Hydrogen detection device and hydrogen detection method

Abstract

A hydrogen detection device (30) is provided with a hydrogen sensor element (100), a first reference element (100a), and a second reference element (100b) that are formed above one semiconductor substrate (102) and that are connected in series. Each of the hydrogen sensor element (100), the first reference element (100a), and the second reference element (100b) includes a layered body having an identical structure. The hydrogen sensor element (100) includes an opening (110) that exposes a secondary surface of the second electrode (106) facing a primary surface thereof to the outside without the secondary surface being covered by an insulating film (107c) or the like. The first reference element (100a) and the second reference element (100b) do not have an opening that exposes the secondary surface of the second electrode (106) facing the primary surface thereof to the outside. The first reference element (100a) and the second reference element (100b) have different lengths in the direction in which current flows.

Description

Hydrogen detection device and hydrogen detection method

[0001] The present disclosure relates to a hydrogen detection device and a hydrogen detection method, and more particularly to a hydrogen detection device having a sensor chip composed of a resistance element provided on a single semiconductor substrate.

[0002] 2. Description of the Related Art Conventionally, a hydrogen detection device has been proposed that includes a sensor chip that is made up of a resistance element provided on a single semiconductor substrate (see, for example, Patent Document 1).

[0003] JP 2019-152451 A

[0004] However, the sensor chip of Patent Document 1 has a problem in that the area of ​​the sensor chip formed on the semiconductor substrate is large because a bridge circuit is formed using four resistance elements.

[0005] Therefore, an object of the present disclosure is to provide a hydrogen detection device and a hydrogen detection method that have a sensor chip that can be realized in a smaller area than conventional ones and that can detect hydrogen with high sensitivity.

[0006] In order to achieve the above object, a hydrogen detection device according to one embodiment of the present disclosure is a device for detecting hydrogen, the device comprising a first resistor element, a second resistor element, and a third resistor element formed on a single semiconductor substrate and connected in series, the first resistor element, the second resistor element, and the third resistor element each having a first electrode and a second electrode arranged with their main surfaces facing each other, a metal oxide layer arranged in contact with the main surface of the first electrode and the main surface of the second electrode, and an insulating film covering the first electrode, the second electrode, and the metal oxide layer, the first resistor element having an opening that exposes its other surface facing the main surface of the second electrode to the outside without being covered by the insulating film, the second resistor element and the third resistor element each not having an opening that exposes its other surface facing the main surface of the second electrode to the outside, and the second resistor element and the third resistor element each having a different length in the direction of current flow.

[0007] In order to achieve the above-mentioned object, a hydrogen detection method according to one embodiment of the present disclosure is a method for detecting hydrogen, and includes the steps of: preparing the hydrogen detection device; a current application step of applying current to the first resistance element, the second resistance element, and the third resistance element connected in series, which are included in the prepared hydrogen detection device; a voltage measurement step of measuring the voltage across each of the first resistance element, the second resistance element, and the third resistance element when a current is being applied by the current application step; and a signal processing step of generating and outputting a signal indicating a hydrogen concentration using the voltage across each of the first resistance element, the second resistance element, and the third resistance element obtained in the voltage measurement step.

[0008] The present disclosure provides a hydrogen detection device and a hydrogen detection method that have a sensor chip that can be realized in a smaller area than conventional devices and that can detect hydrogen with high sensitivity.

[0009] FIG. 1 is a block diagram showing the configuration of a hydrogen detection device according to an embodiment. FIG. 2A is a cross-sectional view showing an example of the configuration of the sensor chip shown in FIG. 1. FIG. 2B is a top view showing the example of the configuration of the sensor chip shown in FIG. 2A. FIG. 3 is a flowchart showing a method for manufacturing the sensor chip shown in FIGS. 2A and 2B. FIG. 4 is a flowchart showing the procedure for hydrogen detection using a hydrogen detection device according to an embodiment (i.e., a hydrogen detection method). FIG. 5 is a diagram showing an example plot of the relationship between the length (horizontal axis) of the internal resistance of the first reference element and the second reference element and the voltage across the first reference element and the second reference element when a current is applied (vertical axis). FIG. 6 is a diagram explaining the results of an experiment to detect hydrogen concentration using a hydrogen detection device according to an embodiment. FIG. 7A is a cross-sectional view showing an example of the configuration of a sensor chip according to a modified embodiment. FIG. 7B is a top view showing the example of the configuration of the sensor chip shown in FIG. 7A. FIG. 8 is a flowchart showing a method for manufacturing the sensor chip shown in FIGS. 7A and 7B.

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that each embodiment described below represents a specific example of the present disclosure. The numerical values, shapes, materials, components, component arrangement and connection configurations, steps, and step order shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, each figure is not necessarily an exact illustration. In each figure, substantially identical configurations are assigned the same reference numerals, and redundant explanations are omitted or simplified. Furthermore, "connection" means electrical connection, and includes not only cases where two circuit elements are directly connected, but also cases where two circuit elements are indirectly connected with another circuit element inserted between them.

[0011] 1 is a block diagram showing the configuration of a hydrogen detection device 30 according to an embodiment. The hydrogen detection device 30 is composed of a sensor chip 10 and a measurement unit 20.

[0012] The sensor chip 10 is formed on a single semiconductor substrate and has a hydrogen sensor element 100 (an example of a first resistor element), a first reference element 100a (an example of a second resistor element), and a second reference element 100b (an example of a third resistor element) connected in series. The sensor chip 10 also has terminals for connection to the outside: terminal A connected to one end of the hydrogen sensor element 100, terminal B connected to the connection point between the other end of the hydrogen sensor element 100 and one end of the first reference element 100a, terminal C connected to the connection point between the other end of the first reference element 100a and one end of the second reference element 100b, and terminal D connected to the other end of the second reference element 100b.

[0013] Here, the hydrogen sensor element 100 has a structure that is exposed to hydrogen and is a variable resistance element that changes its resistance value according to the hydrogen concentration. Meanwhile, the first reference element 100a and the second reference element 100b have different lengths in the direction of current flow, but are both fixed resistance elements for reference use that do not react to hydrogen. More specifically, the first reference element 100a and the second reference element 100b are provided to offset the temperature dependence of the resistance value of the hydrogen sensor element 100 and to remove unnecessary voltages caused by unnecessary resistance components contained in the hydrogen sensor element 100 (i.e., external resistance, which is a parasitic resistance that does not contribute to the reaction with hydrogen). They have basically the same structure as the hydrogen sensor element 100, but are not exposed to hydrogen.

[0014] The hydrogen sensor element 100, the first reference element 100a, and the second reference element 100b only need to be connected in series, and are not limited to the connection order shown in the figure; for example, they may be connected in the order of the first reference element 100a, the hydrogen sensor element 100, and the second reference element 100b.

[0015] The measurement unit 20 is a circuit that uses the sensor chip 10 to detect the hydrogen concentration in the environment in which the sensor chip 10 is placed and outputs a signal indicating the detected hydrogen concentration, and includes a current source 21, a voltmeter 22, and a signal processing unit 23. The current source 21 is a circuit that applies a predetermined constant current between terminals A and D of the sensor chip 10 under instructions from the signal processing unit 23, and is composed of, for example, a transistor. The voltmeter 22 is a circuit that, under instructions from the signal processing unit 23, measures the voltage across the hydrogen sensor element 100 (i.e., the voltage drop between terminals A and B), the voltage across the first reference element 100a (i.e., the voltage drop between terminals B and C), and the voltage across the second reference element 100b (i.e., the voltage drop between terminals C and D) while switching between them, and is composed of, for example, a switch circuit, a voltage amplifier, an A / D converter, etc. The signal processing unit 23 is a circuit that instructs the current source 21 to apply current, reads out three types of measurement voltages from the voltmeter 22, and generates and outputs a signal indicating the hydrogen concentration from the three types of measurement voltages that have been read out, and is composed of, for example, a microprocessor that executes a built-in program.

[0016] The measurement unit 20 may be a circuit formed on the same semiconductor substrate as the sensor chip 10, or may be a circuit, a measuring instrument, a measuring computer device, or the like provided on a separate substrate or device connected to the sensor chip 10. Furthermore, the voltmeter 22 is not limited to a configuration that measures three types of voltages while switching between them, but may be configured as a set of three voltmeters that measure each of the three types of voltages in parallel.

[0017] FIG. 2A is a cross-sectional view showing an example of the configuration of the sensor chip 10 shown in FIG. 1. This view includes a cross-sectional view of the hydrogen sensor element 100, first reference element 100a, and second reference element 100b connected in series. For ease of explanation, the upper part of the cross-sectional view shows schematic wiring indicating the connections to each of terminals A to D. The lower part of the cross-sectional view shows the equivalent circuit of the sensor chip 10 (resistances Rext, Rs, Rf1, Rf2, etc.) and the voltages (Vh, Vf1, Vf2, etc.) generated across each resistor when a current is applied. FIG. 2B is a top view showing an example of the configuration of the sensor chip 10 shown in FIG. 2A. Note that FIG. 2A shows a schematic cross-section taken along the line IIA-IIA in FIG. 2B, viewed in the direction of the arrows.

[0018] 2A is formed on a semiconductor substrate 102 and an insulating film 107a thereon, and includes, as its main components, a first electrode 103 and a second electrode 106 whose principal surfaces face each other, a metal oxide layer 104 that is disposed in contact with the principal surface (i.e., the upper surface) of the first electrode 103 and the principal surface (i.e., the lower surface) of the second electrode 106, and insulating films (insulating films 107a-107c, 109a, and 109b) that cover the first electrode 103, the second electrode 106, and the metal oxide layer 104. In order to expose the hydrogen sensor element 100 to hydrogen, the insulating films 107b, 107c, 109a, and 109b each have an opening 110 at the center of the other surface (i.e., the upper surface) that faces the principal surface of the second electrode 106, which is not covered by the insulating film and is exposed to the outside. In this embodiment, the opening 110 also has the metal layer 106s removed to expose the second electrode 106.

[0019] This hydrogen sensor element 100 has a first terminal TE1 for connection to terminal A, and a second terminal TE2 for connection to terminal B and the first reference element 100a. The second terminal TE2 is shared by the hydrogen sensor element 100 and the first reference element 100a. The first terminal TE1 and the second terminal TE2 are connected to the other surface of the second electrode 106 through a via 108. When a current is applied laterally in FIG. 2A , the hydrogen sensor element 100 changes its resistance value depending on the hydrogen concentration at the opening 110.

[0020] The first reference element 100a located in the center of the sensor chip 10 shown in Fig. 2A and the second reference element 100b located at the right end of the sensor chip 10 shown in Fig. 2A basically have the same structure as the hydrogen sensor element 100. In other words, the first reference element 100a and the second reference element 100b are formed on a semiconductor substrate 102 and an insulating film 107a thereon, and have, as main components, a first electrode 103 and a second electrode 106 arranged with their main surfaces facing each other, a metal oxide layer 104 arranged in contact with the main surface (i.e., the upper surface) of the first electrode 103 and the main surface (i.e., the lower surface) of the second electrode 106, and insulating films (insulating films 107a to 107c, 109a, and 109b) that cover the first electrode 103, the second electrode 106, and the metal oxide layer 104.

[0021] However, unlike the hydrogen sensor element 100, the first reference element 100a and the second reference element 100b do not have the opening 110 that is provided in the hydrogen sensor element 100. As described above, the first reference element 100a and the second reference element 100b are fixed resistance elements that do not depend on the hydrogen concentration, and are provided to offset the temperature dependence of the resistance value of the hydrogen sensor element 100 and to remove external resistance, which is unnecessary parasitic resistance included in the hydrogen sensor element 100.

[0022] The first reference element 100a has a second terminal TE2 for connection to terminal B and the hydrogen sensor element 100, and a third terminal TE3 for connection to terminal C and the second reference element 100b. The third terminal TE3 is shared by the first reference element 100a and the second reference element 100b. The second reference element 100b has a third terminal TE3 for connection to terminal C and the first reference element 100a, and a fourth terminal TE4 for connection to terminal D.

[0023] In this embodiment, the lengths of the hydrogen sensor element 100, first reference element 100a, and second reference element 100b in the direction of current flow (the horizontal direction in Figure 2A) are formed at a ratio of 1:1:2. Also, as shown in the upper part of the cross-sectional view in Figure 2A, the hydrogen sensor element 100 has an opening 110 with a length L1 in the direction of current flow, the first reference element 100a has a structure equivalent to the structure in which the opening 110 with length L1 in the hydrogen sensor element 100 is blocked with an insulating film or the like, and the second reference element 100b has a structure equivalent to the structure in which the opening 110 with length L2 (= 2 x L1) in the hydrogen sensor element 100 is blocked with an insulating film or the like.

[0024] The length ratio of the hydrogen sensor element 100, the first reference element 100a, and the second reference element 100b is not limited to 1:1:2. In order to maintain the accuracy of calculations (calculation of straight lines, calculation of voltage ratios, etc.) in the signal processing unit 23 described below, the length of the first reference element 100a is preferably about the same as that of the hydrogen sensor element 100, but is not necessarily limited to this and may be 0.5 to 2 times the length of the hydrogen sensor element 100. Furthermore, the length of the second reference element 100b is preferably at least twice the length of the first reference element 100a, but is not necessarily limited to this and may be 0.5 times the length of the first reference element 100a.

[0025] Details of the components common to the hydrogen sensor element 100, the first reference element 100a, and the second reference element 100b that make up the sensor chip 10 are as follows.

[0026] The first electrode 103 is a planar electrode having two surfaces. One of the two surfaces (i.e., the upper surface in FIG. 2A ) of the first electrode 103 contacts the metal oxide layer 104, and the other surface (i.e., the lower surface in FIG. 2A ) contacts the insulating film 107a. In FIG. 2B , the first electrode 103 has a rectangular shape with the same size as the second electrode 106. The first electrode 103 may be made of a material with a lower standard electrode potential than the metal constituting the metal oxide, such as tungsten, nickel, tantalum, titanium, aluminum, tantalum nitride, or titanium nitride. A higher standard electrode potential indicates a more resistant to oxidation. The first electrode 103 in FIG. 2A is formed of, for example, a transition metal nitride such as tantalum nitride (TaN) or titanium nitride (TiN), or a laminate thereof.

[0027] The metal oxide layer 104 is sandwiched between the two opposing principal 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 reversibly changes depending on the presence or absence of a hydrogen-containing gas in the gas that contacts the second electrode 106. The metal oxide layer 104 only needs to have the property that its resistance changes with hydrogen. The base metal of the metal oxide layer 104 may be at least one selected from a transition metal such as tantalum (Ta), hafnium (Hf), titanium (Ti), zirconium (Zr), niobium (Nb), tungsten (W), nickel (Ni), iron (Fe), etc., and aluminum (Al).

[0028] 2A includes 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 oxygen deficiency of the second layer 104b is smaller than that of the first layer 104a. For example, the first layer 104a is made of TaO Ｘ The second layer 104b is made of Ta, which has a smaller oxygen deficiency than the first layer 104a. ２ O ５ The metal oxide layer 104 also has an insulating separation layer 104i on the outer periphery of the first electrode 103 in a plan view.

[0029] Here, a planar view refers to a planar view of the semiconductor substrate 102, and refers to viewing the sensor chip 10 according to the present disclosure from a viewpoint in the stacking direction of Figure 2A, in other words, viewing from a viewpoint in the normal direction of either the planar first electrode 103, the planar second electrode 106, etc., for example, viewing the top surface of the sensor chip 10 shown in Figure 2B.

[0030] In the hydrogen sensor element 100, the resistance state of the metal oxide layer 104 decreases in accordance with (the greater the amount of) the hydrogen-containing gas that contacts the second electrode 106 through the opening 110. 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 impurity levels. In particular, they are concentrated near the interface with the second electrode 106, making the apparent thickness of the second layer 104b thinner. As a result, the resistance value of the metal oxide layer 104 decreases. Note that the first reference element 100a and the second reference element 100b do not have openings 110, and therefore do not react with the hydrogen-containing gas.

[0031] The second electrode 106 is a planar electrode with hydrogen dissociation properties and has two surfaces. One of the two surfaces of the second electrode 106 (i.e., the bottom surface in FIG. 2A ) is in contact with the metal oxide layer 104, and the other surface (i.e., the top surface in FIG. 2A ) is in contact with the metal layer 106s (and in the hydrogen sensor element 100, the outside air). In the hydrogen sensor element 100, the second electrode 106 has an exposed portion 106e exposed to the outside air within the opening 110. The second electrode 106 is made of a material that has catalytic properties that dissociate hydrogen atoms from hydrogen-containing gas molecules, such as a noble metal such as platinum (Pt), iridium (Ir), or palladium (Pd), or nickel (Ni), or an alloy containing at least one of these. The second electrode 106 in FIG. 2A is made of platinum (Pt). Four terminals, namely, a first terminal TE1, a second terminal TE2, a third terminal TE3, and a fourth terminal TE4, are connected to the second electrode 106 through vias 108. The first terminal TE1, the second terminal TE2, the third terminal TE3, and the fourth terminal TE4 are connected to terminals A, B, C, and D of the sensor chip 10 by wiring through openings TE1a, TE2a, TE3a, and TE4a, respectively.

[0032] As shown in FIG. 2B , the first terminal TE1 and the second terminal TE2 are disposed at positions sandwiching the exposed portion 106e in a plan view of the second electrode 106. With this arrangement, when a current is applied between the first terminal TE1 and the second terminal TE2, the exposed portion 106e of the second electrode 106 is energized, that is, a current flows through the exposed portion 106e. This energization of the exposed portion 106e of the second electrode 106 is thought to activate the hydrogen dissociation action of the exposed portion 106e. Note that the first reference element 100a and the second reference element 100b do not have openings 110, and therefore do not have the exposed portion 106e of the second electrode 106, and therefore do not react with hydrogen.

[0033] The insulating films 107a to 107c and the insulating films 109a and 109b that cover the main parts of the hydrogen sensor element 100 are made of silicon oxide film, silicon nitride film, or the like.

[0034] A metal layer 106s is formed on the upper surface of the second electrode 106 except for the opening 110. The metal layer 106s is made of, for example, TiAlN and is formed as an etching stopper for forming a via, but is not essential.

[0035] In FIG. 2A, the metal oxide layer 104 is TaO ｘ The first layer 104a is made of Ta, which has a low oxygen deficiency. ２ O ５ The example of the two-layer structure composed of the first layer 104b made of Ta and the second layer 104b made of Ta is shown. ２ O ５ or TaO ｘ It may also have a single layer structure made of the material.

[0036] The lower part of the cross-sectional view in FIG. 2A shows the equivalent resistances (Rext, Rs, Rf1, Rf2) in the sensor chip 10 and the voltages (Vh, Vf1, Vf2, etc.) generated at each resistance when a current is applied.

[0037] 2A, the resistance of the hydrogen sensor element 100 is composed of a series connection of resistance Rs, which is the resistance component of the second electrode 106 directly below the opening 110 of length L1 (i.e., the exposed portion 106e of the second electrode 106), unnecessary parasitic resistance from resistance Rs to terminal A (i.e., half (Rext / 2) of the external resistance Rext), and unnecessary parasitic resistance from resistance Rs to terminal B (i.e., half (Rext / 2) of the external resistance Rext). The external resistance Rext corresponds to the total value of the parasitic resistances in the hydrogen sensor element 100 that do not contribute to the reaction with hydrogen.

[0038] As shown in Figure 2A, the resistance of the first reference element 100a is composed of a series connection of resistance Rf1 (hereinafter also referred to as "internal resistance Rf1"), which is the resistance component at a location of length L1 corresponding to the resistance component Rs of the hydrogen sensor element 100, unnecessary parasitic resistance from the internal resistance Rf1 to terminal B (i.e., half of the external resistance Rext (Rext / 2)), and unnecessary parasitic resistance from the internal resistance Rf1 to terminal C (i.e., half of the external resistance Rext (Rext / 2)).

[0039] As shown in Figure 2A, the resistance of the second reference element 100b is composed of a series connection of resistance Rf2 (hereinafter also referred to as "internal resistance Rf2"), which is the resistance component at a location of length L2 corresponding to the resistance component Rs of the hydrogen sensor element 100, unnecessary parasitic resistance from the internal resistance Rf2 to terminal C (i.e., half of the external resistance Rext (Rext / 2)), and unnecessary parasitic resistance from the internal resistance Rf2 to terminal D (i.e., half of the external resistance Rext (Rext / 2)).

[0040] In addition, the structure of the second electrode 106 (i.e., the exposed portion 106e of the second electrode 106) directly below the opening 110 of length L1 of the hydrogen sensor element 100 from the end closer to terminal A to terminal A, the structure of the exposed portion 106e from the end closer to terminal B to terminal B, the structure of the internal resistance Rf1 of length L1 of the first reference element 100a from the end closer to terminal B to terminal B, the structure of the internal resistance Rf1 of length L1 from the end closer to terminal C to terminal C, the structure of the internal resistance Rf2 of length L2 of the second reference element 100b from the end closer to terminal C to terminal C, and the structure of the internal resistance Rf2 of length L2 from the end closer to terminal D to terminal D are all identical structures, and all have resistance values ​​of half the external resistance Rext (Rext / 2).

[0041] 2A, when a current is applied, the voltage Vh generated in the hydrogen sensor element 100 is expressed as the sum of the voltage Vh0 generated across the resistance Rs, which varies depending on the hydrogen concentration, and the voltage Vext generated across the unnecessary external resistance Rext (= Rext / 2 + Rext / 2), which is independent of the hydrogen concentration. Furthermore, the voltage Vf1 generated in the first reference element 100a is expressed as the sum of the voltage Vf10 generated across the fixed internal resistance Rf1 and the voltage Vext generated across the unnecessary external resistance Rext (= Rext / 2 + Rext / 2), which is independent of the hydrogen concentration. Furthermore, the voltage Vf2 generated in the second reference element 100b is expressed as the sum of the voltage Vf20 generated across the fixed internal resistance Rf2 and the voltage Vext generated across the unnecessary external resistance Rext (= Rext / 2 + Rext / 2), which is independent of the hydrogen concentration.

[0042] 3 is a flowchart showing a method for manufacturing the sensor chip 10 shown in Fig. 2A and Fig. 2B. First, film formation and photolithography (pattern transfer and etching) for forming a laminate for three resistance elements (hydrogen sensor element 100, first reference element 100a, and second reference element 100b) are repeated on the semiconductor substrate 102, thereby forming, from the bottom up, the semiconductor substrate 102, the insulating film 107a as an interlayer insulating film made of P-TEOS (tetraethoxysilane by plasma) or the like, the first electrode 103 made of TaN or TiN or the like, the Ta ２ O ５ and TaO １．５ A laminate is formed (stack formation step S10) including the metal oxide layer 104, the second electrode 106 made of Pt or the like, the metal layer 106s made of TiAlN or the like, the insulating film 107b as an interlayer insulating film made of P-TEOS or the like, the insulating film 109a as a protective film made of P-SiON (plasma-produced silicon oxynitride film) or the like, the first terminals TE1 to the fourth terminals TE4 as electrodes made of Au or the like, the insulating film 107c as an interlayer insulating film made of HDP-NSG (high-density plasma-produced nitrogen-doped glass) or the like, and the insulating film 109b as a protective film made of P-SiON or the like. This process produces an intermediate product of the hydrogen sensor element 100 before the opening 110 is formed, and the first and second reference elements 100a and 100b.

[0043] Next, photolithography (pattern transfer and etching) is used to remove rectangular portions of the metal layer 106s, insulating film 107b, insulating film 109a, insulating film 107c, and insulating film 109b from the laminate (i.e., the intermediate product of the hydrogen sensor element 100) so as to expose the top surface of the second electrode 106, thereby forming an opening 110 in the hydrogen sensor element 100 (opening formation step S11). This process completes the hydrogen sensor element 100 and the manufacture of the sensor chip 10.

[0044] Next, a description will be given of the operation of the hydrogen detection device 30 configured as above. Figure 4 is a flowchart showing the procedure for hydrogen detection (i.e., the hydrogen detection method) by the hydrogen detection device 30 according to the embodiment.

[0045] First, after completing preparations for installing the hydrogen detection device 30 in the environment to be detected, the hydrogen detection device 30 applies a current to the hydrogen sensor element 100, first reference element 100a, and second reference element 100b, which are connected in series (current application step S30). That is, in the measurement unit 20 of the hydrogen detection device 30, the current source 21 applies a predetermined constant current between terminals A and D of the sensor chip 10 under instructions from the signal processing unit 23.

[0046] Next, the hydrogen detection device 30 measures the voltages across the hydrogen sensor element 100, the first reference element 100a, and the second reference element 100b when a current is applied in the current application step S30 (voltage measurement step S31). That is, in the measurement section 20 of the hydrogen detection device 30, the voltmeter 22, under instructions from the signal processing section 23, measures the voltage Vh across the hydrogen sensor element 100, the voltage Vf1 across the first reference element 100a, and the voltage Vf2 across the second reference element 100b while switching between them when a current is applied.

[0047] Next, the hydrogen detection device 30 generates and outputs a signal indicating the hydrogen concentration using the voltage Vh across the hydrogen sensor element 100 obtained in the voltage measurement step S31, the voltage Vf1 across the first reference element 100a, and the voltage Vf2 across the second reference element 100b (signal processing step S32).

[0048] Specifically, in the measurement unit 20 of the hydrogen detection device 30, the signal processing unit 23 first calculates the voltage Vf1 across the first reference element 100a and the voltage Vf2 across the second reference element 100b obtained in the voltage measurement step S31, and the length L1 of the portion corresponding to the internal resistance Rf1 of the first reference element 100a and the length L2 of the portion corresponding to the internal resistance Rf2 of the second reference element 100b, and calculates the voltage Vext across the external resistance Rext as the intercept with the vertical axis (S32a). Figure 5 is a diagram showing an example of a plot of the relationship between the length (horizontal axis) of the internal resistances Rf1 and Rf2 of the first reference element 100a and the second reference element 100b when a current is applied, and the voltage Vext across the first reference element 100a and the second reference element 100b when a current is applied. The voltage Vf1 across the first reference element 100a and the voltage Vf2 across the second reference element 100b are expressed as the sum of a voltage component generated in proportion to the length of the internal resistances Rf1 and Rf2 and an offset voltage Vext generated in the fixed external resistance Rext. Utilizing this, the voltage Vext generated in the external resistance Rext is calculated from a straight line passing through the two points.

[0049] Then, the signal processing unit 23 generates a voltage ratio expressed by the following equation 1 from the calculated voltage Vext, the voltage Vh across the hydrogen sensor element 100 obtained in the voltage measurement step S31, and the voltage Vf1 across the first reference element 100a as a signal indicating the hydrogen concentration and outputs it to the outside (S32b).

[0050] (Vh-Vext) / (Vf1-Vext)...(Formula 1)

[0051] In the numerator of the above formula 1, Vh-Vext=Vh0 holds, and in the denominator of the above formula 1, Vf1-Vext=Vf0 holds, so the above formula 1 can be expressed as the following formula 2.

[0052] Vh0 / Vf10...(Formula 2)

[0053] As can be seen from the above equation 2, the numerator Vh0 in the above equation 2 excludes the voltage generated across the unnecessary external resistance Rext in the hydrogen sensor element 100, and indicates only the voltage generated across the resistance Rs that changes depending on the hydrogen concentration. Furthermore, the denominator Vf10 in the above equation 2 also excludes the voltage generated across the unnecessary external resistance Rext, and indicates only the voltage generated across the fixed internal resistance Rf1 used as a reference.

[0054] The voltage ratio expressed by the above formula 2 is also the ratio (Rs / Rf1) of the net resistance Rs of the hydrogen sensor element 100, which is sensitive to hydrogen, to the net internal resistance Rf1 of the first reference element 100a, which is not sensitive to hydrogen and has the same structure formed on the same semiconductor substrate. Therefore, the voltage ratio expressed by the above formula 2 can be said to be a value that indicates the hydrogen concentration with high sensitivity, with temperature dependency suppressed and the unnecessary external resistance Rext component of the hydrogen sensor element 100 removed.

[0055] 6A and 6B are diagrams illustrating the results of a hydrogen concentration detection experiment using the hydrogen detection device 30 according to the embodiment. In this experiment, the atmosphere in which the sensor chip 10 is placed is switched from a low hydrogen concentration state to a high hydrogen concentration state in four stages, and the graph shows the time changes in two types of voltage ratios (i.e., reaction amounts) obtained from the sensor chip 10. (a) of FIG. 6A shows the time change in the voltage ratio (Vh / Vf1) according to the reference example, including the voltage Vext due to the external resistance Rext of the hydrogen sensor element 100 and the first reference element 100a. (b) of FIG. 6B shows the time change in the voltage ratio (Vh0 / Vf10) according to the embodiment, excluding the voltage Vext due to the external resistance Rext of the hydrogen sensor element 100 and the first reference element 100a.

[0056] The voltage ratio (Vh / Vf1) according to the reference example shown in Fig. 6(a) is both (Vh0+Vext) / (Vf10+Vext) and (Rs+Rext) / (Rf1+Rext), as shown in the figure. On the other hand, the voltage ratio (Vh0 / Vf10) according to the embodiment shown in Fig. 6(b) is both (Vh-Vext) / (Vf1-Vext) and (Rs / Rf1), as shown in the figure.

[0057] 6(b) of the embodiment, the obtained voltage ratio (i.e., reaction amount) is about 1.5 times higher than that of the reference example shown in FIG. 6(a). In other words, compared to the reaction amount of the reference example including the voltage caused by the external resistance Rext, the reaction amount of the embodiment excluding the voltage caused by the external resistance Rext increases sensitivity by about 1.5 times. Therefore, it can be seen that the hydrogen detection device 30 of the embodiment can detect low concentrations of hydrogen with high sensitivity compared to the hydrogen detection method of the reference example.

[0058] The sensor chip 10 constituting the hydrogen detection device 30 according to the embodiment is not limited to the structure shown in FIGS. 2A and 2B, and may have the following modified examples.

[0059] Fig. 7A is a cross-sectional view showing an example of the configuration of a sensor chip 10a according to a modified example of the embodiment. Fig. 7B is a top view showing the example of the configuration of the sensor chip 10a shown in Fig. 7A. Fig. 7A shows a schematic cross-section taken along line VIIA-VIIA in Fig. 7B, as viewed in the direction of the arrow.

[0060] In this modified example, the sensor chip 10a is formed on a single semiconductor substrate and has a hydrogen sensor element 100, which is an example of a first resistor element, a first reference element 100c, which is an example of a second resistor element, and a second reference element 100d, which is an example of a third resistor element, connected in series.

[0061] 2A and 2B, the sensor chip 10a according to this modification is different from the sensor chip 10 according to the embodiment shown in Figures 2A and 2B in that after the hydrogen sensor element 100, the first reference element 100c, and the second reference element 100d are formed as a laminate using the same manufacturing process, the openings 110, 110a, and 110b are formed once, and then the inner surfaces and bottom surfaces of the opening 110a of the first reference element 100c and the opening 110b of the second reference element 100d are covered with hydrogen-impermeable films 111a and 111b. The hydrogen-impermeable films 111a and 111b are films that do not allow hydrogen to pass through, such as silicon oxide film, silicon nitride film, or silicon oxynitride film.

[0062] 8 is a flowchart showing a method for manufacturing the sensor chip 10a shown in FIGS. 7A and 7B. First, film formation and photolithography (pattern transfer and etching) for forming stacks for the three resistance elements (hydrogen sensor element 100, first reference element 100c, and second reference element 100d) are repeated on the semiconductor substrate 102 to form stacks for the hydrogen sensor element 100, first reference element 100c, and second reference element 100d (stack formation step S10). This step is the same as the stack formation step S10 shown in FIG. 3. In this modification, this step produces intermediate products of the hydrogen sensor element 100, first reference element 100c, and second reference element 100d before the openings 110, 110a, and 110b and the hydrogen-impermeable films 111a and 111b are formed.

[0063] Next, photolithography (pattern transfer and etching) is used to remove rectangular portions of the metal layer 106s, the insulating film 107b, the insulating film 109a, the insulating film 107c, and the insulating film 109b from the three resistor element laminates (i.e., the three intermediate products) so as to expose the top surface of the second electrode 106, thereby forming an opening 110 in the hydrogen sensor element 100, an opening 110a in the first reference element 100c, and an opening 110b in the second reference element 100d (opening formation step S21). This process completes the hydrogen sensor element 100.

[0064] Finally, the inner surfaces and bottom surfaces of the openings 110a and 110b formed in the first reference element 100c and the second reference element 100d are covered with hydrogen-impermeable films 111a and 111b made of P-SiON or the like (hydrogen-impermeable film forming step S22). This step completes the first reference element 100c and the second reference element 100d, each having the openings 110a and 110b whose inner surfaces and bottoms are covered with the hydrogen-impermeable films 111a and 111b. The formation of the hydrogen-impermeable films 111a and 111b may be performed in the same process as the formation of the insulating film 109b (i.e., by forming a film using the same material), or may be performed in an independent process. This step completes the manufacture of the sensor chip 10a according to the modified embodiment.

[0065] Even in a hydrogen detection device 30 that includes the sensor chip 10a manufactured in this manner instead of the sensor chip 10 according to the embodiment, the signal processing unit 23 can generate the voltage ratio shown in the above equation 1, i.e., the above equation 2, as a signal indicating the hydrogen concentration, in accordance with the flowchart shown in Figure 4, just as in the embodiment. In other words, even in this modified example, temperature dependency is suppressed and the component of the unnecessary external resistance Rext of the hydrogen sensor element 100 is removed, just like in the embodiment, so a signal indicating the hydrogen concentration can be generated with high sensitivity.

[0066] In the above embodiment, hydrogen detection device 30 is a measurement system configured by combining sensor chip 10 or 10a with measurement unit 20, but it may also be a device equipped with sensor chip 10 or 10a alone. This is because sensor chip 10 or 10a has a characteristic sensor structure that enables highly sensitive detection of hydrogen while suppressing temperature dependency.

[0067] As described above, the hydrogen detection device 30 according to this embodiment is a device for detecting hydrogen, and includes the hydrogen sensor element 100, the first reference element 100a, and the second reference element 100b, which are formed on a single semiconductor substrate 102 and connected in series. The hydrogen sensor element 100, the first reference element 100a, and the second reference element 100b each include a first electrode 103 and a second electrode 106, which are arranged with their main surfaces facing each other, and a metal oxide layer 101 disposed in contact with the main surface of the first electrode 103 and the main surface of the second electrode 106. 4 and an insulating film 107c that covers the first electrode 103, the second electrode 106, and the metal oxide layer 104, and the hydrogen sensor element 100 has an opening 110 that exposes the other surface opposite the main surface of the second electrode 106 to the outside without being covered by the insulating film 107c, etc., and each of the first reference element 100a and the second reference element 100b does not have an opening that exposes the other surface opposite the main surface of the second electrode 106 to the outside, and the first reference element 100a and the second reference element 100b have different lengths in the direction in which current flows.

[0068] As a result, the hydrogen detection device 30 is equipped with a characteristic sensor chip that enables high-sensitivity detection of hydrogen with suppressed temperature dependence due to three characteristic resistance elements, thereby realizing a hydrogen detection device 30 that can be realized in a smaller area and that can detect hydrogen with high sensitivity without requiring four resistance elements as in the conventional case.

[0069] Here, as in the modified example of the embodiment, each of the first reference element 100c and the second reference element 100d has openings 110a and 110b that expose the other surface facing the main surface of the second electrode 106 from the insulating film 107c without being covered by the insulating film 107c, etc., and the inner side and bottom surfaces of the openings 110a and 110b of the first reference element 100c and the second reference element 100d may be covered with hydrogen-impermeable films 111a and 111b, respectively. In this way, the three resistance elements are provided with a common opening, which ensures a very high level of structural uniformity and can improve the effect of suppressing temperature dependency.

[0070] Furthermore, the hydrogen sensor element 100 and the first reference element 100a may have the same length in the direction of current flow, so that the voltage ratio using the two resistance elements, in other words, the resistance ratio, becomes approximately 1 when no hydrogen is present, thereby ensuring the accuracy of the signal indicating the hydrogen concentration.

[0071] Furthermore, the first reference element 100a and the second reference element 100b may differ in length in the direction of current flow by at least two times, thereby ensuring calculation accuracy when calculating the voltage Vext due to the external resistance Rext from the linear relationship between the lengths of the internal resistances of the two reference elements and the voltages across the two reference elements, and as a result, the hydrogen detection device 30 can calculate a signal indicating the hydrogen concentration with high accuracy.

[0072] The hydrogen detection device 30 may further include a current source 21 that applies current to the hydrogen sensor element 100, the first reference element 100a, and the second reference element 100b connected in series, a voltmeter 22 that measures the voltage across each of the hydrogen sensor element 100, the first reference element 100a, and the second reference element 100b when current is applied by the current source 21, and a signal processing unit 23 that generates and outputs a signal indicative of the hydrogen concentration using the voltage across each of the hydrogen sensor element 100, the first reference element 100a, and the second reference element 100b obtained by the voltmeter 22. In this way, by taking advantage of the characteristics of the sensor chip 10 composed of three resistive elements, a signal indicative of the hydrogen concentration is generated with high sensitivity and reduced temperature dependency.

[0073] At this time, the resistance of the hydrogen sensor element 100 includes a resistance component Rs at the location of the opening 110 of the hydrogen sensor element 100 and an external resistance Rext, which is the resistance component excluding the resistance component, and the signal processing unit 23 calculates the voltage Vext generated across the external resistance Rext using the voltages Vf1 and Vf2 across the first and second reference elements 100a and 100b, respectively, and generates a signal indicating the hydrogen concentration using the calculated voltage Vext. This eliminates unnecessary voltage caused by the external resistance Rext, and generates a signal indicating the hydrogen concentration with high sensitivity.

[0074] Specifically, the signal processing unit 23 calculates a ratio expressed as (Vh-Vext) / (Vf-Vext), where Vext is the voltage generated by the external resistor, Vh is the voltage across the hydrogen sensor element 100, and Vf is the voltage across the first reference element 100a, and generates a signal indicating the calculated ratio as a signal indicating the hydrogen concentration. In this way, unnecessary voltage caused by the external resistor Rext is eliminated using a simple formula, and a signal indicating the hydrogen concentration is generated with high sensitivity.

[0075] Furthermore, the hydrogen detection method according to this embodiment is a method for detecting hydrogen, and includes the steps of preparing the hydrogen detection device 30, a current application step S30 for applying current to the hydrogen sensor element 100, the first reference element 100a, and the second reference element 100b connected in series and provided in the prepared hydrogen detection device 30, a voltage measurement step S31 for measuring the voltage across each of the hydrogen sensor element 100, the first reference element 100a, and the second reference element 100b when current is being applied by the current application step S30, and a signal processing step S32 for generating and outputting a signal indicating the hydrogen concentration using the voltage across each of the hydrogen sensor element 100, the first reference element 100a, and the second reference element 100b obtained in the voltage measurement step S31.

[0076] As a result, by using a sensor chip that has three distinctive resistor elements and is realized with an area smaller than conventional ones, a signal that indicates the hydrogen concentration with high sensitivity can be generated.

[0077] While the hydrogen detection device and hydrogen detection method according to the present disclosure have been described above based on the embodiments and modifications, the present disclosure is not limited to these embodiments and modifications. As long as they do not deviate from the gist of the present disclosure, various modifications that would occur to a person skilled in the art to the present embodiments and modifications, and other forms constructed by combining some of the components of the embodiments and modifications, are also included within the scope of the present disclosure.

[0078] For example, in the embodiments, the signal indicating the hydrogen concentration is calculated from the above formula 1 using the voltage Vh across the hydrogen sensor element 100 and the voltage Vf1 across the first reference element 100a, but this formula is not limited to this. Instead, the calculation may be performed using the voltage Vh across the hydrogen sensor element 100 and the voltage Vf2 across the second reference element 100b, as shown in the following formula 3.

[0079] (Vh-Vext) / (Vf2-Vext)...(Formula 3)

[0080] Furthermore, in the embodiments, two reference elements (such as the first reference element 100a and the second reference element 100b) are used to calculate the voltage Vext generated across the external resistance Rext from a straight line passing through two points. However, the number of points is not limited to two. Three or more reference elements of different lengths connected in series with the hydrogen sensor element 100 may be connected to the sensor chip 10, and the voltage Vext generated across the external resistance Rext may be calculated from an approximate straight line passing through three or more points using three or more reference elements.

[0081] Furthermore, the present disclosure may be realized as a program that causes a processor to execute the steps included in the hydrogen detection method according to the embodiment, or as a non-transitory recording medium such as a DVD on which the program is recorded, or as a program product that includes the program.

[0082] The present disclosure can be used as a hydrogen detection device having a sensor chip composed of a resistance element provided on a single semiconductor substrate, for example, as a hydrogen detection device that is installed in hydrogen vehicles or hydrogen stations and detects hydrogen leaks.

[0083] 10, 10a Sensor chip 20 Measurement unit 21 Current source 22 Voltmeter 23 Signal processing unit 30 Hydrogen detection device 100 Hydrogen sensor element (first resistor element) 100a, 100c First reference element (second resistor element) 100b, 100d Second reference element (third resistor element) 102 Semiconductor substrate 103 First electrode 104 Metal oxide layer 104a First layer 104b Second layer 104i Insulating separation layer 106 Second electrode 106e Exposed portion 106s Metal layer 107a, 107b, 107c, 109a, 109b Insulating film 108 Via 110, 110a, 110b Opening 111a, 111b Hydrogen impermeable film TE1 First terminal TE2 Second terminal TE3 Third terminal TE4 Fourth terminal TE1a, TE2a, TE3a, TE4a Openings A to D Terminals

Claims

1. A hydrogen detection device for detecting hydrogen, comprising a first resistance element, a second resistance element, and a third resistance element formed on one semiconductor substrate and connected in series, wherein the first resistance element, the second resistance element, and the third resistance element each have a first electrode and a second electrode with main surfaces facing each other, a metal oxide layer disposed in contact with the main surfaces of the first electrode and the second electrode, and an insulating film covering the first electrode, the second electrode, and the metal oxide layer; the first resistance element has an opening exposing the other surface facing the main surface of the second electrode to the outside without being covered by the insulating film; each of the second resistance element and the third resistance element does not have an opening exposing the other surface facing the main surface of the second electrode to the outside; and the second resistance element and the third resistance element have different lengths in the direction in which current flows.

2. Each of the second resistance element and the third resistance element has an opening exposing the other surface facing the main surface of the second electrode from the insulating film without being covered by the insulating film, and the inner surface and the bottom surface of each of the openings of the second resistance element and the third resistance element are covered with a hydrogen-impermeable film. The hydrogen detection device according to claim 1.

3. The first resistance element and the second resistance element have the same length in the direction in which current flows. The hydrogen detection device according to claim 1.

4. The second resistance element and the third resistance element have lengths different by a factor of two or more in the direction in which current flows. The hydrogen detection device according to claim 1.

5. Further comprising a current source for applying a current to the first resistance element, the second resistance element, and the third resistance element connected in series, a voltmeter for measuring the voltage across each of the first resistance element, the second resistance element, and the third resistance element when a current is applied by the current source, and a signal processing unit for generating and outputting a signal indicating the hydrogen concentration using the voltage across each of the first resistance element, the second resistance element, and the third resistance element obtained by the voltmeter. The hydrogen detection device according to claim 1.

6. The resistance of the first resistor includes a resistance component at a location of the first resistor that is located at the opening and an external resistance that is a resistance component other than the resistance component. The signal processing unit calculates a voltage generated in the external resistance using the voltages at both ends of the second resistor and the third resistor, and generates a signal indicating the hydrogen concentration using the calculated voltage. The hydrogen detection device according to claim 5.

7. When the voltage generated in the external resistance is Vext, the voltage across the first resistor is Vh, and the voltage across the second resistor is Vf, the signal processing unit calculates a ratio represented by (Vh - Vext) / (Vf - Vext), and generates a signal indicating the calculated ratio as the signal indicating the hydrogen concentration. The hydrogen detection device according to claim 6.

8. A method for detecting hydrogen, comprising: preparing the hydrogen detection device according to claim 1; applying a current to the first resistor, the second resistor, and the third resistor connected in series provided in the prepared hydrogen detection device; measuring the voltages at both ends of the first resistor, the second resistor, and the third resistor when the current is being applied by the current application step; and generating and outputting a signal indicating the hydrogen concentration using the voltages at both ends of the first resistor, the second resistor, and the third resistor obtained in the voltage measurement step. A hydrogen detection method.

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