Hydrogen sensor, hydrogen detection method and hydrogen detection device

Abstract

A hydrogen sensor (1) comprises: a planar first electrode (103); a planar second electrode (106) which is formed so as to face the first electrode and has an exposed portion (106e); a metal oxide layer (104) which is sandwiched between two faces, i.e., the first electrode (103) and the second electrode (106), and of which the resistance can vary by the action of hydrogen; and two terminals, i.e., a first terminal (111) and a second terminal (112), which are 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 technology]

[0002] Patent Documents 1 and 2 disclose gas sensors that detect gas molecules including hydrogen atoms. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2017 / 037984 [Patent Document 2] JP 2017-22938 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the conventional technology has a problem in that it is inferior in detection performance, particularly for low concentrations of hydrogen.

[0005] Therefore, the present disclosure provides a hydrogen sensor, a hydrogen detection method, and a hydrogen detection device that have improved detection performance for low concentrations of hydrogen. [Means for solving the problem]

[0006] A hydrogen sensor according to one embodiment of the present disclosure comprises a first planar electrode, a second planar electrode formed opposite the first electrode and having an exposed portion, a metal oxide layer sandwiched between the two opposing surfaces of the first electrode and the second electrode, the resistance of which changes with hydrogen, two terminals connected to the second electrode, and a drive circuit that detects a gas containing hydrogen atoms 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 while a voltage is applied between the two terminals to pass a current through the exposed portion.

[0007] Furthermore, a hydrogen detection method according to one embodiment of the present disclosure is a hydrogen detection method in a hydrogen sensor comprising a first planar electrode, a second planar electrode formed opposite the first electrode and having an exposed portion, a metal oxide layer sandwiched between the two opposing surfaces of the first electrode and the second electrode, the resistance of which changes with hydrogen, and two terminals connected to the second electrode, the two terminals being connected to the second electrode at positions that sandwich the exposed portion in a planar view of the second electrode, wherein a voltage is applied between the two terminals to pass a current through the exposed portion, 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.

[0008] Moreover, a hydrogen detection device according to one embodiment of the present disclosure includes a first planar electrode, a second planar electrode formed opposite the first electrode and having an exposed portion, a metal oxide layer sandwiched between the two opposing surfaces of the first electrode and the second electrode, the resistance of which changes with hydrogen, two terminals connected to the second electrode, and a drive circuit that detects a gas containing hydrogen atoms 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 while a voltage is applied between the two terminals to cause a current to flow through the exposed portion. Effect of the Invention

[0009] The hydrogen sensor, hydrogen detection method, and hydrogen detection device disclosed herein can improve the detection performance for low concentrations of hydrogen. [Brief description of the drawings]

[0010] [Figure 1A] FIG. 1A is a cross-sectional view showing an example of the configuration of a hydrogen sensor in accordance with a first embodiment. [Figure 1B] FIG. 1B is a top view showing an example of the configuration of the hydrogen sensor in the first embodiment. [Diagram 2]FIG. 2 is a block diagram showing an example of the configuration of a hydrogen detection device including a hydrogen sensor and a drive circuit that performs the hydrogen detection method in the first embodiment. [Diagram 3] FIG. 3 is a flowchart showing a hydrogen detection method using a hydrogen sensor including a drive circuit according to the first embodiment. [Figure 4] FIG. 4 shows the experimental results of the hydrogen sensor of the comparative example. [Diagram 5] FIG. 5 shows experimental results of the hydrogen sensor according to the first embodiment. [Figure 6] FIG. 6 shows experimental results of the hydrogen sensor according to the first embodiment. [Figure 7] FIG. 7 is a cross-sectional view showing an example of the configuration of the hydrogen sensor according to the second embodiment. [Figure 8] FIG. 8 shows the experimental results of the hydrogen sensor of the comparative example. [Figure 9] FIG. 9 shows the experimental results of the hydrogen sensor according to the second embodiment. [Figure 10] FIG. 10 is a cross-sectional view showing an example of the configuration of the hydrogen sensor according to the third embodiment. [Figure 11] FIG. 11 shows the experimental results of the hydrogen sensor of the comparative example. [Figure 12] FIG. 12 shows the experimental results of the hydrogen sensor according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiment will be specifically described with reference to the drawings.

[0012] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, the arrangement and connection of the components, steps, and the order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0013] (Embodiment 1) [1.1 Configuration of hydrogen sensor 1] Fig. 1A is a cross-sectional view showing a configuration example of a hydrogen sensor 1 according to embodiment 1. Fig. 1B is a top view showing the configuration example of a hydrogen sensor 1 in embodiment 1. Fig. 1A shows a schematic cross section seen in the direction of the arrow along the IA-IA cutting line in Fig. 1B.

[0014] 1A and 1B, the main portion of the hydrogen sensor 1 includes a first electrode 103, a metal oxide layer 104, a second electrode 106, a first terminal 111, a second terminal 112, and a third terminal 113. The main portion of the hydrogen sensor 1 is covered by an insulating film 102, insulating films 107a to 107c, and insulating films 109a and 109b. However, these insulating films have openings 106a, 111a, 112a, and 113a.

[0015] The first electrode 103 is a planar electrode having two surfaces. One of the two surfaces of the first electrode 103 (i.e., the upper surface in FIG. 1A) contacts the metal oxide layer 104, and the other surface (i.e., the lower surface in FIG. 1A) contacts the insulating film 107b and the via 108. In FIG. 1B, the first electrode 103 has a rectangular shape having the same size as the second electrode 106. The first electrode 103 may be made of a material having a lower standard electrode potential than the metal constituting the metal oxide, such as tungsten, nickel, tantalum, titanium, aluminum, tantalum nitride, or titanium nitride. The higher the standard electrode potential, the less likely it is to be oxidized. The first electrode 103 in FIG. 1A is made of, for example, tantalum nitride (TaN) or titanium nitride (TiN) or a laminate thereof.

[0016] The metal oxide layer 104 is sandwiched between two opposing surfaces of the first electrode 103 and the second electrode 106, and is composed of a metal oxide as a resistive film having gas sensitivity, and has a resistance value that changes reversibly depending on the presence or absence of a hydrogen-containing gas in the gas with which the second electrode 106 is in contact. The metal oxide layer 104 may have a property that its resistance changes depending on hydrogen. The metal oxide layer 104 is composed of an oxygen-deficient metal oxide. The base metal of the metal oxide layer 104 may be at least one 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). Since transition metals can be in a plurality of oxidation states, different resistance states can be realized by oxidation-reduction reactions. Here, the "oxygen deficiency" of a metal oxide refers to the ratio of the oxygen deficiency in the metal oxide to the amount of oxygen in an oxide of a stoichiometric composition composed of the same elements as the metal oxide. Here, the oxygen deficiency is a value obtained by subtracting the amount of oxygen in the metal oxide from the amount of oxygen in the metal oxide of the stoichiometric composition. If there are multiple metal oxides of a stoichiometric composition composed of the same elements as the metal oxide, the oxygen deficiency of the metal oxide is defined based on the one having the highest resistance value among the metal oxides of the stoichiometric composition. A metal oxide of a stoichiometric composition is more stable and has a higher resistance value than metal oxides of other compositions. For example, when the base metal of the metal oxide layer 104 is tantalum (Ta), the oxide of the stoichiometric composition defined above is Ta2O5, and can be expressed 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%. Moreover, metal oxides with excess oxygen have a negative oxygen deficiency. In this disclosure, unless otherwise specified, the oxygen deficiency can be a positive value, 0, or a negative value. Oxides with a small oxygen deficiency are closer to oxides with a stoichiometric composition and therefore have a high resistance, while oxides with a large oxygen deficiency are closer to the metals that make up the oxide and therefore have a low resistance.

[0017] The metal oxide layer 104 shown in FIG. 1A has a first layer 104a in contact with the first electrode 103, a second layer 104b in contact with the first layer 104a and the second electrode 106, and an insulating isolation layer 104i. The second layer 104b has a smaller degree of oxygen deficiency than the first layer 104a. For example, the first layer 104a is TaOX. The second layer 104b is Ta2O5, which has a smaller degree of oxygen deficiency than the first layer 104a. The metal oxide layer 104 also has an insulating isolation layer 104i on the outer periphery of the first electrode 103 in a plan view.

[0018] Here, a planar view refers to viewing the hydrogen sensor 1 of the present invention from a viewpoint in the stacking direction of Figure 1A, in other words, from a viewpoint in the normal direction of any of the surfaces of the planar first electrode 103, the planar second electrode 106, etc., for example, viewing the top surface of the hydrogen sensor 1 shown in Figure 1B.

[0019] The resistance state of the metal oxide layer 104 decreases in response to the hydrogen-containing gas in contact with the second electrode 106. More specifically, when the hydrogen-containing gas is present in the gas to be detected, hydrogen atoms are dissociated from the hydrogen-containing gas at the second electrode 106. The dissociated hydrogen atoms penetrate the metal oxide layer 104 and form an impurity level. In particular, they are concentrated near the interface with the second electrode, making the second layer 104b appear thinner. As a result, the resistance value of the metal oxide layer 104 decreases.

[0020] The second electrode 106 is a planar electrode having hydrogen dissociation properties and has two surfaces. One of the two surfaces of the second electrode 106 (i.e., the lower surface in FIG. 1A) is in contact with the metal oxide layer 104, and the other surface (i.e., the upper surface in FIG. 1A) is in contact with the metal layer 106s and the outside air. The second electrode 106 has an exposed portion 106e exposed to the outside air within the opening 106a. The second electrode 106 is made of a material having a catalytic effect of dissociating hydrogen atoms from gas molecules having hydrogen atoms, such as platinum (Pt), iridium (Ir), palladium (Pd), nickel (Ni), or an alloy containing at least one of these. The second electrode 106 in FIG. 1A is assumed to be platinum (Pt). Two terminals, namely, a first terminal 111 and a second terminal 112, are connected to the second electrode 106.

[0021] The first terminal 111 is connected to the second electrode 106 through a via 108 .

[0022] The second terminal 112 is connected to the second electrode 106 through the via 108. The first terminal 111 and the second terminal 112 are connected to an external drive circuit that drives the hydrogen sensor 1 through the openings 111a, 112a.

[0023] As shown in FIG. 1B, the first terminal 111 and the second terminal 112 are disposed at positions sandwiching the exposed portion 106e in a plan view of the second electrode 106. With this arrangement, when a predetermined voltage is applied between the first terminal 111 and the second terminal 112, the exposed portion 106e of the second electrode 106 is electrified, that is, a current flows through the exposed portion 106e. It is considered that the electrification of the exposed portion 106e of the second electrode 106 activates the hydrogen dissociation action of the exposed portion 106e. Note that the predetermined voltages may be voltages having opposite polarities.

[0024] When gas molecules containing hydrogen atoms come into contact with exposed portion 106e while current is flowing through exposed portion 106e, hydrogen sensor 1 changes the resistance between first terminal 111 and second terminal 112. The change in resistance is detected by the driving circuit described above, thereby detecting the gas molecules containing hydrogen atoms.

[0025] The third terminal 113 is connected to the first electrode 103 through the opening 113a, the via 108, the wiring 114, and the via 108. The third terminal 113 is connected to an external drive circuit that drives the hydrogen sensor 1 through the opening 113a. The hydrogen sensor 1 changes the resistance between the first electrode 103 and the second electrode 106 when gas molecules containing hydrogen atoms come into contact with the exposed portion 106e while the exposed portion 106e is energized. In other words, the hydrogen sensor 1 changes the resistance value between the first terminal 111 or the second terminal 112 and the third terminal 113 when gas molecules containing hydrogen atoms come into contact with the exposed portion 106e while the exposed portion 106e is energized. The drive circuit detects this change in resistance value, thereby detecting gas molecules containing hydrogen atoms.

[0026] The insulating film 102, insulating films 107a to 107c, and insulating films 109a and 109b, which cover the main portion of the hydrogen sensor 1, are made of a silicon oxide film, a silicon nitride film, or the like.

[0027] A metal layer 106s is formed on the upper surface of the second electrode 106 except for the opening 106a. The metal layer 106s is made of, for example, TiAlN and is formed as an etching stopper for forming the via 108, but is not essential.

[0028] Furthermore, the laminate of the first electrode 103, the metal oxide layer 104, and the second electrode 106 has a configuration that can be used as a memory element of a resistance change memory (ReRAM). In a resistance change memory, two states, a high resistance state and a low resistance state, among the states that the metal oxide layer 104 can take, are used as a digital memory element. In the hydrogen sensor 1 of the present disclosure, the high resistance state among the states that the metal oxide layer 104 can take is used.

[0029] In FIG. 1A, the metal oxide layer 104 has a two-layer structure including a first layer 104a made of TaOx and a second layer 104b made of Ta2O5 having a small oxygen deficiency. However, the metal oxide layer 104 may have a one-layer structure made of Ta2O5 or TaOx having a small oxygen deficiency.

[0030] [1.2 Hydrogen detection method and hydrogen detection device] Next, a hydrogen detection method and device using the hydrogen sensor 1 will be described.

[0031] Fig. 2 is a block diagram showing an example configuration of hydrogen detection device 2 including hydrogen sensor 1 and drive circuit 200 which implements the hydrogen detection method in embodiment 1. In Fig. 2, hydrogen detection device 2 comprises drive circuit 200 and hydrogen sensor 1. Drive circuit 200 is connected to hydrogen sensor 1 by at least three wires which are connected to first terminal 111, second terminal 112, and third terminal 113 of hydrogen sensor 1. Drive circuit 200 is composed of, for example, a microcomputer having a CPU, ROM, and RAM. The at least three wires are connected to ports of the microcomputer.

[0032] 3 is a flowchart showing a hydrogen detection method using the hydrogen sensor 1 with the drive circuit 200. In the figure, first, the drive circuit 200 starts the passage of electricity 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, voltages +V1 and -V1 of opposite polarities are applied to the first terminal 111 and the second terminal 112. As a result, the current passed through the exposed portion 106e of the second electrode 106 may be, for example, several mA to several tens of mA.

[0033] Next, the drive circuit 200 measures the resistance value Rh between the first terminal 111 and the second terminal 112 (S2), and further 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 smaller than a threshold value th1, and also determines whether the measured resistance value Rv is smaller than a threshold value th2 (S4). If it is determined that at least one of the resistance values ​​Rh and Rv is small as a result of the determination, it determines that "hydrogen is present" (S5), and if not, it determines that "hydrogen is not present" (S6).

[0034] The driving circuit 200 may repeat steps S2 to S6 at a constant cycle of, for example, several hundred milliseconds to several seconds.

[0035] Although FIG. 3 shows an example in which electricity is constantly applied between first terminal 111 and second terminal 112, electricity may be applied only during the processing of steps S2 and S3.

[0036] Also, in step S5, it may be determined that "hydrogen is present" when it is determined that both the resistance value Rh and the resistance value Rv are smaller than their respective threshold values.

[0037] Moreover, one of steps S2 and S3 may be omitted, and only one of the resistance value Rh and the resistance value Rv may be used for the determination.

[0038] [1.3 Experimental data] Next, the operation of the hydrogen sensor 1 according to the first embodiment will be described using experimental data.

[0039] FIG. 4 is a diagram showing experimental data of a hydrogen sensor of a comparative example. The hydrogen sensor of the comparative example is configured without the second terminal 112, or configured with the first terminal 111 and the second terminal 112 shorted in the hydrogen sensor 1 of the first embodiment. In FIG. 4, the horizontal axis indicates time. The vertical axis indicates 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 that a voltage of 1.2 V is normally applied between the third terminal 113 and the first terminal 111, and a voltage of −2.2 V is applied for 50 ms every second. In addition, from 0 seconds to 300 seconds, the exposed portion 106e of the second electrode 106 is in contact with a gas containing 0% hydrogen. From time 300 seconds to time 600 seconds, a gas containing 1.2% hydrogen is in contact with exposed portion 106e of second electrode 106. From time 600 seconds to time 900 seconds, a gas containing 0% hydrogen is in contact with exposed portion 106e of second electrode 106.

[0040] Under these measurement conditions, the current i3 of the comparative hydrogen sensor was constant regardless of the presence or absence of hydrogen, as shown in Figure 4. In other words, the comparative hydrogen sensor did not react to gas containing 1.2% hydrogen, and was unable to detect hydrogen.

[0041] 5 is a diagram showing the experimental results of the hydrogen sensor 1 in the first embodiment. The horizontal axis of FIG. 5 indicates the same time axis as FIG. 4. The vertical axis indicates 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. Compared to FIG. 4, the measurement conditions are further modified such that a current is passed between the first terminal 111 and the second terminal 112. That is, in FIG. 5, a current of about 11 mA is passed between the first terminal 111 and the second terminal 112.

[0042] Under these measurement conditions, the hydrogen sensor 1 of the first embodiment has a higher current i3 in the section from 300 seconds to 600 seconds than in other sections. That is, in the section from 300 seconds to 600 seconds, hydrogen atoms are dissociated from the gas that comes into contact with the exposed portion 106e of the second electrode 106, and the dissociated hydrogen atoms penetrate into the metal oxide layer 104, forming an impurity level, and the resistance value of the metal oxide layer 104 decreases. As a result, the current i3 increases in the section from 300 seconds to 600 seconds. Furthermore, in the section from 600 seconds to 900 seconds, the current i3 in the previous section decreases. According to FIG. 5, the current between the first terminal 111 and the third terminal 113 increases and decreases in response to the presence or absence of hydrogen. It can be seen that the hydrogen sensor 1 has improved hydrogen detection performance compared to the hydrogen sensor of FIG. 4.

[0043] FIG. 6 is a diagram showing the experimental results of the hydrogen sensor 1 in the first embodiment. The horizontal axis of FIG. 6 indicates the same time axis as FIG. 4. Unlike FIG. 5, the vertical axis indicates the current i1 between the first terminal 111 and the second terminal 112. The measurement conditions are the same as those of FIG. 5. However, it is assumed that voltages of opposite polarity, for example, +0.1 V and −0.1 V, are applied to the first terminal 111 and the second terminal 112, and a current of about 11 mA is passed through them. The value of the passing current is determined by the resistance value of the second electrode 106.

[0044] Under these measurement conditions, in the hydrogen sensor 1 of embodiment 1, the current i1 is greater in the section from 300 seconds to 600 seconds than in other sections. Furthermore, in the section from 600 seconds to 900 seconds, the current i1 is less than in the immediately preceding section. According to Fig. 6, the current between first terminal 111 and second terminal 112 increases and decreases in response to the presence or absence of hydrogen.

[0045] 4, 5 and 6, it can be seen that hydrogen detection capability is improved by passing a current between the first terminal 111 and the second terminal 112. Furthermore, when hydrogen comes into contact with the exposed portion 106e, the resistance between the first terminal 111 and the third terminal 113 decreases, and the resistance between the first terminal 111 and the second terminal 112 also decreases. In other words, two types of hydrogen detection are possible. That is, hydrogen detection is based on a change in resistance between the first terminal 111 and the second terminal 112, and hydrogen detection is based on a change in resistance between the first terminal 111 and the third terminal 113.

[0046] As described above, the hydrogen sensor 1 of embodiment 1 comprises a planar first electrode 103, a planar second electrode 106 formed opposite 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 due to hydrogen, and a first terminal 111 and a second terminal 112 as two terminals connected to the second electrode 106.

[0047] According to this, since the second electrode 106 itself is provided with two terminals for passing current therethrough, the hydrogen detection performance can be improved by passing current therethrough.

[0048] Here, the two terminals, that is, the first terminal 111 and the second terminal 112, may be located at positions sandwiching the exposed portion 106e in a plan view of the planar second electrode.

[0049] This allows current to flow through the exposed portion 106e that is in contact with the gas, thereby efficiently improving the hydrogen detection performance.

[0050] Here, the two terminals 111 and 112 may apply a predetermined voltage to conduct electricity through the exposed portion 106e.

[0051] Here, voltages having opposite polarities to each other may be applied to the two terminals as the predetermined voltages.

[0052] This allows the voltage applied to the central portion of the exposed portion 106e to be substantially 0 V, thereby efficiently improving the hydrogen detection performance.

[0053] Here, in the hydrogen sensor 1, the resistance between the first electrode 103 and the second electrode 106 may change when gas molecules containing hydrogen atoms come into contact with the exposed portion 106e while a current is passed through the exposed portion.

[0054] This makes it possible to detect hydrogen as a change in resistance between the first electrode 103 and the second electrode 106.

[0055] Here, in the hydrogen sensor 1, the resistance between the two terminals may change when gas molecules containing hydrogen atoms come into contact with exposed portion 106e while exposed portion 106e is energized.

[0056] According to this, hydrogen can be detected as a change in resistance between the two terminals, the first terminal 111 and the second terminal 112.

[0057] Here, the first electrode 103 may be provided with a first via that is connected to the principal surface of the first electrode 103 opposite the metal oxide layer 104 and overlaps with the exposed portion 106e in a planar view of the planar second electrode 106, and a connection terminal (i.e., third terminal 113) that is connected to the first via.

[0058] Here, the two terminals are connected to the second electrode 106 through two second vias connected to the second electrode 106, and the first via may be located in the center portion of the two second vias.

[0059] According to this configuration, the first terminal 111 and the second terminal 112 are disposed approximately symmetrically around the exposed portion 106e to which electricity is applied, so that the main current path between the first electrode 103 and the second electrode 106 can be formed in the central portion of the exposed portion 106e, thereby improving the hydrogen detection performance.

[0060] Here, the metal oxide layer 104 has a first layer 104a in contact with the first electrode and a second layer 104b in contact with the first layer 104a and the second electrode, and the degree of oxygen deficiency of the second layer may be smaller than that of the first layer 104a.

[0061] This makes it possible to further increase the gas sensitivity of the second layer 104b to hydrogen atoms dissociated in the second electrode .

[0062] Furthermore, the hydrogen detection method according to embodiment 1 is a hydrogen detection method for a hydrogen sensor comprising a planar first electrode 103, a planar second electrode 106 formed opposite 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 due to hydrogen, and two terminals (i.e., the first terminal 111 and the second terminal 112) connected to the second electrode, the two terminals being connected to the second electrode 106 at positions sandwiching the exposed portion 106e in a planar view of the planar second electrode 106, and a current is applied between the two terminals to pass through the exposed portion, and a decrease in resistance between the first electrode 103 and the second electrode 106 is detected, or a decrease in resistance between the first terminal 111 and the second terminal 112 is detected to detect a gas containing hydrogen atoms.

[0063] According to this, by passing a current between the two terminals, that is, the first terminal 111 and the second terminal 112, the hydrogen detection performance can be improved.

[0064] Moreover, the hydrogen detection device 2 of embodiment 1 comprises a planar first electrode 103, a planar second electrode 106 formed opposite 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, and whose resistance changes due 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 detects a gas containing hydrogen atoms by detecting a decrease in resistance between the first electrode 103 and the second electrode 106 or by detecting a decrease in resistance between the two terminals when a voltage is applied between the two terminals to pass a current through the exposed portion 106e.

[0065] According to this, by passing a current between the two terminals, that is, the first terminal 111 and the second terminal 112, the hydrogen detection performance can be improved.

[0066] (Embodiment 2) In the second embodiment, a configuration example of the hydrogen sensor 1 of the first embodiment will be described, which further has a local region called a filament inside the metal oxide layer 104. By providing the local region, the hydrogen sensor 1 can further improve the hydrogen detection performance and increase the reaction speed of hydrogen detection.

[0067] [2.1 Configuration of hydrogen sensor 1] Fig. 7 is a cross-sectional view showing an example of the configuration of hydrogen sensor 1 in embodiment 2. The hydrogen sensor 1 in this figure differs from Fig. 1A in that a local region 105 is added. Below, the following description will focus on the differences, avoiding duplicate explanations of the same points.

[0068] The local region 105 is a region that is not in contact with the first electrode 103 but in contact with the second electrode 106, and has a greater degree of oxygen deficiency than the surrounding metal oxide layer 104. The local region 105 is a region through which a current flows more easily than the metal oxide layer 104. In other words, the local region 105 is a minute region that includes a filament (conductive path) composed of oxygen defects. The local region 105 is formed in the approximate center of the exposed portion 106e in a plan view of the second electrode 106. The local region 105 or filament is formed by a process called forming. In the forming process, a pulse that becomes an electrical stress is applied between the second electrode 106 and the first electrode 103. The local region 105 can be formed depending on the magnitude and time of the pulse.

[0069] In addition, in FIG. 7, an example of a two-layer structure of the metal oxide layer 104 is shown, which is composed of the first layer 104a made of TaOx and the second layer 104b made of Ta2O5 having a small oxygen deficiency, but it may be a one-layer structure made of Ta2O5 or TaOx having a small oxygen deficiency.

[0070] [2.2 Experimental data] Next, the operation of the hydrogen sensor 1 according to the second embodiment will be described using experimental data.

[0071] 8 is a diagram showing experimental data for a hydrogen sensor of a comparative example. Compared to hydrogen sensor 1 of embodiment 2, this hydrogen sensor of the comparative example does not include second terminal 112, or has a configuration in which first terminal 111 and second terminal 112 are short-circuited in hydrogen sensor 1 of embodiment 2. The measurement conditions for FIG. 8 are the same as those for FIG. 4.

[0072] Under the same measurement conditions as in FIG. 4, the hydrogen sensor of the comparative example reacted to hydrogen, but the increase in current i3 over time was gradual, as shown in FIG.

[0073] 9 is a diagram showing the experimental results of the hydrogen sensor 1 in the embodiment 2. The measurement conditions in FIG. 9 are the same as those in FIG.

[0074] In the hydrogen sensor 1 of the second embodiment, as shown in FIG. 9, the current i3 increases more rapidly in the section from 300 seconds to 600 seconds than in other sections, and the increase over time is steeper. That is, in the section from 300 seconds to 600 seconds, hydrogen atoms are dissociated from the gas that comes into contact with the exposed portion 106e of the second electrode 106 more quickly, and the dissociated hydrogen atoms penetrate into the metal oxide layer 104 and form an impurity level, thereby reducing the resistance value of the metal oxide layer 104. As a result, the current i3 increases steeply in the section from 300 seconds to 600 seconds. Furthermore, in the section from 600 seconds to 900 seconds, the current i3 in the previous section decreases. According to FIG. 9, the current between the first terminal 111 and the third terminal 113 increases and decreases in response to the presence or absence of hydrogen. Also, the amount of change in FIG. 9 is larger than that in FIG. 5.

[0075] As described above, the hydrogen sensor 1 according to the second embodiment has a local region inside the metal oxide layer 104 that contacts the second electrode 106 and has a greater degree of oxygen deficiency than the metal oxide layer 104 .

[0076] This makes it possible to improve the hydrogen detection performance and, in addition, to increase the response speed of hydrogen detection.

[0077] Furthermore, the hydrogen sensor 1 has a local region inside the metal oxide layer 104 that is in contact with the second electrode 106 and through which a current flows more easily than in the metal oxide layer 104 .

[0078] This also makes it possible to improve the hydrogen detection performance and, in addition, to increase the response speed of hydrogen detection.

[0079] (Embodiment 3) In the third embodiment, a configuration example in which the metal oxide layer 104 has a three-layer structure will be described in addition to the hydrogen sensor 1 of the first embodiment. In this configuration example, the hydrogen detection performance can be further improved, and the reaction speed of hydrogen detection can be made faster.

[0080] [3.1 Configuration of hydrogen sensor 1] Fig. 10 is a cross-sectional view showing an example of the configuration of hydrogen sensor 1 in embodiment 3. The hydrogen sensor 1 in this figure differs from Fig. 1A in that a third layer 104c is added within metal oxide layer 104. Below, the following description will focus on the differences, avoiding redundant explanations of the same points.

[0081] The third layer 104c is in contact with the second layer 104b and the second electrode 106. The third layer 104c has a higher oxygen deficiency than the second layer 104b. For example, the third layer 104c is made of Ta2O5 or TaOx, which has a higher oxygen deficiency than the second layer 104b, which is made of Ta2O5. The third layer 104c has a lower oxygen deficiency than the first layer 104a.

[0082] In addition, in FIG. 10, an example of a three-layer structure of the metal oxide layer 104 is shown, which is composed of the first layer 104a made of TaOx, the second layer 104b made of Ta2O5 having a smaller degree of oxygen deficiency, and the third layer 104c made of Ta2O5 having a larger degree of oxygen deficiency than the second layer 104b. However, a two-layer structure composed of Ta2O5 having a smaller degree of oxygen deficiency and either Ta2O5 or TaOx having a larger degree of oxygen deficiency than Ta2O5 may also be used.

[0083] [3.2 Experimental data] Next, the operation of the hydrogen sensor 1 according to the third embodiment will be described using experimental data.

[0084] 11 is a diagram showing experimental data for a hydrogen sensor of a comparative example. Compared to hydrogen sensor 1 of embodiment 3, this hydrogen sensor of the comparative example does not include second terminal 112, or has a configuration in which first terminal 111 and second terminal 112 are short-circuited in hydrogen sensor 1 of embodiment 3. The measurement conditions for FIG. 11 are the same as those for FIG. 4.

[0085] Under the same measurement conditions as in Figure 4, the hydrogen sensor of the comparative example had a constant current i3 regardless of the presence or absence of hydrogen, as shown in Figure 11. In other words, the hydrogen sensor of the comparative example did not react to gas containing 1.2% hydrogen, and was unable to detect hydrogen.

[0086] 12 is a diagram showing the experimental results of the hydrogen sensor 1 in the embodiment 3. The measurement conditions in FIG. 12 are the same as those in FIG.

[0087] In the hydrogen sensor 1 of embodiment 3, as shown in Fig. 12, the current i3 is higher in the section from 300 seconds to 600 seconds than in other sections. Furthermore, in the section from 600 seconds to 900 seconds, the current i3 in the section immediately preceding it is lower. According to Fig. 12, the current i3 between the first terminal 111 and the third terminal 113 increases and decreases in response to the presence or absence of hydrogen. Furthermore, Fig. 12 shows a faster response speed for hydrogen detection than Fig. 5.

[0088] As described above, the metal oxide layer 104 according to the third embodiment has a first layer 104a in contact with the first electrode, a second layer 104b in contact with the first layer 104a, and a third layer 104c in contact with the second layer 104b and the second electrode 106, and the degree of oxygen deficiency in the third layer 104c is greater than that in the second layer 104b.

[0089] This makes it possible to further increase the gas sensitivity of the third layer 104c to hydrogen atoms dissociated in the second electrode .

[0090] Furthermore, the degree of oxygen deficiency in the third layer 104c may be smaller than that in the first layer 104a.

[0091] It goes without saying that the hydrogen detection device and hydrogen detection method shown in FIGS. 2 and 3 can be similarly implemented using the hydrogen sensors 1 of the second and third embodiments.

[0092] In each embodiment, an example has been shown in which second electrode 106 is connected to two terminals, i.e., first terminal 111 and second terminal 112, but the number of terminals connected to second electrode 106 is not limited to two and may be three or more. When second electrode 106 has three or more terminals, at least one of the three or more terminals may be equivalent to first terminal 111, and at least one of the three or more terminals may be equivalent to second terminal 112.

[0093] The hydrogen sensor, hydrogen detection method, and hydrogen detection device according to one or more aspects have been described above based on the embodiments, but the present disclosure is not limited to these embodiments. As long as they do not deviate from the spirit of the present disclosure, various modifications conceivable by those skilled in the art to the present embodiments and configurations constructed by combining components in different embodiments may also be included within the scope of one or more aspects. [Industrial Applicability]

[0094] The hydrogen sensor, hydrogen detection method, and hydrogen detection device according to the present disclosure can be widely used, for example, to detect leakage of hydrogen-containing gas. [Explanation of symbols]

[0095] 1 Hydrogen sensor 102 Insulating film 103 1st electrode 104 Metal oxide layer 104a First Layer 104b Second layer 104c Third Layer 105 Local Area 106 2nd electrode 106a, 111a, 112a opening 106e Exposed part 106s metal layer 107a, 107b, 107c, 109a, 109b Insulating film 108 Via 111 1st terminal 112 2nd terminal 113 3rd terminal (connection terminal) 200 Drive circuit

Claims

1. A planar first electrode; a planar second electrode formed opposite the first electrode and having an exposed portion; a metal oxide layer sandwiched between two opposing surfaces of the first electrode and the second electrode, the resistance of which changes depending on hydrogen; and two terminals connected to the second electrode. Hydrogen sensor.

2. The two terminals are located at positions sandwiching the exposed portion in a plan view of the planar second electrode. The hydrogen sensor according to claim 1 .

3. The two terminals are applied with voltages having opposite polarities as predetermined voltages. The hydrogen sensor according to claim 2 .

4. When gas molecules including hydrogen atoms come into contact with the exposed portion while a current is being applied to the exposed portion, the resistance between the first electrode and the second electrode changes.

4. The hydrogen sensor according to claim 2 or 3.

5. When gas molecules containing hydrogen atoms come into contact with the exposed portion while the exposed portion is conducting, the resistance between the two terminals changes. The hydrogen sensor according to any one of claims 2 to 4.

6. The metal oxide layer includes a local region in contact with the second electrode and having a greater degree of oxygen deficiency than the metal oxide layer. The hydrogen sensor according to any one of claims 1 to 5.

7. a local region in the metal oxide layer that is in contact with the second electrode and through which a current flows more easily than in the metal oxide layer; The hydrogen sensor according to any one of claims 1 to 5.

8. a first via connected to one of the two surfaces of the first electrode opposite to the metal oxide layer and overlapping the exposed portion in a plan view; a connection terminal connected to the first via. The hydrogen sensor according to any one of claims 1 to 7.

9. the two terminals are connected to the second electrode through two second vias connected to the second electrode; The first via is located at a center between two of the second vias in the plan view. The hydrogen sensor according to claim 8.

10. the metal oxide layer has a first layer in contact with the first electrode and a second layer in contact with the first layer and the second electrode; The second layer has a smaller oxygen deficiency than the first layer. The hydrogen sensor according to any one of claims 1 to 9.

11. 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 third layer has a greater degree of oxygen deficiency than the second layer. The hydrogen sensor according to any one of claims 1 to 10.

12. A method for detecting hydrogen in a hydrogen sensor comprising: a first planar electrode; a second planar electrode formed opposite the first electrode and having an exposed portion; a metal oxide layer sandwiched between two opposing surfaces of the first electrode and the second electrode, the metal oxide layer having a resistance that changes due to hydrogen; and two terminals connected to the second electrode, the two terminals being connected to the second electrode at positions that sandwich the exposed portion when viewed from above, the method comprising: Applying a voltage between the two terminals causes a current to flow through the exposed portion; 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. Hydrogen detection methods.

13. A planar first electrode; a planar second electrode formed opposite the first electrode and having an exposed portion; a metal oxide layer sandwiched between two opposing surfaces of the first electrode and the second electrode, the resistance of which changes depending on hydrogen; Two terminals connected to the second electrode; and a drive circuit that detects a gas containing hydrogen atoms 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 while a current is flowing through the exposed portion by applying a voltage between the two terminals. Hydrogen detector.

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