen-doped carbon nanowalls on the first layer of the first laminate; a third step S110-3 in which a third laminate is manufactured by attaching one or more catalyst particles to the plurality of carbon nanowalls constituting the second layer of the second laminate; and a fourth step S110-4 in which the third laminate is subjected to hydrogen treatment.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a humidity-sensitive material, a humidity-sensitive material, and a humidity sensor.

Background Art

[0002] Conventionally, an electric resistance type humidity sensor including a hygroscopic polymer in which conductive particles are dispersed as a humidity-sensitive film has been developed (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the humidity-sensitive film composed of a conventional hygroscopic polymer such as that in Patent Document 1, the change in resistance value according to humidity change is extremely different between the low humidity range and the high humidity range and the medium humidity range. For example, in the medium humidity range of 30 [%RH] or more and 50 [%RH] or less, when the humidity changes by 10 [%RH], the resistance value changes by 100 times or more. On the other hand, in the low humidity range of 0 [%RH] or more and less than 30 [%RH], and in the high humidity range of more than 50 [%RH] and 100 [%RH] or less, even when the humidity changes by 10 [%RH], the resistance value changes by less than 5 times.

[0005] For this reason, the humidity-sensitive film composed of a conventional hygroscopic polymer has a problem that the change in resistance value becomes non-linear depending on the humidity range, and the responsiveness of the resistance value to humidity fluctuation is low.

[0006] In view of such problems, an object of the present disclosure is to provide a method for manufacturing a humidity-sensitive material, a humidity-sensitive material, and a humidity sensor capable of improving the responsiveness of the resistance value to humidity fluctuation.

Means for Solving the Problems

[0007] To solve the above problems, a method for manufacturing a moisture-sensitive material according to one aspect of the present disclosure includes: a first step of manufacturing a first laminate by forming a first layer made of graphite on a substrate; a second step of manufacturing a second laminate by forming a second layer made of a plurality of nitrogen-doped carbon nanowalls on the first layer of the first laminate; a third step of manufacturing a third laminate by attaching one or more catalyst particles to the plurality of carbon nanowalls constituting the second layer of the second laminate; and a fourth step of subjecting the third laminate to hydrogen treatment.

[0008] The third step involves attaching catalyst particles to the second laminate by sputtering. During sputtering, the second laminate may be kept at a temperature of 500°C or higher and 800°C or lower, the ambient pressure during sputtering may be set to less than atmospheric pressure, and the sputtering time may be set to 3 minutes or more and 30 minutes or less.

[0009] In the fourth step, when performing hydrogen treatment, the third laminate may be kept at a temperature of 500°C or higher and 800°C or lower, and the hydrogen treatment time may be set to 60 minutes or higher and 180 minutes or lower.

[0010] The catalyst particles may include one or more selected from the group consisting of iron, copper, and nickel.

[0011] To solve the above problems, a moisture-sensitive material according to one aspect of the present disclosure comprises a substrate, a first layer made of graphite and provided on the substrate, and a second layer made of a plurality of nitrogen-doped carbon nanowalls and provided on the first layer, wherein the second layer has a first region in which the spacing between opposing wall surfaces of the carbon nanowalls is a first spacing, and a plurality of second regions in which the spacing between opposing wall surfaces of the carbon nanowalls is a second spacing that is greater than the first spacing, and in the second layer, the plurality of second regions are scattered within the first region.

[0012] To solve the above problems, a humidity sensor according to one aspect of the present disclosure comprises a substrate, a first layer made of graphite and provided on the substrate, and a second layer made of a plurality of nitrogen-doped carbon nanowalls and provided on the first layer, wherein the second layer has a first region in which the distance between opposing wall surfaces of the carbon nanowalls is a first distance, and a plurality of second regions in which the distance between opposing wall surfaces of the carbon nanowalls is a second distance greater than the first distance, and the plurality of second regions in the second layer comprises a humidity-sensing material scattered within the first region. [Effects of the Invention]

[0013] According to this disclosure, it is possible to improve the responsiveness of the resistance value to humidity fluctuations. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a first schematic diagram of a humidity sensor according to an embodiment of the present disclosure. [Figure 2] Figure 2 is a second schematic diagram of the humidity sensor according to the same embodiment. [Figure 3] Figure 3 is a schematic diagram of the measuring device according to the same embodiment. [Figure 4] Figure 4 is a schematic diagram of the second layer according to the same embodiment. [Figure 5] Figure 5 is a schematic diagram illustrating the positional relationship between the first and second regions of the second layer according to the same embodiment. [Figure 6] Figure 6 is a flowchart showing the processing flow for the manufacturing method of the humidity sensor according to the same embodiment. [Figure 7] Figure 7 is a process diagram illustrating the first, second, and third steps according to the same embodiment. [Figure 8] Figure 8 is a process diagram illustrating the fourth step and the adhesion step according to the same embodiment. [Figure 9] Figure 9 shows images of the results of observing Examples 1-4 with a scanning electron microscope (SEM). [Figure 10]FIG. 10 is an image showing the results of observing Examples 1 and 5 to 7 with a scanning electron microscope (SEM). [Figure 11] FIG. 11 is a diagram for explaining the relationship between relative humidity [%RH] and resistance value [Ω] in the humidity sensor of Example 5.

Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating understanding, and do not limit the present disclosure unless otherwise specified. In the present specification and drawings, elements having substantially the same functions and configurations are denoted by the same reference numerals, and redundant explanations are omitted. Also, elements not directly related to the present disclosure are not shown.

[0016] [1. Outline of Humidity Sensor] First, referring to FIG. 1, the outline of a humidity sensor 100 according to an embodiment of the present disclosure will be described. FIG. 1 is a first schematic diagram of the humidity sensor 100 according to an embodiment of the present disclosure. FIG. 2 is a second schematic diagram of the humidity sensor 100 according to the present embodiment. In FIGS. 1 and 2 of the present embodiment, the X-axis, Y-axis, and Z-axis that intersect vertically are defined as shown in the drawing.

[0017] As shown in FIGS. 1 and 2, the humidity sensor 100 includes a humidity-sensitive material 110. The humidity-sensitive material 110 includes a substrate 210, a first layer 220, and a second layer 230. The humidity-sensitive material 110 is, for example, in the form of a film.

[0018] The substrate 210 is preferably made of a material containing an element that easily forms a carbide. The substrate 210 is, for example, made of Si (silicon).

[0019] The first layer 220 is provided on the substrate 210. The first layer 220 is made of graphite. In the present embodiment, the graphite constituting the first layer 220 is doped with nitrogen.

[0020] The second layer 230 is provided on top of the first layer 220. The second layer 230 is composed of multiple nitrogen-doped carbon nanowalls. The second layer 230 will be described in detail later.

[0021] Furthermore, in this embodiment, the length of the second layer 230 in the X-axis direction in Figures 1 and 2 is shorter than that of the first layer 220. For this reason, the second layer 230 is not provided in the regions 220a and 220b at both ends of the first layer 220.

[0022] In this embodiment, the humidity sensor 100 may also include electrodes 120 and 122 and a measuring device 130, in addition to the humidity-sensitive material 110.

[0023] Electrode 120 is provided in region 220a of the first layer 220. Electrode 122 is provided in region 220b of the first layer 220. Electrodes 120 and 122 are made of, for example, metal paste. Electrode 120 and electrode 122 are electrically connected by wiring 124.

[0024] The measuring device 130 is electrically connected to the wiring 124. The measuring device 130 is a device that calculates humidity by obtaining the resistance value between electrode 120 and electrode 122.

[0025] Figure 3 is a schematic diagram of the measuring device 130 according to this embodiment. The measuring device 130 includes a control device 132 and a display device 134.

[0026] The control device 132 includes one or more processors 132a and one or more memories 132b connected to the processors 132a. The processors 132a include, for example, a CPU (Central Processing Unit). The memories 132b include, for example, ROM (Read Only Memory) and RAM (Random Access Memory). ROM is a memory element that stores programs and arithmetic parameters used by the CPU. RAM is a memory element that temporarily stores data such as variables and parameters used in processing executed by the CPU.

[0027] In this embodiment, various processes, including the resistance calculation process and humidity calculation process described below, can be performed by the processor 132a. More specifically, the various processes are performed by the processor 132a executing a program stored in the memory 132b. However, the functions of the control device 132 may be divided among multiple devices, or multiple functions may be realized by a single device.

[0028] Furthermore, in this embodiment, memory 132b stores, for example, calibration information. Calibration information is information that associates resistance value with humidity. Calibration information is created in advance by conducting experiments or the like.

[0029] In this embodiment, the processor 132a performs a resistance calculation process to calculate the resistance value (electrical resistance value) between electrode 120 and electrode 122. For example, the processor 132a passes current between electrode 120 and electrode 122 and calculates the resistance value based on the voltage and current values ​​between electrode 120 and electrode 122. The processor 132a also refers to calibration information stored in memory 132b and performs a humidity calculation process to calculate humidity (relative humidity [%RH]) based on the resistance value calculated in the resistance calculation process. The humidity calculated in the humidity calculation process is displayed, for example, on the display device 134.

[0030] The display device 134 consists of a liquid crystal display, an organic EL (Electro-Luminescence) display, and the like.

[0031] [2. Overview of Layer 2] Next, the second layer 230 according to this embodiment will be described with reference to Figures 4 and 5. Figure 4 is a schematic diagram of the second layer 230 according to this embodiment. Figure 5 is a schematic diagram illustrating the positional relationship between the first region 240 and the second region 242 of the second layer 230 according to this embodiment. In Figure 4, the cross-hatching indicates catalyst particles 250, and the black circles indicate gold particles 234. In Figures 4 and 5 of this embodiment, the perpendicularly intersecting X, Y, and Z axes are defined as shown in the figures.

[0032] As shown in Figure 4, the second layer 230 is composed of multiple carbon nanowalls 232. Each carbon nanowall 232 is composed of one or more graphene sheets. As described above, in this embodiment, the carbon nanowalls 232 constituting the second layer 230 are doped with nitrogen.

[0033] The carbon nanowall 232 is erected approximately perpendicular to the surface of the first layer 220 (in the Z-axis direction in Figures 4 and 5). The angle between the carbon nanowall 232 and the first layer 220 is, for example, between 45 degrees and 135 degrees.

[0034] The average thickness T of carbon nanowall 232 in 1 is, for example, between 1 nm and 100 nm. Thickness T is the length on the XY plane in Figures 4 and 5. The average height H of carbon nanowall 232 in 1 is, for example, between 500 nm and 700 nm. Height H is the length in the Z-axis direction in Figures 4 and 5.

[0035] Furthermore, the second layer 230 has a first region 240 and a plurality of second regions 242. In this embodiment, the second layer 230 consists of a first region 240 and second regions 242; that is, regions other than the second regions 242 are the first region 240. The density of carbon nanowalls 232 in the first region 240 is higher than the density of carbon nanowalls 232 in the second region 242. The first region 240 is a region of the second layer 230 where the distance between opposing wall surfaces of the carbon nanowalls 232 is a first distance W1. The second region 242 is a region of the second layer 230 where the distance between opposing wall surfaces of the carbon nanowalls 232 is a second distance W2 which is greater than the first distance W1. The first distance W1 and the second distance W2 are lengths on the XY plane in Figures 4 and 5. The average value of the first spacing W1 is, for example, between 1 nm and 5 μm. The second layer 230, in which the average value of the first spacing W1 is between 1 nm and 5 μm, can be manufactured at low cost.

[0036] The first interval W1 and the second interval W2 can also be said to be the width of the gap 232a formed between opposing wall surfaces in the carbon nanowall 232. In other words, the width of the gap 232a in the first region 240 is smaller than the width of the gap 232a in the second region 242. For example, if one carbon nanowall 232 is curved and there is a place where the wall surfaces of one carbon nanowall 232 face each other, a gap 232a is formed between those opposing wall surfaces. Also, if there is a place where the wall surfaces of adjacent carbon nanowalls 232 face each other among multiple carbon nanowalls 232, a gap 232a is formed between those opposing wall surfaces. The first interval W1 and the second interval W2, i.e., the width of the gap 232a, is, for example, the shortest distance between opposing wall surfaces in the carbon nanowall 232.

[0037] Furthermore, as shown in Figure 5, in the second layer 230, multiple second regions 242 are scattered within the first region 240. These multiple second regions 242 can also be described as holes formed in the first region 240.

[0038] The shape of the XY cross-section in Figures 4 and 5 of the second region 242 is, for example, a perfect circle or an ellipse. If the shape of the XY cross-section in Figures 4 and 5 of the second region 242 is a perfect circle or approximately a perfect circle, the second interval W2 can be said to be the diameter of the second region 242. Also, if the shape of the XY cross-section in Figure 4 of the second region 242 is an ellipse or approximately an ellipse, the second interval W2 can be said to be the major axis of the second region 242.

[0039] The average value of the second interval W2 is, for example, 20 nm or more and 2 μm or less, preferably 50 nm or more and 1 μm or less, and more preferably 100 nm or more and 1 μm or less. If the average value of the second interval W2 is less than 25 nm, the number of water vapor molecules trapped between adjacent carbon nanowalls 232 is small, and the humidity detection sensitivity of the humidity sensor 100 decreases. On the other hand, if the average value of the second interval W2 exceeds 2 μm, there is variation in the number of water vapor molecules trapped between adjacent carbon nanowalls 232, and the humidity detection accuracy of the humidity sensor 100 decreases. For this reason, by setting the average value of the second interval W2 in the second region 242 of the second layer 230 to 25 nm or more and 2 μm or less, it is possible to suppress the decrease in humidity detection sensitivity of the humidity sensor 100 and suppress the decrease in humidity detection accuracy of the humidity sensor 100.

[0040] Furthermore, an ambient gas such as air enters the gap 232a formed between opposing walls in the carbon nanowall 232. Therefore, if the ambient gas is an insulator, the opposing walls in the carbon nanowall 232 are insulated by the gap 232a.

[0041] Furthermore, as shown in Figure 4, in this embodiment, it is preferable that one or more gold (Au) particles 234 are attached to the tip portion of the carbon nanowall 232 constituting the second layer 230. It is preferable that the gold particles 234 are smaller than the first spacing W1.

[0042] The tip portion of carbon nanowall 232 is approximately 20% of the length of the tip 232b relative to the height H of the carbon nanowall 232. The length of the tip portion of carbon nanowall 232 (length in the Z-axis direction in Figure 4) is, for example, approximately 100 nm.

[0043] In this embodiment, the second layer 230 may also have catalyst particles 250. The region on the first layer 220 where the catalyst particles 250 are present becomes the second region 242. The catalyst particles 250 are catalyst particles that have the function of promoting a production reaction that generates hydrocarbons such as methane from solid carbon and hydrogen. The hydrocarbons produced by this production reaction are hydrocarbons that exist in a gaseous state at atmospheric pressure.

[0044] The catalyst particles 250 include, for example, one or more selected from the group consisting of iron (Fe), copper (Cu), and nickel (Ni).

[0045] Furthermore, carbon nanowalls 232 may or may not be provided between the catalyst particles 250 and the first layer 220. In other words, the catalyst particles 250 may be provided on the first layer 220 via carbon nanowalls 232, or they may be provided directly on the first layer 220.

[0046] [3. Method for manufacturing a humidity sensor] Next, the manufacturing method of the humidity sensor 100 according to this embodiment will be described with reference to Figure 6. Figure 6 is a flowchart showing the processing flow of the manufacturing method of the humidity sensor 100 according to this embodiment. Figure 7 is a process diagram illustrating the first step S110-1, the second step S110-2, and the third step S110-3 according to this embodiment. Figure 8 is a process diagram illustrating the fourth step S110-4 and the adhesion step S110-5 according to this embodiment. In Figures 7 and 8, as in Figure 4, cross-hatching indicates catalyst particles 250, and black circles indicate gold particles 234.

[0047] As shown in Figure 6, the manufacturing method of the humidity sensor 100 according to this embodiment includes a manufacturing method S110 for the humidity-sensitive material 110, an etching step S120, and an assembly step S130. The manufacturing method S110 for the humidity-sensitive material 110 according to this embodiment includes a first step S110-1, a second step S110-2, a third step S110-3, and a fourth step S110-4. Furthermore, the manufacturing method S110 for the humidity-sensitive material 110 according to this embodiment may also include an adhesion step S110-5. Each step will be described below.

[0048] [1st process S110-1] As shown in Figure 7, the first step S110-1 is a step in which the first laminate 10 is manufactured by forming (depositing) a first layer 220 made of graphite on the substrate 210.

[0049] [Second process S110-2] The second step S110-2 is a step in which a second laminate 20 is manufactured by forming (depositing) a second layer 230 composed of multiple nitrogen-doped carbon nanowalls 232 on the first layer 220 of the first laminate 10 manufactured in the first step S110-1.

[0050] The first step S110-1 and the second step S110-2 are carried out, for example, using a film deposition apparatus. The film deposition apparatus is, for example, a sheet plasma CVD apparatus. When using a sheet plasma CVD apparatus, the substrate 210 is placed in the chamber of the sheet plasma CVD apparatus. The substrate 210 is then maintained at, for example, 650°C in the chamber. A mixed gas is supplied into the chamber to carry out the first step S110-1 and the second step S110-2. The mixed gas contains at least an inert gas (for example, argon gas), methane gas, and nitrogen gas. The mixed gas may also further contain hydrogen.

[0051] Furthermore, the second layer 230 of the second laminate 20 has only the first region 240. In other words, the second region 242 is not formed in the second layer 230 of the second laminate 20.

[0052] [Third process S110-3] The third step S110-3 is a step in which one or more catalyst particles 250 are attached to a plurality of carbon nanowalls 232 that constitute the second layer 230 of the second laminate 20 to produce the third laminate 30.

[0053] In the third step S110-3, it is preferable to attach catalyst particles 250 to the second laminate 20 by sputtering. Furthermore, when sputtering, it is preferable to maintain the second laminate 20 at a temperature of 500°C or higher and 800°C or lower, more preferably at 600°C or higher and 700°C or lower, and even more preferably at 625°C or higher and 675°C or lower. Furthermore, it is preferable to set the atmospheric pressure when sputtering to less than atmospheric pressure. -7 [Pa] or more, 10 -3 It is more preferable to be less than or equal to Pa, 10 -6 [Pa] or more, 10 -4 It is even more preferable that the pressure be less than or equal to [Pa]. Furthermore, it is preferable that the sputtering execution time be 3 minutes or more and 30 minutes or less, more preferably 4 minutes or more and 10 minutes or less, and even more preferably 5 minutes or more and 7 minutes or less.

[0054] The third step S110-3 is carried out, for example, using a sputtering apparatus. In the third step S110-3, for example, the second laminate 20 and a sputtering target are placed inside the chamber of the sputtering apparatus. The target is made of the metal that constitutes the catalyst particles 250. The distance between the second laminate 20 and the target inside the chamber of the sputtering apparatus is, for example, 80 mm or more and 100 mm or less, preferably 90 mm.

[0055] The sputtering apparatus described above is, for example, a sheet plasma sputtering apparatus. When the sheet plasma sputtering apparatus also functions as a CVD apparatus, or when the sheet plasma CVD apparatus also functions as a sputtering apparatus, it is preferable that the first step S110-1, the second step S110-2, and the third step S110-3 are performed within the same sheet plasma CVD-sputtering apparatus.

[0056] [4th process S110-4] Step 4, S110-4, is a step of subjecting the third laminate 30 to hydrogen treatment. Step 4, S110-4 is carried out, for example, using an electric furnace. In step 4, S110-4, hydrogen treatment is performed by heating the third laminate 30 in a hydrogen atmosphere. The hydrogen atmosphere is, for example, an atmosphere containing hydrogen and an inert gas (for example, argon gas).

[0057] In step S110-4, when performing the hydrogen treatment, it is preferable to maintain the third laminate 30 at a temperature of 500°C or higher and 800°C or lower, more preferably at 500°C or higher and 700°C or lower, and even more preferably at 550°C or higher and 650°C or lower. Furthermore, the execution time (heating time) of the hydrogen treatment is preferably 60 minutes or more and 180 minutes or lower, more preferably 90 minutes or more and 150 minutes or lower, and even more preferably 110 minutes or more and 130 minutes or lower. In addition, it is preferable to perform the hydrogen treatment under atmospheric pressure.

[0058] By performing the fourth step S110-4, as shown in Figure 8, first, the catalyst particles 250 attached to the multiple carbon nanowalls 232 of the second layer 230 of the third laminate 30 aggregate, and the particle size of the catalyst particles 250 increases. The particle size of the aggregated catalyst particles 250 becomes larger than the first spacing W1 described above. The aggregated catalyst particles 250 then promote the production reaction that generates hydrocarbons from solid carbon and hydrogen. As a result, the carbon nanowalls 232 (solid carbon) to which the catalyst particles 250 are attached react with hydrogen and are converted into hydrocarbons. Thus, in the second layer 230, the carbon nanowalls 232 disappear in the areas where the catalyst particles 250 were attached, and multiple second regions 242 are formed (drilled) within the first region 240. In this way, the moisture-sensitive material 110 according to this embodiment is manufactured.

[0059] [Adhesion process S110-5] The adhesion step S110-5 is a step of attaching one or more gold particles 234 to a plurality of carbon nanowalls 232 of the second layer 230 of the moisture-sensitive material 110 after the fourth step S110-4 has been performed. In the adhesion step S110-5, it is preferable to attach the gold particles 234 to the carbon nanowalls 232 by sputtering. The atmospheric pressure when performing sputtering is preferably higher than that of the third step S110-3 described above, for example, atmospheric pressure. The adhesion step S110-5 is performed, for example, using a sputtering apparatus.

[0060] [Etching process S120] Returning to Figure 6, the etching process S120 is a process of etching two predetermined regions of the second layer 230 of the moisture-sensitive material 110. The etching process S120 is performed, for example, using a laser irradiation device. When using a laser irradiation device, for example, the pulse width is 10 -12 A laser beam of less than a second is irradiated onto two mutually separated regions in the second layer 230 of the moisture-sensitive material 110. As a result, regions 220a and 220b are formed on the first layer 220 of the moisture-sensitive material 110 that do not have the second layer 230.

[0061] [Assembly process S130] In assembly step S130, electrode 120 is placed in region 220a and electrode 122 is placed in region 220b. Then, wiring 124 is connected to electrodes 120 and 122, and measuring device 130 is connected to wiring 124. In this way, humidity sensor 100 is manufactured.

[0062] [4. Summary] As described above, the manufacturing method S110 of the moisture-sensitive material 110 according to this embodiment includes: a first step S110-1 of manufacturing a first laminate 10 by forming a first layer 220 made of graphite on a substrate 210; a second step S110-2 of manufacturing a second laminate 20 by forming a second layer 230 made of a plurality of nitrogen-doped carbon nanowalls 232 on the first layer 220 of the first laminate 10; a third step S110-3 of manufacturing a third laminate 30 by attaching one or more catalyst particles 250 to the plurality of carbon nanowalls 232 constituting the second layer 230 of the second laminate 20; and a fourth step S110-4 of subjecting the third laminate 30 to hydrogen treatment.

[0063] The manufacturing method S110 for the moisture-sensitive material 110 according to this embodiment allows for the production of a moisture-sensitive material 110 having a second layer 230 composed of multiple carbon nanowalls 232 by performing a first step S110-1 and a second step S110-2. In this embodiment, the carbon nanowalls 232 are not physically or electrically connected at their upper ends. On the other hand, as described above, in the moisture-sensitive material 110 according to this embodiment, a first layer 220 is continuously formed between the substrate 210 and the second layer 230 (carbon nanowalls 232). Therefore, in the moisture-sensitive material 110 according to this embodiment, the carbon nanowalls 232 are physically and electrically connected to each other at their bottoms by the first layer 220 (graphite).

[0064] Furthermore, a gap 232a is provided between opposing wall surfaces in the carbon nanowall 232 according to this embodiment. Therefore, when nothing is attached to the second layer 230 of the moisture-sensitive material 110 according to this embodiment (hereinafter referred to as the "initial state"), the opposing wall surfaces of the carbon nanowall 232 are insulated by the gap 232a. Consequently, in the initial state, the resistance value (electrical resistance value) of the second layer 230 of the moisture-sensitive material 110 becomes large. On the other hand, in the second layer 230 of the moisture-sensitive material 110 according to this embodiment, when water enters the gap 232a, the carbon nanowalls 232 are electrically connected to each other by the water, and the electrical properties of the second layer 230 change.

[0065] As a result, the resistance value of the second layer 230 of the humidity-sensitive material 110 according to this embodiment becomes smaller than the initial state. Furthermore, in the second layer 230 of the humidity-sensitive material 110 according to this embodiment, the resistance value of the second layer 230 of the humidity-sensitive material 110 decreases as the amount of water entering the gap 232a increases. Also, in the second layer 230 of the humidity-sensitive material 110 according to this embodiment, the rate of change of the resistance value in response to the amount of water entering the gap 232a is substantially constant regardless of the humidity range. In other words, in the humidity-sensitive material 110 manufactured by the manufacturing method S110 of the humidity-sensitive material 110 according to this embodiment, the rate of change of the resistance value is substantially constant from low humidity to high humidity (for example, from 20 [%RH] to 90 [%RH]). For this reason, the manufacturing method S110 of the humidity-sensitive material 110 according to this embodiment can manufacture a humidity-sensitive material 110 that can improve the responsiveness of the resistance value to humidity fluctuations from low humidity to high humidity. Furthermore, the manufacturing method S110 for the moisture-sensitive material 110 according to this embodiment can produce a moisture-sensitive material 110 in which the change in resistance value is generally linear, regardless of the humidity range.

[0066] Furthermore, the carbon nanowalls 232 constituting the second layer 230 of the humidity-sensitive material 110 manufactured by the manufacturing method S110 according to this embodiment are doped with nitrogen. Carbon nanowalls that are not doped with nitrogen have low affinity for water. On the other hand, since the carbon nanowalls 232 according to this embodiment are doped with nitrogen, they have a higher affinity for water compared to carbon nanowalls that are not doped with nitrogen. Therefore, the manufacturing method S110 according to this embodiment can manufacture a humidity-sensitive material 110 that has a high affinity for water. As a result, the manufacturing method S110 according to this embodiment can manufacture a humidity-sensitive material 110 that can increase the amount of water that enters the gaps 232a in the second layer 230, regardless of the humidity range. Thus, the manufacturing method S110 according to this embodiment can manufacture a humidity-sensitive material 110 that can improve the rate of change of resistance value from low humidity to high humidity.

[0067] Furthermore, as described above, carbon nanowalls have low affinity for water, and even if carbon nanowalls are doped with nitrogen, there is a limit to how much their affinity for water can be improved. Therefore, in the manufacturing method S110 of the moisture-sensitive material 110 according to this embodiment, by performing the third step S110-3 and the fourth step S110-4, a second region 242 can be formed in the second layer 230, where the width of the gaps 232a is the second interval W2, within the first region 240, where the width of the gaps 232a is the first interval W1. As described above, the second interval W2 is larger than the first interval W1. For this reason, in the second layer 230 of the moisture-sensitive material 110 according to this embodiment, the amount of water that penetrates into the second region 242 is greater than the amount of water that penetrates into the first region 240.

[0068] Therefore, in the moisture-sensitive material 110 according to this embodiment, the amount of water that enters the second layer 230 can be further increased compared to the second layer 230 which has only the first region 240. Accordingly, the manufacturing method S110 of the moisture-sensitive material 110 according to this embodiment can produce a moisture-sensitive material 110 that has a higher affinity for water. Accordingly, the manufacturing method S110 of the moisture-sensitive material 110 according to this embodiment can produce a moisture-sensitive material 110 in which the amount of water that enters the gap 232a in the second layer 230 can be further increased, regardless of the humidity range. As a result, the manufacturing method S110 of the moisture-sensitive material 110 according to this embodiment can produce a moisture-sensitive material 110 that can further improve the responsiveness of the resistance value to humidity fluctuations from low humidity to high humidity.

[0069] In the third step S110-3 of this embodiment, catalyst particles 250 are attached to the second laminate 20 by sputtering. When sputtering, the second laminate 20 may be kept at a temperature of 500°C or higher and 800°C or lower, the atmospheric pressure during sputtering may be set to less than atmospheric pressure, and the sputtering execution time may be 3 minutes or more and 30 minutes or less.

[0070] In the third step S110-3 of this embodiment, the catalyst particles 250 are attached to the second laminate 20 by sputtering. Compared to the case in which the catalyst particles 250 are attached using a liquid phase, the catalyst particles 250 can be suitably attached to the carbon nanowalls 232 of the second laminate 20.

[0071] Furthermore, if the temperature of the second laminate 20 during sputtering is less than 500°C or more than 800°C, plasma will not be generated, and sputtering cannot be performed effectively. In the third step S110-3 of this embodiment, by maintaining the temperature of the second laminate 20 between 500°C and 800°C during sputtering, sputtering can be performed effectively, and catalyst particles 250 can be effectively attached to the second laminate 20.

[0072] Furthermore, if the sputtering execution time is less than 3 minutes, the amount of catalyst particles 250 adhering to the second laminate 20 is small, and even if the subsequent fourth step S110-4 is performed, the size of the second gap W2 in the second region 242 may become less than or equal to the first gap W1. In the third step S110-3 according to this embodiment, by setting the sputtering execution time to 3 minutes or more, the size of the second gap W2 in the second region 242 of the second layer 230 can be made larger than the first gap W1.

[0073] Furthermore, if the sputtering execution time exceeds 30 minutes, too much catalyst particles 250 may adhere to the second laminate 20, and when the subsequent fourth step S110-4 is performed, the second gap W2 of the second region 242 may become too large. In this case, there is a risk of variation in the rate of change of the resistance value of the second layer 230 due to water entering the second region 242. In the third step S110-3 according to this embodiment, by setting the sputtering execution time to 30 minutes or less, the size of the second gap W2 of the second region 242 of the second layer 230 can be set to a suitable size, and it is possible to suppress variation in the rate of change of the resistance value of the second layer 230 due to water entering the second region 242.

[0074] In the fourth step S110-4 according to this embodiment, when performing hydrogen treatment, the third laminate 30 may be kept at a temperature of 500°C or higher and 800°C or lower, and the execution time of the hydrogen treatment may be set to 60 minutes or higher and 180 minutes or lower.

[0075] If the temperature of the third laminate 30 during hydrogen treatment is less than 500°C, the aggregation of catalyst particles 250 is suppressed, resulting in insufficient formation of the second region 242. Conversely, if the temperature of the third laminate 30 during hydrogen treatment exceeds 800°C, the aggregation of catalyst particles 250 is promoted too much, resulting in an excessively large area of ​​carbon nanowall 232 being removed. In the fourth step S110-4 according to this embodiment, by maintaining the temperature of the third laminate 30 during hydrogen treatment between 500°C and 800°C, it becomes possible to suitably form the second region 242 in the second layer 230.

[0076] Furthermore, if the hydrogen treatment execution time is less than 60 minutes, the size of the second interval W2 in the second region 242 may become less than or equal to the first interval W1. In the fourth step S110-4 according to this embodiment, by making the hydrogen treatment execution time 60 minutes or more, the size of the second interval W2 in the second region 242 of the second layer 230 can be made larger than the first interval W1.

[0077] Furthermore, even when the hydrogen treatment execution time exceeds 180 minutes, the size of the second interval W2 in the second region 242 remains almost unchanged compared to when it is 180 minutes or less. Therefore, in the fourth step S110-4 according to this embodiment, by setting the hydrogen treatment execution time to 180 minutes or less, it is possible to reduce the raw material costs and energy consumption required for hydrogen treatment.

[0078] The catalyst particles 250 may contain one or more selected from the group consisting of iron, copper, and nickel.

[0079] As a result, the manufacturing method S110 of the moisture-sensitive material 110 according to this embodiment makes it possible to suitably form the second region 242 in the second layer 230.

[0080] Furthermore, the moisture-sensitive material 110 according to this embodiment comprises a substrate 210, a first layer 220 made of graphite and provided on the substrate 210, and a second layer 230 made of a plurality of nitrogen-doped carbon nanowalls 232 and provided on the first layer 220, wherein the second layer 230 has a first region 240 in which the distance between opposing wall surfaces of the carbon nanowalls 232 is a first distance W1, and a plurality of second regions 242 in which the distance between opposing wall surfaces of the carbon nanowalls 232 is a second distance W2 which is greater than the first distance W1, and the plurality of second regions 242 are scattered within the first region 240 in the second layer 230.

[0081] As a result, the moisture-sensitive material 110 according to this embodiment provides the same effects as the manufacturing method S110 for the moisture-sensitive material 110 described above.

[0082] Furthermore, the humidity sensor 100 according to this embodiment comprises a substrate 210, a first layer 220 made of graphite and provided on the substrate 210, and a second layer 230 made of a plurality of nitrogen-doped carbon nanowalls 232 and provided on the first layer 220, wherein the second layer 230 has a first region 240 in which the distance between opposing wall surfaces of the carbon nanowalls 232 is a first distance W1, and a plurality of second regions 242 in which the distance between opposing wall surfaces of the carbon nanowalls 232 is a second distance W2 which is greater than the first distance W1, and the plurality of second regions 242 in the second layer 230 comprises a humidity-sensing material 110 scattered within the first region 240.

[0083] As a result, the humidity sensor 100 according to this embodiment achieves the same effects as the manufacturing method S110 for the humidity-sensitive material 110 described above. Furthermore, the humidity sensor 100 according to this embodiment can measure humidity based on resistance. Moreover, since the humidity sensor 100 according to this embodiment is equipped with a humidity-sensitive material 110 whose resistance changes are generally linear regardless of the humidity range, it is possible to reduce the variation in humidity detection sensitivity regardless of the humidity range. Furthermore, since the humidity sensor 100 according to this embodiment is equipped with a humidity-sensitive material 110 having a second layer 230 composed of a plurality of nitrogen-doped carbon nanowalls 232, it is possible to measure water in the air, i.e., humidity, with high sensitivity. Moreover, since the humidity sensor 100 according to this embodiment is equipped with a humidity-sensitive material 110 having a second layer 230 having a second region 242 in addition to the first region 240, it is possible to measure humidity with even higher sensitivity.

[0084] Furthermore, as described above, it is preferable that one or more gold particles 234 are attached to the multiple carbon nanowalls 232 of the second layer 230 according to this embodiment. The gold particles 234 can maintain the affinity of the carbon nanowalls 232 for water over a long period of time. Therefore, the gold particles 234 can improve the durability of the moisture-sensitive material 110.

[0085] Furthermore, as described above, it is preferable that the particle size of the gold particles 234 attached to the carbon nanowall 232 is smaller than the gap 232a. Also, it is preferable that the particle size of the gold particles 234 attached to the carbon nanowall 232 is smaller than the first spacing W1. This prevents the situation in which the gap 232a of the first region 240 and the gap 232a of the second region 242 are blocked by the gold particles 234. Therefore, it is possible to suppress the obstruction of air entering the gap 232a by the gold particles 234. As a result, a decrease in the sensitivity of the humidity sensor 100 can be prevented.

[0086] [5. Examples] Next, a method for manufacturing a moisture-sensitive material, a moisture-sensitive material, and a humidity sensor according to the embodiments of this disclosure will be described. It should be noted that the following embodiments are merely examples to demonstrate the effectiveness and feasibility of the method for manufacturing a moisture-sensitive material, the moisture-sensitive material, and the humidity sensor according to this disclosure, and this disclosure is not limited to the following embodiments.

[0087] [5.1. Examination of the execution time of hydrogen processing] The first step S110-1 and the second step S110-2 of the manufacturing method S110 for the moisture-sensitive material 110 described above were performed to produce the second laminate 20 of Example 1. Then, the third step S110-3 and the fourth step S110-4 were performed on the second laminate 20 of Example 1 to produce the moisture-sensitive materials 110 of Examples 2 to 4. In Examples 2 to 4, the third step S110-3 was performed under the same conditions.

[0088] The first step S110-1, the second step S110-2, and the third step S110-3 were performed using the same sheet plasma CVD sputtering apparatus. In the first step S110-1 and the second step S110-2, the substrate 210 was placed in the chamber of the sheet plasma CVD sputtering apparatus, and argon gas was supplied to the chamber as a carrier gas at 80 ml / min to generate plasma in the chamber. Subsequently, the substrate 210 was maintained at 650 °C, and methane gas at 10 ml / min, nitrogen gas at 10 ml / min, and hydrogen at 10 ml / min were supplied to the chamber as raw material gases. The film deposition time was set to 10 minutes. In this way, the second laminate 20 of Example 1 was manufactured.

[0089] Then, in the third step S110-3, while maintaining the second laminate 20 of Example 1 at 650 [°C], the pressure inside the chamber is increased to 10 -5 The temperature was set to [Pa], and sputtering was performed using a target in the chamber. In this way, the third laminate 30 was manufactured. Then, the fourth step S110-4 was performed on the third laminate 30 to manufacture the moisture-sensitive material 110 of Examples 2 to 4. Examples 2 to 4 differed only in the execution time of the hydrogen treatment in the fourth step S110-4; all other conditions were the same.

[0090] In Examples 2-4, the fourth step S110-4 was performed using an electric furnace. In the fourth step S110-4, the third laminate 30 was placed inside the furnace, and argon gas was supplied into the chamber at a rate of 1 [L / min] as a carrier gas, and hydrogen gas was supplied into the chamber at a rate of 1 [L / min]. The temperature of the third laminate 30 was maintained at 650 [°C] while the hydrogen treatment was performed.

[0091] In Example 2, the hydrogen treatment time for the third laminate 30 in the fourth step S110-4 was set to 60 minutes. In Example 3, the hydrogen treatment time for the third laminate 30 in the fourth step S110-4 was set to 120 minutes. In Example 4, the hydrogen treatment time for the third laminate 30 in the fourth step S110-4 was set to 180 minutes.

[0092] Figure 9 shows images of the results of observing Examples 1-4 with a scanning electron microscope (SEM). As shown in Figure 9, it was confirmed that the second region 242 was not formed in Example 1. Furthermore, as shown in Examples 2-4, it was confirmed that the second region 242 became larger as the hydrogen treatment execution time increased.

[0093] [5.2. Examination of Hydrogen Treatment Temperature] Using the second laminate 20 from Example 1 described above, the third step S110-3 was performed to produce the third laminate 30. The third step S110-3 was performed under the same conditions as in Examples 2 to 4 described above. The fourth step S110-4 was then performed on the third laminate 30 to produce the moisture-sensitive material 110 from Examples 5 to 7. Examples 5 to 7 differed only in the temperature of the hydrogen treatment in the fourth step S110-4; all other conditions were the same.

[0094] In Examples 5-7, the fourth step S110-4 was performed using an electric furnace. In the fourth step S110-4, the third laminate 30 was placed inside the furnace, and argon gas was supplied into the chamber at a rate of 1 [L / min] as the carrier gas, and hydrogen gas was supplied into the chamber at a rate of 1 [L / min]. The hydrogen treatment was performed for 120 minutes.

[0095] In Example 5, the temperature of the third laminate 30 was set to 550°C during the hydrogen treatment in step S110-4. In Example 6, the temperature of the third laminate 30 was set to 650°C during the hydrogen treatment in step S110-4. In Example 7, the temperature of the third laminate 30 was set to 750°C during the hydrogen treatment in step S110-4.

[0096] Figure 10 shows images of the results of scanning electron microscopy (SEM) observation of Examples 1 and 5-7. As shown in Figure 10, it was confirmed that the second region 242 was not formed in Example 1. Furthermore, as shown in Examples 5-7, it was confirmed that the second region 242 becomes larger as the hydrogen treatment temperature increases.

[0097] [5.3. Relationship between resistance and relative humidity] Using the humidity-sensitive material 110 of Example 5, the humidity sensor 100 of Example 5 was manufactured by performing the adhesion step S110-5, etching step S120, and assembly step S130 of the manufacturing method for the humidity sensor 100 described above. Then, the relationship between relative humidity [%RH] and resistance value [Ω] was obtained using the humidity sensor 100 of Example 5.

[0098] Figure 11 illustrates the relationship between relative humidity [%RH] and resistance [Ω] in the humidity sensor 100 of Example 5. In Figure 11, the vertical axis represents resistance [Ω], and the horizontal axis represents relative humidity [%RH].

[0099] As shown in Figure 11, it was confirmed that the resistance value [Ω] of the humidity sensor 100 in Example 5 changed in accordance with the change in relative humidity [%RH] over a wide humidity range from 25 [%RH] to 90 [%RH]. Furthermore, it was confirmed that the rate of change of the resistance value [Ω] in the humidity sensor 100 in Example 5 remained approximately constant over the wide humidity range from 25 [%RH] to 90 [%RH]. From these results, it was found that the humidity-sensitive material 110 in Example 5 can make the change in resistance value approximately linear regardless of the humidity range. In addition, Example 5 showed a tendency to have high humidity sensitivity not only compared to the untreated Example 1, but also compared to Examples 6 and 7, which had higher hydrogen treatment temperatures than Example 5.

[0100] While embodiments have been described above with reference to the attached drawings, it goes without saying that this disclosure is not limited to the embodiments described above. It will be obvious to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these will naturally also fall within the technical scope of this disclosure.

[0101] For example, one or more of the substrate 210, the first layer 220 (graphite), the second layer 230 (carbon nanowall 232), the catalyst particles 250, and the gold particles 234 may contain unavoidable impurities.

[0102] This disclosure can, for example, contribute to Sustainable Development Goal (SDG) 13, "Take urgent action to combat climate change and its impacts." [Explanation of Symbols]

[0103] 10. First layer 20 Second Laminate 30. Third layer 100 Humidity Sensor 110 Moisture-sensitive materials 210 circuit boards 220 1st layer 230 2nd layer 232 Carbon Nanowall 240 1st area 242 Second Domain 250 catalyst particles

Claims

1. The first step involves manufacturing a first laminate by forming a first layer made of graphite on a substrate, The second step involves forming a second layer on the first layer of the first laminate, which is composed of a plurality of nitrogen-doped carbon nanowalls, thereby producing a second laminate. A third step is to manufacture a third laminate by attaching one or more catalyst particles to the plurality of carbon nanowalls constituting the second layer of the second laminate, A fourth step is to perform hydrogen treatment on the third laminate, A method for manufacturing a moisture-sensitive material, including

2. The third step involves attaching the catalyst particles to the second laminate by sputtering, When performing the sputtering described above, the second laminate is kept at a temperature of 500°C or higher and 800°C or lower. The atmospheric pressure when performing the aforementioned sputtering is set to be less than atmospheric pressure. The method for manufacturing a moisture-sensitive material according to claim 1, wherein the execution time of the sputtering is 3 minutes or more and 30 minutes or less.

3. In the fourth step, when performing the hydrogen treatment, the third laminate is kept at a temperature of 500°C or higher and 800°C or lower. A method for producing a moisture-sensitive material according to claim 1 or 2, wherein the execution time of the hydrogen treatment is 60 minutes or more and 180 minutes or less.

4. The method for producing a moisture-sensitive material according to claim 1 or 2, wherein the catalyst particles include one or more selected from the group consisting of iron, copper, and nickel.

5. circuit board and A first layer made of graphite and provided on the substrate, It consists of multiple nitrogen-doped carbon nanowalls, and a second layer is provided on the first layer, Equipped with, The aforementioned second layer is, The distance between opposing wall surfaces in the carbon nanowall is a first distance, and The carbon nanowall comprises a plurality of second regions in which the distance between opposing wall surfaces is greater than the first distance, It has, In the second layer, the plurality of second regions are moisture-sensitive materials scattered within the first region.

6. circuit board and A first layer made of graphite and provided on the substrate, It consists of multiple nitrogen-doped carbon nanowalls, and a second layer is provided on the first layer, Equipped with, The aforementioned second layer is, The distance between opposing wall surfaces in the carbon nanowall is a first distance, and The carbon nanowall comprises a plurality of second regions in which the distance between opposing wall surfaces is greater than the first distance, It has, In the second layer, the plurality of second regions are humidity sensors, each comprising a humidity-sensitive material scattered within the first region.

Images