Hydrogen sensor, hydrogen detection method, and hydrogen detection device

Abstract

A hydrogen sensor (1) includes a first electrode (103) in a planar shape; a second electrode (106) in a planar shape, formed to face the first electrode, and having an exposed portion (106e); a metal oxide layer (104) sandwiched by both surfaces of the first electrode (103) and the second electrode (106), and having a resistance change according to hydrogen; and two first terminals (111) and a second terminal (112) connected to the second electrode (106).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a hydrogen sensor, a hydrogen detection method, and a hydrogen detection device. BACKGROUND

[0002] Patent Documents 1 and 2 disclose a gas sensor that detects a gas molecule containing a hydrogen atom.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT DOCUMENTS

[0005] Patent Document 1: International Publication No. 2017 / 037984

[0006] Patent Document 2: Japanese Patent Application Publication No. 2017-22938 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] However, according to the related art, there is a problem that the detection performance for hydrogen of low concentration is poor.

[0009] Therefore, the present disclosure provides a hydrogen sensor, a hydrogen detection method, and a hydrogen detection device that improve the detection performance for hydrogen of low concentration.

[0010] MEANS FOR SOLVING THE PROBLEMS

[0011] The hydrogen sensor according to the present disclosure includes a first electrode having a flat shape; a second electrode having a flat shape, formed so as to face the first electrode, and having an exposed portion; a metal oxide layer sandwiched by two opposing surfaces of the first electrode and the second electrode, and having a resistance that changes in accordance with hydrogen; two terminals connected to the second electrode; and a drive circuit that detects a gas containing a hydrogen atom by detecting a decrease in a resistance value between the first electrode and the second electrode, or by detecting a decrease in a resistance value between the two terminals, in a state where a current flows through the exposed portion by applying a voltage between the two terminals.

[0012] Further, a hydrogen detection method according to one aspect of the present disclosure is a hydrogen detection method in a hydrogen sensor including a first electrode in a planar shape, a second electrode in a planar shape formed so as to face the first electrode and having an exposed portion, a metal oxide layer sandwiched by the first electrode and two opposing surfaces of the second electrode and changing in resistance in accordance with hydrogen, and two terminals connected to the second electrode, the two terminals being connected to the second electrode at positions sandwiching the exposed portion in a planar view of the second electrode. In the hydrogen detection method, current is caused to flow through the exposed portion by applying a voltage between the two terminals, and a gas containing hydrogen atoms is detected by detecting a decrease in resistance between the first electrode and the second electrode or by detecting a decrease in resistance between the two terminals.

[0013] Further, a hydrogen detection device according to one aspect of the present disclosure includes a first electrode in a planar shape, a second electrode in a planar shape formed so as to face the first electrode and having an exposed portion, a metal oxide layer sandwiched by the first electrode and two opposing surfaces of the second electrode and changing in resistance in accordance with hydrogen, two terminals connected to the second electrode, and a drive circuit. In a state in which current is caused to flow through the exposed portion by applying a voltage between the two terminals, the drive circuit detects a decrease in resistance between the first electrode and the second electrode or detects a decrease in resistance between the two terminals, and a gas containing hydrogen atoms is detected.

[0014] Effects of Invention

[0015] The hydrogen sensor, the hydrogen detection method, and the hydrogen detection device according to the present disclosure can improve the detection performance for low-concentration hydrogen. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1A is a cross-sectional view showing a configuration example of a hydrogen sensor in Embodiment 1.

[0017] Figure 1B is a plan view showing a configuration example of a hydrogen sensor in Embodiment 1.

[0018] Figure 2 is a block diagram showing a configuration example of a hydrogen detection device including a drive circuit in which a hydrogen detection method is implemented and a hydrogen sensor in Embodiment 1.

[0019] Figure 3 is a flowchart showing a hydrogen detection method using a hydrogen sensor based on a drive circuit in Embodiment 1.

[0020] Figure 4 is a graph showing experimental results of a hydrogen sensor in a comparative example.

[0021] Figure 5This is a graph showing the experimental results of the hydrogen sensor in Implementation Method 1.

[0022] Figure 6 This is a graph showing the experimental results of the hydrogen sensor in Implementation Method 1.

[0023] Figure 7 This is a cross-sectional view showing an example of the configuration of the hydrogen sensor in Embodiment 2.

[0024] Figure 8 This is a graph showing the experimental results of the hydrogen sensor in the comparative example.

[0025] Figure 9 This is a graph showing the experimental results of the hydrogen sensor in Embodiment 2.

[0026] Figure 10 This is a cross-sectional view showing an example of the configuration of the hydrogen sensor in Embodiment 3.

[0027] Figure 11 This is a graph showing the experimental results of the hydrogen sensor in the comparative example.

[0028] Figure 12 This is a graph showing the experimental results of the hydrogen sensor in Embodiment 3. Detailed Implementation

[0029] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings.

[0030] Furthermore, the embodiments described below are all general or specific examples. The numerical values, shapes, materials, constituent elements, the arrangement and location of constituent elements, connection methods, steps, and the order of steps shown in the following embodiments are examples and are not intended to limit this disclosure.

[0031] (Implementation Method 1)

[0032] [1.1 Composition of Hydrogen Sensor 1]

[0033] Figure 1A This is a cross-sectional view showing a configuration example of the hydrogen sensor 1 according to Embodiment 1. Figure 1B This is a top view showing an example of the configuration of the hydrogen sensor 1 in Embodiment 1. Additionally, Figure 1A Indicates observation Figure 1B A schematic cross-section showing the direction of the arrow on the IA-IA cut line.

[0034] like Figure 1A as well as Figure 1BAs shown, the main part of the hydrogen sensor 1 includes a first electrode 103, a metal oxide layer 104, a second electrode 106, and a first terminal 111, a second terminal 112, and a third terminal 113. Furthermore, the main part of the hydrogen sensor 1 is covered by insulating films 102, 107a-107c, 109a, and 109b. However, these insulating films have openings 106a, 111a, 112a, and 113a.

[0035] The first electrode 103 is a planar electrode with two surfaces. One of the two surfaces of the first electrode 103 (i.e. Figure 1A The upper surface) is in contact with the metal oxide layer 104, and the other surface (i.e. Figure 1A The lower surface of the first electrode 103 is in contact with the insulating film 107b and the through hole 108. Figure 1B The first electrode 103 is rectangular in shape, the same size as the second electrode 106. The first electrode 103 can be made of materials with a lower standard electrode potential than the metals constituting the metal oxide, such as tungsten, nickel, tantalum, titanium, aluminum, tantalum nitride, or titanium nitride. A higher standard electrode potential indicates greater resistance to oxidation. Figure 1A The first electrode 103 is formed, for example, of tantalum nitride (TaN), or titanium nitride (TiN), or a stack thereof.

[0036] The metal oxide layer 104 is sandwiched between the opposing surfaces of the first electrode 103 and the second electrode 106. It is composed of a metal oxide as a gas-sensitive resistive film and has a resistance value that reversibly changes with the presence or absence of hydrogen-containing gas in the gas contacted with the second electrode 106. The metal oxide layer 104 only needs to possess the property of resistance changing according to hydrogen. The metal oxide layer 104 is composed of an oxygen-deficient metal oxide. The parent metal of the metal oxide layer 104 can be at least selected from transition metals such as tantalum (Ta), hafnium (Hf), titanium (Ti), zirconium (Zr), niobium (Nb), tungsten (W), nickel (Ni), and iron (Fe) and aluminum (Al). Transition metals can be in multiple oxidation states; therefore, different resistance states can be achieved through redox reactions. Here, the "oxygen deficiency" of the metal oxide refers to the ratio of the insufficient amount of oxygen in the metal oxide to the amount of oxygen in an oxide with a stoichiometric composition composed of the same elements as the metal oxide. Here, oxygen deficiency refers to the value obtained by subtracting the amount of oxygen in a stoichiometric metal oxide from the amount of oxygen in that metal oxide. If multiple stoichiometric metal oxides composed of the same elements as the metal oxide exist, the oxygen deficiency of the metal oxide is defined based on the one with the highest resistivity among these stoichiometric metal oxides. Stoichiometric metal oxides are more stable and have higher resistivity compared to metal oxides with other components. For example, if the parent metal of metal oxide layer 104 is tantalum (Ta), the stoichiometric oxide based on the above definition is Ta₂O₅, and therefore, it can be represented as TaO₂.₅. The oxygen deficiency of TaO₂.₅ is 0%, and the oxygen deficiency of TaO₁.₅ is (2.5 - 1.5) / 2.5 = 40%. Furthermore, the oxygen deficiency of oxygen-excess metal oxides is negative. Additionally, in this disclosure, unless otherwise specified, the oxygen deficiency can be positive, 0, or negative. Oxides with low oxygen deficiency are closer to the stoichiometric composition of oxides and therefore have higher resistance values, while oxides with high oxygen deficiency are closer to the metals that make up the oxides and therefore have lower resistance values.

[0037] Figure 1A The metal oxide layer 104 shown has a first layer 104a connected to the first electrode 103, a second layer 104b connected to the first layer 104a and the second electrode 106, and an insulating separation layer 104i. The oxygen deficiency of the second layer 104b is less than that of the first layer 104a. For example, the first layer 104a is TaOX, and the second layer 104b is Ta2O5, which has a lower oxygen deficiency than the first layer 104a. Furthermore, the metal oxide layer 104 has an insulating separation layer 104i on the outer periphery of the first electrode 103 in the plan view.

[0038] Here, a floor plan refers to a plan taken from the perspective of... Figure 1AThe hydrogen sensor 1 of the present invention is viewed from the perspective of the stacking direction; in other words, it is viewed from the perspective of the normal direction of one of the planar first electrode 103, planar second electrode 106, etc. For example, it refers to... Figure 1B The image shows the observation of the upper surface of hydrogen sensor 1.

[0039] The resistance of the metal oxide layer 104 decreases depending on the presence of hydrogen-containing gas in contact with the second electrode 106. Specifically, when hydrogen-containing gas is present in the gas being detected, hydrogen atoms dissociate from the hydrogen-containing gas within the second electrode 106. These dissociated hydrogen atoms penetrate the metal oxide layer 104, forming impurity energy levels. In particular, they concentrate near the interface with the second electrode, apparently thinning the thickness of the second layer 104b. As a result, the resistance of the metal oxide layer 104 decreases.

[0040] The second electrode 106 is a planar electrode with hydrogen dissociation properties, having two surfaces. One of the two surfaces of the second electrode 106 (i.e. Figure 1A The lower surface) is in contact with the metal oxide layer 104, and the other surface (i.e. Figure 1A The upper surface of the second electrode 106 is in contact with the metal layer 106s and the outside gas. The second electrode 106 has an exposed portion 106e in the opening 106a that is exposed to the outside gas. The second electrode 106 is made of a material that has a catalytic effect, such as platinum (Pt), iridium (Ir), palladium (Pd), or nickel (Ni), or an alloy containing at least one of them, which has the effect of catalyzing the dissociation of hydrogen atoms from gas molecules containing hydrogen atoms. Figure 1A The second electrode 106 is made of platinum (Pt). The second electrode 106 is connected to two terminals, namely the first terminal 111 and the second terminal 112.

[0041] The first terminal 111 is connected to the second electrode 106 via the through hole 108.

[0042] The second terminal 112 is connected to the second electrode 106 via the through hole 108. The first terminal 111 and the second terminal 112 are connected to the external drive circuit of the hydrogen sensor 1 via openings 111a and 112a.

[0043] The first terminal 111 and the second terminal 112 are as follows Figure 1B The electrode is positioned in a plan view of the second electrode 106, sandwiching the exposed portion 106e. With this configuration, a predetermined voltage is applied between the first terminal 111 and the second terminal 112, thereby energizing the exposed portion 106e of the second electrode 106, i.e., allowing current to flow through the exposed portion 106e. This energization of the exposed portion 106e of the second electrode 106 can be considered as activating the hydrogen dissociation of the exposed portion 106e. Alternatively, the predetermined voltage can also be a voltage with opposite polarities.

[0044] The hydrogen sensor 1 detects hydrogen-containing gas molecules by causing a change in resistance between the first terminal 111 and the second terminal 112 when the exposed portion 106e is energized. This change in resistance is detected by the aforementioned drive circuit.

[0045] The third terminal 113 is connected to the first electrode 103 via an opening 113a, a through-hole 108, wiring 114, and the through-hole 108. The third terminal 113 is connected to an external driving circuit for driving the hydrogen sensor 1 via the opening 113a. When the exposed portion 106e is energized, gas molecules containing hydrogen atoms come into contact with the exposed portion 106e, causing a change in resistance between the first electrode 103 and the second electrode 106. In other words, when the exposed portion 106e is energized, gas molecules containing hydrogen atoms come into contact with the exposed portion 106e, causing a change in resistance between the first terminal 111 or the second terminal 112 and the third terminal 113. The driving circuit detects this change in resistance and also detects the presence of gas molecules containing hydrogen atoms.

[0046] In addition, the insulating films 102, 107a to 107c, 109a, and 109b covering the main part of the hydrogen sensor 1 are formed of silicon oxide film, silicon nitride film, etc.

[0047] Furthermore, a metal layer 106s is formed on the upper surface of the second electrode 106, other than the opening 106a. The metal layer 106s is formed, for example, using TiAlN as a material, as an etching stop layer for forming the via 108, but it is not mandatory.

[0048] Furthermore, the stack of the first electrode 103, the metal oxide layer 104, and the second electrode 106 is configured to be used as a storage element in a resistive random access memory (ReRAM). In a ReRAM, the metal oxide layer 104 is used as a digital storage element in both a high-resistance state and a low-resistance state. In the hydrogen sensor 1 of this disclosure, the high-resistance state of the metal oxide layer 104 is utilized.

[0049] In addition, Figure 1A The image shows an example of a bilayer metal oxide layer 104 consisting of a first layer 104a made of TaOx and a second layer 104b made of Ta2O5 with low oxygen deficiency. However, it can also consist of a single layer made of either Ta2O5 or TaOx with low oxygen deficiency.

[0050] [1.2 Hydrogen Detection Methods and Devices]

[0051] Next, the hydrogen detection method and hydrogen detection device using hydrogen sensor 1 will be described.

[0052] Figure 2 This is a block diagram illustrating an example of the configuration of a hydrogen detection device 2, including a drive circuit 200 for implementing a hydrogen detection method and a hydrogen sensor 1, in Embodiment 1. Figure 2 In this embodiment, the hydrogen detection device 2 includes a drive circuit 200 and a hydrogen sensor 1. The drive circuit 200 is connected to the hydrogen sensor 1 via at least three wires connected to a first terminal 111, a second terminal 112, and a third terminal 113. The drive circuit 200 is, for example, composed of a microcomputer having a CPU, ROM, and RAM. The at least three wires are connected to the ports of the microcomputer.

[0053] Figure 3 This is a flowchart illustrating a hydrogen detection method using a hydrogen sensor 1 based on a drive circuit 200. In this diagram, firstly, the drive circuit 200 initiates energization between the first terminal 111 and the second terminal 112 (S1). That is, the drive circuit 200 applies a predetermined voltage between the first terminal 111 and the second terminal 112. For example, the first terminal 111 and the second terminal 112 are applied with voltages of opposite polarities, +V1 and -V1. Therefore, the current energized to the exposed portion 106e of the second electrode 106 can be, for example, several mA to several tens of mA.

[0054] Next, the drive circuit 200 measures the resistance value Rh between the first terminal 111 and the second terminal 112 (S2), and measures the resistance value Rv between the first terminal 111 or the second terminal 112 and the third terminal 113 (S3). Furthermore, the drive circuit 200 determines whether the measured resistance value Rh is less than a threshold th1, and further determines whether the measured resistance value Rv is less than a threshold th2 (S4). Based on the determination, if at least one of the resistance values ​​Rh and Rv is determined to be low, it is determined to be "containing hydrogen" (S5); otherwise, it is determined to be "without hydrogen" (S6).

[0055] The driving circuit 200 may, for example, repeat steps S2 to S6 based on a certain period from several hundred milliseconds to several seconds.

[0056] In addition, Figure 3 The example shown is that the first terminal 111 and the second terminal 112 are always energized, but energization can also be performed only in the processes of steps S2 and S3.

[0057] In addition, in step S5, it can also be determined that "hydrogen is present" when both the resistance value Rh and the resistance value Rv are less than their respective thresholds.

[0058] Alternatively, one of steps S2 and S3 can be omitted, and only one of the resistance values ​​Rh and Rv can be used for determination.

[0059] [1.3 Experimental Data]

[0060] Next, the operation of the hydrogen sensor 1 in Embodiment 1 will be explained using experimental data.

[0061] Figure 4 This is a graph showing experimental data from a comparative example hydrogen sensor. The comparative example hydrogen sensor, compared to the hydrogen sensor 1 of Embodiment 1, lacks the second terminal 112, or, in the hydrogen sensor 1 of Embodiment 1, short-circuits the first terminal 111 with the second terminal 112. Figure 4 In the diagram, the horizontal axis represents time. The vertical axis represents the current i3 between the third terminal 113 and the first terminal 111, that is, the current i3 flowing between the first electrode 103 and the second electrode 106. The measurement conditions are as follows: a voltage of 1.2V is normally applied between the third terminal 113 and the first terminal 111, and a voltage of -2.2V is applied every 50ms. Furthermore, from time 0 to 300 seconds, the exposed portion 106e of the second electrode 106 is in contact with a gas containing 0% hydrogen. From time 300 to 600 seconds, the exposed portion 106e of the second electrode 106 is in contact with a gas containing 1.2% hydrogen. From time 600 to 900 seconds, the exposed portion 106e of the second electrode 106 is in contact with a gas containing 0% hydrogen.

[0062] Under these measurement conditions, the hydrogen sensor in the comparative example is as follows: Figure 4 As shown, the current i3 remains constant regardless of the presence or absence of hydrogen. That is, the hydrogen sensor in the comparative example did not respond to a gas containing 1.2% hydrogen and therefore failed to detect hydrogen.

[0063] Figure 5 This is a graph showing the experimental results of hydrogen sensor 1 in Embodiment 1. Figure 5 The horizontal axis represents the relationship between... Figure 4 Same time axis. The vertical axis represents the current i3 between the third terminal 113 and the first terminal 111, that is, the current i3 flowing between the first electrode 103 and the second electrode 106. Measurement conditions and Figure 4 Compared to the previous version, an additional current is applied between the first terminal 111 and the second terminal 112. That is, in Figure 5 In the middle, a current of about 11mA flows between the first terminal 111 and the second terminal 112.

[0064] Under the measurement conditions, the hydrogen sensor 1 of Embodiment 1 exhibits an increased current i3 in the interval from 300 seconds to 600 seconds compared to other intervals. Specifically, in the interval from 300 seconds to 600 seconds, hydrogen atoms dissociate from the gas in contact with the exposed portion 106e of the second electrode 106. These dissociated hydrogen atoms penetrate the metal oxide layer 104, forming impurity energy levels and reducing the resistance of the metal oxide layer 104. Consequently, the current i3 increases in the interval from 300 seconds to 600 seconds. Furthermore, in the interval from 600 seconds to 900 seconds, the current i3 decreases compared to the previous interval. Figure 5 The current between the first terminal 111 and the third terminal 113 increases or decreases in response to the presence or absence of hydrogen. It can be seen that the hydrogen detection performance of the hydrogen sensor 1 is better than that of the third terminal 1. Figure 4 The hydrogen sensor has been improved.

[0065] Figure 6 This is a graph showing the experimental results of hydrogen sensor 1 in Embodiment 1. Figure 6 The horizontal axis represents the relationship between... Figure 4 Same timeline. Vertical axis and... Figure 5 The difference represents the current i1 between the first terminal 111 and the second terminal 112. The measurement conditions are the same as... Figure 5 The same applies. However, when voltages of opposite polarities, such as +0.1V and -0.1V, are applied between the first terminal 111 and the second terminal 112, a current of approximately 11mA is passed. Furthermore, the value of the current is determined by the resistance value of the second electrode 106.

[0066] Under these measurement conditions, the current i1 of the hydrogen sensor 1 in Embodiment 1 increases in the interval from 300 seconds to 600 seconds compared to other intervals. Furthermore, in the interval from 600 seconds to 900 seconds, the current i1 decreases compared to the previous interval. According to... Figure 6 The current between the first terminal 111 and the second terminal 112 increases or decreases in response to the presence or absence of hydrogen.

[0067] If comparison Figure 4 , Figure 5 as well as Figure 6 It can be seen that by energizing the first terminal 111 and the second terminal 112, the hydrogen detection capability is improved. Furthermore, by exposing the portion 106e to contact the hydrogen, not only is the resistance between the first terminal 111 and the third terminal 113 reduced, but the resistance between the first terminal 111 and the second terminal 112 is also reduced. In other words, two types of hydrogen detection are possible: hydrogen detection based on the resistance change between the first terminal 111 and the second terminal 112, and hydrogen detection based on the resistance change between the first terminal 111 and the third terminal 113.

[0068] As described above, the hydrogen sensor 1 of Embodiment 1 includes: a planar first electrode 103; a planar second electrode 106 formed opposite to the first electrode 103 and having an exposed portion 106e; a metal oxide layer 104 sandwiched between the two opposing surfaces of the first electrode 103 and the second electrode 106, and whose resistance changes according to hydrogen; and a first terminal 111 and a second terminal 112, which serve as two terminals connected to the second electrode 106.

[0069] Accordingly, it has two terminals for energizing the second electrode 106 itself, thus enabling the hydrogen detection performance to be improved by energizing.

[0070] Here, the two terminals, namely the first terminal 111 and the second terminal 112, can also be located in the planar view of the planar second electrode at the position sandwiching the exposed portion 106e.

[0071] Accordingly, current can flow through the exposed portion 106e in contact with the gas, thereby improving the efficiency of hydrogen detection.

[0072] Here, the two terminals 111 and 112 can also be energized by applying a specified voltage to the exposed portion 106e.

[0073] Here, the two terminals can also be subjected to voltages with opposite polarities as a specified voltage.

[0074] Accordingly, the voltage applied to the central portion of the exposed portion 106e can be substantially 0V, and the hydrogen detection performance can be improved efficiently.

[0075] Here, the hydrogen sensor 1 can also change the resistance between the first electrode 103 and the second electrode 106 by having gas molecules containing hydrogen atoms come into contact with the exposed part 106e when the exposed part is energized.

[0076] Accordingly, hydrogen can be detected by the resistance change between the first electrode 103 and the second electrode 106.

[0077] Here, the hydrogen sensor 1 can also change the resistance between the two terminals by having gas molecules containing hydrogen atoms come into contact with the exposed portion 106e when the exposed portion 106e is energized.

[0078] Therefore, hydrogen can be detected by the change in resistance between the two terminals, the first terminal 111 and the second terminal 112.

[0079] Here, it may also include: a first through hole, which is connected to the main surface of the first electrode 103 opposite to the metal oxide layer 104, and overlaps with the exposed portion 106e in the planar view of the planar second electrode 106; and a connecting terminal (i.e., a third terminal 113), which is connected to the first through hole.

[0080] Alternatively, the two terminals can be connected to the second electrode 106 via two second through holes connected to the second electrode 106, with the first through hole located in the central portion of the two second through holes.

[0081] With this configuration, the first terminal 111 and the second terminal 112 are arranged approximately symmetrically around the energized exposed portion 106e, thus forming the main current path between the first electrode 103 and the second electrode 106 in the central portion of the exposed portion 106e. This improves the hydrogen detection performance.

[0082] Alternatively, the metal oxide layer 104 may have a first layer 104a connected to the first electrode and a second layer 104b connected to the first layer 104a and the second electrode, wherein the oxygen deficiency of the second layer is less than that of the first layer 104a.

[0083] Accordingly, the gas sensitivity of the second layer 104b to hydrogen atoms dissociated from the second electrode 106 can be further improved.

[0084] Furthermore, the hydrogen detection method in Embodiment 1 is a hydrogen detection method in a hydrogen sensor. This hydrogen sensor includes: a planar first electrode 103; a planar second electrode 106 formed opposite to the first electrode 103, having an exposed portion 106e; a metal oxide layer 104 sandwiched between the two opposing surfaces of the first electrode 103 and the second electrode 106, whose resistance changes according to hydrogen; and two terminals (i.e., a first terminal 111 and a second terminal 112) connected to the second electrode. In a planar view of the planar second electrode 106, the two terminals are connected to the second electrode 106 at positions sandwiching the exposed portion 106e. In this hydrogen detection method, a voltage is applied between the two terminals, causing current to flow through the exposed portion. The presence of hydrogen atoms is detected by detecting a decrease in the resistance between the first electrode 103 and the second electrode 106, or by detecting a decrease in the resistance between the first terminal 111 and the second terminal 112.

[0085] Accordingly, the hydrogen detection performance can be improved by energizing the two terminals, namely the first terminal 111 and the second terminal 112.

[0086] Furthermore, the hydrogen detection device 2 of Embodiment 1 includes: a planar first electrode 103; a planar second electrode 106 formed opposite to the first electrode 103 and having an exposed portion 106e; a metal oxide layer 104 sandwiched between the two surfaces of the first electrode 103 and the second electrode 106, the resistance of which changes according to hydrogen; two terminals (i.e., the first terminal 111 and the second terminal 112) connected to the second electrode; and a drive circuit 200 that, in a state where current flows through the exposed portion 106e by applying a voltage between the two terminals, detects a gas containing hydrogen atoms by detecting a decrease in the resistance value between the first electrode 103 and the second electrode 106, or by detecting a decrease in the resistance value between the two terminals.

[0087] Accordingly, the hydrogen detection performance can be improved by energizing the two terminals, namely the first terminal 111 and the second terminal 112.

[0088] (Implementation Method 2)

[0089] In Embodiment 2, compared to the hydrogen sensor 1 of Embodiment 1, a configuration example of a hydrogen sensor 1 having a local region called a filament inside the metal oxide layer 104 will be further described. By having a local region, the hydrogen sensor 1 can further improve hydrogen detection performance and further accelerate the response speed of hydrogen detection.

[0090] [2.1 Composition of Hydrogen Sensor 1]

[0091] Figure 7 This is a cross-sectional view showing a configuration example of the hydrogen sensor 1 in Embodiment 2. The hydrogen sensor 1 in this figure is... Figure 1A This differs from the point where a local region 105 was added. Below, to avoid repeating the same points, we will focus on different points in our explanations.

[0092] Local region 105 is a region that is not connected to the first electrode 103 but to the second electrode 106, and has a higher oxygen deficiency compared to the surrounding metal oxide layer 104. Local region 105 refers to a region where current can flow more easily compared to the metal oxide layer 104. That is, local region 105 is a small region containing a wire pole (conductive path) formed by oxygen defects. Furthermore, local region 105 is formed approximately at the center of the exposed portion 106e in the plan view of the second electrode 106. Local region 105, or wire pole, is formed by a process called forming. In the forming process, a pulse, which is called electrical stress, is applied between the second electrode 106 and the first electrode 103. Local region 105 can be formed depending on the size and duration of the pulse.

[0093] In addition, Figure 7The example shown is a two-layer structure consisting of a first layer 104a made of TaOx and a second layer 104b made of Ta2O5 with low oxygen deficiency. However, it can also be a single layer made of either Ta2O5 or TaOx with low oxygen deficiency.

[0094] [2.2 Experimental Data]

[0095] Next, the operation of the hydrogen sensor 1 in Embodiment 2 will be explained using experimental data.

[0096] Figure 8 This is a graph showing experimental data of the hydrogen sensor of the comparative example. The hydrogen sensor of this comparative example is configured to not have the second terminal 112 compared to the hydrogen sensor 1 of Embodiment 2. Furthermore, it is configured to short-circuit the first terminal 111 and the second terminal 112 in the hydrogen sensor 1 of Embodiment 2. Figure 8 The determination conditions and Figure 4 same.

[0097] In Figure 4 Under the same measurement conditions, the hydrogen sensor in the comparative example, such as Figure 8 The response to hydrogen is shown, but the current i3 increases slowly over time.

[0098] Figure 9 This is a graph showing the experimental results of hydrogen sensor 1 in Embodiment 2. Figure 9 The determination conditions and Figure 5 same.

[0099] In the hydrogen sensor 1 of Embodiment 2, as follows Figure 9 As shown, the current i3 increases more sharply in the interval from 300 seconds to 600 seconds compared to other intervals. Specifically, in the interval from 300 seconds to 600 seconds, hydrogen atoms in the gas in contact with the exposed portion 106e of the second electrode 106 dissociate more rapidly. These dissociated hydrogen atoms penetrate the metal oxide layer 104, forming impurity energy levels, thereby reducing the resistance of the metal oxide layer 104. As a result, the current i3 increases sharply in the interval from 300 seconds to 600 seconds. Furthermore, in the interval from 600 seconds to 900 seconds, the current i3 decreases compared to the previous interval. Figure 9 The current between the first terminal 111 and the third terminal 113 increases or decreases in response to the presence or absence of hydrogen. Furthermore, Figure 9 and Figure 5 In comparison, the amount of change is larger.

[0100] As explained above, the hydrogen sensor 1 of Embodiment 2 has a local region inside the metal oxide layer 104 that is in contact with the second electrode 106 and has a higher degree of oxygen deficiency compared to the metal oxide layer 104.

[0101] This can improve hydrogen detection performance and accelerate the response speed of hydrogen detection.

[0102] Furthermore, the hydrogen sensor 1 has a local region inside the metal oxide layer 104 that is connected to the second electrode 106 and where current can flow more easily compared to the metal oxide layer 104.

[0103] This improves hydrogen detection performance and speeds up the response time for hydrogen detection.

[0104] (Implementation Method 3)

[0105] In Embodiment 3, a configuration example will be described where the metal oxide layer 104 of the hydrogen sensor 1 is further composed of three layers compared to Embodiment 1. In this configuration example, hydrogen detection performance can be further improved, and the response speed of hydrogen detection can be further accelerated.

[0106] [3.1 Composition of Hydrogen Sensor 1]

[0107] Figure 10 This is a cross-sectional view showing a configuration example of the hydrogen sensor 1 in Embodiment 3. The hydrogen sensor 1 in this figure is... Figure 1A In contrast, a third layer 104c is added within the metal oxide layer 104. The following explanation will focus on these different points to avoid repeating the same details.

[0108] The third layer 104c is connected to the second layer 104b and the second electrode 106. The oxygen deficiency of the third layer 104c is greater than that of the second layer 104b. For example, compared with the second layer 104b, which is made of Ta2O5, the third layer 104c is made of Ta2O5 or TaOx, which have a higher oxygen deficiency. In addition, the oxygen deficiency of the third layer 104c is smaller than that of the first layer 104a.

[0109] In addition, Figure 10 The example shown is a three-layer metal oxide layer 104 consisting of a first layer 104a made of TaOx, a second layer 104b made of Ta2O5 with low oxygen deficiency, and a third layer 104c made of Ta2O5 with high oxygen deficiency compared to the second layer 104b. However, it can also be a two-layer consisting of Ta2O5 with low oxygen deficiency and Ta2O5 or TaOx with high oxygen deficiency compared to it.

[0110] [3.2 Experimental Data]

[0111] Next, the operation of the hydrogen sensor 1 in Embodiment 3 will be explained using experimental data.

[0112] Figure 11This is a graph showing experimental data of the hydrogen sensor of the comparative example. The hydrogen sensor of this comparative example is configured to not have the second terminal 112 compared to the hydrogen sensor 1 of Embodiment 3. Furthermore, it is configured to short-circuit the first terminal 111 and the second terminal 112 in the hydrogen sensor 1 of Embodiment 3. Figure 11 The determination conditions and Figure 4 same.

[0113] In Figure 4 Under the same measurement conditions, the hydrogen sensor of the comparative example, such as Figure 11 As shown, the current i3 remains constant regardless of the presence or absence of hydrogen. That is, the hydrogen sensor in the comparative example does not respond to a gas containing 1.2% hydrogen and therefore fails to detect hydrogen.

[0114] Figure 12 This is a graph showing the experimental results of hydrogen sensor 1 in embodiment 3. Figure 12 The determination conditions and Figure 5 same.

[0115] In the hydrogen sensor 1 of embodiment 3, such as Figure 12 As shown, the current i3 increases in the interval from 300 seconds to 600 seconds compared to other intervals. Furthermore, in the interval from 600 seconds to 900 seconds, the current i3 decreases compared to the previous interval. According to... Figure 12 The current i3 between the first terminal 111 and the third terminal 113 increases or decreases in response to the presence or absence of hydrogen. Furthermore, Figure 12 and Figure 5 In comparison, hydrogen detection has a faster response time.

[0116] As explained above, the metal oxide layer 104 in Embodiment 3 has a first layer 104a connected to the first electrode, a second layer 104b connected to the first layer 104a, and a third layer 104c connected to the second layer 104b and the second electrode 106. The oxygen deficiency of the third layer 104c is greater than that of the second layer 104b.

[0117] Accordingly, the gas sensitivity to the third layer 104c of hydrogen atoms dissociated from the second electrode 106 can be further improved.

[0118] Furthermore, the anoxic level of the third layer 104c can be lower than that of the first layer 104a.

[0119] in addition, Figure 2 as well as Figure 3 The hydrogen detection device and method shown can of course be implemented in the same way using the hydrogen sensor 1 of embodiments 2 and 3.

[0120] Furthermore, in various embodiments, an example is shown where the second electrode 106 is connected to two terminals, namely the first terminal 111 and the second terminal 112. However, the number of terminals connected to the second electrode 106 is not limited to two, and may be three or more. When the second electrode 106 has three or more terminals, at least one of the three or more terminals may be equivalent to the first terminal 111, and at least one of the three or more terminals may be equivalent to the second terminal 112.

[0121] The above description illustrates one or more embodiments of hydrogen sensors, hydrogen detection methods, and hydrogen detection devices, but this disclosure is not limited to these embodiments. Various modifications conceived by those skilled in the art, and combinations of different components from these embodiments, can be incorporated into these embodiments without departing from the spirit of this disclosure and may be included within the scope of one or more embodiments.

[0122] Industrial availability

[0123] The hydrogen sensor, hydrogen detection method, and hydrogen detection device disclosed herein can be widely used, for example, in the detection of leaks of hydrogen-containing gases.

[0124] Explanation of reference numerals in the attached figures

[0125] 1. Hydrogen sensor

[0126] 102 Insulating film

[0127] 103 First Electrode

[0128] 104 Metal Oxide Layer

[0129] 104a First Layer

[0130] 104b Second Layer

[0131] 104c Third Layer

[0132] 105 Local Area

[0133] 106 Second Electrode

[0134] Openings in 106a, 111a, and 112a

[0135] 106e Exposed portion

[0136] 106s metal layer

[0137] 107a, 107b, 107c, 109a, 109b insulating films

[0138] 108 through hole

[0139] 111 First terminal

[0140] 112 Second Terminal

[0141] 113 Third terminal (connection terminal)

[0142] 200 drive circuit

Claims

1. A hydrogen sensor, comprising: A planar first electrode; A planar second electrode is formed opposite to the first electrode and has an exposed portion; The metal oxide layer is sandwiched between two opposing surfaces of the first electrode and the second electrode, and its resistance changes according to hydrogen. as well as Two terminals are connected to the second electrode. The exposed portion is an opening located on the second electrode.

2. The hydrogen sensor according to claim 1, In the planar view of the second electrode, the two terminals are located at the position sandwiching the exposed portion.

3. The hydrogen sensor according to claim 2, The two terminals are subjected to voltages of opposite polarities as a predetermined voltage.

4. The hydrogen sensor according to claim 2 or 3, When the exposed portion is energized, gas molecules containing hydrogen atoms come into contact with the exposed portion, thereby causing a change in resistance between the first electrode and the second electrode.

5. The hydrogen sensor according to any one of claims 2 or 3, When the exposed portion is energized, gas molecules containing hydrogen atoms come into contact with the exposed portion, thereby causing a change in resistance between the two terminals.

6. The hydrogen sensor according to any one of claims 1 to 3, The metal oxide layer contains a local region that is in contact with the second electrode and has a higher degree of oxygen deficiency compared to the metal oxide layer.

7. The hydrogen sensor according to any one of claims 1 to 3, The metal oxide layer contains a local region that is connected to the second electrode and where current can flow more easily compared to the metal oxide layer.

8. The hydrogen sensor according to any one of claims 1 to 3, comprising: The first through-hole, connected to the side opposite to the metal oxide layer of one of the two faces of the first electrode, overlaps with the exposed portion in the plan view; and Connect the terminal to the first through hole.

9. The hydrogen sensor according to claim 8, The two terminals are connected to the second electrode via two second through holes that are connected to the second electrode. The first through hole is located at the center of the two second through holes in the plan view.

10. The hydrogen sensor according to any one of claims 1 to 3, The metal oxide layer has a first layer in contact with the first electrode and a second layer in contact with both the first layer and the second electrode. The oxygen deficiency in the second layer is less than that in the first layer.

11. The hydrogen sensor according to any one of claims 1 to 3, The metal oxide layer has a first layer in contact with the first electrode, a second layer in contact with the first layer, and a third layer in contact with the second layer and the second electrode. The oxygen deficiency in the third layer is greater than that in the second layer.

12. A hydrogen detection method, which is a hydrogen detection method in a hydrogen sensor, wherein the hydrogen sensor comprises: A planar first electrode; a planar second electrode, formed opposite to the first electrode, having an exposed portion; a metal oxide layer sandwiched between the two opposing surfaces of the first and second electrodes, its resistance varying with hydrogen; and two terminals connected to the second electrode, wherein, in a planar view of the planar second electrode, the two terminals are connected to the second electrode at positions sandwiching the exposed portion, the exposed portion being an opening in the second electrode. In the hydrogen detection method, Current flows through the exposed portion by applying a voltage between the two terminals. The gas containing hydrogen atoms is detected by detecting a decrease in the resistance between the first electrode and the second electrode, or by detecting a decrease in the resistance between the two terminals.

13. A hydrogen detection device, comprising: A planar first electrode; A planar second electrode is formed opposite to the first electrode and has an exposed portion; The metal oxide layer is sandwiched between two opposing surfaces of the first electrode and the second electrode, and its resistance changes according to hydrogen. Two terminals are connected to the second electrode; as well as The driving circuit, while a current flows through the exposed portion by applying a voltage between the two terminals, detects the presence of hydrogen-containing gas by detecting a decrease in the resistance between the first and second electrodes, or by detecting a decrease in the resistance between the two terminals. The exposed portion is an opening located on the second electrode.

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