Heat flow sensor and gas sensor

Abstract

To provide a heat flow sensor and a gas sensor which can increase the detection accuracy.SOLUTION: The thermal flow sensor includes: a thermoelectric conversion layer (11) showing an abnormal Nernst effect which generates a current in a direction which is perpendicular to a magnetization direction and a thermal flow direction; and a pinning layer (12) provided in contact with a first surface as one surface of the thermoelectric conversion layer which is perpendicular to the thermal flow direction and having magnetism in the magnetization direction which acts on the thermoelectric conversion layer. The heat flow sensor may be formed so that the magnetization direction is perpendicular to the direction in which the thermoelectric conversion layer and the pinning layer is laminated.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to heat flow sensors and gas sensors. [Background technology]

[0002] In recent years, gas sensors have been proposed that measure the concentration of a target gas by measuring heat generated by the target gas. For example, Patent Document 1 discloses a gas sensor equipped with a thermoelectric conversion element made of a material that exhibits the anomalous Nernst effect. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2022 / 176966 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, thermoelectric conversion elements are made of soft magnetic materials and are easily affected by external magnetic fields. When the magnetization direction of the thermoelectric conversion element fluctuates due to the influence of an external magnetic field, the direction of the current generated according to the magnetization direction also changes, making the detected current value inaccurate and reducing the detection accuracy of the gas sensor.

[0005] In view of the above circumstances, an object of the present disclosure is to provide a heat flow sensor and a gas sensor capable of improving detection accuracy. [Means for solving the problem]

[0006] (1) A heat flow sensor according to an embodiment of the present disclosure includes: a thermoelectric conversion layer that exhibits the anomalous Nernst effect, which generates a current in a direction perpendicular to both the magnetization direction and the heat flow direction; the pinning layer is provided in contact with a first surface, which is one surface of the thermoelectric conversion layer perpendicular to the heat flow direction, and has magnetism in the magnetization direction acting on the thermoelectric conversion layer.

[0007] (2) As an embodiment of the present disclosure, in (1), The magnetization direction is perpendicular to the stacking direction of the thermoelectric conversion layer and the pinning layer.

[0008] (3) As an embodiment of the present disclosure, in (1), The magnetization direction is parallel to the stacking direction of the thermoelectric conversion layer and the pinning layer.

[0009] (4) As an embodiment of the present disclosure, in any one of (1) to (3), The thermoelectric conversion layer is made of a material selected from the group consisting of an Fe-Ga alloy, an Fe-Al alloy, Co2MnGa, an Fe-Ni alloy, Mn3Sn, and Mn3Ge.

[0010] (5) As an embodiment of the present disclosure, in any one of (1) to (4), The pinning layer is made of a ferromagnetic or antiferromagnetic material.

[0011] (6) As an embodiment of the present disclosure, in any one of (1) to (5), a spacer layer made of a non-magnetic material having a spin diffusion length longer than that of the thermoelectric conversion layer; The pinning layer is in contact with the first surface via the spacer layer.

[0012] (7) As an embodiment of the present disclosure, in (6), The spacer layer is made of Ru, Ir, Ag, AgSn, Pt, Cu, Ta, ZnO, GaOx, ITO, IZO, C, SiC, AlN, SiN, BN, Al2O3, or MgO.

[0013] (8) A gas sensor according to an embodiment of the present disclosure includes: Any of the heat flow sensors (1) to (7) above; The thermoelectric conversion layer further includes a catalyst layer that is provided in contact with a surface of the thermoelectric conversion layer other than the first surface and that promotes a chemical reaction of the gas to be detected to generate or absorb heat. Effect of the Invention

[0014] According to the present disclosure, it is possible to provide a heat flow sensor and a gas sensor capable of improving detection accuracy. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a gas sensor according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a diagram for explaining a thermoelectric conversion layer that exhibits the anomalous Nernst effect. [Diagram 3] FIG. 3 is a diagram showing a configuration example of a heat flow sensor (gas sensor). [Figure 4] FIG. 4 is a diagram for explaining the effect of providing a pinning layer. [Diagram 5] FIG. 5 is a diagram showing a configuration example of a heat flow sensor (gas sensor) having a spacer layer. [Figure 6] FIG. 6 is a diagram showing another example of the configuration of a gas sensor. [Figure 7] FIG. 7 is a diagram showing another example of the configuration of a heat flow sensor (gas sensor). [Figure 8] FIG. 8 is a diagram showing another example of the configuration of a heat flow sensor (gas sensor). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] A gas sensor 10 according to an embodiment of the present disclosure will be described below with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals. In the description of this embodiment, the description of the same or corresponding parts will be omitted or simplified as appropriate.

[0017] FIG. 1 is a diagram showing the configuration of a gas sensor 10 according to this embodiment. The gas sensor 10 includes a thermoelectric conversion layer 11, a pinning layer 12, and a catalyst layer 13. The gas sensor 10 may further include a circuit that controls the entire gas sensor 10 and calculates the concentration of the detected gas. The circuit may include one or more processors. The processor may include, for example, a general-purpose processor, or a dedicated processor specialized for a specific process. In this embodiment, the gas sensor 10 measures the presence or concentration of the detected gas by using a catalyst to measure the heat generated by the detected gas. The detected gas is a gas to be detected, and is, for example, hydrogen, but is not limited to a specific type. In FIG. 1, the detected gas is indicated as "gas".

[0018] The thermoelectric conversion layer 11 is a layer that exhibits the anomalous Nernst effect, which generates a current (or voltage) in a direction perpendicular to both the magnetization direction and the heat flow direction. In this embodiment, the thermoelectric conversion layer 11 has a rectangular parallelepiped shape, and orthogonal coordinates are set to correspond to each side. The orthogonal coordinates may be commonly used in the drawings from FIG. 2 onwards. In addition, in the following, it will be described that the z-axis direction corresponds to the heat flow direction, and the heat flow occurs in the negative z-axis direction. As shown in FIG. 2, the thermoelectric conversion layer 11 is magnetized so that the magnetization direction is the negative y-axis direction, and when a heat flow occurs in the negative z-axis direction, a current flows in the x-axis direction due to the anomalous Nernst effect. In other words, in the thermoelectric conversion layer 11, a current is generated in the direction of a cross product perpendicular to the magnetization direction and the heat flow direction. Since a potential difference is generated in the thermoelectric conversion layer 11 in proportion to the heat flow, i.e., the temperature gradient, the heat flow can be measured, for example, based on the amount of current detected. In other words, the thermoelectric conversion layer 11 functions as a heat flow sensor. In this embodiment, the heat flow sensor includes at least a thermoelectric conversion layer 11 and a pinning layer 12, and constitutes a part of the gas sensor 10 (a functional part that measures the heat generated by the gas to be detected).

[0019] A material exhibiting the anomalous Nernst effect is used for the thermoelectric conversion layer 11. Examples of the material exhibiting the anomalous Nernst effect include an Fe-Ga alloy, an Fe-Al alloy, Co2MnGa, an Fe-Ni alloy, Mn3Sn, and Mn3Ge.

[0020] The pinning layer 12 is provided to stabilize the magnetization direction of the thermoelectric conversion layer 11 having the properties of a soft magnetic material. As shown in FIG. 3, the pinning layer 12 is provided so as to be in contact with the first surface 11a, which is one surface of the thermoelectric conversion layer 11 perpendicular to the heat flow direction (z-axis direction). The pinning layer 12 has magnetism in the magnetization direction (y-axis negative direction) acting on the thermoelectric conversion layer 11. The pinning layer 12 may be made of a ferromagnetic material such as Fe, Co, Ni, and alloys thereof. Here, the phrase "provided so as to be in contact" between the two layers includes not only that the two layers are arranged in direct contact with each other, but also that the two layers are arranged so that heat conduction is not hindered by sandwiching a magnetic structure and a member that transmits heat between them. For example, a configuration in which a spacer layer 14 (see FIG. 5), which will be described later, is sandwiched between the thermoelectric conversion layer 11 and the pinning layer 12, is included in the configuration in which the pinning layer 12 is provided so as to be in contact with the thermoelectric conversion layer 11.

[0021] As shown in the left diagram of FIG. 4, the thermoelectric conversion layer 11 alone exhibits the properties of a soft magnetic material and has a small coercive force. Here, in FIG. 4, H indicates an external magnetic field, and M indicates the magnetization of the thermoelectric conversion layer 11. By providing the pinning layer 12 as described above, as shown in the right diagram of FIG. 4, the coercive force of the thermoelectric conversion layer 11 can be strengthened and the layer 11 can be made less susceptible to the influence of an external magnetic field, so that the magnetization direction of the thermoelectric conversion layer 11 is stabilized. When the magnetization direction of the thermoelectric conversion layer 11 is stabilized, fluctuations in the direction of the current that occur in response to heat flow are suppressed. This allows the current to be detected accurately, and the detection accuracy of the gas sensor 10 or heat flow sensor can be improved.

[0022] The catalyst layer 13 is provided so as to be in contact with a surface of the thermoelectric conversion layer 11 that is different from the first surface 11a. Referring again to FIG. 3, the second surface 11b is another surface of the thermoelectric conversion layer 11 that is perpendicular to the heat flow direction (z-axis direction). The catalyst layer 13 may be provided so as to be in contact with the second surface 11b. As another example, the arrangement of the layers of the gas sensor 10 may be reversed in the z-axis direction. That is, the positions of the first surface 11a and the second surface 11b may be interchanged, so that the pinning layer 12 is on the positive z-axis side of the thermoelectric conversion layer 11 and the catalyst layer 13 is on the negative z-axis side of the thermoelectric conversion layer 11.

[0023] As described above, the catalyst layer 13 promotes the chemical reaction of the gas to be detected, generating or absorbing heat, and generating a heat flow in the z-axis direction. The material of the catalyst layer 13 is selected according to the gas to be detected. For example, when the gas to be detected is hydrogen, the material of the catalyst layer 13 may be Pb. Pb promotes the combination (combustion) of hydrogen with oxygen in the air to generate heat and water.

[0024] The basic configurations of the gas sensor 10 and the heat flow sensor have been described with reference to FIGS. 1 to 3. The gas sensor 10 and the heat flow sensor may have, for example, the configuration described below.

[0025] As shown in FIG. 5, the gas sensor 10 and the heat flow sensor may further include a spacer layer 14 made of a material having a longer spin diffusion length than the thermoelectric conversion layer 11. In this case, the pinning layer 12 contacts the first surface 11a via the spacer layer 14. The spacer layer 14 may be made of a material having a long spin diffusion length, such as Ru, Ir, Ag, AgSn, Pt, Cu, Ta, ZnO, GaOx, ITO, IZO, C, SiC, AlN, SiN, BN, Al2O3, or MgO. By using a material having a long spin diffusion length, the magnetic structure of the pinning layer 12 can be effectively transmitted to the thermoelectric conversion layer 11, the magnetic structures of the pinning layer and the thermoelectric conversion layer 11 are effectively coupled, and the thermoelectric conversion layer 11, which has a small coercive force, can be strengthened by the large coercive force of the pinning layer. The material having a long spin diffusion length may be a nonmagnetic material having a small spin-orbit interaction. The thickness (length in the z-axis direction) of the spacer layer 14 is not limited, but is preferably several nm or less, for example. By inserting the spacer layer 14, for example, it becomes possible to adjust the RKKY interaction, and the degree of freedom in designing the gas sensor 10 and the heat flow sensor can be increased.

[0026] As shown in FIG. 6, the gas sensor 10 may be configured as a bridge circuit of four sensor elements U1, U2, U3, and U4. Each of the sensor elements U1, U2, U3, and U4 includes at least a thermoelectric conversion layer 11 and a pinning layer 12. The sensor elements U2 and U4 further include a catalyst layer 13. The arrows attached to the four sensor elements indicate the magnetization direction of each. The heat flow direction is from the front to the back. The first detection terminal D1 is a connection point between the sensor elements U4 and U1. The second detection terminal D2 is a connection point between the sensor elements U1 and U2. The third detection terminal D3 is a connection point between the sensor elements U2 and U3. The fourth detection terminal D4 is a connection point between the sensor elements U3 and U4. The gas sensor 10 includes the above circuit (processor), and the processor controls the connection of the bridge circuit. The processor may short-circuit the first detection terminal D1 and the third detection terminal D3, obtain a voltage difference between the second detection terminal D2 and the fourth detection terminal D4, and calculate the concentration of the detection target gas based on the obtained voltage difference. The processor may further short-circuit the second detection terminal D2 and the fourth detection terminal D4, obtain a voltage difference between the first detection terminal D1 and the third detection terminal D3, and calculate the concentration of the detection target gas based on the obtained voltage difference. In this case, the processor may perform a calculation process (for example, an average) on the concentration of the detection target gas based on the voltage difference between the second detection terminal D2 and the fourth detection terminal D4 and the concentration of the detection target gas based on the voltage difference between the first detection terminal D1 and the third detection terminal D3. Then, the processor may use the concentration of the detection target gas after the calculation process as a final measured value. By being configured as a bridge circuit, the gas sensor 10 can further improve the detection accuracy of the measured value of the detection target gas.

[0027] 7, the pinning layer 12 may be an antiferromagnetic material instead of a ferromagnetic material. In other words, as long as the magnetism of the pinning layer 12 acting on the thermoelectric conversion layer 11 is aligned in the magnetization direction, the pinning layer 12 as a whole does not need to have a magnetic moment. In other words, the pinning layer 12 may be made of a ferromagnetic or antiferromagnetic material.

[0028] In the above gas sensor 10 and heat flow sensor, the magnetization direction is perpendicular to the stacking direction of the thermoelectric conversion layer 11 and the pinning layer 12. In other words, the stacking direction of the thermoelectric conversion layer 11 and the pinning layer 12 is the z-axis direction, which is parallel to the heat flow direction. As shown in FIG. 8, the gas sensor 10 and the heat flow sensor may be configured so that the magnetization direction is parallel to the stacking direction (y-axis direction) of the thermoelectric conversion layer 11 and the pinning layer 12. In this case, the catalyst layer 13 may be provided so as to contact a partial area of ​​the second surface 11b of the thermoelectric conversion layer 11, and may be configured so as to pass a heat flow through the thermoelectric conversion layer 11 and the pinning layer 12 toward a low-temperature heat source (not shown) that is in contact with a part of the thermoelectric conversion layer 11. In this way, the stacking direction of the thermoelectric conversion layer 11 and the pinning layer 12 can be perpendicular or parallel to the heat flow direction, and the gas sensor 10 and the heat flow sensor have a high degree of freedom in design.

[0029] As described above, the heat flow sensor and gas sensor 10 according to this embodiment can stabilize the magnetization direction of the thermoelectric conversion layer 11 by the pinning layer 12, thereby improving the detection accuracy.

[0030] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications or corrections based on the present disclosure. Therefore, it should be noted that these modifications and corrections are included in the scope of the present disclosure. [Explanation of symbols]

[0031] 10 Gas Sensor 11 Thermoelectric conversion layer 11a 1st page 11b Side 2 12 Pinning layer 13 Catalyst layer 14 Spacer layer

Claims

1. a thermoelectric conversion layer that exhibits the anomalous Nernst effect, which generates a current in a direction perpendicular to both the magnetization direction and the heat flow direction; A heat flow sensor comprising: a pinning layer that is arranged in contact with a first surface, which is one surface of the thermoelectric conversion layer perpendicular to the heat flow direction, and has magnetism in the magnetization direction acting on the thermoelectric conversion layer.

2. The heat flow sensor according to claim 1 , wherein the magnetization direction is perpendicular to a stacking direction of the thermoelectric conversion layer and the pinning layer.

3. The heat flow sensor according to claim 1 , wherein the magnetization direction is parallel to a stacking direction of the thermoelectric conversion layer and the pinning layer.

4. The thermoelectric conversion layer is made of an Fe—Ga alloy, an Fe—Al alloy, or a Co ２ MnGa, Fe-Ni alloy, Mn ３ Sn or Mn ３ The heat flow sensor according to claim 1 , wherein the heat flow sensor is made of Ge.

5. The heat flow sensor according to claim 1 , wherein the pinning layer is made of a ferromagnetic or antiferromagnetic material.

6. a spacer layer made of a non-magnetic material having a spin diffusion length longer than that of the thermoelectric conversion layer; The heat flow sensor according to claim 1 , wherein the pinning layer is in contact with the first surface via the spacer layer.

7. The spacer layer is made of Ru, Ir, Ag, AgSn, Pt, Cu, Ta, ZnO, GaOx, ITO, IZO, C, SiC, AlN, SiN, BN, Al ２ O ３ The heat flow sensor according to claim 6, wherein the material is selected from the group consisting of SiO2 and MgO.

8. A heat flow sensor according to any one of claims 1 to 3; a catalyst layer provided in contact with a surface of the thermoelectric conversion layer other than the first surface, the catalyst layer promoting a chemical reaction of the gas to be detected to generate or absorb heat.

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