Gas detector and gas detection method

Abstract

This gas detector comprises: a gas sensor element; a reference element that has been deactivated with regard to the gas; a control unit that controls an applied voltage or an applied current applied to the gas sensor element and the reference element; and a calculation unit that calculates the gas concentration from the respective output measurement results from the gas sensor element and the reference element. The control unit controls the applied voltage or the applied current on the basis of the output measurement result from the reference element.

Description

Gas detector and gas detection method

[0001] This disclosure relates to a gas detector and a gas detection method.

[0002] Conventionally, gas detectors using gas sensors are known. Furthermore, a method using a heater has been proposed as a technique to reduce the ambient temperature dependence characteristics of gas sensors (see, for example, Patent Document 1).

[0003] U.S. Patent No. 10791589

[0004] However, a method that reduces ambient temperature dependence using a heater has the problem that the size of the gas detector increases due to the inclusion of the heater, making miniaturization of the gas detector difficult. On the other hand, there are concerns that changes in ambient temperature may affect the gas detection characteristics of the gas detector, and in particular, there are concerns about the impact on gas detection speed and accuracy in low-temperature environments.

[0005] Therefore, this disclosure provides a gas detector, etc., that can reduce the influence of ambient temperature and can be miniaturized.

[0006] A gas detector according to one embodiment of the present disclosure comprises a gas sensor element, a reference element deactivated by gas, a control unit that controls the applied voltage or current to the gas sensor element and the reference element, and a calculation unit that calculates the gas concentration from the measurement results of the outputs of the gas sensor element and the reference element, wherein the control unit controls the applied voltage or the applied current based on the measurement results of the output of the reference element.

[0007] Furthermore, a gas detection method according to one embodiment of the present disclosure is a gas detection method using a gas detector comprising a gas sensor element and a reference element deactivated by gas, comprising: a control step of controlling an applied voltage or applied current to the gas sensor element and the reference element; and a calculation step of calculating a gas concentration from the measurement results of the outputs of the gas sensor element and the reference element, wherein in the control step, the applied voltage or applied current is controlled based on the measurement results of the output of the reference element.

[0008] This disclosure makes it possible to provide a gas detector, etc., that can reduce the influence of ambient temperature and can be miniaturized.

[0009] Figure 1 is a block diagram showing the configuration of a hydrogen detection device according to an embodiment. Figure 2A is a cross-sectional view showing an example of the configuration of the sensor chip shown in Figure 1. Figure 2B is a top view showing an example of the configuration of the sensor chip shown in Figure 2A. Figure 3 is a flowchart showing the manufacturing method of the sensor chip shown in Figures 2A and 2B. Figure 4 is a flowchart showing the procedure (i.e., hydrogen detection method) for hydrogen detection by the hydrogen detection device according to an embodiment. Figure 5A is a diagram showing an example plotting the relationship between time (horizontal axis), ambient temperature, and the resistance of the reference element (vertical axis) when there is no current correction. Figure 5B is a diagram showing an example plotting the relationship between time (horizontal axis), ambient temperature, and the resistance of the reference element (vertical axis) when there is current correction. Figure 6 is a diagram illustrating the results of a hydrogen concentration detection experiment by the hydrogen detection device according to an embodiment. Figure 7 is a block diagram showing the configuration of a hydrogen detection device according to Modification 1 of the embodiment. Figure 8 is a flowchart showing the procedure (i.e., hydrogen detection method) for hydrogen detection by the hydrogen detection device according to Modification 1 of the embodiment. Figure 9A is a cross-sectional view showing an example of the configuration of a sensor chip according to Modification 2 of the embodiment. Figure 9B is a top view showing an example configuration of the sensor chip shown in Figure 9A. Figure 10 is a diagram illustrating the results of a hydrogen concentration detection experiment using the sensor chip according to a modified example 2 of the embodiment.

[0010] The embodiments of this disclosure will be described in detail below with reference to the drawings. The embodiments described below are all specific examples of this disclosure. The numerical values, shapes, materials, components, arrangement and connection configurations of components, steps, and the order of steps shown in the following embodiments are examples only and are not intended to limit this disclosure. Furthermore, the figures are not necessarily strictly accurate. In each figure, substantially identical components are denoted by the same reference numerals, and redundant explanations are omitted or simplified.

[0011] Furthermore, in this specification, "connection" means an 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.

[0012] Furthermore, in this specification, the terms "upper" and "lower" do not refer to the upward (vertically upward) and downward (vertically downward) directions in absolute spatial perception, but rather to terms defined by the relative positional relationship based on the stacking order in the stacked configuration. Similarly, the "upper surface" and "lower surface" of each component do not refer to the upward (vertically upward) and downward (vertically downward) surfaces in absolute spatial perception. It should be noted that terms such as "upper," "lower," "upper surface," and "lower surface" are used solely to specify the relative arrangement of components and are not intended to limit the orientation when the hydrogen detection device is in use. Moreover, the terms "upper" and "lower" apply not only when two components are spaced apart and another component exists between them, but also when two components are placed in close proximity and touching each other.

[0013] Furthermore, in this specification, the "principal surface" of a component is the surface with the largest area among the surfaces of that component.

[0014] Furthermore, in this specification, "planar view" refers to a planar view of the sensor chip with respect to the semiconductor substrate, and means viewing the sensor chip from a viewpoint in the stacking direction. In other words, "planar view" means viewing from a viewpoint in the direction normal to the principal surface of either the planar first electrode or the second electrode.

[0015] Furthermore, in this specification, ordinal numbers such as "first," "second," etc., unless otherwise specified, do not mean the number or order of constituent elements, etc., but are used for the purpose of avoiding confusion and distinguishing similar constituent elements, etc.

[0016] (Embodiment) First, the overall configuration of the hydrogen detection device according to the embodiment will be described. Figure 1 is a block diagram showing the configuration of the hydrogen detection device 30 according to the embodiment.

[0017] As shown in Figure 1, the hydrogen detection device 30 comprises a sensor chip 10 and a measurement unit 20. The hydrogen detection device 30 is an example of a gas detector.

[0018] The sensor chip 10 includes a hydrogen sensor element 100 connected in series with a current source 21 (described later), and a reference element 100a. The hydrogen sensor element 100 is an example of a gas sensor element. The hydrogen sensor element 100 and the reference element 100a are formed, for example, on a single semiconductor substrate. The sensor chip 10 also has terminals for external connection, including 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 reference element 100a, and terminal C connected to the other end of the reference element 100a.

[0019] Here, the hydrogen sensor element 100 is a variable resistance element that has a structure exposed to gases such as hydrogen and changes its resistance value according to the hydrogen concentration. On the other hand, the reference element 100a is a reference resistance element that does not react to gases such as hydrogen. More specifically, the reference element 100a is provided to cancel out the temperature dependence of the resistance value of the hydrogen sensor element 100, and has basically the same structure as the hydrogen sensor element 100, but has a structure that does not expose it to gases such as hydrogen and is deactivated by the gas. The resistance values ​​of the hydrogen sensor element 100 and the reference element 100a change in the same way or in a predetermined relationship with respect to the ambient temperature, for example. Therefore, by calculating the ratio or difference of the outputs of the hydrogen sensor element 100 and the reference element 100a, an output from which the temperature dependence of the resistance value of the hydrogen sensor element 100 has been removed can be obtained.

[0020] The hydrogen sensor element 100 and the reference element 100a only need to be connected in series with the current source 21, and are not limited to the connection order shown in the figure. For example, the hydrogen sensor element 100 and the reference element 100a may be connected in the order of reference element 100a and hydrogen sensor element 100 from left to right.

[0021] 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. The measurement unit 20 includes a current source 21, a voltmeter 22, a switch circuit 22S, and a signal processing unit 23. The signal processing unit 23 is a processing circuit that includes a control unit 41 and a calculation unit 42.

[0022] The current source 21 is a circuit that applies a predetermined constant current between terminals A and C of the sensor chip 10 under instructions from the control unit 41 of the signal processing unit 23. The current source 21 is composed of, for example, a transistor.

[0023] The voltmeter 22 is a measurement circuit that measures the outputs of the hydrogen sensor element 100 and the reference element 100a. Specifically, the voltmeter 22 is a circuit that measures the voltage across the hydrogen sensor element 100 (i.e., the voltage drop between terminal A and terminal B) and the voltage across the reference element 100a (i.e., the voltage drop between terminal B and terminal C) as electrical characteristic values ​​related to the hydrogen sensor element 100 and the reference element 100a, under instructions from the control unit 41 of the signal processing unit 23. The voltmeter 22 is composed of, for example, a voltage amplifier and an A / D converter. In the example shown in Figure 1, two types of voltages, the voltage across the hydrogen sensor element 100 and the voltage across the reference element 100a, are measured by a single voltmeter 22 while being switched by the switch circuit 22S.

[0024] The signal processing unit 23 is a circuit that instructs the current source 21 to apply current, reads two types of measurement voltages from the voltmeter 22, and generates and outputs a signal indicating hydrogen concentration from the two types of measurement voltages read. These operations by the signal processing unit 23 are performed by the control unit 41 and the arithmetic unit 42. The signal processing unit 23 is composed of, for example, one or more processors that execute a built-in program. In the signal processing unit 23, the control unit 41 and the arithmetic unit 42 may be composed of a common processor or may be composed of separate processors. Furthermore, the signal processing unit 23 may be a dedicated logic circuit that executes the processing performed by the control unit 41 and the arithmetic unit 42.

[0025] The measurement unit 20 may be a circuit formed on the same semiconductor substrate as the sensor chip 10, or it may be a circuit provided on a separate substrate or device connected to the sensor chip 10 (for example, a measuring instrument or a computer device for measurement). Furthermore, a part of the measurement unit 20 (for example, the calculation unit 42 of the signal processing unit 23) may be provided on a separate substrate or device connected to the sensor chip 10. In addition, the measurement unit 20 is not limited to a configuration that measures two types of voltages (specifically, the voltage across the hydrogen sensor element 100 and the voltage across the reference element 100a) while switching between them, but may also have a configuration with two voltmeters that measure each of the two types of voltages in parallel.

[0026] Next, the detailed configuration of the sensor chip 10 will be described. Figure 2A is a cross-sectional view showing an example of the configuration of the sensor chip 10 shown in Figure 1. Figure 2B is a top view showing an example of the configuration of the sensor chip 10 shown in Figure 2A. Note that Figure 2A shows a schematic cross-section viewed in the direction of the arrow along the IIA-IIA cutting line in Figure 2B. In addition, in Figure 2A, along with the cross-sectional views of the hydrogen sensor element 100 and the reference element 100a, schematic wiring showing the connections from terminal A to terminal C is illustrated at the top of the cross-sectional view for explanatory purposes, and the equivalent circuit of the sensor chip 10 (resistor R) is shown at the bottom of the cross-sectional view. ｈ , R Ｒ ), and the voltage generated across each resistive element when current is applied (voltage across both ends V ｈ , V Ｒ ) is shown in Figure 2A and in the following description, R ｈ R indicates the resistance of the hydrogen sensor element 100. Ｒ This indicates the resistance of the reference element 100a. Also, in Figure 2A and the following description, V ｈ This indicates the voltage across the hydrogen sensor element 100, V Ｒ This indicates the voltage across the reference element 100a.

[0027] As shown in Figure 2A, the hydrogen sensor element 100 located on the left side of the sensor chip 10 is formed above the semiconductor substrate 102 and the insulating film 107a above the semiconductor substrate 102. The hydrogen sensor element 100 has as its main components a first electrode 106 and a second electrode 103 arranged with their main surfaces facing each other, a metal oxide layer 104 arranged in contact with one main surface of the first electrode 106 (specifically, the lower surface) and one main surface of the second electrode 103 (specifically, the upper surface), and insulating films (insulating films 107b, 107c, 109a, and 109b) covering the second electrode 103, the first electrode 106, and the metal oxide layer 104 from above. The insulating films 107b, 107c, 109a, and 109b of the hydrogen sensor element 100 have an opening 110 at the center of the other main surface (specifically, the top surface) of the first electrode 106 of the hydrogen sensor element 100, facing away from one main surface, in order to expose the first electrode 106 to hydrogen. In this embodiment, the metal layer 106s is also removed in the opening 110 in order to expose the first electrode 106.

[0028] The 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 reference element 100a. In this embodiment, the second terminal TE2 is shared by the hydrogen sensor element 100 and the reference element 100a. The first terminal TE1 and the second terminal TE2 are connected to the other main surface (specifically, the upper surface) of the first electrode 106 via a via 108 and a metal layer 106s. When a current is applied to the hydrogen sensor element 100 in the lateral direction in Figure 2A, the resistance value changes depending on the hydrogen concentration in the opening 110.

[0029] The reference element 100a located on the right side of the sensor chip 10 shown in Figure 2A has basically the same structure as the hydrogen sensor element 100. Like the hydrogen sensor element 100, the reference element 100a is formed above the semiconductor substrate 102 and the insulating film 107a above the semiconductor substrate 102. Therefore, the hydrogen sensor element 100 and the reference element 100a are formed side by side in a plan view above the same semiconductor substrate 102 and insulating film 107a. The reference element 100a has as its main components a second electrode 103 and a first electrode 106 arranged with their main surfaces facing each other, a metal oxide layer 104 arranged in contact with one main surface of the second electrode 103 (specifically, the upper surface) and one main surface of the first electrode 106 (specifically, the lower surface), and insulating films (insulating films 107b, 107c, 109a, and 109b) covering the second electrode 103, the first electrode 106, and the metal oxide layer 104 from above.

[0030] However, as described above, the reference element 100a is provided to counteract the temperature dependence of the resistance value of the hydrogen sensor element 100, and is a fixed resistance element whose resistance value does not depend on the hydrogen concentration of the environment. Therefore, unlike the hydrogen sensor element 100, the reference element 100a does not have the opening 110 that is provided in the hydrogen sensor element 100. In other words, the insulating films 107b, 107c, 109a, and 109b of the reference element 100a do not have openings that expose the upper surface of the first electrode 106 of the reference element 100a. Note that the insulating films 107b, 107c, 109a, and 109b of the reference element 100a may have openings as long as the upper surface of the first electrode 106 is not exposed to the outside world, for example, they may have openings filled with insulating material.

[0031] The 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. In this embodiment, the second terminal TE2 is shared by the hydrogen sensor element 100 and the reference element 100a. The third terminal TE3 and the second terminal TE2 are connected to the other main surface (specifically, the upper surface) of the first electrode 106 via a via 108 and a metal layer 106s.

[0032] In the examples shown in Figures 2A and 2B, the length of the hydrogen sensor element 100 and the length of the reference element 100a in the direction of current flow (the lateral direction in Figure 2A) are formed in a 1:1 ratio. However, the ratio of the length of the hydrogen sensor element 100 and the length of the reference element 100a in the direction of current flow is not limited to 1:1. Even if the lengths of the hydrogen sensor element 100 and the reference element 100a are different, it is possible to cancel out the temperature dependence of the resistance value of the hydrogen sensor element 100 through calculations or other means.

[0033] Furthermore, as shown in the upper part of the cross-sectional view in Figure 2A, the hydrogen sensor element 100 has an opening 110 of length L in the direction in which the current flows, and the reference element 100a has a structure equivalent to the structure in which the opening 110 of length L in the hydrogen sensor element 100 is closed with an insulating film or the like.

[0034] Details of the components common to the hydrogen sensor element 100 and the reference element 100a that constitute the sensor chip 10 are as follows.

[0035] The second electrode 103 is positioned in contact with the lower surface of the metal oxide layer 104. The second electrode 103 is a planar electrode and has two main surfaces. One of the two main surfaces of the second electrode 103 (specifically, the upper surface) is in contact with the metal oxide layer 104, and the other main surface (specifically, the lower surface) is in contact with the insulating film 107a. In the example shown in Figures 2A and 2B, the second electrode 103 is rectangular in shape and the same size as the first electrode 106. The second electrode 103 is made of a material that has a lower standard electrode potential compared to the base metal of the metal oxide layer 104, such as tungsten, nickel, tantalum, titanium, aluminum, tantalum nitride, or titanium nitride. A higher standard electrode potential indicates a property that is less susceptible to oxidation. In this embodiment, the second electrode 103 is formed of a transition metal nitride such as tantalum nitride (TaN) or titanium nitride (TiN), or a laminate of films thereof.

[0036] The metal oxide layer 104 is sandwiched between two opposing main surfaces of the main surface of the second electrode 103 and the main surface of the first electrode 106, and is formed of a metal oxide as a gas-sensitive resistance film. The metal oxide layer 104 has a characteristic that its resistance value reversibly changes depending on the presence or absence of a hydrogen-containing gas having hydrogen atoms in the gas in contact with the first electrode 106. In the present embodiment, the hydrogen-containing gas is hydrogen (gaseous hydrogen molecules). The metal oxide layer 104 only needs to have a property that its resistance changes due to the hydrogen-containing gas. For example, the metal oxide layer 104 includes a transition metal oxide containing a transition metal as a base metal. The base metal of the metal oxide layer 104 is at least one selected from the group consisting of tantalum (Ta), hafnium (Hf), titanium (Ti), zirconium (Zr), niobium (Nb), tungsten (W), nickel (Ni), iron (Fe), aluminum (Al), chromium (Cr), cobalt (Co), manganese (Mn), vanadium (V), cerium (Ce) and copper (Cu).

[0037] In the example shown in FIG. 2A, the metal oxide layer 104 includes a first layer 104a in contact with the second electrode 103, a second layer 104b located between the first layer 104a and the first electrode 106 and in contact with both the first layer 104a and the first 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, for example, Ta ２ O ５ having lower oxygen deficiency than the first layer 104a. Further, the insulating isolation layer 104i is arranged on the outer periphery of the second electrode 103 so as to overlap with the second electrode 103 in a plan view.

[0038] In the hydrogen sensor element 100, the resistance of the metal oxide layer 104 decreases in proportion to the amount of hydrogen-containing gas that comes into contact with the first electrode 106 through the opening 110. Specifically, when hydrogen-containing gas is present in the gas to be detected, hydrogen atoms are dissociated from the hydrogen-containing gas at the first electrode 106. The dissociated hydrogen atoms penetrate into the metal oxide layer 104 and form impurity levels. In particular, the locations where impurity levels are formed are concentrated near the interface between the first electrode 106 and the metal oxide layer 104, effectively reducing the thickness of the second layer 104b. As a result, the resistance of the metal oxide layer 104 decreases. In other words, the resistance of the metal oxide layer 104 of the hydrogen sensor element 100 decreases as the amount of hydrogen-containing gas that comes into contact with the first electrode 106 through the opening 110 increases. Note that in the reference element 100a, since there is no opening 110, no reaction occurs between the first electrode 106 and the hydrogen-containing gas. Therefore, the resistance value of the metal oxide layer 104 of the reference element 100a does not change depending on whether or not hydrogen-containing gas is present in the gas being detected.

[0039] In the above specific example, the metal oxide layer 104 is TaO ｘ The first layer 104a is made of the material Ta ２ O ５ An example of a two-layer structure consisting of a second layer 104b made of the material Ta ２ O ５ or TaO ｘ A single-layer structure using this material is also acceptable.

[0040] The first electrode 106 is laminated on the upper surface of the metal oxide layer 104. The first electrode 106 is a planar electrode with hydrogen dissociability and has two main surfaces. One of the two main surfaces of the first electrode 106 (specifically, the lower surface) is in contact with the metal oxide layer 104, and the other main surface (specifically, the upper surface) is in contact with the metal layer 106s. In the hydrogen sensor element 100, the first electrode 106 has an exposed portion 106e that is exposed to the outside air within the opening 110. Therefore, in the hydrogen sensor element 100, the upper surface of the first electrode 106 is also in contact with the outside air. On the other hand, in the reference element 100a, the upper surface of the first electrode 106 is not in contact with the outside air and is in contact only with the metal layer 106s. The exposed portion 106e is located in the central part of the first electrode 106 in a plan view.

[0041] The first electrode 106 is made of a material that has catalytic activity in dissociating hydrogen atoms from gas molecules containing hydrogen atoms, such as a precious metal such as platinum (Pt), iridium (Ir), or palladium (Pd), or nickel (Ni), or an alloy containing at least one of these. Among these, the first electrode 106 may be made of platinum (Pt), palladium (Pd), or an alloy of Pt and Pd. A specific example in this embodiment is an example in which the first electrode 106 is made of platinum (Pt).

[0042] Two terminals are connected to the first electrode 106 via a via 108 and a metal layer 106s. Specifically, the first electrode 106 of the hydrogen sensor element 100 is connected to a first terminal TE1 and a second terminal TE2, and the first electrode 106 of the reference element 100a is connected to a second terminal TE2 and a third terminal TE3. The first terminal TE1, the second terminal TE2, and the third terminal TE3 are covered from above by insulating films 107c and 109b. The insulating films 107c and 109b are provided with openings TE1a, TE2a, and TE3a, respectively, in a plan view, at positions that overlap with the first terminal TE1, the second terminal TE2, and the third terminal TE3, respectively, exposing the first terminal TE1, the second terminal TE2, and the third terminal TE3. The first terminal TE1, the second terminal TE2, and the third terminal TE3 are connected to terminals A, B, and C of the sensor chip 10 by wiring via openings TE1a, TE2a, and TE3a, respectively. The first terminal TE1, the second terminal TE2, and the third terminal TE3 are layered metal terminals.

[0043] As shown in Figure 2B, the first terminal TE1 and the second terminal TE2 are positioned on either side of the exposed portion 106e in a plan view of the first electrode 106. The first terminal TE1 is connected to one end of the first electrode 106 in a predetermined direction parallel to the upper surface of the first electrode 106, and the second terminal TE2 is connected to the other end of the first electrode 106 in the same predetermined direction. With this arrangement, current flows between the first terminal TE1 and the second terminal TE2 (in other words, between terminal A and terminal B), thereby energizing the exposed portion 106e of the first electrode 106, that is, current flows through the exposed portion 106e. This energization of the exposed portion 106e of the first electrode 106 is thought to activate the hydrogen dissociation action of the exposed portion 106e.

[0044] Furthermore, since the reference element 100a does not have an opening 110 and there is no exposed portion 106e of the first electrode 106, no reaction with hydrogen-containing gas occurs. The second terminal TE2 and the third terminal TE3 are positioned in a plan view of the first electrode 106, sandwiching the central part of the first electrode 106 in the reference element 100a. The second terminal TE2 is connected to one end of the first electrode 106 in a predetermined direction parallel to the upper surface of the first electrode 106, and the third terminal TE3 is connected to the other end of the first electrode 106 in the same predetermined direction. In the reference element 100a, when current flows between the second terminal TE2 and the third terminal TE3 (in other words, between terminal B and terminal C), the portion of the first electrode 106 corresponding to the exposed portion 106e in the hydrogen sensor element 100 is energized, that is, current flows through that portion. For example, the distance over which current flows at the first electrode 106 is the same for both the hydrogen sensor element 100 and the reference element 100a.

[0045] The insulating films 107a, 107b, 107c, 109a, and 109b are formed, for example, from a silicon oxide film or a silicon nitride film.

[0046] Furthermore, a metal layer 106s is formed on the upper surface of the first electrode 106 other than the opening 110. The metal layer 106s is made of, for example, TiAlN and is formed as an etching stopper during via formation, but it is not essential that the metal layer 106s is formed on the upper surface of the first electrode 106.

[0047] In the above description, the hydrogen detection device 30 was configured to pass current between the ends of the first electrode 106 in both the hydrogen sensor element 100 and the reference element 100a. However, it is not limited to this configuration, and the hydrogen sensor element 100 and the reference element 100a may be configured to pass current between the first electrode 106 and the second electrode 103. For example, terminal A may be connected to the second electrode 103 of the hydrogen sensor element 100, and terminal C may be connected to the second electrode of the reference element 100a. This makes it possible to realize a hydrogen detection device 30 having a configuration in which current is passed between the first electrode 106 and the second electrode 103, either as an alternative to the configuration in which current is passed between the ends of the first electrode 106, or as a switchable configuration between the two.

[0048] Figure 3 is a flowchart showing the manufacturing method of the sensor chip 10 shown in Figures 2A and 2B. First, film deposition and photolithography (pattern transfer and etching) are repeated on the semiconductor substrate 102 to form a laminate for two resistive elements (i.e., hydrogen sensor element 100 and reference element 100a) (step S20). As a result, from the bottom layer upwards, (i) semiconductor substrate 102, (ii) insulating film 107a as an interlayer insulating film formed from P-TEOS (tetraethoxysilane by plasma), (iii) second electrode 103 such as TaN or TiN, (iv) Ta ２ O ５ and TaO １．５ A laminate is formed in which a metal oxide layer 104 composed of a laminate of (v) Pt or the like is laminated, a first electrode 106 such as (vi) TiAlN or the like is laminated, an insulating film 107b as an interlayer insulating film formed from P-TEOS or the like is laminated, an insulating film 109a as a protective film such as P-SiON (silicon oxynitride film made by plasma) is laminated, a first terminal TE1, a second terminal TE2 and a third terminal TE3 as electrodes such as Au is laminated, an insulating film 107c as an interlayer insulating film such as HDP-NSG (nitrogen-doped glass made by high-density plasma) is laminated, and an insulating film 109b as a protective film such as P-SiON is laminated. Through this process, an intermediate product of the hydrogen sensor element 100 before the opening 110 is formed and a finished reference element 100a are produced.

[0049] Next, the metal layer 106s, insulating film 107b, insulating film 109a, insulating film 107c, and a portion of insulating film 109b are removed in a rectangular shape in a plan view from the laminate (i.e., the intermediate product of the hydrogen sensor element 100) by photolithography (pattern transfer and etching) so that the upper surface of the first electrode 106 is exposed, thereby forming the opening 110 of the hydrogen sensor element 100 (step S21). This process completes the hydrogen sensor element 100 and the manufacturing of the sensor chip 10 is completed.

[0050] Next, the operation of the hydrogen detection device 30 configured as described above will be explained. Figure 4 is a flowchart showing the procedure (i.e., hydrogen detection method) for hydrogen detection by the hydrogen detection device 30 according to the embodiment. In Figure 4, steps S32 to S36 are an example of a control step, and step S37 is an example of a calculation step. In the control step, the control unit 41 controls the current applied to the hydrogen sensor element 100 and the reference element 100a based on the measurement result of the output of the reference element 100a. In the calculation step, the calculation unit 42 calculates the gas concentration from the measurement results of the outputs of the hydrogen sensor element 100 and the reference element 100a. Furthermore, the hydrogen detection method described below is an example of a gas detection method.

[0051] First, after preparing to install the hydrogen detection device 30 in the environment to be detected, the hydrogen detection device 30 applies an initial current I (n=0) to the series-connected hydrogen sensor element 100 and reference element 100a using the current source 21 (step S30). In other words, in the measurement unit 20 of the hydrogen detection device 30, the current source 21 applies a predetermined constant initial current I (n=0) between terminals A and C of the sensor chip 10 under instructions from the control unit 41 of the signal processing unit 23. As a result, the same initial current I (n=0) flows through the series-connected hydrogen sensor element 100 and reference element 100a. Here, n is the resistance R of the reference element 100a, which will be described later. Ｒ It is a positive integer corresponding to the calculation of n. For each number of n, the voltage across the reference element 100a V ＲThe resistance R of the reference element 100a was measured. Ｒ This is calculated.

[0052] Next, the hydrogen detection device 30 performs a warm-up process to heat the hydrogen sensor element 100 and the reference element 100a to their operating temperature (step S31). During the warm-up process, the control unit 41 applies current (initial current I (n=0)) to the hydrogen sensor element 100 and the reference element 100a using the current source 21 for a predetermined time to energize them. The predetermined time is the time it takes for the hydrogen sensor element 100 and the reference element 100a to heat up to their operating temperature after being energized, and is determined in advance, for example, by experimentation. The predetermined time is also determined by the voltage V across the respective hydrogen sensor element 100 and reference element 100a, which will be described later. ｈ and V Ｒ It is longer than the measurement interval.

[0053] After the warm-up process (step S31), the hydrogen detection device 30 measures the voltage V across the hydrogen sensor element 100 and the reference element 100a when the initial current I (n=0) is applied. ｈ and V Ｒ Measure the resistance R of the reference element 100a. Ｒ (n=0) is calculated (step S32). At this time, in the measurement unit 20 of the hydrogen detection device 30, the voltmeter 22, under the instruction from the control unit 41 of the signal processing unit 23, calculates the voltage across the hydrogen sensor element 100 when the initial current I (n=0) is applied. ｈ and the voltage V across the reference element 100a Ｒ The measurement is performed by switching the voltage across the reference element 100a V Ｒ If this is measured, the voltage across the hydrogen sensor element 100 V ｈ It is not necessary to measure this. Next, the hydrogen detection device 30 (specifically the control unit 41) determines the initial current I (n=0) and the obtained voltage V across the reference element 100a. Ｒ Using the resistor R of the reference element 100a ＲThe value of (n=0) is calculated. Then, the hydrogen detection device 30 (specifically the control unit 41) increases n by 1 (i.e., adds 1) and applies a current I(n) to the hydrogen sensor element 100 and the reference element 100a using the current source 21 (step S33). The initial current I(n=0) and the current I(n=1) are, for example, the same, but may be different.

[0054] Resistor R of reference element 100a Ｒ The reaction characteristics of (n) and the hydrogen sensor element 100 are affected by ambient temperature. Therefore, the control unit 41 of the signal processing unit 23 reduces the influence of ambient temperature by controlling the applied current based on the measurement result of the output of the reference element 100a. In this embodiment, the control unit 41 of the signal processing unit 23 controls the applied current I(n) and the measured voltage V across the reference element 100a. Ｒ The resistor R of the reference element 100a Ｒ (n) is calculated, and the resistance R of the reference element 100a is calculated. Ｒ The change in (n) is fed back, and temperature correction is performed to reduce the influence of ambient temperature by adjusting the current.

[0055] Specifically, first, as in step S33, in the measurement unit 20 of the hydrogen detection device 30, the current source 21 applies a current I(n) between terminals A and C of the sensor chip 10 under instructions from the control unit 41 of the signal processing unit 23. After step S33, the hydrogen detection device 30 measures the voltage V across the hydrogen sensor element 100 and the reference element 100a when the current I(n) is applied. ｈ and V Ｒ Measure the resistance R of the reference element. Ｒ (n) is calculated (step S34). At this time, in the measurement unit 20 of the hydrogen detection device 30, the voltmeter 22, under the instruction from the control unit 41 of the signal processing unit 23, calculates the voltage across the hydrogen sensor element 100 when the current I(n) is applied V ｈ and the voltage V across the reference element 100a Ｒ The measurement is performed by switching the voltage across the hydrogen sensor element 100 and the reference element 100a, respectively. ｈand V Ｒ The measurement results are the output measurements for the hydrogen sensor element 100 and the reference element 100a, respectively. Next, the hydrogen detection device 30 (specifically the control unit 41) measures the current I(n) and the obtained voltage V across the reference element 100a. Ｒ Using the resistor R of the reference element 100a Ｒ Calculate (n).

[0056] Next, the control unit 41 controls the voltage V across the reference element 100a. Ｒ The resistance R of the reference element 100a is calculated based on the measurement results. Ｒ Step S35 determines whether the change is greater than a predetermined threshold. In this embodiment, the control unit 41 determines whether the resistance R of the reference element 100a that does not react to the gas is greater than a predetermined threshold. Ｒ (n) is the reference point for the resistor R Ｒ The absolute value of the rate of change is calculated as shown in equation 1 below, and it is determined whether or not it exceeds the set threshold rate of change δ. The threshold rate of change δ is set, for example, based on the thickness and material of the first electrode 106. For example, the threshold rate of change δ is increased as the resistance of the first electrode 106 increases, depending on the thickness and material of the first electrode 106.

[0057]

[0058] R in formula 1 above Ｒ (n-1) is the voltage V across the reference element 100a measured in the previous measurement. Ｒ The resistance, R, calculated using Ｒ (n) is the voltage V across the reference element 100a that was measured this time. Ｒ The resistance calculated using the following formula is shown. The left side of Equation 1 is the resistance R of the reference element 100a. Ｒ This shows the absolute value of the rate of change. Note that in step S35, the resistor R of the reference element 100a Ｒ As a change, the resistor R of the reference element 100a Ｒ It is not the rate of change of the resistor R of the reference element 100a. Ｒ The amount of change (the numerator on the left side of equation 1 above) may also be used for the determination.

[0059] Resistor R of reference element 100aＲ If the change does not exceed a predetermined threshold, in the example using formula 1 above, the resistance R of the reference element 100a Ｒ If the absolute value of the rate of change does not exceed the threshold rate of change δ (No in step S35), the control unit 41 does not modify the current applied to the reference element 100a and the hydrogen sensor element 100, and the calculation unit 42 calculates the voltage across the reference element 100a V Ｒ and the voltage across the hydrogen sensor element 100 V ｈ Based on the ratio, the hydrogen concentration is calculated and output (steps S37 and S38). Specifically, in the measurement unit 20 of the hydrogen detection device 30, the calculation unit 42 of the signal processing unit 23 calculates the voltage V across the reference element 100a obtained in step S34. Ｒ and the voltage across the hydrogen sensor element 100 V ｈ Voltage ratio V Ｒ / V ｈ This is generated as a signal indicating the hydrogen concentration, and this signal is converted to a concentration and output externally. After step S38, the hydrogen detection device 30 increments n by 1, making n+1 the new n, and shifts to step S33. The hydrogen concentration is the voltage ratio V Ｒ / V ｈ The following equation 2 is used to calculate the value using a function f derived from the dependence data between the gas concentration and the function f. The calculation unit 42 uses the voltage ratio V as a signal indicating the hydrogen concentration. Ｒ / V ｈ The output may be sent directly to the outside. Furthermore, the calculation unit 42 uses the voltage across the reference element 100a obtained in step S34 as a signal indicating the hydrogen concentration V Ｒ and the voltage across the hydrogen sensor element 100 V ｈ You may also calculate the difference between the two.

[0060]

[0061] On the other hand, the resistor R of the reference element 100a Ｒ If the change is greater than a predetermined threshold, in the example using formula 1 above, the resistance R of the reference element 100a ＲIf the absolute value of the rate of change of (n) is greater than the threshold rate of change δ (Yes in step S35), the control unit 41 corrects the current applied to the reference element 100a and the hydrogen sensor element 100 (step S36). In this embodiment, the control unit 41 performs temperature correction by changing the current applied to the reference element 100a and the hydrogen sensor element 100 as shown in the following equation 3.

[0062]

[0063] In equation 3 above, the corrected current I(n+1) is the sum of the original current I(n) and the correction amount Δ. The current correction changes the current applied to the reference element 100a and the hydrogen sensor element 100, and at the same time, the Joule heat generated in the reference element 100a and the hydrogen sensor element 100 changes.

[0064] The correction amount Δ in the above equation 3 is set based on, for example, the specific heat capacity of the first electrode 106. For example, the larger the specific heat capacity of the first electrode 106, the larger the correction amount Δ should be. Also, the correction amount Δ is a positive value when the hydrogen detection device 30 is used in a low-temperature environment. Note that the correction amount Δ may also be a negative value. Furthermore, the correction amount Δ is determined in step S35 by the resistance R of the reference element 100a. Ｒ It may change in response to changes in the reference element 100a. For example, the resistor R Ｒ If the rate of change or amount of change is negative (i.e., resistance R Ｒ If the value is low, the correction amount Δ is set to a positive value, and the resistor R Ｒ If the rate of change or amount of change is positive (i.e., resistance R Ｒ If (the value is increasing), the correction amount Δ shall be set to a negative value. Also, the resistor R Ｒ The larger the absolute value of the rate of change or the amount of change, the larger the absolute value of the correction amount Δ may be.

[0065] Thus, in step S36, the control unit 41 controls the applied current by adding or subtracting the applied current to the hydrogen sensor element 100 and the reference element 100a. Alternatively, the control unit 41 may control the applied current by multiplying the applied current to the hydrogen sensor element 100 and the reference element 100a by a correction coefficient.

[0066] After step S36, the hydrogen detection device 30 (specifically the control unit 41) sets n+1 to a new n, that is, the modified current I(n+1) to a new current I(n), and applies it to the reference element 100a and the hydrogen sensor element 100 (step S33).

[0067] After shifting from step S36 or step S38 to step S33, steps S34 and S35 are performed again, and the resistor R of the reference element 100a is... Ｒ It is determined whether the change is greater than a predetermined threshold. In this way, steps S33 to S38 are repeated according to the flowchart shown in Figure 4. That is, the voltage V across the hydrogen sensor element 100 and the reference element 100a are determined. ｈ and V Ｒ Measurement and the resistance R of the reference element 100a Ｒ The determination of whether the change is greater than a predetermined threshold is repeated. Through this operation of the hydrogen detection device 30, the control unit 41 determines the resistance R of the reference element 100a. Ｒ The current applied to the reference element 100a and the hydrogen sensor element 100 is controlled so that the value falls within a certain range.

[0068] Resistor R of reference element 100a Ｒ This does not change depending on whether or not hydrogen is present in the gas being detected, but depends on the temperature of the reference element 100a. Therefore, the resistance R of the reference element 100a ＲWhen the value falls within a certain range, the temperatures of the reference element 100a and the hydrogen sensor element 100, which are connected in series and to which the same current is applied, are also controlled within a certain range. In this way, since the temperatures of the reference element 100a and the hydrogen sensor element 100 are maintained within a certain range through current correction, the hydrogen reaction characteristics of the hydrogen sensor element 100 can be stabilized. Therefore, a change in the output of the hydrogen detection device 30 when the hydrogen sensor element 100 is exposed to hydrogen is less likely to be affected by changes in environmental temperature. That is, through the operation of the hydrogen detection device 30 as described above, the control unit 41 controls the voltage V across the reference element 100a Ｒ and the voltage V across the hydrogen sensor element 100 ｈ The applied current to the hydrogen sensor element 100 and the reference element 100a is controlled such that the influence of changes in environmental temperature on changes in the ratio or difference between them can be reduced.

[0069] Here, the reference element 100a and the hydrogen sensor element 100 are formed on the same semiconductor substrate 102 and have substantially the same structure. Further, the voltage ratio V between the hydrogen sensor element 100 and the reference element 100a that is insensitive to hydrogen Ｒ / V ｈ is generated as a signal indicating the hydrogen concentration. Therefore, the voltage ratio V Ｒ / V ｈ , the resistance R of the hydrogen sensor element 100 ｈ temperature dependence is canceled out by the temperature dependence of the resistance R of the reference element 100a Ｒ . Therefore, the voltage ratio V Ｒ / V ｈ and the hydrogen concentration represented by the above Equation 2 depend on the resistance R of the hydrogen sensor element 100 ｈ the influence of temperature dependence is suppressed, and it can be said that the value indicates hydrogen concentration with high accuracy.

[0070] As described above, the hydrogen detection device 30 according to the embodiment uses the resistance R of the hydrogen sensor element 100 ｈ The measurement result of the output of the reference element 100a, which is used to reduce the influence of temperature dependence, is also used for current correction to stabilize the hydrogen reaction characteristics of the hydrogen sensor element 100. Therefore, the influence of environmental temperature can be reduced, and miniaturization can be achieved.

[0071] Figures 5A and 5B illustrate the results of a detection experiment using the hydrogen detection device 30 according to the embodiment. Specifically, Figure 5A shows the time (horizontal axis), ambient temperature, and the resistance R of the reference element 100a when there is no current correction. Ｒ This figure shows an example plotting the relationship with (vertical axis). Figure 5A shows the resistance R of the reference element 100a when the atmosphere in which the sensor chip 10 is placed is cooled from 33°C to -10°C in an atmospheric environment, and no current correction is made. Ｒ Figure 5B also shows the time change in the ambient temperature in which the sensor chip 10 is placed. Furthermore, Figure 5B shows the time (horizontal axis), ambient temperature, and the resistance R of the reference element 100a when current correction is applied. Ｒ This figure shows an example plotting the relationship with (vertical axis). Figure 5B shows the resistance R of the reference element 100a when the current is corrected in the same environment as in Figure 5A. Ｒ The graph also shows the time change in the temperature of the atmosphere in which the sensor chip 10 is placed.

[0072] Here, "no current correction" refers to the case where a constant current is applied to the hydrogen sensor element 100 and the reference element 100a without correction during the detection experiment. "Current correction" refers to the case where the hydrogen detection method using the hydrogen detection device 30 shown in Figure 4 is performed.

[0073] Figure 5A shows the resistor R of the reference element 100a when there is no current correction as in the reference example. Ｒ The characteristics are shown, and Figure 5B shows the resistance R of the reference element 100a when there is current correction according to the embodiment. Ｒ This shows the characteristics. As shown in Figure 5A, when the atmosphere in which the sensor chip 10 is placed is cooled, the resistance R of the reference element 100a when there is no current correction. Ｒ The same decrease as the ambient temperature T. On the other hand, as shown in Figure 5B, when the ambient temperature in which the sensor chip 10 is placed decreases, the resistance R of the reference element 100a when there is current correction. ＲUnlike the ambient temperature T, the temperature of the reference element 100a is maintained within a certain range. This is because the Joule heat generated by the current applied to the reference element 100a is adjusted by current correction, and the temperature of the reference element 100a is maintained within a certain range. Furthermore, the hydrogen sensor element 100, to which the same current as the reference element 100a is applied, can also be said to have the same temperature maintenance effect as the reference element 100a. Therefore, according to the hydrogen detection method using the hydrogen detection device 30 according to the embodiment, even in a temperature-changing environment, hydrogen detection with reduced influence of ambient temperature can be achieved compared to the hydrogen detection method without current correction according to the reference example. In addition, according to the hydrogen detection device 30 according to the embodiment, since the Joule heat generated in the reference element 100a and the hydrogen sensor element 100 is utilized without using a separate heater, it is possible to reduce dependence on ambient temperature without a heater, and it is possible to achieve a configuration that can detect the target gas with high sensitivity while reducing power consumption and miniaturizing the device.

[0074] Figure 6 illustrates the results of a hydrogen concentration detection experiment using the hydrogen detection device 30 according to the embodiment. Figure 6 shows the two types of voltage ratios (V) obtained from the sensor chip 10 when the atmosphere in which the sensor chip 10 is placed is -15°C. Ｒ / V ｈ This shows the time variation of the voltage ratio (V). Ｒ / V ｈ ) can also be said to indicate the amount of hydrogen reaction in the hydrogen sensor element 100. In the graphs (A), (B), and (C) of Figure 6, the solid line represents the voltage ratio (V) of the hydrogen sensor element 100 and the reference element 100a when current correction is performed. Ｒ / V ｈ The dotted line shows the time variation of the voltage ratio (V) between the hydrogen sensor element 100 and the reference element 100a when no current correction is performed. Ｒ / V ｈ This shows the time change of the voltage ratio (V) in the hydrogen detection method according to the embodiment. In other words, in the graphs (A), (B), and (C) of Figure 6, the solid line represents the time change of the voltage ratio (V) in the hydrogen detection method according to the embodiment. Ｒ / V ｈ The dotted line shows the time change of the voltage ratio (V) in the hydrogen detection method according to the reference example. Ｒ / Vｈ This shows the time change of ).In addition, in the detection experiment shown in Figure 6, the same concentration of hydrogen was introduced into the atmosphere in which the sensor chip 10 was placed for a period of 300 to 600 seconds, both when current correction was performed and when current correction was not performed.Note that in Figure 6, the vertical axis of the graph is set to V in order to set the reaction amount to 0 when no reaction with hydrogen occurs. Ｒ / V ｈ It is set to -1.

[0075] Figure 6(B) shows the voltage ratio (V Ｒ / V ｈ To explain the rise characteristics, Figure 6(A) shows an enlarged view of the time from the start of hydrogen introduction in the graph. Also, Figure 6(C) shows the voltage ratio (V Ｒ / V ｈ To explain the fall-off characteristics, the time after the end of hydrogen introduction in the graph of Figure 6(A) is shown in an enlarged view.

[0076] The rise time was evaluated using a method called T80 evaluation. Compared to the dotted line (no current correction), the rise time obtained with the solid line (with current correction) is approximately 2.3 times higher. The T80 evaluation is based on the maximum reaction volume (in the example shown in Figure 6, V Ｒ / V ｈ This method compares reaction rates by measuring the time it takes to reach 80% of the maximum value (V) of -1. The falling reaction rate is evaluated using a method called T20 evaluation, and the solid line (with current correction) shows a falling rate approximately 2.5 times higher than the dotted line (without current correction). The T20 evaluation uses the maximum reaction amount (V in the example shown in Figure 6). Ｒ / V ｈThis method compares reaction rates by measuring the time it takes to reach 20% of the maximum value of -1. As shown, the reaction rate in the hydrogen detection method according to the embodiment is more than twice as high as that in the hydrogen detection method according to the reference example. This is because the hydrogen detection method according to the reference example includes the influence of changes in the external ambient temperature in a low-temperature environment, whereas, as shown in Figure 5B, the hydrogen detection method according to the embodiment suppresses the influence of changes in the external ambient temperature in a low-temperature environment by current correction. More specifically, in the hydrogen detection method according to the embodiment, the temperature of the hydrogen sensor element 100 is maintained at the same level as in a non-low-temperature environment by current correction, and the decrease in the reaction rate in the hydrogen sensor element 100 is suppressed. Therefore, according to the hydrogen detection method using the hydrogen detection device 30 according to the embodiment, high-speed detection of hydrogen can be achieved in a low-temperature environment by current correction compared to the hydrogen detection method without current correction according to the reference example.

[0077] [Modification 1] Next, Modification 1 of the embodiment will be described. In the following, the differences from the above embodiment will be explained in detail, and the explanation of the common points will be omitted or simplified. The measurement unit 20 that constitutes the hydrogen detection device 30 according to the embodiment is not limited to the configuration of the hydrogen detection device 30 shown in Figure 1, but may be, for example, the measurement unit of the hydrogen detection device according to Modification 1 of the embodiment shown below.

[0078] Figure 7 is a block diagram showing the configuration of the hydrogen detection device 30a according to the first modified example of the embodiment.

[0079] As shown in Figure 7, the hydrogen detection device 30a according to the first modification of the embodiment differs from the hydrogen detection device 30 according to the embodiment mainly in that it has a measurement unit 20a instead of the measurement unit 20. The hydrogen detection device 30a according to the first modification of the embodiment comprises a sensor chip 10 and a measurement unit 20a. The hydrogen detection device 30a is an example of a gas detector.

[0080] The hydrogen detection device 30 according to the embodiment and the hydrogen detection device 30a according to the modified embodiment 1 are the same in that they have a hydrogen sensor element 100 and a reference element 100a formed on a single semiconductor substrate. In the hydrogen detection device 30a, the sensor chip 10 has the hydrogen sensor element 100 and the reference element 100a connected in parallel to a voltage source 21a, which will be described later. The hydrogen sensor element 100 and the reference element 100a are formed, for example, on a single semiconductor substrate. The sensor chip 10 also has terminals for external connection, including 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 reference element 100a, and terminal C connected to the other end of the reference element 100a.

[0081] Here, the hydrogen sensor element 100 is a variable resistance element that has a structure exposed to hydrogen and changes its resistance value according to the hydrogen concentration. On the other hand, the reference element 100a is a reference resistance element that does not react to hydrogen. More specifically, the reference element 100a is provided to counteract the temperature dependence of the resistance value of the hydrogen sensor element 100, and has basically the same structure as the hydrogen sensor element 100, but is deactivated by the gas and has a structure that is not exposed to hydrogen.

[0082] The structure of the sensor chip 10 is the same, for example, in the hydrogen detection device 30 according to the embodiment and the hydrogen detection device 30a according to the modified example 1 of the embodiment, as explained with reference to Figures 2A and 2B.

[0083] The measurement unit 20a 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. The measurement unit 20a includes a voltage source 21a, ammeters 22a and 22b, and a signal processing unit 23. The signal processing unit 23 is a processing circuit that includes a control unit 41 and a calculation unit 42.

[0084] The voltage source 21a is a circuit that applies a predetermined constant voltage between terminals A and B of the sensor chip 10, and between terminals B and C of the sensor chip 10, under instructions from the signal processing unit 23, and is composed of, for example, a transistor.

[0085] The ammeters 22a and 22b are measurement circuits that measure the output of the hydrogen sensor element 100 and the reference element 100a. Specifically, the ammeters 22a and 22b are circuits that measure the current of the hydrogen sensor element 100 (i.e., the current flowing between terminal A and terminal B) and the current of the reference element 100a (i.e., the current flowing between terminal B and terminal C) as electrical characteristic values ​​related to the hydrogen sensor element 100 and the reference element 100a, respectively, under instructions from the control unit 41 of the signal processing unit 23. The ammeters 22a and 22b are composed of, for example, a shunt resistor, an amplifier, and an A / D converter.

[0086] The signal processing unit 23 is a circuit that instructs the voltage source 21a to apply a voltage, reads two types of measurement currents from the ammeters 22a and 22b, and generates and outputs a signal indicating the hydrogen concentration from the two types of measurement currents read out. These operations by the signal processing unit 23 are performed by the control unit 41 and the arithmetic unit 42. The signal processing unit 23 is composed of, for example, one or more processors that execute a built-in program. In the signal processing unit 23, the control unit 41 and the arithmetic unit 42 may be composed of a common processor or may be composed of separate processors. Furthermore, the signal processing unit 23 may be a dedicated logic circuit that executes the processing performed by the control unit 41 and the arithmetic unit 42.

[0087] The measurement unit 20a may be a circuit formed on the same semiconductor substrate as the sensor chip 10, or it may be a circuit provided on a separate substrate or device (for example, a measuring instrument or a computer device for measurement) connected to the sensor chip 10. Furthermore, the measurement unit 20a is not limited to a configuration having two ammeters 22a and 22b that measure two types of current (specifically, the current of the hydrogen sensor element 100 and the current of the reference element 100a), but may also have a configuration having one ammeter that measures while switching between the two types of current using a switch circuit or the like.

[0088] Next, the operation of the hydrogen detection device 30a configured as described above will be explained. Figure 8 is a flowchart showing the procedure (i.e., hydrogen detection method) for hydrogen detection by the hydrogen detection device 30a according to Modification 1 of the Embodiment. In Figure 8, steps S42 to S46 are an example of a control step, and step S47 is an example of a calculation step. In the control step, the control unit 41 controls the applied voltage to the hydrogen sensor element 100 and the reference element 100a based on the measurement result of the output of the reference element 100a. In the calculation step, the calculation unit 42 calculates the gas concentration from the measurement results of the outputs of the hydrogen sensor element 100 and the reference element 100a. Furthermore, the hydrogen detection method described below is an example of a gas detection method.

[0089] First, after preparing to install the hydrogen detection device 30a in the environment to be detected, the hydrogen detection device 30a applies an initial voltage V(n=0) to the parallel-connected hydrogen sensor element 100 and reference element 100a using a voltage source 21a (step S40). In other words, in the measurement unit 20a of the hydrogen detection device 30a, the voltage source 21a applies a predetermined constant initial voltage V(n=0) between terminals B and A and between terminals B and C of the sensor chip 10, under instructions from the control unit 41 of the signal processing unit 23. As a result, the same initial voltage V(n=0) flows through the parallel-connected hydrogen sensor element 100 and reference element 100a. Here, n is the resistance R of the reference element 100a, which will be described later. Ｒ It is a positive integer corresponding to the calculation of n. For each number of n, the current I of the reference element 100a Ｒ The resistance R of the reference element 100a was measured. Ｒ This is calculated.

[0090] Next, the hydrogen detection device 30a performs a warm-up process to heat the hydrogen sensor element 100 and the reference element 100a to their operating temperature (step S41). In the warm-up process, the control unit 41 applies a voltage (initial voltage V(n=0)) to the hydrogen sensor element 100 and the reference element 100a using the voltage source 21a for a predetermined time to energize them. The predetermined time is the time it takes for the hydrogen sensor element 100 and the reference element 100a to heat up to their operating temperature after being energized, and is determined in advance, for example, by experimentation. The predetermined time is also determined by the current I of the hydrogen sensor element 100 and the reference element 100a, which will be described later. ｈ and I Ｒ It is longer than the measurement interval.

[0091] After the warm-up process (step S41), the hydrogen detection device 30a checks the current I of the hydrogen sensor element 100 and the reference element 100a when the initial voltage V (n=0) is applied. ｈ and I Ｒ Measure the resistance R of the reference element. Ｒ (n=0) is calculated (step S42). At this time, in the measurement unit 20a of the hydrogen detection device 30a, the ammeters 22a and 22b, under the instruction from the control unit 41 of the signal processing unit 23, calculate the current I of the hydrogen sensor element 100 when the initial voltage V (n=0) is applied. ｈ and the current I of the reference element 100a Ｒ The current I of at least the reference element 100a is measured. In step S42, the current I of at least the reference element 100a is measured. Ｒ If measured, the current I of the hydrogen sensor element 100 ｈ It is not necessary to measure this. Next, the hydrogen detection device 30a (specifically the control unit 41) measures the initial voltage V (n=0) and the obtained current I of the reference element 100a. Ｒ Using the resistor R of the reference element 100a Ｒ The value of (n=0) is calculated. Then, the hydrogen detection device 30a (specifically the control unit 41) increases n by 1 (i.e., adds 1) and applies a voltage V(n) to the hydrogen sensor element 100 and the reference element 100a using the voltage source 21a (step S43). The initial voltage V(n=0) and the voltage V(n=1) are, for example, the same, but may be different.

[0092] Resistor R of reference element 100a Ｒ The reaction characteristics of (n) and the hydrogen sensor element 100 are affected by ambient temperature. Therefore, the control unit 41 of the signal processing unit 23 reduces the influence of ambient temperature by controlling the applied voltage based on the measurement result of the output of the reference element 100a. In this embodiment, the control unit 41 of the signal processing unit 23 controls the applied voltage V(n) and the measured current I of the reference element 100a. Ｒ The resistor R of the reference element 100a Ｒ (n) is calculated, and the resistance R of the reference element 100a is calculated. Ｒ The change in (n) is fed back, and temperature correction is performed to reduce the influence of ambient temperature through voltage modification.

[0093] Specifically, first, as in step S43, in the measurement unit 20a of the hydrogen detection device 30a, the voltage source 21a applies a voltage V(n) between terminals B and A and between terminals B and C of the sensor chip 10, under instructions from the control unit 41 of the signal processing unit 23. After step S43, the hydrogen detection device 30a measures the current I of the hydrogen sensor element 100 and the reference element 100a when the voltage V(n) is applied. ｈ and I Ｒ Measure the resistance R of the reference element. Ｒ (n) is calculated (step S44). At this time, in the measurement unit 20a of the hydrogen detection device 30a, the ammeters 22a and 22b, under the instruction from the control unit 41 of the signal processing unit 23, calculate the current I of the hydrogen sensor element 100 when the voltage V(n) is applied. ｈ and the current I of the reference element 100a Ｒ The current I flowing through the hydrogen sensor element 100 and the reference element 100a is measured. In this modified example, the current I flowing through the hydrogen sensor element 100 and the reference element 100a is measured. ｈ and I Ｒ The measurement results are the output measurements of the hydrogen sensor element 100 and the reference element 100a, respectively. Next, the hydrogen detection device 30a (specifically the control unit 41) measures the voltage V(n) and the obtained current I of the reference element 100a. Ｒ Using the resistor R of the reference element 100a ＲCalculate (n).

[0094] Next, the control unit 41 controls the current I of the reference element 100a. Ｒ The resistance R of the reference element 100a is calculated based on the measurement results. Ｒ Step S45 determines whether the change is greater than a predetermined threshold. In this modified example, the control unit 41 determines whether the resistance R of the reference element 100a that does not react to the gas is greater than a predetermined threshold. Ｒ (n) is the reference point for the resistor R Ｒ The absolute value of the rate of change is calculated as shown in equation 1 below, and it is determined whether or not it exceeds the set threshold rate of change δ. The threshold rate of change δ is set, for example, based on the thickness and material of the first electrode 106. For example, the threshold rate of change δ is increased as the resistance of the first electrode 106 increases, depending on the thickness and material of the first electrode 106.

[0095]

[0096] R in formula 1 above Ｒ (n-1) is the current I of the reference element 100a measured in the previous measurement. Ｒ The resistance, R, calculated using Ｒ (n) is the current I of the reference element 100a measured in this study. Ｒ The resistance calculated using the following formula is shown. The left side of Equation 1 is the resistance R of the reference element 100a. Ｒ This shows the absolute value of the rate of change of (n). Note that in step S45, the resistor R of the reference element 100a Ｒ As a change, the resistor R of the reference element 100a Ｒ It is not the rate of change of the resistor R of the reference element 100a. Ｒ The amount of change (the numerator on the left side of equation 1 above) may also be used for the determination.

[0097] Resistor R of reference element 100a Ｒ If the change does not exceed a predetermined threshold, in the example using formula 1 above, the resistance R of the reference element 100a ＲIf the absolute value of the rate of change of (n) does not exceed the threshold rate of change δ (No in step S45), the control unit 41 does not change the voltage applied to the reference element 100a and the hydrogen sensor element 100, and the calculation unit 42 calculates the current I of the reference element 100a. Ｒ and the current I of the hydrogen sensor element 100 ｈ Based on the ratio, the hydrogen concentration is calculated and output (steps S47 and S48). Specifically, in the measurement unit 20a of the hydrogen detection device 30a, the calculation unit 42 of the signal processing unit 23 calculates the current I of the reference element 100a obtained in step S44. Ｒ and the current I of the hydrogen sensor element 100 ｈ Current ratio I Ｒ / I ｈ This is generated as a signal indicating the hydrogen concentration, and this signal is converted to a concentration and output externally. After step S48, the hydrogen detection device 30a increases n by 1, making n+1 the new n, and shifts to step S43. The hydrogen concentration is current ratio I Ｒ / I ｈ The following equation 4 is calculated using the function f derived from the dependence data between the gas concentration and the current ratio I. Ｒ / I ｈ The output may be left as is. Furthermore, the calculation unit 42 uses the current I of the reference element 100a obtained in step S44 as a signal indicating the hydrogen concentration. Ｒ and the current I of the hydrogen sensor element 100 ｈ You may also calculate the difference between the two.

[0098]

[0099] On the other hand, the resistor R of the reference element 100a Ｒ If the change is greater than a predetermined threshold, in the example using formula 1 above, the resistance R of the reference element 100a Ｒ If the absolute value of the rate of change of (n) is greater than the threshold rate of change δ (Yes in step S45), the control unit 41 corrects the voltage applied to the reference element 100a and the hydrogen sensor element 100 next (step S46). In this modified example, the control unit 41 performs temperature correction by changing the voltage applied to the reference element 100a and the hydrogen sensor element 100 as shown in the following equation 5.

[0100]

[0101] In equation 5 above, the corrected voltage V(n+1) is the sum of the original voltage V(n) and the correction amount Δ. The voltage correction changes the voltage applied to the reference element 100a and the hydrogen sensor element 100, and at the same time, the Joule heat generated in the reference element 100a and the hydrogen sensor element 100 changes.

[0102] The correction amount Δ in the above equation 5 is set by, for example, the specific heat capacity of the first electrode 106. For example, the larger the specific heat capacity of the first electrode 106, the larger the correction amount Δ should be. Also, the correction amount Δ is a positive value when the hydrogen detection device 30a is used in a low-temperature environment. Note that the correction amount Δ may also be a negative value. Furthermore, the correction amount Δ is determined by the resistance R of the reference element 100a, which is determined in step S45. Ｒ It may change in response to changes in the reference element 100a. For example, the resistor R Ｒ If the rate of change or amount of change is negative (i.e., resistance R Ｒ If the value is low, the correction amount Δ is set to a positive value, and the resistor R Ｒ If the rate of change or amount of change is positive (i.e., resistance R Ｒ If (the value is increasing), the correction amount Δ shall be set to a negative value. Also, the resistor R Ｒ The larger the absolute value of the rate of change or the amount of change, the larger the absolute value of the correction amount Δ may be.

[0103] Thus, in step S46, the control unit 41 controls the applied voltage by adding or subtracting the applied voltage to the hydrogen sensor element 100 and the reference element 100a. Alternatively, the control unit 41 may control the applied voltage by multiplying the applied voltage to the hydrogen sensor element 100 and the reference element 100a by a correction coefficient.

[0104] After step S46, the hydrogen detection device 30a (specifically the control unit 41) sets n+1 to a new n, that is, the modified voltage V(n+1) to a new voltage V(n), and applies it to the reference element 100a and the hydrogen sensor element 100 (step S43).

[0105] After shifting from step S46 or step S48 to step S43, steps S44 and S45 are performed again, and the resistor R of the reference element 100a is checked. Ｒ It is determined whether the change is greater than a predetermined threshold. In this way, steps S43 to S48 are repeated according to the flowchart shown in Figure 8. That is, the current I of the hydrogen sensor element 100 and the reference element 100a are determined. ｈ and I Ｒ Measurement and the resistance R of the reference element 100a Ｒ The determination of whether the change is greater than a predetermined threshold is repeated. Based on the operation of the hydrogen detection device 30a in this way, the control unit 41 determines whether the resistance R of the reference element 100a is greater than a predetermined threshold. Ｒ The applied voltage to the reference element 100a and the hydrogen sensor element 100 is controlled so that the value falls within a certain range.

[0106] Resistor R of reference element 100a Ｒ This does not change depending on whether or not hydrogen is present in the gas being detected, but depends on the temperature of the reference element 100a. Therefore, the resistance R of the reference element 100a Ｒ When the current I of the reference element 100a is within a certain range, the temperatures of the reference element 100a and the hydrogen sensor element 100, which are connected in parallel and to which the same voltage is applied, are also controlled to be within a certain range. In this way, the temperature of the reference element 100a and the hydrogen sensor element 100 is maintained within a certain range by voltage correction, which enables the stabilization of the hydrogen reaction characteristics of the hydrogen sensor element 100. Therefore, the change in the output of the hydrogen detection device 30a when the hydrogen sensor element 100 is exposed to hydrogen becomes less susceptible to changes in ambient temperature. In other words, through the operation of the hydrogen detection device 30a as described above, the control unit 41 controls the current I of the reference element 100a. Ｒ and the current I of the hydrogen sensor element 100 ｈ The applied voltage to the hydrogen sensor element 100 and the reference element 100a is controlled so as to reduce the influence of changes in ambient temperature on changes in the ratio or difference between them.

[0107] Here, the reference element 100a and the hydrogen sensor element 100 are formed on the same semiconductor substrate 102 and have substantially the same structure. Also, the current ratio I between the hydrogen sensor element 100 and the hydrogen-insensitive reference element 100a is... Ｒ / I ｈ This is generated as a signal indicating hydrogen concentration. Therefore, the current ratio I Ｒ / I ｈ The hydrogen concentration represented by the above formula 4 is determined by the resistance R of the hydrogen sensor element 100. ｈ The influence of temperature dependence is suppressed, and it can be said that this value indicates hydrogen concentration with high accuracy.

[0108] As described above, the hydrogen detection device 30a according to the modified example 1 of the embodiment has a hydrogen sensor element 100 with a resistor R ｈ The measurement results of the output of the reference element 100a, which is used to reduce the influence of temperature dependence, are also used for voltage correction to stabilize the hydrogen reaction characteristics of the hydrogen sensor element 100. This makes it possible to reduce the influence of ambient temperature and to miniaturize the device.

[0109] Furthermore, the hydrogen detection method according to this modified example is a method for detecting hydrogen, and includes the steps of: preparing the hydrogen detection device 30a; applying a voltage to the parallel-connected hydrogen sensor element 100 and reference element 100a provided in the prepared hydrogen detection device 30a in step S43; measuring the currents of the hydrogen sensor element 100 and reference element 100a respectively when the voltage is applied in step S43 in step S44; and generating and outputting a signal indicating the hydrogen concentration using the currents of the hydrogen sensor element 100 and reference element 100a obtained in step S44 in steps S47 and S48.

[0110] As a result, a sensor chip 10 equipped with two distinctive resistive elements, a hydrogen sensor element 100 and a reference element 100a, can be made to have a smaller area than conventional sensors, and a signal indicating hydrogen concentration with reduced temperature dependence is generated.

[0111] [Modification 2] Next, Modification 2 of the embodiment will be described. In the following, the differences from the above embodiment and Modification 1 of the embodiment will be described in detail, and the explanation of the common points will be omitted or simplified. The sensor chip 10 that constitutes the hydrogen detection device 30, 30a according to the embodiment or Modification 1 of the embodiment is not limited to the structure shown in Figures 2A and 2B, but may be the sensor chip according to Modification 2 shown below.

[0112] Figure 9A is a cross-sectional view showing an example of the configuration of a sensor chip 10a according to a modified example 2 of the embodiment. Figure 9B is a top view showing an example of the configuration of the sensor chip 10a shown in Figure 9A. Note that Figure 9A shows a schematic cross-section viewed in the direction of the arrow due to the IXA-IXA disconnection in Figure 9B. In addition, in Figure 9A, along with the cross-sectional views of the hydrogen sensor element 100b and the reference element 100c, schematic wiring showing the connections from terminal A to terminal C is illustrated at the top of the cross-sectional view for explanatory purposes, and the equivalent circuit of the sensor chip 10a (resistor R) is shown at the bottom of the cross-sectional view. ｈ , R Ｒ ), and the voltage generated across each resistor when current is applied (voltage across both ends V ｈ , V Ｒ ) is shown in Figure 9A. ｈ This indicates the resistance of the hydrogen sensor element 100b, and R Ｒ This indicates the resistance of the reference element 100c. Also, in Figure 9A, V ｈ This indicates the voltage across the hydrogen sensor element 100b, V Ｒ This indicates the voltage across the reference element 100c.

[0113] As shown in Figures 9A and 9B, in this modified example, the sensor chip 10a is formed on a single semiconductor substrate 102 and includes a hydrogen sensor element 100b and a reference element 100c that can be connected in series or parallel. The hydrogen sensor element 100b is an example of a gas sensor element.

[0114] In the sensor chip 10a according to this modified example, the difference from the sensor chip 10 according to the embodiment shown in Figures 2A and 2B is that the second electrode 103 of the deposited laminate is not deposited. In other words, the hydrogen sensor element 100b and the reference element 100c differ from the hydrogen sensor element 100 and the reference element 100a in that they do not have the second electrode 103.

[0115] Figure 10 illustrates the results of a hydrogen concentration detection experiment using a sensor chip 10a according to a modified example 2 of the embodiment. Figure 10 shows the results of two types of voltage ratios (V) obtained from the sensor chip 10a when the atmosphere in which the sensor chip 10a is placed has hydrogen concentrations of 100 ppm, 1000 ppm, 1%, and 4% at room temperature. Ｒ / V ｈ This shows the time variation of the voltage ratio (V). Ｒ / V ｈ ) can also be said to indicate the amount of hydrogen reaction in the hydrogen sensor element 100b. As shown in Figure 10, even when using the sensor chip 10a, the voltage ratio (V) corresponding to the hydrogen concentration is also shown. Ｒ / V ｈ Changes in the following were observed. Furthermore, the hydrogen reaction characteristics of sensor chip 10a and sensor chip 10 were almost identical. From these results, it became clear that there are no problems even in a configuration without the second electrode 103.

[0116] (Other) The hydrogen detection device and hydrogen detection method relating to this disclosure have been described above based on embodiments and modifications thereof. However, this disclosure is not limited to these embodiments and modifications thereof. Without departing from the spirit of this disclosure, various modifications that a person skilled in the art could conceive of are applied to these embodiments and modifications thereof, as well as other forms constructed by combining some of the components of the embodiments and modifications thereof, are also included within the scope of this disclosure.

[0117] For example, the hydrogen detection devices 30 and 30a according to the above embodiment may detect gases other than hydrogen. For example, it is possible to detect gases containing hydrogen atoms, such as ammonia, using a gas detector having the same configuration as the hydrogen detection devices 30 and 30a. In other words, the hydrogen detection devices 30 and 30a can be gas detectors that detect the gas concentration of gases other than hydrogen and output the detected gas concentration. Furthermore, in this disclosure, the elements used for detecting gas concentration are not limited to the configurations shown as hydrogen sensor elements 100 and 100b and reference elements 100a and 100c in the above embodiment. For example, any gas sensor element whose resistance value changes depending on the presence of the gas to be detected and a reference element capable of canceling out the temperature dependence of the resistance of the gas sensor element can be used in this disclosure.

[0118] Furthermore, in the above embodiment, for example, the control unit 41 determined whether the change in the resistance of the reference element 100a was greater than a predetermined threshold when controlling the applied voltage or applied current, but it is not limited to this. For example, the control unit 41 may feedback control the applied voltage or applied current so that the resistance of the reference element 100a becomes a predetermined value. For example, if the resistance of the reference element 100a is lower than a predetermined value, the control unit 41 increases the applied voltage or applied current. In this case, the predetermined value is set to, for example, the resistance value of the reference element 100a at a temperature higher than the maximum temperature of the environment in which the hydrogen detection devices 30, 30a are used.

[0119] Furthermore, the general or specific embodiments of this disclosure may be implemented as systems, apparatus, methods, integrated circuits, computer programs, computer program products, or recording media such as computer-readable CD-ROMs. They may also be implemented as any combination of systems, apparatus, methods, integrated circuits, computer programs, computer program products, and recording media.

[0120] For example, this disclosure may be implemented as a hydrogen detection device (gas detector) according to the above embodiment, as a control device for controlling a hydrogen detection device (gas detector), as a hydrogen detection method (gas detection method) that includes steps (processes) performed by the components constituting the hydrogen detection device (gas detector), as a program that causes a processor to execute the steps included in the hydrogen detection method (gas detection method) according to the embodiment, or as a recording medium such as a DVD on which the program is recorded.

[0121] Examples of gas detectors and gas detection methods relating to this disclosure, as described based on the embodiments described above, are shown below. The gas detectors and gas detection methods relating to this disclosure are not limited to the following examples.

[0122] For example, a gas detector according to a first aspect of the present disclosure comprises a gas sensor element, a reference element deactivated by gas, a control unit that controls the applied voltage or current to the gas sensor element and the reference element, and a calculation unit that calculates the gas concentration from the measurement results of the outputs of the gas sensor element and the reference element, wherein the control unit controls the applied voltage or current based on the measurement results of the output of the reference element.

[0123] As a result, the reference element is deactivated by the gas, and the output of the reference element is affected by ambient temperature, not by the gas concentration. Therefore, based on the measurement result of the reference element's output, it becomes possible to control the applied voltage or current to the gas sensor element and the reference element so that the output of the reference element is less affected by ambient temperature. Furthermore, since the measurement result of the reference element's output, which is used for calculating the gas concentration, is also used to control the applied voltage or current, it becomes possible to control the effect of ambient temperature without using a separate heater or other configuration. Thus, the gas detector according to this embodiment can reduce the effect of ambient temperature and can be miniaturized.

[0124] Furthermore, for example, a gas detector according to a second aspect of this disclosure is a gas detector according to a first aspect, wherein the control unit controls the applied voltage or applied current by adding or subtracting the applied voltage or applied current.

[0125] This simplifies the process of controlling the applied voltage or current to the gas sensor element and the reference element.

[0126] Furthermore, for example, a gas detector according to a third aspect of the present disclosure is a gas detector according to the first or second aspect, wherein the control unit controls the applied voltage or applied current so that the resistance of the reference element is within a certain range.

[0127] This allows the temperature of the reference element, which is correlated with the resistance of the reference element, to be controlled within a certain range. As a result, the temperature of the gas sensor element to which voltage or current is applied along with the reference element is also controlled within a certain range, effectively reducing the influence of ambient temperature on the gas sensor element.

[0128] Furthermore, for example, a gas detector according to a fourth aspect of the present disclosure is a gas detector according to any one of the first to third aspects, wherein the control unit determines whether the change in the resistance of the reference element, calculated based on the measurement result of the output of the reference element, is greater than a predetermined threshold, and if the change in resistance is greater than the predetermined threshold, the control unit modifies the applied voltage or the applied current, and if the change in resistance does not exceed the predetermined threshold, the control unit does not modify the applied voltage or the applied current, and the calculation unit calculates and outputs the gas concentration based on the ratio or difference between the output of the reference element and the output of the gas sensor element.

[0129] As a result, the applied voltage or current is adjusted until the change in the resistance of the reference element falls below a predetermined threshold, after which the gas concentration is output. Furthermore, in the calculation of the gas concentration, the ratio or difference between the output of the reference element and the output of the gas sensor element is used, and the temperature dependence of the output of the hydrogen sensor element in the calculated gas concentration is canceled out by the temperature dependence of the output of the reference element. Therefore, a more accurate gas concentration calculation result can be output.

[0130] Furthermore, for example, a gas detector according to a fifth aspect of the present disclosure is a gas detector according to any one of the first to fourth aspects, wherein the control unit energizes the gas sensor element and the reference element for a predetermined period of time, and then controls the applied voltage or the applied current based on the measurement result of the output of the reference element.

[0131] This allows the gas sensor element and reference element to be energized for a predetermined period of time to enhance the reaction characteristics of the gas sensor element, and then the applied voltage or applied current can be controlled.

[0132] Furthermore, for example, a gas detector according to the sixth aspect of this disclosure is a gas detector according to any one of the first to fifth aspects, wherein the gas sensor element and the reference element are connected in series, the control unit controls the applied current, and the measurement results of the outputs of the reference element and the gas sensor element are the measurement results of the voltages across the respective ends of the reference element and the gas sensor element.

[0133] This ensures that the same current is applied to both the gas sensor element and the reference element, allowing the voltage measurement results to be used for controlling the applied current and calculating the gas concentration.

[0134] Furthermore, for example, the gas detector according to the seventh aspect of this disclosure is a gas detector according to any one of the first to fifth aspects, wherein the gas sensor element and the reference element are connected in parallel, the control unit controls the applied voltage, and the measurement results of the outputs of the reference element and the gas sensor element are the measurement results of the current flowing through the reference element and the gas sensor element, respectively.

[0135] This ensures that the same voltage is applied to both the gas sensor element and the reference element, allowing the current measurement results to be used for controlling the applied voltage and calculating the gas concentration.

[0136] Furthermore, for example, a gas detector according to the eighth aspect of the present disclosure is a gas detector according to any one of the first to seventh aspects, wherein the gas sensor element comprises a first electrode, a metal oxide layer, and an insulating film covering the first electrode and the metal oxide layer from above, the first electrode being laminated on the upper surface of the metal oxide layer, and the insulating film of the gas sensor element having an opening that exposes the upper surface of the first electrode.

[0137] As a result, in the gas sensor element, the first electrode is exposed to the gas at the opening, and the resistance of the metal oxide layer changes according to the amount of gas reaction at the first electrode. Therefore, high-precision gas detection becomes possible.

[0138] Furthermore, for example, a gas detector according to the ninth aspect of this disclosure is a gas detector according to the eighth aspect, wherein the gas sensor element further comprises a second electrode that is positioned opposite the first electrode and in contact with the lower surface of the metal oxide layer.

[0139] This makes it possible to measure the resistance between the first electrode and the second electrode.

[0140] Furthermore, for example, a gas detector according to the tenth aspect of the present disclosure is a gas detector according to the eighth aspect, wherein each of the gas sensor element and the reference element has the first electrode, the metal oxide layer, and the insulating film, and the insulating film of the reference element does not have an opening that exposes the upper surface of the first electrode of the reference element.

[0141] As a result, the reference element has the same configuration as the gas sensor element, except that the first electrode is not exposed to the gas, and the temperature dependence of the hydrogen sensor element's output is effectively canceled out by the output of the reference element.

[0142] Furthermore, for example, a gas detector according to an eleventh aspect of the present disclosure is a gas detector according to a tenth aspect, wherein each of the gas sensor element and the reference element further has a second electrode that faces the first electrode and is positioned in contact with the lower surface of the metal oxide layer.

[0143] This makes it possible to measure the resistance between the first electrode and the second electrode.

[0144] Furthermore, for example, a gas detector according to a twelfth aspect of the present disclosure is a gas detector according to a tenth or eleventh aspect, wherein the gas sensor element and the reference element have terminals that are connected to the first electrode of the gas sensor element and the first electrode of the reference element and are shared by the gas sensor element and the reference element.

[0145] This allows the gas sensor element and the reference element to share terminals, further miniaturizing the gas detector.

[0146] Furthermore, for example, a gas detector according to a 13th aspect of the present disclosure is a gas detector according to any one of the 8th to 12th aspects, wherein the metal oxide layer includes a transition metal oxide comprising at least one of tantalum (Ta), hafnium (Hf), titanium (Ti), zirconium (Zr), niobium (Nb), tungsten (W), nickel (Ni), iron (Fe), aluminum (Al), chromium (Cr), cobalt (Co), manganese (Mn), vanadium (V), cerium (Ce), and copper (Cu).

[0147] This makes it possible to create a gas sensor element whose resistance is easily affected by the presence of hydrogen-containing gas.

[0148] Furthermore, for example, a gas detector according to a 14th aspect of the present disclosure is a gas detector according to any one of the 8th to 13th aspects, wherein the first electrode is composed of platinum (Pt), palladium (Pd), or an alloy of Pt and Pd.

[0149] This makes it possible to create a gas sensor element whose resistance is easily affected by the presence of hydrogen-containing gas.

[0150] Furthermore, for example, a gas detection method according to a 15th aspect of the present disclosure is a gas detection method using a gas detector comprising a gas sensor element and a reference element deactivated by gas, comprising a control step of controlling an applied voltage or applied current to the gas sensor element and the reference element, and a calculation step of calculating a gas concentration from the measurement results of the outputs of the gas sensor element and the reference element, wherein in the control step, the applied voltage or applied current is controlled based on the measurement results of the output of the reference element.

[0151] This makes it possible to reduce the influence of ambient temperature on the gas detector, similar to the gas detector according to the first embodiment, and also enables miniaturization.

[0152] This disclosure can be used as a gas detector and gas detection method for detecting gases such as hydrogen. For example, the gas detector according to this disclosure can be installed in a hydrogen vehicle or hydrogen station and used as a gas detector for detecting hydrogen leaks.

[0153] 10, 10a Sensor chip 20, 20a Measurement unit 21 Current source 21a Voltage source 22 Voltmeter 22a, 22b Ammeter 22S Switch circuit 23 Signal processing unit 30, 30a Hydrogen detection device 41 Control unit 42 Calculation unit 100, 100b Hydrogen sensor element 100a, 100c Reference element 102 Semiconductor substrate 103 Second electrode 104 Metal oxide layer 104a First layer 104b Second layer 104i Insulating separation layer 106 First electrode 106e Exposed portion 106s Metal layer 107a, 107b, 107c, 109a, 109b Insulating film 108 Via 110 Aperture TE1 First terminal TE2 Second terminal TE3 Third terminal TE1a, TE2a, TE3a opening A, B, C terminal

Claims

1. A gas detector comprising: a gas sensor element; a reference element deactivated by gas; a control unit that controls the applied voltage or current to the gas sensor element and the reference element; and a calculation unit that calculates the gas concentration from the measurement results of the outputs of the gas sensor element and the reference element, wherein the control unit controls the applied voltage or current based on the measurement results of the output of the reference element.

2. The control unit controls the applied voltage or the applied current by adding or subtracting the applied voltage or the applied current, as described in claim 1.

3. The control unit controls the applied voltage or applied current so that the resistance of the reference element is within a certain range, as described in claim 1.

4. The control unit determines whether the change in the resistance of the reference element, calculated based on the measurement result of the output of the reference element, is greater than a predetermined threshold; if the change in resistance is greater than the predetermined threshold, the control unit modifies the applied voltage or the applied current; if the change in resistance does not exceed the predetermined threshold, the control unit does not modify the applied voltage or the applied current; and the calculation unit calculates and outputs the gas concentration based on the ratio or difference between the output of the reference element and the output of the gas sensor element, according to claim 1.

5. The gas detector according to claim 1, wherein the control unit energizes the gas sensor element and the reference element for a predetermined period of time, and then controls the applied voltage or the applied current based on the measurement result of the output of the reference element.

6. The gas detector according to claim 1, wherein the gas sensor element and the reference element are connected in series, the control unit controls the applied current, and the measurement results of the outputs of the reference element and the gas sensor element are the measurement results of the voltages across the respective ends of the reference element and the gas sensor element.

7. The gas sensor element and the reference element are connected in parallel, the control unit controls the applied voltage, and the measurement results of the outputs of the reference element and the gas sensor element are the measurement results of the current flowing through the reference element and the gas sensor element, respectively, as described in claim 1.

8. The gas sensor element comprises a first electrode, a metal oxide layer, and an insulating film covering the first electrode and the metal oxide layer from above, wherein the first electrode is laminated on the upper surface of the metal oxide layer, and the insulating film of the gas sensor element has an opening that exposes the upper surface of the first electrode, as described in claim 1.

9. The gas detector according to claim 8, wherein the gas sensor element further comprises a second electrode that is positioned opposite the first electrode and in contact with the lower surface of the metal oxide layer.

10. The gas detector according to claim 8, wherein each of the gas sensor element and the reference element comprises the first electrode, the metal oxide layer, and the insulating film, and the insulating film of the reference element does not have an opening that exposes the upper surface of the first electrode of the reference element.

11. The gas detector according to claim 10, wherein each of the gas sensor element and the reference element further comprises a second electrode that faces the first electrode and is positioned in contact with the lower surface of the metal oxide layer.

12. The gas detector according to claim 10 or claim 11, wherein the gas sensor element and the reference element have terminals connected to the first electrode of the gas sensor element and the first electrode of the reference element, and which are shared by the gas sensor element and the reference element.

13. The gas detector according to any one of claims 8 to 11, wherein the metal oxide layer comprises a transition metal oxide comprising at least one of tantalum (Ta), hafnium (Hf), titanium (Ti), zirconium (Zr), niobium (Nb), tungsten (W), nickel (Ni), iron (Fe), aluminum (Al), chromium (Cr), cobalt (Co), manganese (Mn), vanadium (V), cerium (Ce), and copper (Cu).

14. The gas detector according to any one of claims 8 to 11, wherein the first electrode is made of platinum (Pt), palladium (Pd), or an alloy of Pt and Pd.

15. A gas detection method using a gas detector comprising a gas sensor element and a reference element deactivated by gas, comprising: a control step of controlling the applied voltage or applied current to the gas sensor element and the reference element; and a calculation step of calculating the gas concentration from the measurement results of the outputs of the gas sensor element and the reference element, wherein in the control step, the applied voltage or applied current is controlled based on the measurement results of the output of the reference element.

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