Hydrogen sensor and manufacturing method thereof

Abstract

Provided is a hydrogen gas sensor which has high sensitivity and excellent response / recovery characteristics, and which is capable of detecting hydrogen gas with low power consumption. This hydrogen gas sensor (100) is provided with: a substrate (10) having an insulating surface; a first pad electrode (12A) and a second pad electrode (12B) formed on the insulating surface of the substrate (10); and a nanowire (14). The nanowire (14) is formed on the insulating surface of the substrate (10) so as to connect the first pad electrode (12A) and the second pad electrode (12B), has a line width of 50 nm or more and 150 nm or less and a thickness of 10 nm or more and 60 nm or less, and is formed of a hydrogen-absorbing metal. A hydrogen gas sensor (100) causes an electric current to flow between a first pad electrode (12A) and a second pad electrode (12B), and detects hydrogen gas on the basis of a change in an electric signal detected between the first pad electrode (12A) and the second pad electrode (12B).

Description

Technical Field

[0001] The present invention relates to a hydrogen gas sensor using nanowires formed of a specific metal and a method for manufacturing the same. Background Art

[0002] Various types of hydrogen gas sensors have been developed for detecting hydrogen gas leaks from various hydrogen processing devices, such as fuel cells, or for measuring hydrogen gas concentrations within hydrogen processing devices. Among these, a known hydrogen gas sensor detects hydrogen gas based on changes in current or resistance detected between a pair of electrodes sandwiching a hydrogen gas detection portion and applying a constant voltage between the electrodes.

[0003] As such a hydrogen gas sensor, for example, as described in Non-Patent Document 1, there is known a hydrogen gas sensor having a hydrogen gas detection portion formed of palladium (Pd), which is a hydrogen absorbing metal, in a thin film.

[0004] Prior art literature

[0005] Non-patent literature

[0006] Non-patent document 1: T. Xu and MP Zach, Self-assembled monolayer-enhance dhydrogen sensing with ultrathin palladium films, Appl. Phys. Lett. 86, 203104 (2005). Summary of the Invention

[0007] Problems to be solved by the invention

[0008] However, existing hydrogen gas sensors, including those based on Pd thin films, have room for improvement in characteristics important for practical application, such as sensitivity, response and recovery speed, and power consumption.

[0009] Therefore, in view of the above problems, an object of the present invention is to provide a hydrogen gas sensor having high sensitivity, excellent response and recovery characteristics, and capable of detecting hydrogen gas with low power consumption, and a preferred method for manufacturing the same.

[0010] Solutions for solving problems

[0011] In order to solve the above problems, the present inventors conducted in-depth research and obtained the following insights. The present inventors conceived a hydrogen gas sensor using nanowires formed from specific hydrogen-absorbing metals such as palladium (Pd). It can be seen that by making the hydrogen gas detection part into the shape of nanowires instead of a thin film of Pd, etc., the sensor characteristics such as sensitivity, response and recovery characteristics, and power consumption are improved. In particular, it is known that by setting the line width and thickness of the nanowires to a specific range, the cross-sectional shape of the nanowires perpendicular to the extension direction becomes appropriate. The mechanism is speculated to be described later, but hydrogen is easily adsorbed and desorbed from the nanowires, and the characteristics of the above-mentioned sensor are significantly improved.

[0012] The gist of the present invention, which has been accomplished based on the above findings, is as follows.

[0013] [1] A hydrogen gas sensor comprising:

[0014] a substrate having an insulating surface;

[0015] a first pad electrode and a second pad electrode formed on the insulating surface of the substrate; and

[0016] a nanowire formed on the insulating surface of the substrate so as to connect the first pad electrode and the second pad electrode, having a line width of 50 nm to 150 nm and a thickness of 10 nm to 60 nm, and made of a hydrogen-absorbing metal;

[0017] A current is passed between the first pad electrode and the second pad electrode, and hydrogen gas is detected based on a change in an electrical signal detected between the first pad electrode and the second pad electrode.

[0018] [2] The hydrogen gas sensor according to [1] above, wherein the nanowire has a line width of 80 nm to 100 nm.

[0019] [3] The hydrogen gas sensor according to [1] or [2] above, wherein the thickness of the nanowire is greater than or equal to 20 nm and less than or equal to 50 nm.

[0020] [4] The hydrogen gas sensor according to any one of [1] to [3] above, wherein the length of the nanowire is greater than or equal to 10 μm and less than or equal to 300 mm.

[0021] [5] The hydrogen gas sensor according to [4] above, wherein the length of the nanowire is greater than or equal to 0.07 mm.

[0022] [6] The hydrogen gas sensor according to [5] above, wherein the length of the nanowire is greater than or equal to 0.5 mm.

[0023] [7] The hydrogen gas sensor according to any one of [1] to [6] above, wherein the hydrogen absorbing metal is selected from one or more of the following (I) and (II),

[0024] (I) Exothermic metals A that readily form stable hydrides, such as palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), osmium (Os), vanadium (V), titanium (Ti), zirconium (Zr), lanthanum (La), tungsten (W), calcium (Ca), magnesium (Mg), strontium (Sr), barium (Ba), and beryllium (Be), as well as solid solution alloys of these exothermic metals A;

[0025] (II) AB5 type alloys, AB2 type alloys, AB type alloys, and A2B type alloys obtained by combining the exothermic metal A and one or more endothermic metals B selected from nickel (Ni), iron (Fe), cobalt (Co), manganese (Mn), and zinc (Zn) that do not have an affinity for hydrogen.

[0026] [8] The hydrogen gas sensor according to any one of [1] to [6] above, wherein the hydrogen absorbing metal is palladium (Pd).

[0027] [9] The hydrogen sensor according to [8] above, wherein the palladium constituting the nanowires is polycrystallized.

[0028]

[10] The hydrogen sensor according to [9] above, wherein the lattice constant of palladium constituting the nanowire is

[0029]

[11] A method for manufacturing a hydrogen sensor, comprising:

[0030] A process for preparing a substrate having an insulating surface;

[0031] forming a first pad electrode and a second pad electrode on the insulating surface of the substrate; and

[0032] forming a nanowire on the insulating surface of the substrate so as to connect the first pad electrode and the second pad electrode, wherein the nanowire has a line width of 50 nm to 150 nm and a thickness of 10 nm to 60 nm and is formed of a hydrogen-absorbing metal;

[0033] The hydrogen gas sensor manufactured by the method for manufacturing a hydrogen gas sensor allows current to flow between the first pad electrode and the second pad electrode, and detects hydrogen gas based on a change in an electrical signal detected between the first pad electrode and the second pad electrode.

[0034]

[12] The method for manufacturing a hydrogen sensor according to

[11] , comprising:

[0035] exposing the nanowires to an environment comprising hydrogen and an inert gas; and

[0036] Thereafter, a step of heat-treating the nanowires is performed in an environment containing hydrogen and an inert gas.

[0037]

[13] The method for manufacturing a hydrogen sensor according to

[12] above, wherein the heat treatment is an RTA treatment performed at a heat treatment temperature of 350°C to 650°C.

[0038]

[14] The method for manufacturing a hydrogen gas sensor according to any one of

[11] to

[13] above, wherein the hydrogen absorbing metal is palladium (Pd).

[0039] Effects of the Invention

[0040] The hydrogen gas sensor of the present invention has high sensitivity, excellent response and recovery characteristics, and can detect hydrogen gas with low power consumption. Furthermore, the method for manufacturing a hydrogen gas sensor of the present invention can produce a hydrogen gas sensor having high sensitivity, excellent response and recovery characteristics, and can detect hydrogen gas with low power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1A 1 is a schematic perspective view of a hydrogen gas sensor 100 according to an embodiment of the present invention.

[0042] Figure 1B FIG. 1 is a schematic top view of the hydrogen sensor 100 .

[0043] Figure 1C yes Figure 1B II sectional view.

[0044] Figure 1D yes Figure 1B II-II sectional view.

[0045] Figure 2 1 is a circuit diagram showing an example of measuring the sensor characteristics of the hydrogen gas sensor 100 (resistance voltage division measurement).

[0046] Figure 3 FIG. 4 is a cross-sectional view perpendicular to the extending direction of the nanowire 14 of the hydrogen sensor 100 .

[0047] Figure 4 This is a plan view showing an example of arrangement of the nanowires 14 when the nanowires 14 are long in the hydrogen gas sensor 100 according to one embodiment of the present invention.

[0048] Figure 5(A) to (D) are diagrams illustrating a manufacturing process of the gas sensor 100 according to one embodiment of the present invention.

[0049] Figure 6 1 is a cross-sectional SEM image of nanowires of various line widths perpendicular to the extension direction in Experimental Example 1.

[0050] Figure 7 1 is a graph showing the change in current value with time for various line widths in Experimental Example 1 (top) and a graph showing the change in resistance change rate with time (bottom).

[0051] Figure 8 This is a graph showing the relationship between line width and sensitivity (sensitivity based on resistance change rate) at various operating temperatures T obtained in Experimental Example 1.

[0052] Figure 9 The line width and response time t at various operating temperatures T obtained in Experimental Example 1 are shown. res50 diagram of the relationship between .

[0053] Figure 10 The line width and recovery time t at various operating temperatures T obtained in Experimental Example 1 are shown. rec50 diagram of the relationship between .

[0054] Figure 11 It is shown that in Experimental Example 1, based on Figure 9 and Figure 10 The graph shown is a graph showing the relationship between the line width obtained from the results and the activation energy of the response (hydrogen adsorption reaction) and the recovery (hydrogen desorption reaction).

[0055] Figure 12 3 is an SEM image showing a portion of a Pd nanowire (length: 7 mm) produced using electron beam lithography (EBL) in Experimental Example 2.

[0056] Figure 13A This is a graph showing the temporal change in current values at various wire lengths in Experimental Example 2.

[0057] Figure 13B This is a graph showing the temporal change in current values at various wire lengths in Experimental Example 2.

[0058] Figure 14 This is a graph showing the change in resistance over time at various line lengths in Experimental Example 2.

[0059] Figure 15 The relationship between line length and response time t obtained in Experimental Example 2 is shown in FIG. res50 The graph (above) shows the relationship between line length and recovery time t rec50 The relationship diagram (below).

[0060] Figure 16 This is a graph showing the temporal change in the voltage change rate at various hydrogen gas concentrations in Experimental Example 3.

[0061] Figure 17 This is a graph showing the temporal change in the voltage change rate at various applied voltages in Experimental Example 4.

[0062] Figure 18 Graph showing temporal changes in the voltage change rate at various operating temperatures in Experimental Example 5.

[0063] Figure 19 Graphs showing changes in resistance over time in Experimental Example 6 when the carrier gas is dry air (top) and when the carrier gas is nitrogen (bottom).

[0064] Figure 20 This is a graph showing the change in resistance over time when the carrier gas is dry air and when the carrier gas is nitrogen in Experimental Example 6.

[0065] Figure 21 This is a graph showing the change in resistance over time at various line thicknesses in Experimental Example 7.

[0066] Figure 22 This is a graph showing the change in resistance over time when hydrogen gas was repeatedly introduced in Experimental Example 8 with a line thickness of 30 nm and a line length of 31 mm.

[0067] Figure 23 This is a graph showing the change in resistance over time when hydrogen gas was repeatedly introduced in Experimental Example 8 with a line thickness of 10 nm and a line length of 18 mm.

[0068] Figure 24 : This is a cross-sectional SEM image perpendicular to the extension direction of the nanowire in Experimental Example 9 (top) and an EDS-based element mapping of the same area as the cross-sectional SEM image (bottom).

[0069] Figure 25 1 is a graph showing the change in resistance value over time at an operating temperature of 24° C. in Experimental Example 9 (upper graph) and a graph showing the change in resistance rate over time (lower graph).

[0070] Figure 26 1 is a graph showing the change in resistance value over time at an operating temperature of 50° C. in Experimental Example 9 (upper graph) and a graph showing the change in resistance rate over time (lower graph).

[0071] Figure 27 1 and 2 are a graph showing the change in resistance value with time at an operating temperature of 100° C. in Experimental Example 9 (top) and a graph showing the change in resistance rate with time (bottom).

[0072] Figure 28 1 is a graph showing the change in resistance value over time at an operating temperature of 150° C. in Experimental Example 9 (upper graph) and a graph showing the change in resistance rate over time (lower graph).

[0073] Figure 29 1 and 2 are a graph (upper) showing the change in resistance value over time at an operating temperature of 21° C. (room temperature) in Experimental Example 9 and a graph (lower) showing the change in resistance rate over time.

[0074] Figure 30 The relationship between the operating temperature and the response time t obtained in Experimental Example 9 is shown. res50 The graph (above) shows the relationship between operating temperature and recovery time t rec50 The relationship diagram (below).

[0075] Figure 31 This is a graph showing the relationship between operating temperature and sensitivity (sensitivity based on resistance change rate) obtained in Experimental Example 9.

[0076] Figure 32 This is a graph showing X-ray diffraction patterns obtained by GI-WAXS measurement under three conditions (condition 1: no heat treatment, condition 2: 250°C, annealing for 5 minutes, condition 3: 500°C, RTA treatment) in Experimental Example 10.

[0077] Figure 33 These are SEM images of the upper surfaces of the nanowires under three conditions (Condition 3: 500°C, RTA treatment, Condition 4: 400°C, RTA treatment, Condition 5: 600°C, RTA treatment) in Experimental Example 10.

[0078] Figure 34 This is a graph showing the change in resistance over time under conditions 1 to 3 of Experimental Example 10.

[0079] Figure 35 This is a graph showing the change in resistance over time under conditions 2 to 5 of Experimental Example 10.

[0080] Figure 36 This is a graph showing the change in resistance over time under Condition 3 of Experimental Example 10. DETAILED DESCRIPTION

[0081] (Hydrogen sensor)

[0082] Reference Figure 1A 、 Figure 1B 、 Figure 1C as well as Figure 1DA hydrogen gas sensor 100 according to one embodiment of the present invention includes a substrate 10, a first pad electrode 12A, a second pad electrode 12B, and a nanowire 14 formed of a specific hydrogen-absorbing metal. The first pad electrode 12A and the second pad electrode 12B are formed on the substrate 10. The nanowire 14 is formed on the substrate 10 to connect the first pad electrode 12A and the second pad electrode 12B. The detailed effects will be described later, but in this embodiment, the nanowire 14 improves sensor characteristics such as sensitivity, response and recovery characteristics, and power consumption.

[0083] [Mechanism for detecting hydrogen]

[0084] In the hydrogen gas sensor 100, a current flows between the first pad electrode 12A and the second pad electrode 12B, and hydrogen gas is detected based on a change in an electrical signal detected between the first pad electrode 12A and the second pad electrode 12B. Figure 1B As shown, a power supply 18 and an ammeter 20 are connected in series between the first pad electrode 12A and the second pad electrode 12B, and a voltmeter 22 is connected in parallel with these. In this case, while a constant voltage, measurable by the voltmeter 22, is applied between the first and second pad electrodes 12A and 12B by the power supply 18, the ammeter 20 detects changes in the current between the first and second pad electrodes, and hydrogen gas is detected based on the detected current changes. Alternatively, while a constant current flows between the first and second pad electrodes 12A and 12B, gas can be detected based on changes in the voltage detected between the first and second pad electrodes 12A and 12B. Alternatively, instead of using changes in current or voltage, gas can be detected based on changes in resistance detected between the first and second pad electrodes 12A and 12B. In other words, the "electrical signal" mentioned above refers to current, voltage, or resistance. In this embodiment, since the gas sensor circuit can be constructed using only two terminals, a hydrogen gas sensor can be constructed without increasing wiring or circuitry.

[0085] In addition, when measuring sensor characteristics, it is also possible to Figure 2 The voltage is measured by the resistor divider shown. Figure 2In addition to the hydrogen gas sensor 100, power supply 18, and ammeter 20, a resistor 24 with a known resistance value is connected in series, and a voltmeter 22 is connected in parallel with the resistor 24. In this case, while a constant voltage is applied between the first pad electrode (not shown) and the second pad electrode (not shown) of the hydrogen gas sensor 100 by the power supply 18, the voltmeter 22 detects changes in the voltage applied to the resistor 24, and hydrogen gas is detected based on the detected voltage changes. Even with this method, the voltmeter 22 can indirectly detect changes in the voltage of the hydrogen gas sensor 100 (i.e., between the first pad electrode and the second pad electrode).

[0086] Furthermore, it is also possible to Figure 2 The voltmeter 22 that was previously connected in parallel with the resistor 24 is changed to be connected in parallel with the hydrogen gas sensor 100. In this case, while a constant voltage is applied between the first pad electrode (not shown) and the second pad electrode (not shown) of the hydrogen gas sensor 100 by the power supply 18, the voltmeter 22 directly detects changes in the voltage applied to the hydrogen gas sensor 100 (i.e., between the first pad electrode and the second pad electrode), and hydrogen gas is detected based on the detected voltage changes.

[0087] [Substrate]

[0088] The substrate 10 supports the first pad electrode 12A and the second pad electrode 12B, as well as the nanowire 14 serving as the hydrogen gas detection unit. The substrate 10 is not particularly limited as long as it has an insulating surface. For example, any insulating substrate such as a glass substrate, an alumina substrate, or a zirconia substrate, or a silicon substrate with a silicon oxide film or a silicon nitride film formed on its surface can be used. The shape and dimensions of the substrate 10 are not particularly limited; however, if a substrate with a rectangular main surface is used, the dimensions can be, for example, 1 to 300 mm in length, 1 to 300 mm in width, and 0.1 to 1.2 mm in thickness.

[0089] [First Pad Electrode and Second Pad Electrode]

[0090] The first and second pad electrodes 12A and 12B supply current to the nanowires 14 and are a pair of electrodes necessary for detecting changes in the electrical signal corresponding to changes in hydrogen gas concentration. The shape and dimensions of the first and second pad electrodes 12A and 12B are not particularly limited, as long as they are formed on the insulating surface of the substrate 10. However, if the main surface is rectangular, the dimensions can be, for example, 30 to 1000 μm in length, 30 to 1000 μm in width, and 5 to 500 nm in thickness. The metal constituting the first and second pad electrodes 12A and 12B is not particularly limited and can be any metal, for example, one or more selected from platinum, gold, and palladium. For ease of processing, the metal can also be the same as that of the nanowires 14, described later.

[0091] [Nanowires]

[0092] Nanowires 14 are formed on the insulating surface of substrate 10 to connect first pad electrode 12A and second pad electrode 12B, and constitute a gas detection unit. Importantly, nanowires 14 are formed of a hydrogen-absorbing metal. The hydrogen-absorbing metal is preferably selected from one or more of palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), osmium (Os), vanadium (V), titanium (Ti), zirconium (Zr), lanthanum (La), tungsten (W), calcium (Ca), magnesium (Mg), strontium (Sr), barium (Ba), and beryllium (Be), which are exothermic metals A that readily form stable hydrides, and solid solution alloys of these exothermic metals A. Furthermore, the hydrogen-absorbing metal is preferably selected from one or more of an AB5 alloy, an AB2 alloy, an AB alloy, and an A2B alloy, obtained by combining the aforementioned exothermic metal A with one or more of nickel (Ni), iron (Fe), cobalt (Co), manganese (Mn), and zinc (Zn), which are endothermic metals B that do not have an affinity for hydrogen. Examples of AB5 alloys include LaNi5 and CaNi5, examples of AB2 alloys include MaZn2 and ZrNi2, examples of AB alloys include TiFe and TiNi, and examples of A2B alloys include Mg2Ni and Ca2Fe. The hydrogen-absorbing metal is more preferably formed from palladium (Pd). Thus, hydrogen adsorbed by the nanowires 14 causes the hydrogen sensor 100 to respond (detect hydrogen), and hydrogen desorbed from the nanowires 14 causes the hydrogen sensor 100 to recover (detect hydrogen disconnection).

[0093] [Nanowire Linewidth]

[0094] Reference Figure 1A ~D and Figure 3It is important that the line width W of the nanowire 14 is greater than 50 nm and less than 150 nm. As a result, significant effects such as high sensitivity and excellent response and recovery characteristics can be achieved. The present inventors believe that the following is the role in achieving such effects. Figure 3 As shown, in the nanowire 14, both ends in the width direction are curved portions 14B1 and 14B2, and the upper surface connecting the pair of curved portions 14B1 and 14B2 is a flat portion 14A. The internal stress ΔP applied to the nanowire 14 is expressed by the following formula (1).

[0095] ΔP=γ(1 / R1+1 / R2)…(1)

[0096] Here, γ is the surface tension of the metal constituting the nanowire 14, R1 is the radius of curvature in the width direction of the nanowire 14, and R2 is the radius of curvature in the extension direction of the nanowire 14. The nanowire 14 has no curvature in its extension direction, so R2 is infinite, and the term 1 / R2 in formula (1) is considered to be zero. Therefore, the smaller the radius of curvature R1 in the width direction, the greater the internal stress ΔP. Figure 3As shown, the cross-sectional shape of the nanowire 14 perpendicular to the extension direction is a so-called semi-cylindrical shape, so the internal stress is distributed in the transverse direction (width direction) of the cross-sectional shape. For example, the surface tension of the clean surface of palladium is about 1000 mN / m. When the radius of curvature R1 of the curved surface portions 14B1 and 14B2 of the nanowire 14 is set to, for example, 5 to 30 nm, the internal stress applied to the curved surface portions 14B1 and 14B2 of the nanowire 14 is estimated to be around 200 to 30 MPa. Although the clean surface of palladium cannot be maintained in the nanowire, the catalytic effect of palladium is strong, so there is a surface that allows hydrogen to adsorb and dissociate. However, the surface tension of the surface with a curvature radius of the actual nanowire is nearly two digits smaller than the above estimate, and is approximately 0.6 to 1 MPa. Here, in the PCT (P: pressure, C: hydrogen absorption amount, T: temperature) characteristic curve of a typical hydrogen-absorbing metal, the range of hydrogen equilibrium pressure of 0.6 to 1 MPa indicates that the change in hydrogen equilibrium pressure is smaller than the change in hydrogen absorption amount at room temperature during both adsorption (exothermic reaction) and desorption (endothermic reaction). Therefore, hydrogen is easily absorbed and desorbed in the curved surface portions 14B1 and 14B2 of the nanowire 14, where the internal stress is approximately 0.6 to 1 MPa. In contrast, the flat portion 14A of the nanowire 14 (particularly its central portion) is in a state substantially similar to that of a thin film, thus exhibiting no internal stress and only atmospheric pressure (approximately 0.1 MPa). In the PCT (P: pressure, C: hydrogen absorption amount, T: temperature) characteristic curve of a typical hydrogen-absorbing metal, the range of hydrogen equilibrium pressure around 0.1 MPa indicates that the change in hydrogen equilibrium pressure is larger than the change in hydrogen absorption amount at room temperature during both adsorption (exothermic reaction) and desorption (endothermic reaction) (a region where the hydrogen absorption amount barely changes relative to changes in hydrogen equilibrium pressure). Therefore, hydrogen is less likely to be adsorbed or desorbed in the flat portion 14A of the nanowire 14 (particularly its central portion). By using the nanowire 14 as the hydrogen detector, the ratio of the curved portion to the flat portion can be increased compared to a thin film, which contributes to improved sensor characteristics.

[0097] From another perspective, even when the curved surfaces 14B1 and 14B2 of the nanowire 14 are completely free of hydrogen, their shape exerts internal stress as if a certain amount of hydrogen has already been absorbed. In other words, the amount of hydrogen that can be absorbed by the curved surfaces 14B1 and 14B2 is less than that of the thin film or flat portion 14A. Therefore, it can be assumed that hydrogen is absorbed in areas of the curved surfaces 14B1 and 14B2 where it can easily enter and exit.

[0098] The adsorption process of hydrogen in palladium goes through the following steps: [1] H2 adsorption, [2] H2 dissociation into atomic hydrogen 2H, and [3] atomic hydrogen diffusion within the palladium. The desorption process of hydrogen in palladium goes through the following steps: [A] atomic hydrogen adsorbed within the palladium diffuses to the surface, [B] atomic hydrogen forms a covalent bond to become H2, and [C] H2 desorbs from the surface. The diffusion of atomic hydrogen is the rate-limiting process in both adsorption and desorption. Here, when internal stress is high, the diffusion of atomic hydrogen within the palladium is suppressed. Therefore, it is believed that the diffusion of atomic hydrogen is suppressed in the curved surface portions 14B1 and 14B2, resulting in hydrogen being adsorbed in areas where hydrogen can easily enter and exit.

[0099] Next, let's return to the line width W of the nanowire 14. It's believed that when the line width W is between 50 nm and 150 nm, the balance between the curved portions 14B1 and 14B2 and the flat portion 14A is optimal, making hydrogen adsorption and desorption from the nanowire 14 more likely, and significantly improving sensor characteristics. When the line width W is less than 50 nm, the proportion of the curved portions 14B1 and 14B2, where internal stress is high, becomes excessively large relative to the flat portion 14A. Consequently, the nanowire 14 has difficulty adsorbing hydrogen, and sufficient sensitivity cannot be achieved. Furthermore, when the line width W is greater than 150 nm, the proportion of the flat portion 14A, where only atmospheric pressure is applied, becomes excessive relative to the curved portions 14B1 and 14B2. In this case, due to the near-thin film state, atomic hydrogen easily diffuses within the nanowire 14, and is adsorbed even in areas where hydrogen is difficult to enter and exit, making hydrogen difficult to adsorb and desorb. Consequently, sufficient response and recovery characteristics cannot be achieved. When the line width W is between 50 nm and 150 nm, the balance between curved portions 14B1 and 14B2 and flat portion 14A is optimal, and internal stress is applied to curved portions 14B1 and 14B2 and their vicinity. In this case, while atomic hydrogen diffusion is suppressed, a small amount of hydrogen is adsorbed in areas where it can easily enter and exit. This facilitates hydrogen adsorption and desorption from the nanowires 14, significantly improving sensor characteristics. From this perspective, the line width W is preferably 50 nm or greater, preferably 80 nm or greater. Alternatively, the line width W is 150 nm or less, preferably 100 nm or less.

[0100] In this specification, the line width W of the nanowire 14 is as follows: Figure 3 As shown in FIG, it refers to the width of the bottom portion of the nanowire 14 (the boundary with the substrate 10). In addition, the line width W of the nanowire 14 is obtained by performing SEM observation on a cross section perpendicular to the extension direction of the nanowire 14 at equal intervals (e.g., 0.1 to 100 μm intervals) at 10 locations in the extension direction of the nanowire 14, and using the arithmetic average of the line widths obtained in each SEM image. Figure 4 and Figure 12In the case of the nanowire arrangement shown, cross sections at ten locations spaced at equal intervals can be observed in one SEM image.

[0101] [Thickness of nanowires]

[0102] Reference Figure 3 It is important that the thickness D of the nanowire 14 is greater than 10 nm and less than 60 nm. If the thickness D is less than 10 nm, the thin thickness causes the curved surface to narrow, which in turn reduces the volume of palladium, thereby reducing sensitivity and failing to achieve good response and recovery characteristics. Therefore, the thickness D is greater than 10 nm, preferably greater than 20 nm. On the other hand, if the thickness D is greater than 60 nm, the distance that atomic hydrogen diffuses in the thickness direction becomes longer, failing to achieve good response and recovery characteristics. Therefore, the thickness D is less than 60 nm, preferably less than 50 nm.

[0103] In this specification, the thickness D of the nanowire 14 is as follows Figure 3 As shown in FIG, it refers to the distance from the bottom of the nanowire 14 (the boundary with the substrate 10) to the top (the flat portion 14A). In addition, the thickness D of the nanowire 14 is obtained by performing SEM observation on a cross section perpendicular to the extension direction of the nanowire 14 at equal intervals (e.g., 0.1 to 100 μm intervals) at 10 locations in the extension direction of the nanowire 14, and using the arithmetic average of the thicknesses obtained in each SEM image. Figure 4 and Figure 12 In the case of the nanowire arrangement shown, cross sections at ten locations spaced at equal intervals can be observed in one SEM image.

[0104] [Length of nanowire]

[0105] Reference Figure 1B , the length L of the nanowire 14 is not particularly limited, but from the viewpoint of further improving the response and recovery characteristics and sensitivity to hydrogen, it is preferably 10 μm or more. In order to obtain the response and recovery characteristics even when the operating temperature is room temperature, the length L is more preferably 0.07 mm or more, and further preferably 0.5 mm or more. From the viewpoint of sensor characteristics, it is preferred that the length L is long, so its upper limit is not particularly limited. However, from the viewpoint of manufacturing process limitations and sensor size, it is preferably 300 mm or less. In addition, regarding the hydrogen sensor 100 of this embodiment, the large length L of the nanowire 14 as described above is also one of the characteristics. In the case of lengthening the nanowire 14, as Figure 4As shown, by arranging the nanowires 14 in a zigzag pattern on the substrate 10, the size of the sensor can be reduced. In this specification, the length L of the nanowire 14 refers to the length of a single nanowire connecting the first pad electrode 12A and the second pad electrode 12B. The length L of the nanowire 14 can be measured by SEM observation of the top surface of the hydrogen sensor 100.

[0106] [Crystalline State of Hydrogen-Absorbing Metal Constituting Nanowires]

[0107] For example, in nanowires 14 recently formed by electron beam evaporation or sputtering (as deposition), the crystalline state of the hydrogen-absorbing metal is a mixture of amorphous and polycrystalline. Details are described in the manufacturing method and Experimental Example 10 below. However, when the hydrogen-absorbing metal constituting nanowires 14 is palladium, heat-treating the nanowires 14 while the palladium is absorbing hydrogen causes the palladium to crystallize and become polycrystalline. Polycrystallizing the palladium constituting the nanowires is preferred because the response and recovery characteristics are further improved. Furthermore, "polycrystallization of the palladium" means that the palladium crystallizes as the crystallization progresses, the amorphous phase disappears, and the palladium crystallizes into a polycrystalline state. Whether the palladium has become polycrystalline can be determined based on the intensity and area of the peak attributed to Pd(111) in an X-ray diffraction pattern obtained by grazing incidence wide-angle X-ray scattering (GI-WAXS). Compared with the state of mixed amorphous phase before heat treatment, the peak intensity and peak area are significantly increased in the polycrystalline phase after heat treatment.

[0108] While details will be described later in the manufacturing method and Experimental Example 10, it was found that when the heat treatment performed with hydrogen adsorbed on palladium is RTA (Rapid Thermal Annealing), crystallization progresses while the palladium lattice constant is increased, and the increased lattice constant is maintained even after the heat treatment. Furthermore, it was found that the use of nanowires 14 with such an increased palladium lattice constant further significantly improves the response and recovery characteristics.

[0109] The α phase of palladium is a hydrogen solid solution phase (Pd+H) and exists as PdHx (x: the atomic ratio of H to Pd) when x < 0.02. In the α phase, hydrogen atoms are randomly dissolved in the crystal lattice, and the lattice constant of the α phase is In contrast, the β phase of palladium is a hydride phase (Pd-H) and exists when x>0.6. In the β phase, hydrogen atoms occupy the regular octahedral sites (O-site) in the crystal lattice, and the lattice constant of the β phase is That is, the lattice constant of the β phase is 2 to 3% larger than that of the α phase. In addition, near room temperature, there is a coexistence region of the α phase and the β phase (0.02≤x≤0.6). According to the research of the present inventors, when the RTA treatment is performed in a state where the palladium absorbs hydrogen, the lattice constant of the palladium constituting the nanowire 14 is In other words, although it cannot be said that the palladium constituting the nanowires 14 has undergone a phase change to the β phase, its value has reached near the upper limit of the lattice constant of the α phase.

[0110] In this case, the present inventors believe that the mechanism by which the response and recovery characteristics are further significantly improved is as follows. If RTA treatment is performed in a state where palladium absorbs hydrogen, crystallization is developed by heat treatment in a state where the lattice constant of palladium increases. Here, a large internal stress is applied to the nanowire 14 due to its curvature radius. Therefore, even after heat treatment (i.e., in the absence of hydrogen), the state of increased lattice constant is maintained by the large internal stress. For example, in the case of a thin film of palladium, even if the lattice constant is increased by the adsorption of hydrogen, the lattice constant returns to its original state if hydrogen is not present afterwards. Taking this into account, in the present invention, by applying a large internal stress to the nanowire 14, the state of lattice expansion is maintained even in a state that is not a hydrogen environment after heat treatment, which is a special phenomenon. Moreover, it is believed that in this lattice expansion state, atomic hydrogen can easily enter and exit, so the response and recovery characteristics are significantly improved.

[0111] The lattice constant of palladium constituting the nanowires 14 can be calculated based on the peak due to Pd(111) and the peak due to Pd(200) in the X-ray diffraction pattern obtained by GI-WAXS measurement, and it can be confirmed that the lattice constants of both are the same.

[0112] [Effect]

[0113] As described above, the hydrogen gas sensor 100 of this embodiment has high sensitivity, excellent response and recovery characteristics, and can detect hydrogen gas with low power consumption. Furthermore, the hydrogen gas sensor 100 of this embodiment can detect hydrogen gas even at low operating temperatures (e.g., even at room temperature). Furthermore, the hydrogen gas sensor 100 of this embodiment can detect hydrogen gas even at low concentrations, thus achieving a wide detectable hydrogen gas concentration range.

[0114] (Method for Manufacturing Hydrogen Sensor)

[0115] Reference Figure 5(A) to (D) describe a method for manufacturing a hydrogen gas sensor 100 according to one embodiment of the present invention. This method includes preparing a substrate 10, forming first and second pad electrodes 12A and 12B, and forming nanowires 14. This method enables the manufacture of the hydrogen gas sensor 100 according to this embodiment.

[0116] First, the substrate 10 is prepared. The details of the substrate 10 are as described above. Next, an example of the process of forming the first pad electrode 12A, the second pad electrode 12B, and the nanowire 14 will be described.

[0117] Reference Figure 5 (A) A resist film 30 is formed on the substrate 10. The resist film 30 can be formed by applying a resist composition for electron beam exposure on the substrate 10 and drying it. The coating method is not particularly limited, and a spin coating method can be preferably used. The thickness of the resist film 30 can be appropriately set to be thicker than the thickness of the nanowires 14 to be formed (in the case of forming the nanowires 14 and the pad electrodes 12A and 12B together, it is formed to be thicker than the two). In addition, after spin coating, the resist film 30 can be annealed under appropriate conditions to volatilize the solvent efficiently and improve the density of the resist film 30.

[0118] Next, if Figure 5 As shown in (B), the resist film 30 is developed to form a mask pattern 32 of a predetermined shape. The resist film 30 is exposed by electron beam exposure and developed to produce a mask pattern 32. The resist film is removed from the mask pattern 32, and the shape and size of the exposed portion of the substrate 10 correspond to the shape and size (line width W and length L) of the nanowire 14 to be formed. Here, the shape of the concave portion of the mask pattern 32 can be adjusted by appropriately controlling the type of resist composition, the thickness of the resist film 30 formed, and the dose of the irradiated electron beam. Thus, the shape and size (i.e., the radius of curvature, the length in the width direction, the length in the height direction, etc.) of the curved surface portions 14B1 and 14B2 at both ends of the nanowire 14 in the width direction can be adjusted. As shown in FIG. Figure 5 As shown in (B) to (D), when the nanowire 14 and the pad electrodes 12A and 12B are formed at the same time, the resist film is removed in the mask pattern 32, and the shape of the exposed portion of the substrate 10 corresponds to the shape and size of the nanowire 14 and the pad electrodes 12A and 12B to be formed.

[0119] Next, if Figure 5As shown in (C), a metal film 34 is formed, for example, by electron beam evaporation or sputtering. At this time, a first portion 34A of the metal film is formed on the mask pattern 32, and a second portion 34B of the metal film is formed on the substrate 10 exposed by removing the resist film in the mask pattern 32. Furthermore, the metal film 34 preferably includes a Ti layer, a Cr layer, or a Ta layer (adhesion layer) having a thickness of approximately 1 to 5 nm; and a layer formed thereon of a hydrogen-absorbing metal (e.g., Pd) constituting the nanowires 14 and the pad electrodes 12A and 12B. Furthermore, the Ti layer, the Cr layer, or the Ta layer functions as an adhesion layer for adhering the layer formed of the metal constituting the nanowires 14 and the pad electrodes 12A and 12B to the substrate 10.

[0120] Next, if Figure 5 As shown in FIG. 3D , the mask pattern 32 is peeled off to remove the first portion 34A of the metal film formed thereon, thereby forming the nanowires 14 and the pad electrodes 12A and 12B on the substrate 10. In this example, as shown in FIG. Figure 5 As shown in (B) to (D) of FIG, the nanowire 14 and the pad electrodes 12A and 12B are formed together. However, it is also possible to form only the nanowire 14 in the above process, and then form the pad electrodes 12A and 12B using, for example, conventional photolithography. In addition, the Ti layer, Cr layer or Ta layer is formed as an adhesive layer for adhering the nanowire 14 to the substrate 10. During the vapor deposition process of the metal constituting the nanowire 14, Ti, Cr or Ta diffuses in the metal layer, and most of the Ti layer, Cr layer or Ta layer disappears. Alternatively, since the film thickness of the adhesive layer is very thin, the adhesive layer can hardly be confirmed in the SEM image. Between the substrate 10 and the nanowire 14, Ti, Cr or Ta remains in the form of islands in some parts, but in most parts, the substrate 10 and the nanowire 14 are in direct contact.

[0121] Afterward, as an optional step, the nanowires 14 may be subjected to heat treatment. Heat treatment changes the cross-sectional shape of the nanowires 14 perpendicular to the extension direction, increasing the radius of curvature and resulting in a nanowire having a so-called truncated circular cross-section, where a portion of a circle is missing. As a result, internal stress is applied to a wide range of the nanowires, further improving sensor characteristics. Heat treatment conditions are preferably: an inert gas atmosphere containing hydrogen, such as Ar, with a heat treatment temperature (maximum temperature during heat treatment) of 250-400°C and a holding time at the heat treatment temperature of 1-90 minutes.

[0122] Furthermore, as optional steps, it is preferable to perform a step of exposing the nanowires 14 to an atmosphere containing hydrogen and an inert gas, and then a step of heat-treating the nanowires 14 in the atmosphere containing hydrogen and an inert gas. This allows the palladium to be polycrystallized when the hydrogen-absorbing metal constituting the nanowires is palladium, further improving the response and recovery characteristics as described above.

[0123] [Exposure process]

[0124] The exposure step is performed by exposing the nanowires 14 to an atmosphere containing hydrogen, with the remainder consisting of an inert gas and, optionally, unavoidable impurity gases. This step allows the palladium constituting the nanowires 14 to absorb hydrogen. The hydrogen content is preferably 1 to 5% by volume, with the remainder being selected from at least one of argon (Ar), helium (He), and neon (Ne). To ensure sufficient hydrogen absorption by the palladium, the exposure time is preferably at least 1 minute, but is preferably no longer than 10 minutes to achieve saturation of the palladium's hydrogen absorption capacity.

[0125] [Heat treatment process]

[0126] After the exposure step, the heat treatment step can be performed at atmospheric pressure in an atmosphere containing hydrogen, with the remainder consisting of an inert gas and, optionally, unavoidable impurity gases. This heat treatment step promotes crystallization of the palladium. The hydrogen content is preferably 1 to 5% by volume, and the remainder of the inert gas can be selected from one or more of argon (Ar), helium (He), and neon (Ne).

[0127] The heat treatment process can be carried out using a conventional heat treatment furnace, preferably an RTA device, by RTA treatment. By RTA treatment, as described above, in a state where the lattice constant of palladium is increased, crystallization is developed by heat treatment, and the increased lattice constant is also maintained after the heat treatment. From the viewpoint of fully obtaining this effect, the heat treatment temperature (the maximum temperature of the environment during heat treatment) is preferably above 350°C and below 650°C. The heat treatment temperature is more preferably above 400°C. In addition, the heat treatment temperature is more preferably below 600°C. From the viewpoint of fully obtaining the above-mentioned effect, the heating rate from the temperature at the start of the heat treatment to the heat treatment temperature is preferably above 2°C / second and below 200°C / second. Maintaining at the heat treatment temperature is not necessary. The holding time at the heat treatment temperature can be above 0 minutes and below 10 minutes.

[0128] Through the above steps, the gas sensor 100 can be manufactured.

[0129] Example

[0130] [Experimental Example 1: Influence of Line Width W]

[0131] <Hydrogen Sensor Fabrication>

[0132] The hydrogen sensor was fabricated according to the following steps: First, a Si substrate (15 mm in length x 15 mm in width x 0.6 mm in thickness) with a surface layer of approximately 1 μm and made of SiO 2 was prepared.

[0133] Pd nanowires were formed on a substrate using an electron beam exposure device EBL (ELS-7500EX manufactured by Elektronik). Specifically, electron beam resist ZEP-520A was applied to the substrate by spin coating to form a resist film. Afterwards, a mask pattern of a prescribed shape was drawn using the EBL device. Afterwards, a Ti layer (thickness: 3 nm) and a Pd layer (thickness: 30 nm) thereon were formed by electron beam evaporation. Afterwards, through a stripping process of stripping off the mask pattern, Pd nanowires were formed on the substrate (five conditions of line width W: 40 nm (comparative example), 50 nm (invention example), 80 nm (invention example), 100 nm (invention example), and 200 nm (comparative example), line thickness D: 30 nm, line length L: 10 μm). Figure 6 Figure 2 shows SEM images of cross-sections perpendicular to the extension direction of nanowires of various widths. Furthermore, the Ti layer serves as an adhesive layer for bonding the Pd nanowires to the substrate. However, the Ti layer is very thin, so during the Pd deposition process, the Ti diffuses into the Pd layer, largely disappearing. Although Ti remains as islands between the substrate and the Pd nanowires in some locations, direct contact between the substrate and the Pd nanowires occurs in most areas.

[0134] Next, using conventional photolithography, first and second pad electrodes (75 μm×75 μm) were formed, each consisting of a Ti layer (thickness: 5 nm) and a Pt layer (thickness: 40 nm) thereon. In this way, a hydrogen sensor using Pd nanowires was fabricated.

[0135] Hydrogen gas detection test

[0136] The above hydrogen sensor was placed in a measurement chamber using Ar + 3% H2 gas and capable of controlling hydrogen concentration. Using a semiconductor parameter analyzer system (B1500A manufactured by Keysight Technologies), a constant voltage (V = 50mV) was applied between the first pad electrode and the second pad electrode. Based on the change in the current detected between the first pad electrode and the second pad electrode, a hydrogen detection test was conducted to evaluate various characteristics of the sensor. Figure 1BAs shown. The operating temperature T is 50°C. Measurements were performed under atmospheric pressure, with N2 gas (flow rate: 1 SLM) introduced into the measurement chamber as a carrier gas. The hydrogen concentration when hydrogen was turned on was 1% (10,000 ppm). The hydrogen gas was switched on / off three times. Specifically, it was turned on at 0 seconds, off at 300 seconds, on at 900 seconds, off at 1200 seconds, on at 1800 seconds, off at 2100 seconds, and the measurement was continued until 3000 seconds.

[0137] <Linewidth dependence of response recovery characteristics>

[0138] Figure 7 (top) is a graph showing how the current value changes with time at various line widths. Figure 7 (Below) is a graph showing the change in resistance rate over time by converting current value into resistance value. Here, regarding ΔR / R0 on the vertical axis, R0 is the resistance value at 0 seconds, and ΔR is the difference between the resistance value at a certain moment and R0. In any line width, it is observed that the current decreases (resistance increases) when hydrogen is connected, and the current increases (resistance decreases) when hydrogen is disconnected. It can be considered that when hydrogen is connected, the volume expansion caused by the diffusion of atomic hydrogen into palladium increases the scattering in electron conduction and increases the resistance.

[0139] <Linewidth dependence of sensitivity at various operating temperatures>

[0140] The same test as above was carried out at the operating temperature T of 60°C, 70°C, 80°C, 90°C, 100°C, and 110°C. Figure 8 The relationship between line width and sensitivity (sensitivity based on resistance change rate) at various operating temperatures T is shown in FIG. Figure 8 The sensitivity ΔR / R0 on the vertical axis is the average value of ΔR / R0 at three times of disconnection (300 seconds, 1200 seconds, and 2100 seconds) when R0 is fixed to the resistance value at 0 seconds.

[0141] according to Figure 8 The sensitivity is maximum when the line width W is in the range of 80 to 100 nm.

[0142] When the wire width W is less than 50 nm, the cross-sectional area of the nanowire perpendicular to its extension direction decreases, leading to a sharp drop in sensitivity. In particular, when the wire width W is 40 nm, the proportion of the curved surface, where internal stress is high, becomes excessively large relative to the flat portion of the nanowire. This internal stress, exerted throughout the nanowire, makes it difficult for atomic hydrogen to enter the nanowire, leading to a sharp drop in sensitivity.

[0143] Compared to the case with a line width W of 100 nm, the sensitivity slightly decreased when the nanowire had a line width W of 200 nm, despite the increase in cross-sectional area perpendicular to the extension direction. The inventors believe this is due to the following mechanism. The increase in cross-sectional area is due to the increase in the flat portion of the nanowire, where no internal stress is applied, only atmospheric pressure. Consequently, the sensitivity slightly decreased due to the near-thin film state.

[0144] <Response time t at various operating temperatures res50 Linewidth dependence of

[0145] exist Figure 9 The line width and response time t at various operating temperatures T are shown in res50 Response time t res50 It is the time required for the current value to change from "the current value when hydrogen is connected" to "the current value when hydrogen is connected - the current value when hydrogen is disconnected" by 50%. The shorter it is, the faster the response. Figure 9 The vertical axis is the t of each of the three on / off res50 The average value of .

[0146] according to Figure 9 , response time t res50 The line width W is shortest in the range of 80 to 100 nm.

[0147] When the line width W is less than 50 nm, the line width approaches the thickness of the nanowire. Consequently, the flat portion of the nanowire's cross-section decreases, and the proportion of the curved surface with a small radius of curvature increases. Consequently, the proportion of the cross-sectional area subjected to internal stress increases compared to when the line width is larger. The high internal stress in this curved surface is applied to the entire nanowire, and the internal stress approaches the equilibrium pressure of hydrogen during hydrogen absorption, making hydrogen difficult to absorb and prolonging the response time.

[0148] When the line width W is 200 nm, the flat portion of the nanowire increases, and no internal stress due to the shape of the nanowire is applied to the flat portion. Therefore, hydrogen diffuses in the depth direction of the flat portion and is continuously adsorbed, which prolongs the response time.

[0149] The higher the operating temperature, the shorter the response time. At high operating temperatures, the equilibrium pressure for hydrogen absorption increases, making it difficult for hydrogen to be adsorbed. Since only a small amount of hydrogen enters, the response time is shortened. This corresponds to the fact that sensitivity decreases with increasing operating temperature.

[0150] <Recovery time t at various operating temperatures rec50 Linewidth dependence of

[0151] exist Figure 10 The line width and recovery time t at various operating temperatures T are shown in rec50Recovery time t rec50 It is the time required for the current value to change from "the current value when hydrogen is turned off" to "the current value when hydrogen is turned on next time - the current value when hydrogen is turned off" by 50%. The shorter it is, the faster the recovery. Figure 10 The vertical axis is the t of each of the three on / off rec50 The average value of .

[0152] according to Figure 10 , recovery time t rec50 The line width W is shortest in the range of 50 to 80 nm.

[0153] When the line width W is less than 50 nm, the line width approaches the thickness of the nanowire, resulting in a reduced flat portion in the nanowire's cross-section and a larger proportion of curved portions with a small radius of curvature. Consequently, the proportion of the cross-sectional area subject to internal stress increases compared to when the line width is larger. The high internal stress in these curved portions is applied to the entire nanowire, and as the internal stress approaches the equilibrium pressure of hydrogen during hydrogen release, hydrogen release becomes difficult, resulting in a prolonged recovery time.

[0154] At operating temperatures below 80°C, recovery time increases when the line width W is greater than 80 nm. This is because the proportion of hydrogen absorbed into the flat portion of the nanowire increases with increasing line width, causing hydrogen to be adsorbed deep within the flat portion, making recovery difficult. This suggests that nanowire structures exhibit better recovery characteristics than flat film structures.

[0155] On the other hand, when the operating temperature is above 90°C and the line width W is larger than 80nm, the recovery time becomes shorter. This is because the hydrogen equilibrium pressure during absorption increases with the temperature rise, and the flat part of the nanowire has a small amount of hydrogen absorbed, making it easier to release.

[0156] When the line width W is 100 nm or greater, the recovery time decreases as the operating temperature increases. This is because the hydrogen equilibrium pressure for hydrogen desorption increases at high temperatures, making hydrogen desorption easier.

[0157] Furthermore, when the line width W is 80nm or less and the operating temperature is above 100°C, the recovery time increases as the line width decreases. Especially when the line width is less than 50nm, the internal stress caused by the shape makes it difficult for hydrogen to be adsorbed, and even then, it is difficult for adsorbed hydrogen to be released. This is expected to be due to the internal stress caused by the shape being greater than the increase in the hydrogen equilibrium pressure required for release due to the temperature increase.

[0158] <Linewidth dependence of activation energy of response and recovery>

[0159] The activation energy of response and recovery was calculated from the Arrhenius curve.

[0160] First, based on Figure 9The results are plotted on the horizontal axis for each line width. -1 ), plot Log(1 / t res50 ), the slope of the straight line obtained by the least squares method for each curve was obtained. Based on this slope, the activation energy Ea of the response (hydrogen adsorption reaction) was obtained.

[0161] Similarly, based on Figure 10 The results are plotted on the horizontal axis for each line width. -1 ), plot Log(1 / t rec50 ), the slope of the straight line obtained by the least squares method of each curve was obtained. Based on this slope, the activation energy Ea of the recovery (hydrogen desorption reaction) was obtained.

[0162] exist Figure 11 Based on Figure 9 and Figure 10 The results shown show the relationship between the line width obtained and the activation energy of response (hydrogen adsorption reaction) and recovery (hydrogen desorption reaction). Up to the line width W of 100nm, the wider the line width, the greater the activation energy of the response, and when the line width W is greater than 100nm, the activation energy of the response is fixed. The wider the line width W, the greater the activation energy of recovery. In addition, the activation energy of the response is about 3 to 4 kcal / mol greater than the activation energy of the recovery. This is because the narrower the line width, the more difficult it is for hydrogen to be adsorbed due to the internal stress caused by the shape, so the adsorption amount is small, and the activation energy relative to the hydrogen that can be adsorbed becomes smaller.

[0163] [Experimental Example 2: Effect of Line Length L]

[0164] The line width W was fixed at 80 nm, the line thickness D was fixed at 30 nm, and the line length L was set to 0.07 mm, 0.7 mm, 7 mm, 14 mm, and 21 mm. A hydrogen sensor was fabricated in the same manner as in Experimental Example 1. In this experimental example, in order to increase the line length L, the following conditions were used in the four conditions where the line length was 0.7 mm or more: Figure 4 The arrangement of nanowires is shown in FIG. The length of each row of wires is 0.07 mm (70 μm), and the nanowires are arranged in an area of 70 μm × 70 μm with the largest wire length. Figure 12 ] shows an SEM image showing a portion of a Pd nanowire (length: 7 mm).

[0165] The hydrogen detection test was carried out in the same manner as in Experimental Example 1. However, in this experimental example, Figure 2The circuit diagram shown in the figure was used to perform a resistance voltage division measurement. The operating temperature T was room temperature, 24°C (297K). The applied voltage V was 1V. The measurement was performed under atmospheric pressure. N2 gas (flow rate: 1 SLM) was introduced into the measurement chamber as a carrier gas. The hydrogen concentration when the hydrogen gas was turned on was 1% (10,000 ppm). The hydrogen gas was turned on for 100 seconds, turned off at 700 seconds, and the measurement was continued until 1300 seconds.

[0166] Figure 13A and Figure 13B This is a graph showing the change in current value over time at various wire lengths. The current value is calculated based on the measured value of the voltage applied to the resistor. Figure 14 The current value is converted into resistance value, showing the change of resistance rate over time. Here, R / R base , R base is the resistance value at 100 seconds (before hydrogen is connected), and R is the resistance value at a certain moment. Figure 14 It can be seen that the longer the wire length, the higher the sensitivity (sensitivity based on the resistance change rate). In addition, this experimental example was performed with the operating temperature T set to room temperature. By increasing the wire length, the response and recovery characteristics at room temperature can be observed.

[0167] Figure 15 It shows the line length and response time t res50 The graph (above) shows the relationship between line length and recovery time t rec50 The relationship between the graph (below). It can be understood that the longer the line length is, the longer the response time t res50 and recovery time t rec50 There is an overall tendency to shorten.

[0168] [Experimental Example 3: Effect of Hydrogen Concentration]

[0169] The line width W is set to 80 nm, the line thickness D is set to 30 nm, and the line length L is set to 14 mm. A hydrogen sensor is produced in the same manner as in Experimental Example 1. In this experimental example, since the line length L is long, the following is used: Figure 4 The configuration of the nanowires is shown.

[0170] The hydrogen detection test was carried out in the same manner as in Experimental Example 1. However, in this experimental example, Figure 2 The circuit diagram shown in the figure was used to perform resistance voltage division measurements. The operating temperature T was room temperature, 21°C (294K). The applied voltage V was 1V. The measurement was performed under atmospheric pressure, with N2 gas (flow rate: 1 SLM) introduced into the measurement chamber as a carrier gas. The hydrogen concentration when hydrogen was turned on was set to 10,000 ppm (1%), 6,000 ppm (0.6%), 1,400 ppm (0.14%), and 300 ppm (0.03%). The hydrogen gas was turned on for 100 seconds, turned off at 400 seconds, and the measurement was continued until 700 seconds.

[0171] Figure 16 This is a graph showing the voltage change rate over time at various hydrogen concentrations. base , V base is the voltage value at 100 seconds (just before hydrogen is connected), and V is the voltage value at a certain moment. Figure 16 The higher the hydrogen concentration, the higher the sensitivity (sensitivity based on the voltage change rate). Sufficient sensitivity can be obtained when the hydrogen concentration is 1400 ppm or higher.

[0172] [Experimental Example 4: Effect of Applied Voltage]

[0173] The line width W is set to 80 nm, the line thickness D is set to 30 nm, and the line length L is set to 14 mm. A hydrogen sensor is produced in the same manner as in Experimental Example 1. In this experimental example, since the line length L is long, the following is used: Figure 4 The configuration of the nanowires is shown.

[0174] The hydrogen detection test was carried out in the same manner as in Experimental Example 1. However, in this experimental example, Figure 2 The circuit diagram shown in the figure was used to perform a resistance voltage division measurement. The operating temperature T was room temperature, 21°C (294K). The applied voltage V was set at four conditions: 10V, 1V, 0.5V, and 0.1V. The measurement was performed under atmospheric pressure, with N2 gas (flow rate: 1 SLM) introduced into the measurement chamber as a carrier gas. The hydrogen concentration when hydrogen was turned on was 1400ppm (0.14%). The hydrogen gas was turned on for 100 seconds, turned off at 400 seconds, and the measurement was continued until 700 seconds.

[0175] Figure 17 This is a graph showing the change in voltage rate over time under various applied voltages. base , V base is the voltage value at 100 seconds (just before hydrogen is connected), and V is the voltage value at a certain moment. Figure 17 The higher the applied voltage, the higher the sensitivity (sensitivity based on the rate of voltage change), and sufficient sensitivity is achieved at an applied voltage of 0.5 V or above. The power consumption corresponding to an applied voltage of 0.5 V is 0.8 μW. In other words, the hydrogen sensor of this experimental example can operate with very low power consumption, in the μW range.

[0176] [Experimental Example 5: Influence of Operating Temperature]

[0177] The line width W is set to 80 nm, the line thickness D is set to 30 nm, and the line length L is set to 14 mm. A hydrogen sensor is produced in the same manner as in Experimental Example 1. In this experimental example, since the line length L is long, the following is used: Figure 4 The configuration of the nanowires is shown.

[0178] The hydrogen detection test was carried out in the same manner as in Experimental Example 1. However, in this experimental example, Figure 2 The circuit diagram shown in the figure was used to perform resistance voltage division measurements. The operating temperatures T were room temperature (21°C (294K), 50°C (323K), 75°C (348K), and 100°C (373K). The applied voltage V was 1V. The measurement was performed under atmospheric pressure, with N2 gas (flow rate: 1 SLM) introduced into the measurement chamber as a carrier gas. The hydrogen concentration when hydrogen was turned on was 6000ppm (0.6%). The hydrogen gas was turned on for 100 seconds, turned off at 400 seconds, and the measurement was continued until 700 seconds.

[0179] Figure 18 This is a graph showing the voltage change rate over time at various operating temperatures. base , V base is the voltage value at 100 seconds (just before hydrogen is connected), and V is the voltage value at a certain moment. Figure 18 It can be seen that the hydrogen sensor of this experimental example can also operate at room temperature.

[0180] [Experimental Example 6: Influence of Carrier Gas]

[0181] The line width W is set to 80 nm, the line thickness D is set to 30 nm, and the line length L is set to 7 mm. A hydrogen sensor is produced in the same manner as in Experimental Example 1. In this experimental example, since the line length L is long, the following is used: Figure 4 The configuration of the nanowires is shown.

[0182] The hydrogen detection test was carried out in the same manner as in Experimental Example 1. However, in this experimental example, Figure 2 The circuit diagram shown is used to measure the resistance voltage divider. The operating temperature T is room temperature 24°C (297K). The applied voltage V is 1V. The measurement is carried out under atmospheric pressure, and two conditions of N2 gas (flow rate: 500sccm) and dry air (flow rate: 500sccm) are introduced into the measurement chamber as carrier gas. The hydrogen concentration when the hydrogen gas is turned on is 10000ppm (1%). The hydrogen gas is switched on / off four times. That is, under the condition of dry air, it is turned on at 100 seconds, turned off at 400 seconds, turned on at 1000 seconds, turned off at 1300 seconds, turned on at 1900 seconds, turned off at 2200 seconds, turned on at 2800 seconds, turned off at 3100 seconds, and the measurement is carried out until 3700 seconds. Under nitrogen conditions, the flow rate was switched on at 150 seconds, off at 400 seconds, on at 1000 seconds, off at 1300 seconds, on at 1900 seconds, off at 2200 seconds, on at 2800 seconds, off at 3180 seconds, and the measurement was performed until 3700 seconds.

[0183] Figure 19This graph shows the change in resistance over time when the carrier gas is dry air (top) and nitrogen (bottom). The resistance value on the vertical axis is the resistance value of the hydrogen sensor converted from the measured value of the voltage applied to the resistor. Figure 20 This is a graph showing the change in resistance over time when the carrier gas is dry air and when the carrier gas is nitrogen. base , R base is the resistance value at 100 seconds (just before hydrogen is first connected), and R is the resistance value at a certain moment. Figure 19 and Figure 20 It can be seen that sufficient sensitivity (sensitivity based on the resistance change rate) is obtained regardless of whether the carrier gas is dry air or nitrogen.

[0184] [Experimental Example 7: Influence of Line Thickness D]

[0185] The line width W was set to 80 nm, the line thickness D was set to 10 nm and 30 nm, and the line length L was set to 7 mm. A hydrogen sensor was produced in the same manner as in Experimental Example 1. In this experimental example, since the line length L was long, the following was used: Figure 4 The configuration of the nanowires is shown.

[0186] The hydrogen detection test was carried out in the same manner as in Experimental Example 1. However, in this experimental example, Figure 2 The circuit diagram shown is used to measure the resistance voltage divider. The operating temperature T is room temperature 24°C (297K). The applied voltage V is 1V. The measurement is carried out under atmospheric pressure, and N2 gas (flow rate: 1SLM) is introduced into the measurement chamber as a carrier gas. The hydrogen concentration when the hydrogen gas is connected is 6000ppm (0.6%). The hydrogen gas is switched on / off four times. That is, it is connected at 100 seconds, disconnected at 400 seconds, connected at 1000 seconds, disconnected at 1300 seconds, connected at 1900 seconds, disconnected at 2200 seconds, connected at 2800 seconds, disconnected at 3100 seconds, and the measurement is carried out until 3700 seconds.

[0187] Figure 21 This is a graph showing the change in resistance over time for various line thicknesses. base , R base The resistance value is 100 seconds (immediately before the hydrogen is first connected), and R is the resistance value at a certain moment. The resistance value of the hydrogen sensor is converted based on the measured value of the voltage applied to the resistor. Figure 21 Even if the line thickness is 10nm, sufficient sensitivity (sensitivity based on the resistance change rate) can be obtained, and when the line thickness is 30nm, higher sensitivity can be obtained.

[0188] [Experimental Example 8: Repeated Introduction of Hydrogen]

[0189] The line width W was set to 80 nm, and a hydrogen sensor was fabricated in the same manner as in Experimental Example 1 under two conditions: "line thickness D: 30 nm / line length L: 31 mm" and "line thickness D: 10 nm / line length L: 18 mm". In this experimental example, since the line length L was long, the following was adopted: Figure 4 The configuration of the nanowires is shown.

[0190] The hydrogen detection test was carried out in the same manner as in Experimental Example 1. However, in this experimental example, Figure 2 The circuit diagram shown was used to measure the resistance voltage divider. The operating temperature T was 100°C (373K). The applied voltage V was 1V. The measurement was carried out under atmospheric pressure, and N2 gas (flow rate: 10SLM) was introduced into the measurement chamber as a carrier gas. The hydrogen gas was switched on / off four times. That is, it was turned on at 300 seconds, turned off at 600 seconds, turned on at 900 seconds, turned off at 1200 seconds, turned on at 1500 seconds, turned off at 1800 seconds, turned on at 2100 seconds, turned off at 2400 seconds, and the measurement was carried out until 3300 seconds. The hydrogen concentration when the hydrogen gas was turned on was 30ppm for the first time, 150ppm for the second time, 750ppm for the third time, and 1500ppm for the fourth time.

[0191] Figure 22 This is a graph showing the change in resistance over time when hydrogen gas is repeatedly introduced into a wire having a thickness of 30 nm and a length of 31 mm. Figure 23 This is a graph showing the change in resistance over time when hydrogen gas is repeatedly introduced into a line with a thickness of 10 nm and a length of 18 mm. base , R base The resistance value is 300 seconds (immediately before the hydrogen is first connected), and R is the resistance value at a certain moment. The resistance value of the hydrogen sensor is converted based on the measured value of the voltage applied to the resistor. Figure 22 and Figure 23 , the sensitivity change depending on the hydrogen concentration can be obtained. Figure 22 The hydrogen sensor shown can detect hydrogen gas at a concentration of 30 ppm at an operating temperature of 373 K and an applied voltage of 1 V.

[0192] [Experimental Example 9: Effect of Heat Treatment on Nanowires]

[0193] The line width W is set to 80 nm, the line thickness D is set to 30 nm, and the line length L is set to 7 mm. A hydrogen sensor is produced in the same manner as in Experimental Example 1. In this experimental example, since the line length L is long, the following is used: Figure 4The configuration of the nanowires shown. In addition, after the peeling process, the nanowires were heat treated. Using an infrared lamp annealing device (desktop lamp heating device MILA-5000 manufactured by ADVANCE RICOH CO., LTD.), the heat treatment was carried out at a heat treatment temperature of 250°C and a holding time of 5 minutes under atmospheric pressure while circulating Ar / H2 (3% by volume) mixed gas. Figure 24 : A cross-sectional SEM image of the nanowire perpendicular to the extension direction (top) and an elemental mapping based on dispersive X-ray spectroscopy (EDS) (bottom) of the same area as the cross-sectional SEM image are shown in FIG. Figure 4 As shown in the figure, the cross section of the nanowires is periodic because the nanowires are arranged in a zigzag shape. The EDS element mapping shows the intensity of the L-ray of Pd, and the bright part is palladium. The nanowires are formed into a cross-sectional shape like a semi-cylinder consisting of two ends with curvature and a flat part. It can be considered that in this SEM image, the curvature radius and the Figure 6 Since the area ratio of the portion surrounded by the curved surface portion increases, the ratio of the cross-sectional area to which the internal stress is applied increases compared to that before the heat treatment.

[0194] The hydrogen detection test was carried out in the same manner as in Experimental Example 1. However, in this experimental example, Figure 2 The circuit diagram shown is used to perform resistance voltage division measurement. The operating temperature T is 4 conditions of 24°C, 50°C, 100°C, and 150°C. The applied voltage V is 1V. The measurement is carried out under atmospheric pressure, and N2 gas (flow rate: 1SLM) is introduced into the measurement chamber as a carrier gas. The hydrogen concentration when the hydrogen is turned on is 3333ppm (0.33%). The hydrogen is switched on / off four times. That is, it is turned on at 100 seconds, turned off at 400 seconds, turned on at 1000 seconds, turned off at 1300 seconds, turned on at 1900 seconds, turned off at 2200 seconds, turned on at 2800 seconds, turned off at 3100 seconds, and the measurement is carried out until 3700 seconds. In addition, after the hydrogen detection test is carried out with the operating temperature set to the above 4 conditions, the operating temperature is set to 21°C (room temperature), and the same hydrogen detection test is carried out again.

[0195] Figures 25-29 The graph (top) shows the change in resistance over time at various operating temperatures, and the graph (bottom) shows the change in resistance over time. The resistance value on the vertical axis of the graph (top) is the resistance value of the hydrogen sensor converted from the measured value of the voltage applied to the resistor. base , R base is the resistance value at 100 seconds (just before hydrogen gas is first connected), and R is the resistance value at a certain moment.

[0196] Figure 30 It shows the operating temperature and response time t res50The graph (above) shows the relationship between the operating temperature and the recovery time t rec50 The vertical axis of the graph (upper) is the relationship between the four on / off times. res50 The vertical axis of the graph (below) is the average value of each t at four times of on / off. rec50 The average value of . Figure 31 This is a graph showing the relationship between operating temperature and sensitivity (sensitivity based on resistance change rate). Figure 31 The sensitivity of the vertical axis is R / R base To R base R / R at four disconnection times (400 seconds, 1300 seconds, 2200 seconds, and 3100 seconds) when the resistance value at 100 seconds is fixed base The average value of .

[0197] Reference Figure 30 , compared with the case without heat treatment ( Figure 9 、 Figure 10 ), the response and recovery characteristics of the hydrogen gas sensor after heat treatment are excellent. When heat treated at each operating temperature, the response time t res50 and recovery time t rec50 All become shorter, enabling high-speed response and high-speed recovery. Figure 31 , the sensitivity decreases with the increase of operating temperature. Figure 8 The tendency is consistent.

[0198] The reason why the response and recovery time are shorter when heat treatment is performed compared to when no heat treatment is performed is that although the radius of curvature is increased by heat treatment, the proportion of the portion surrounded by the curved surface is increased, so the proportion of the cross-sectional area to which internal stress is applied is larger than when the line width is large, and the area where the internal stress increases due to the radius of curvature is more optimized.

[0199] [Experimental Example 10: Effect of Annealing on Nanowires]

[0200] The line width W is set to 55 nm, the line thickness D is set to 30 nm, and the line length L is set to 0.7 mm. A hydrogen sensor is produced in the same manner as in Experimental Example 1. In this experimental example, since the line length L is long, the following is used: Figure 4 After the lift-off process, the nanowires were subjected to an exposure process and a heat treatment under the following conditions.

[0201] <Condition 1>

[0202] No exposure process or heat treatment process is performed.

[0203] <Condition 2>

[0204] The nanowires were exposed to an Ar / H2 (3 vol%) mixed gas for three minutes. Subsequently, they were heat treated using an infrared lamp annealing device (MILA-5000, a benchtop lamp heating device manufactured by ADVANCE RICO Co., Ltd.) in an Ar / H2 (3 vol%) mixed gas atmosphere at atmospheric pressure at a temperature of 250°C, a heating rate of 10°C / minute, and a hold time of 5 minutes.

[0205] <Conditions 3-5>

[0206] The nanowires were exposed to an Ar / H2 (3 vol%) mixed gas for three minutes. Subsequently, RTA treatment was performed using an RTA apparatus (MILA-5000UHV, manufactured by ADVANCE RICO Co., Ltd.) in an Ar / H2 (3 vol%) mixed gas atmosphere at atmospheric pressure, with heat treatment temperatures of 500°C (Condition 3), 400°C (Condition 4), and 600°C (Condition 5), a heating rate of 50°C / second, and a hold time of 0 minutes.

[0207] <Crystalline State of Palladium Constituting Nanowires>

[0208] GI-WAXS measurements were performed on samples under conditions 1 to 3 at beamline BL13XU of SPring-8. The X-ray energy was 12.39797043082328 eV. The X-ray diffraction patterns obtained for each sample were Figure 32 As shown in . Figure 32 It is clear that the intensity and area of the peak attributed to Pd(111) are significantly increased in Conditions 2 and 3, where the exposure and heat treatment steps are performed, compared to Condition 1, where the exposure and heat treatment steps are not performed. This indicates that the palladium constituting the nanowires is polycrystallized in Conditions 2 and 3.

[0209] The lattice constant of palladium calculated based on the peaks due to Pd(111) and Pd(200) in condition 1 is In condition 2, In condition 3, The lattice constant of the α phase of palladium is Therefore, it can be said that all conditions 1 to 3 are α phase, but in condition 3 where RTA treatment is performed in a state where palladium absorbs hydrogen, the lattice expansion state is maintained and the lattice constant becomes a value near the upper limit of the lattice constant of the α phase.

[0210] exist Figure 33 The top surface SEM images of the nanowires in the samples of conditions 3 to 5 are shown in FIG. Figure 33 As shown, in conditions 3 to 5 in which the RTA treatment was performed after the exposure step, a plurality of palladium grains were observed in the nanowires with a uniform line width (about 80 nm), indicating that the palladium was polycrystallized.

[0211] <Hydrogen detection test 1>

[0212] The hydrogen detection test was carried out in the same manner as in Experimental Example 1. The operating temperature T was room temperature 21°C (294K). The applied voltage V was 1V. The measurement was carried out under atmospheric pressure, and N2 gas (flow rate: 3SLM) was introduced into the measurement chamber as a carrier gas. The hydrogen gas was switched on / off three times. That is, it was turned on at 100 seconds, turned off at 250 seconds, turned on at 400 seconds, turned off at 550 seconds, turned on at 700 seconds, turned off at 850 seconds, and the measurement was carried out until 1050 seconds. The hydrogen concentration when the hydrogen gas was turned on was 500ppm for the first time, 1000ppm for the second time, and 5000ppm for the third time.

[0213] Figure 34 This is a graph showing the change in resistance over time under conditions 1 to 3. base , R base is the resistance value at 100 seconds (just before hydrogen is first connected), and R is the resistance value at a certain moment. Figure 34 Compared to condition 1 (As deposition), which did not perform the exposure and heat treatment steps, conditions 2 and 3, which performed both exposure and heat treatment steps, achieved faster response and recovery. In particular, condition 3, which performed RTA treatment after the exposure step, achieved extremely fast response and recovery, significantly improving response and recovery characteristics.

[0214] Figure 35 This is a graph showing the change in resistance over time under conditions 2 to 5. Figure 35 It can be seen that any of conditions 3 to 5, where the heat treatment temperature of the RTA treatment is 400°C, 500°C, and 600°C, can achieve high-speed response and high-speed recovery compared to condition 2, but the response and recovery characteristics of condition 3, where the heat treatment temperature is 500°C, are the best.

[0215] Hydrogen gas detection test 2

[0216] Using the hydrogen sensor of condition 3, a hydrogen detection test was carried out in the same manner as in Experimental Example 1. The operating temperature T was room temperature 21°C (294K). The applied voltage V was 1V. The measurement was carried out under atmospheric pressure, and N2 gas (flow rate: 3SLM) was introduced into the measurement chamber as a carrier gas. The hydrogen was switched on / off five times. That is, it was turned on at 100 seconds, turned off at 250 seconds, turned on at 400 seconds, turned off at 550 seconds, turned on at 700 seconds, turned off at 850 seconds, turned on at 1000 seconds, turned off at 1150 seconds, turned on at 1300 seconds, turned off at 1450 seconds, and the measurement was carried out until 1600 seconds. The hydrogen concentration when the hydrogen was turned on was 297ppm for the first time, 2727ppm for the second time, 4286ppm for the third time, 10000ppm for the fourth time, and 30000ppm for the fifth time.

[0217] Figure 36 Here, the vertical axis represents R / R base , R base is the resistance value at 100 seconds (just before hydrogen is first connected), and R is the resistance value at a certain moment. Figure 36 It can be seen that the hydrogen sensor under condition 3 can detect extremely low concentrations of hydrogen such as 297ppm at high speed and recover quickly.

[0218] Industrial applicability

[0219] The hydrogen gas sensor of the present invention has high sensitivity, excellent response and recovery characteristics, and can detect hydrogen gas with low power consumption. Therefore, it has the potential to be applied to mobile gas sensors and the like.

[0220] Description of Reference Numerals

[0221] 100: hydrogen sensor;

[0222] 10: Substrate;

[0223] 12A: first pad electrode;

[0224] 12B: second pad electrode;

[0225] 14: nanowires;

[0226] 14A: Flat portion of the nanowire;

[0227] 14B1: curved surface of the nanowire;

[0228] 14B2: curved surface of the nanowire;

[0229] 18: Power supply;

[0230] 20: Galvanometer;

[0231] 22: Voltmeter;

[0232] 24: resistance;

[0233] 30: resist film;

[0234] 32: mask pattern;

[0235] 34: Metal film;

[0236] 34A: first part of the metal film;

[0237] 34B: second part of the metal film;

[0238] W: line width of nanowire;

[0239] D: thickness of the nanowire;

[0240] L: length of the nanowire.

Claims

1. A hydrogen sensor comprising: a substrate having an insulating surface; a first pad electrode and a second pad electrode formed on the insulating surface of the substrate; and a nanowire formed on the insulating surface of the substrate so as to connect the first pad electrode and the second pad electrode, having a line width of 50 nm to 150 nm and a thickness of 10 nm to 60 nm, and made of a hydrogen-absorbing metal; A current is passed between the first pad electrode and the second pad electrode, and hydrogen gas is detected based on a change in an electrical signal detected between the first pad electrode and the second pad electrode.

2. The hydrogen sensor according to claim 1, wherein The nanowire has a line width of 80 nm or more and 100 nm or less.

3. The hydrogen sensor according to claim 1, wherein The thickness of the nanowire is greater than or equal to 20 nm and less than or equal to 50 nm.

4. The hydrogen sensor according to claim 1, wherein The length of the nanowire is greater than or equal to 10 μm and less than or equal to 300 mm.

5. The hydrogen sensor according to claim 4, wherein: The length of the nanowire is greater than 0.07 mm. The hydrogen sensor according to claim 5 , wherein: The length of the nanowire is greater than 0.5 mm.

7. The hydrogen gas sensor according to any one of claims 1 to 6, wherein: The hydrogen absorbing metal is selected from one or more of the following (I) and (II), (I) Exothermic metals A that readily form stable hydrides, such as palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), osmium (Os), vanadium (V), titanium (Ti), zirconium (Zr), lanthanum (La), tungsten (W), calcium (Ca), magnesium (Mg), strontium (Sr), barium (Ba), and beryllium (Be), as well as solid solution alloys of these exothermic metals A; (II) AB5 type alloys, AB2 type alloys, AB type alloys, and A2B type alloys obtained by combining the exothermic metal A and one or more endothermic metals B selected from nickel (Ni), iron (Fe), cobalt (Co), manganese (Mn), and zinc (Zn) that do not have an affinity for hydrogen.

8. The hydrogen gas sensor according to any one of claims 1 to 6, wherein: The hydrogen absorbing metal is palladium (Pd).

9. The hydrogen sensor according to claim 8, wherein: The palladium constituting the nanowires is polycrystallized.

10. The hydrogen sensor according to claim 9, wherein: The lattice constant of palladium constituting the nanowire is 3.925± 11. A method for manufacturing a hydrogen sensor, comprising: A process for preparing a substrate having an insulating surface; forming a first pad electrode and a second pad electrode on the insulating surface of the substrate; and forming a nanowire on the insulating surface of the substrate so as to connect the first pad electrode and the second pad electrode, wherein the nanowire has a line width of 50 nm to 150 nm and a thickness of 10 nm to 60 nm and is formed of a hydrogen-absorbing metal; The hydrogen gas sensor manufactured by the method for manufacturing a hydrogen gas sensor allows current to flow between the first pad electrode and the second pad electrode, and detects hydrogen gas based on a change in an electrical signal detected between the first pad electrode and the second pad electrode.

12. The method for manufacturing a hydrogen gas sensor according to claim 11, comprising: exposing the nanowires to an environment comprising hydrogen and an inert gas; and Thereafter, a step of heat-treating the nanowires is performed in an environment containing hydrogen and an inert gas.

13. The method for manufacturing a hydrogen sensor according to claim 12, wherein: The heat treatment is an RTA treatment performed at a heat treatment temperature of 350° C. or higher and 650° C. or lower.

14. The method for manufacturing a hydrogen gas sensor according to any one of claims 11 to 13, wherein: The hydrogen absorbing metal is palladium (Pd).

Images