WO2025009336A1 - 横熱電効果を用いた垂直型熱電変換素子、及び垂直型熱電変換素子の評価方法 - Google Patents

横熱電効果を用いた垂直型熱電変換素子、及び垂直型熱電変換素子の評価方法 Download PDF

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WO2025009336A1
WO2025009336A1 PCT/JP2024/021055 JP2024021055W WO2025009336A1 WO 2025009336 A1 WO2025009336 A1 WO 2025009336A1 JP 2024021055 W JP2024021055 W JP 2024021055W WO 2025009336 A1 WO2025009336 A1 WO 2025009336A1
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thermoelectric
layer
conversion element
vertical
thickness
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偉男 周
裕弥 桜庭
健一 内田
康之 追川
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National Institute for Materials Science
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02N—ELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
    • H02N11/00—Generators or motors not provided for elsewhere; Alleged perpetua mobilia obtained by electric or magnetic means
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N15/00—Thermoelectric devices without a junction of dissimilar materials; Thermomagnetic devices, e.g. using the Nernst-Ettingshausen effect
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N15/00—Thermoelectric devices without a junction of dissimilar materials; Thermomagnetic devices, e.g. using the Nernst-Ettingshausen effect
    • H10N15/20—Thermomagnetic devices using thermal change of the magnetic permeability, e.g. working above and below the Curie point

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  • the present invention relates to a vertical thermoelectric conversion element that uses the lateral thermoelectric effect, and a method for evaluating a vertical thermoelectric conversion element.
  • the Seebeck effect a common thermoelectric effect, is a phenomenon in which an electric field is generated parallel to a temperature gradient ⁇ T when a conductive material is subjected to a temperature gradient ⁇ T.
  • Thermoelectric power generation modules and heat flow sensors that use this effect have already been commercialized and are available on the market, but their applications are limited due to various issues, such as their complex structure, difficulty in making them large-area, low durability and flexibility, and high cost.
  • thermoelectric generation module in which an electric field is generated in a direction perpendicular to ⁇ T, it is possible to function as a thermoelectric generation module or heat flow sensor with an extremely simple in-plane connection type structure, and it is hoped that a new thermoelectric generation laminate that solves the above-mentioned problems will be created (Patent Document 1, Non-Patent Document 1).
  • thermoelectric power of the anomalous Nernst effect of magnetic materials reported to date at room temperature is less than 10 ⁇ V/K (Non-Patent Document 2), and there is active research into materials with greater transverse thermoelectric power.
  • the inventors have proposed a vertical thermoelectric conversion element with a layered structure consisting of a magnetic material, a thermoelectric material, and an insulating material sandwiched between the two, and have demonstrated that a high transverse thermoelectric power can be obtained by converting the Seebeck current of the thermoelectric material into a direction perpendicular to ⁇ T due to the anomalous Hall effect of the magnetic material (Patent Document 2, Non-Patent Documents 3 and 4).
  • thermoelectric power due to the anomalous Nernst effect is still small compared to the Seebeck effect of thermoelectric materials, and it is necessary to realize a higher transverse thermoelectric power for practical applications.
  • a high transverse thermoelectric power can be obtained in the vertical thermoelectric conversion element made of the above-mentioned magnetic material and thermoelectric material, it is necessary to create a closed circuit structure in which the magnetic material and the thermoelectric material are electrically conductive only on the high temperature side and the low temperature side of ⁇ T, and are electrically insulated in other parts. Therefore, there is a problem that the end conductor parts and insulating layers required for the closed circuit complicate the structure of the thermoelectric conversion element, hindering miniaturization and modularization.
  • connection positions of the output terminals are limited to both ends of the magnetic layer in the direction of generating electric potential, which makes the connection of the output terminals complicated. Also, if the connection positions of the output terminals extend to the thermoelectric layer laminated on the magnetic layer, the voltage generated by the thermoelectric power is lowered compared to the case where the output terminals are connected only to the magnetic layer.
  • the present invention has been made to solve the problems of the conventional technology described above, and aims to provide a vertical thermoelectric conversion element that uses the lateral thermoelectric effect and has a laminated structure in which the magnetic material and the thermoelectric material are in direct electrical contact, without requiring end conductor portions and insulating layers.
  • Another object of the present invention is to provide a method for evaluating a vertical thermoelectric conversion element that is suitable for use in material search and optimization design of a vertical thermoelectric conversion element using the lateral thermoelectric effect.
  • the vertical thermoelectric conversion element of the present invention comprises a thermoelectric layer 10 made of a thermoelectric material exhibiting the Seebeck effect, one end of the thermoelectric layer 10 being a low-temperature side and the other end opposite the low-temperature side being a high-temperature side, and a magnetic layer 20 laminated on the thermoelectric layer 10, the magnetic layer 20 having a magnetization component, an external magnetic field, or a magnetization component and an external magnetic field in the film thickness direction of the magnetic layer 20, being electrically conductive, and having a temperature gradient direction of the magnetic layer 20 and a temperature gradient direction of the magnetic layer 20.
  • thermoelectric layer 10 the magnetic layer 20, or the thermoelectric layer 10 and the magnetic layer 20 for extracting the potential generated in the cross product direction, which is the temperature gradient direction of the thermoelectric layer 10, and the magnetization direction of the magnetic layer 20, the external magnetic field direction, or the cross product direction of the magnetization direction and the external magnetic field direction.
  • the ratio (x) of the thickness (L z TE ) of the thermoelectric layer 10 to the sum of the thickness (L z TE ) of the thermoelectric layer 10 and the thickness (L z M ) of the magnetic layer 20 has a lower limit value of 0.2 less than the x value that maximizes the transverse thermoelectric power (S y tot ) and an upper limit value of 0.2 more than the x value, and when the lower limit value is negative, the lower limit value is zero, and when the upper limit value exceeds 1, the upper limit value is 1.
  • the transverse thermoelectric power (S y tot ) is preferably formulated by the following equation:
  • the magnetic material of the magnetic layer is Fe x Ga 1-x (0.5 ⁇ x ⁇ 0.9)
  • the thermoelectric material of the thermoelectric layer is n-type Si
  • the ratio of the thickness (L z TE ) of the thermoelectric layer to the sum of the thickness (L z TE ) of the thermoelectric layer and the thickness (L z M ) of the magnetic layer is: 0.98 ⁇ LzTE /( LzTE + LzM ) ⁇ 0.9995
  • the transverse thermoelectric power S y tot is 6.8 ( ⁇ V/K) or more, which is more than twice the transverse thermoelectric power due to the anomalous Nernst effect of Fe 70 Ga 30 , which is the magnetic material.
  • the magnetic material of the magnetic layer is Fe x Ga 1-x (0.5 ⁇ x ⁇ 0.9)
  • the thermoelectric material of the thermoelectric layer is n-type Si
  • the ratio of the thickness (L z TE ) of the thermoelectric layer to the sum of the thickness (L z TE ) of the thermoelectric layer and the thickness (L z M ) of the magnetic layer is: 0.99 ⁇ LzTE /( LzTE + LzM ) ⁇ 0.999
  • the transverse thermoelectric power S y tot is 10 ( ⁇ V/K) or more, which is four times or more the transverse thermoelectric power due to the anomalous Nernst effect of Fe 70 Ga 30 which is the magnetic material.
  • the magnetic material of the magnetic layer is Fe x Ga 1-x (0.5 ⁇ x ⁇ 0.9)
  • the thermoelectric material of the thermoelectric layer is n-type Si
  • the ratio of the thickness (L z TE ) of the thermoelectric layer to the sum of the thickness (L z TE ) of the thermoelectric layer and the thickness (L z M ) of the magnetic layer is: 0.994 ⁇ LzTE / ( LzTE + LzM ) ⁇ 0.998
  • the transverse thermoelectric power S y tot is 12.5 ( ⁇ V/K) or more, which is five times or more the transverse thermoelectric power due to the anomalous Nernst effect of Fe 70 Ga 30 which is a magnetic material.
  • the magnetic material of the magnetic layer is one type of magnetic material selected from the following group (A) to (H): (A) one or more L10 type ordered alloys selected from the group consisting of FePt, CoPt, FePd, CoPd, FeNi, MnAl, and MnGa; (B) one or two Heusler alloys selected from the group consisting of Co 2 MnGa and Co 2 MnAl; (C) one or more kinds of D022 type ordered alloys selected from the group consisting of Mn3Ga , Mn2FeGa , Mn2CoGa , and Mn2RuGa ; (D) one or more alloys selected from the group consisting of FeCr, FeAl, FeGa, FeSi, FeTa, FeIr, FePt, FeSn, FeSm, FeTb, CoFeB, CoTb, and NiPt; (E) one or more L10 type ordered alloys selected from the group consisting of FePt
  • the FeGa may preferably be Fe x Ga 1-x (0.5 ⁇ x ⁇ 0.9).
  • the thermoelectric material of the thermoelectric layer is preferably one type of thermoelectric material selected from the group of thermoelectric materials consisting of Bi2Te3 , PbTe, Si, Ge, FeSi alloy, CrSi alloy, MgSi alloy, CoSb3 alloy, Fe2VAl -based Heusler alloy, and SrTiO3 .
  • the Bi 2 Te 3 , PbTe, Si, or Ge is doped with a p-type or n-type element to a carrier concentration of 0.1 ⁇ 10 19 to 3 ⁇ 10 19 cm -3 .
  • the Si is p-type Si
  • the sign of the transverse thermoelectric power is opposite to that of n-type Si.
  • the magnetic layer is a single layer or multiple layers, and the thermoelectric layer is a single layer in electrical contact with the magnetic layer, or multiple layers sandwiching the magnetic layer.
  • the method for evaluating a vertical thermoelectric conversion element of the present invention is a method for evaluating a vertical thermoelectric conversion element according to any one of the vertical thermoelectric conversion elements [1] to [10], wherein, in the following formula, Based on the resistivity and Seebeck coefficient of the thermoelectric material, and the resistivity, Seebeck coefficient, anomalous Hall resistivity, and anomalous Nernst coefficient of the magnetic material, the ratio (x) of the thickness of the thermoelectric layer (L z TE ) to the sum of the thickness of the thermoelectric layer (L z TE ) and the thickness of the magnetic layer (L z M ) is determined so as to maximize the transverse thermoelectric power (S y tot ).
  • the symbols are defined as follows: [13] In the evaluation method [12] for a vertical thermoelectric conversion element of the present invention, it is preferable to further define the range of this ratio (x) so that the lower limit is a value obtained by subtracting 0.2 from the value that maximizes the transverse thermoelectric power (S y tot ) and the upper limit is a value obtained by adding 0.2 to the value, and the lower limit is zero when the lower limit is negative, and the upper limit is 1 when the upper limit exceeds 1. [14] In the evaluation method [12] of the vertical thermoelectric conversion element of the present invention, it is preferable to determine the transverse thermoelectric power output coefficient (PF) defined by the following equation so as to maximize it.
  • PF transverse thermoelectric power output coefficient
  • the effective resistivity ( ⁇ eff ) in the plane (xy plane) of the vertical thermoelectric conversion element is defined by the following formula: [15]
  • the evaluation method [14] of the vertical thermoelectric conversion element of the present invention it is preferable to determine the evaluation method so as to maximize an isothermal dimensionless figure of merit (zT) representing the efficiency of the transverse thermoelectric effect defined by the following equation.
  • the effective thermal conductivity (k eff ) in the plane (xy plane) of the vertical thermoelectric conversion element is defined by the following formula:
  • the output terminals may be connected to both ends of the magnetic layer in the electric potential generating direction, as well as to the thermoelectric layer laminated on the magnetic layer, which has the effect of facilitating the connection of the output terminals. Also, even if the output terminals are connected to the thermoelectric layer laminated on the magnetic layer, the decrease in voltage generated by the thermoelectric power remains within an acceptable range, compared to the case where the output terminals are connected only to the magnetic layer.
  • the vertical thermoelectric conversion element of the present invention in a two-layer structure including a magnetic layer made of a magnetic material that has a magnetization component or an external magnetic field in the film thickness direction and is conductive and generates a potential in the temperature gradient direction of the magnetic layer, as well as in the direction of the magnetization direction, the external magnetic field, or the cross product direction of the magnetization direction and the external magnetic field, and a thermoelectric layer made of a thermoelectric material exhibiting the Seebeck effect, or in a structure in which a sandwich structure of a magnetic layer and a thermoelectric layer is laminated in multiple layers, the ratio of the thickness of the thermoelectric layer (L z TE ) to the sum of the thickness of the thermoelectric layer (L z TE ) and the thickness of the magnetic layer (L z M ) is preferably set to a lower limit value obtained by subtracting 0.2 from the value that maximizes the transverse thermoelectric power (S y tot ) and an upper limit value obtained by adding 0.2 to the value, thereby
  • thermoelectric layer thickness LzTE
  • LzM the magnetic layer thickness
  • zT isothermal dimensionless figure of merit
  • FIG. 2 is an explanatory diagram of a vertical thermoelectric conversion element according to one embodiment of the present invention, showing the transverse thermoelectric effect in a two-layer structure of magnetic material and thermoelectric material, the dimensions of the materials, and the ratio (x) of the thermoelectric layer thicknesses.
  • FIG. 2 is an explanatory diagram of a vertical thermoelectric conversion element according to one embodiment of the present invention, showing a two-layer structure of a magnetic material and a thermoelectric material.
  • FIG. 2 is an explanatory diagram of a vertical thermoelectric conversion element according to one embodiment of the present invention, showing a cross-sectional view of a laminated structure in which magnetic materials and thermoelectric materials are multi-layered.
  • FIG. 2 is a structural diagram of a sample used in the examples.
  • thermoelectric layer thickness x
  • vertical axis the transverse thermoelectric power S y tot ( ⁇ V/K).
  • A) is an enlarged view of the entire range of 0 ⁇ x ⁇ 1
  • B) is an enlarged view of 0.97 ⁇ x ⁇ 1.00.
  • Fig. 1 is an explanatory diagram of the main part of a vertical thermoelectric conversion element showing one embodiment of the present invention, and is a perspective view showing a two-layer structure of a magnetic material and a thermoelectric material.
  • the left-right direction is the x-axis
  • the diagonal direction in the front-back direction is the y-axis
  • the up-down direction is the z-axis.
  • the transverse thermoelectric power (S y tot ) is expressed by the following formula (1).
  • the ratio (x) of the thickness of the thermoelectric layer (L z TE ) to the sum of the thickness of the thermoelectric layer (L z TE ) and the thickness of the magnetic layer (L z M ) is determined so as to maximize the transverse thermoelectric power (S y tot ) based on the resistivity and Seebeck coefficient of the thermoelectric material, and the resistivity, Seebeck coefficient, anomalous Hall resistivity, and anomalous Nernst coefficient of the magnetic material. Furthermore, it is advisable to determine the allowable range of the ratio (x) taking into consideration the manufacturing yield.
  • the ratio (x) of the thermoelectric layer thickness (L z TE ) to the sum of the thermoelectric layer thickness (L z TE ) and the magnetic layer thickness (L z M ) is set to a range in which the lower limit is a value obtained by subtracting 0.2 from the value that maximizes the transverse thermoelectric power (S y tot ) and the upper limit is a value obtained by adding 0.2 thereto, and the lower limit is set to zero if the lower limit is negative, and the upper limit is set to 1 if the upper limit exceeds 1.
  • the ratio (x) of the thermoelectric layer thickness (L z TE ) to the sum of the thermoelectric layer thickness (L z TE ) and the magnetic layer thickness (L z M ) may have a lower limit value of 0.1 less than the value that maximizes the transverse thermoelectric power (S y tot ) and an upper limit value of 0.1 more than that, or may have a lower limit value of 0.05 less than the value that maximizes the transverse thermoelectric power (S y tot ) and an upper limit value of 0.05 more than that.
  • the dimensions of the material, length Lx in the x-axis direction, width Ly in the y-axis direction, and thickness Lz in the z-axis direction, are expressed by the following formulas (2) to (4).
  • the thickness LzM of the magnetic material M and the thickness LzTE of the thermoelectric material TE are expressed by the following formulas (5) and (6).
  • the vertical thermoelectric conversion element of the present invention has a two-layer structure of a thermoelectric material layer (thermoelectric layer) TE10 and a magnetic material layer (magnetic layer) M20, and is equipped with output terminals 26a and 26b.
  • B indicates the magnetic field direction of the magnetic flux density
  • ⁇ T indicates the direction of the temperature gradient from the low temperature side to the high temperature side.
  • the magnetic flux density B is expressed by the following formula using the magnetization M, the external magnetic field H, and the magnetic permeability ⁇ 0 .
  • B ⁇ 0 H+M (7)
  • the thermoelectric material layer TE10 is made of a thermoelectric material having the Seebeck effect, and one end of the thermoelectric material layer TE10 is a low-temperature end 12, and the other end opposite the low-temperature end 12 is a high-temperature end 14.
  • electric heating, exhaust heat steam from a boiler device, or high-temperature wastewater can be used to heat the high-temperature end 14.
  • air cooling or water cooling can be used to cool the low-temperature end 12, or a solid heat dissipation member can be attached.
  • thermoelectric materials having the Seebeck effect include Bi 2 Te 3 , PbTe, Si, Ge, FeSi alloy, CrSi alloy, MgSi alloy, CoSb 3 alloy, Fe 2 VAl-based Heusler alloy, and SrTiO 3.
  • Bi 2 Te 3 , PbTe, Si, and Ge In order to adjust the resistivity and thermoelectric figure of merit Z, it is advisable to dope Bi 2 Te 3 , PbTe, Si, and Ge with a p-type or n-type element doping concentration of 0.1x10 19 to 3x10 19 cm -3 .
  • the magnetic material layer M20 is a magnetic material layer M laminated on the thermoelectric material layer TE10, and is magnetized or/and an external magnetic field is applied in the thickness direction of the magnetic material layer M20, and is conductive, generating a potential in the cross product direction of the temperature gradient direction ⁇ T of the magnetic material layer M20 and the magnetization direction M.
  • the magnetic material layer M20 is preferably made of a magnetic material having conductivity and an anomalous Hall angle of 1% or more. A magnetic material will exhibit both the anomalous Nernst effect and the anomalous Hall effect, but in order to obtain a large assist effect, it is preferable to select a magnetic material that exhibits a large anomalous Hall effect (anomalous Hall angle).
  • the anomalous Hall angle is a parameter that indicates the degree to which a current is bent laterally when it is passed through a magnetic material. If the anomalous Hall angle is less than 1%, the potential generated by the cross product direction of the temperature gradient direction ⁇ T of the magnetic material layer M and the magnetization direction M is low, which is not preferable for a vertical thermoelectric conversion element. In addition, since it is necessary for the material to have spontaneous magnetization at room temperature or higher in practical use, it is preferable for the material to have spontaneous magnetization up to 100°C or higher. Furthermore, there are three types of cases where magnetization in the film thickness direction of the magnetic material layer M and/or an external magnetic field is applied. The first type is the magnetization direction when only magnetization occurs and no external magnetic field is applied. The second type is the external magnetic field direction when only an external magnetic field is applied and no magnetization occurs. The third type is the combined magnetic field direction of the magnetization direction and the external magnetic field direction when both magnetization and an external magnetic field are applied.
  • Such magnetic materials having an anomalous Hall angle of 1% or more and spontaneous magnetization up to 100° C. or more include one type of magnetic material selected from the group consisting of L1 0 type ordered alloys, Heusler alloys, D0 22 type ordered alloys, binary disordered alloys, permanent magnet materials, multilayer magnetic materials, perovskite nitride materials, and D0 19 type ordered alloys. That is, examples of L1 0 type ordered alloys include FePt, CoPt, FePd, CoPd, FeNi, MnAl, and MnGa. Examples of Heusler alloys include Co 2 MnGa and Co 2 MnAl.
  • Examples of D0 22 type ordered alloys include Mn 3 Ga, Mn 2 FeGa, Mn 2 CoGa, and Mn 2 RuGa.
  • Examples of binary disordered alloys include FeCr, FeAl, FeGa, FeSi, FeTa, FeIr, FePt, FeSn, FeSm, FeTb, CoFeB, CoTb, and NiPt.
  • Examples of permanent magnet materials include SmCo5- based magnets, Sm2Co17 - based magnets, and Nd2Fe14B -based magnets.
  • Examples of multilayer magnetic materials include Co/Pt and Co/Pd.
  • Examples of perovskite nitride materials include Mn4N and Fe4N .
  • Examples of D019- type ordered alloys include Mn3Ga , Mn3Ge , and Mn3Sn .
  • the output terminals 26a and 26b are output terminals for extracting the electric potential generated in the cross product direction, which is the cross product direction of the temperature gradient direction ⁇ T of the thermoelectric material layer TE and the magnetization direction M of the magnetic material layer M, and are provided at both ends of the cross product direction of the magnetic material layer M.
  • a temperature gradient ⁇ T exists in the length x-axis direction, and when magnetization or an external magnetic field is applied in the thickness z-axis direction, a transverse thermal electric field E y tot is generated in the width y-axis direction.
  • FIG. 2A is a cross-sectional view or a front view in an xz plane of a vertical thermoelectric conversion element showing one embodiment of the present invention, and shows a two-layer structure of a magnetic material and a thermoelectric material.
  • the two-layer structure is made of a magnetic material M and a thermoelectric material TE, and no insulating layer is provided between them.
  • the magnetic material M has a thickness L z M
  • the thermoelectric material TE has a thickness L z TE .
  • FIG. 2B is a cross-sectional view or a front view in the xz plane of a vertical thermoelectric conversion element showing one embodiment of the present invention, and shows a laminated structure in which the two-layer structure of magnetic material and thermoelectric material is further multilayered.
  • m n.
  • thermoelectric layer thicknesses m ⁇ n
  • FIG. 3 shows the structure of a sample to demonstrate that the transverse thermoelectric power reaches a maximum value at an appropriate layer thickness ratio (x) as shown in formula (1) in the laminated structure of the present invention in which the magnetic material and the thermoelectric material are in direct electrical contact.
  • a commercially available SOI (Si-on-insulator) substrate was purchased (manufactured by Ultrasil LLC, California, USA). The 20 ⁇ m-thick n-type Si layer on this SOI substrate is used as the thermoelectric material, and the n-type Si layer acts to insulate from the underlying Si substrate by a 1 ⁇ m-thick SiO 2 insulating layer.
  • An Fe 70 Ga 30 (FeGa) alloy thin film is produced on the n-type Si by sputtering.
  • thermoelectric layer thickness ratio x of the laminated structure The manufacturer of the sputtering device is Eiko Co., Ltd., and the model name is ES-350L.
  • t FeGa samples with different FeGa thin film thicknesses
  • Table 1 shows the thickness tFeGa of the FeGa thin film of each sample and the corresponding ratio x of the thermoelectric layer thickness.
  • FeGa is known as Galfenol
  • its characteristics when the composition ratio x of Fe x Ga 1-x (0.5 ⁇ x ⁇ 0.9) is changed are disclosed in "Development of Next-Generation Thermoelectric Conversion Materials and Modules - The Dawn of Thermoelectric Power Generation” edited by the Thermoelectric Society of Japan (2020) pp. 70-78 and “Thermoelectric Power Generation Using the Anomalous Nernst Effect" by Hiroya Sakuraba, and this description is incorporated herein by reference.
  • thermoelectric layer thickness (x) and the vertical axis is the transverse thermoelectric power S y tot ( ⁇ V/K)
  • A is an enlarged view of the entire range of 0 ⁇ x ⁇ 1
  • B is an enlarged view of 0.97 ⁇ x ⁇ 1.00
  • thermoelectric layer thickness ratio x 0.997.
  • the experimental results tend to have the same maximum value as the calculated results, and both have a maximum value at the same position of the thermoelectric layer thickness ratio x, demonstrating the effect of this embodiment.
  • the experimental results show a larger transverse thermoelectric power than the calculated results, and the amplification of this transverse thermoelectric power is more remarkable when the thickness tFeGa of the FeGa thin film is smaller, suggesting that the effect originating from the interface between the FeGa alloy and n-type Si amplifies the transverse thermoelectric power.
  • thermoelectric layer when extracting power from a vertical thermoelectric conversion element, it is preferable that the internal impedance is low, and therefore it is preferable that the resistivity of the thermoelectric layer is low. Also, since output terminals are connected to both ends of the thermoelectric layer, the magnetic layer, or the thermoelectric layer and the magnetic layer, if the magnetic layer is a single layer or multiple layers and the thermoelectric layer is multiple layers sandwiching the magnetic layer, it is easy to attach the output terminals to the vertical thermoelectric conversion element.
  • the magnetic material of the magnetic layer is Fe x Ga 1-x (0.5 ⁇ x ⁇ 0.9)
  • the thermoelectric material of the thermoelectric layer is n-type Si
  • the ratio (x) of the thickness of the thermoelectric layer (L z TE ) to the sum of the thickness of the thermoelectric layer (L z TE ) and the thickness of the magnetic layer (L z M ) is, for example, 0.98 ⁇ LzTE /( LzTE + LzM ) ⁇ 0.995
  • the present invention is not limited to this, and the thermoelectric material of the thermoelectric layer may be p-type Si.
  • the ratio (x) that maximizes the transverse thermoelectric power (S y tot ) of the vertical thermoelectric conversion element may be 0.3 ⁇ L z TE /(L z TE +L z M ) ⁇ 0.7.
  • thermoelectric conversion element of the present invention we have come up with a laminated structure in which the magnetic material and the thermoelectric material are in direct electrical contact, without the need for end conductors and insulating layers (Figs. 1 and 2).
  • the terminals for extracting the power generated by the lateral thermoelectric power can be attached only to the magnetic material, only to the thermoelectric material, or to both.
  • the in-plane dimensions of the vertical thermoelectric conversion element, with the length L x in the x-axis direction and the width L y in the y-axis direction, are expressed by equation (10).
  • the layer thickness is expressed by equation (11) in the case of a two-layer structure and equation (12) in the case of a multi-layered laminated structure, and it is desirable that both are much smaller, as shown in equations (13) and (14).
  • the transverse thermoelectric power (S y tot ) in the laminated structure can be formulated as in the above-mentioned equation (1).
  • the symbols are the same as those mentioned above.
  • the in-plane (xy plane) effective resistivity ( ⁇ eff ) can be formulated as follows:
  • the power factor (PF) of the transverse thermoelectric power can be formulated using the above results as follows:
  • the in-plane (xy plane) effective thermal conductivity (k eff ) can be formulated as follows:
  • thermoelectric conversion element of the present invention According to the evaluation method for a vertical thermoelectric conversion element of the present invention, the following effects can be obtained.
  • A By using the formula (1) for evaluation, an optimal structure for a vertical thermoelectric conversion element that generates a high lateral thermoelectric power can be obtained.
  • B The interface effect between the magnetic material and the thermoelectric material contributes to improving the transverse thermoelectric power.
  • C Higher transverse thermoelectric power can be obtained by using a magnetic material with a large anomalous Hall effect and a thermoelectric material with a large Seebeck coefficient.
  • D Using equations (1), (15) to (18), the various characteristics (S y tot , PF, zT) of the laminated structure of thermoelectric material and magnetic material can be estimated.
  • thermoelectric conversion element of the present invention is suitable for use in a thermoelectric power generation module or heat flow sensor.
  • a heat flow sensor refers to a sensor that can quantitatively measure the heat flux transmitted as conductive heat as a voltage signal through thermoelectric phenomena, etc. Since it can quickly detect the outflow and inflow of heat as positive and negative signals, it is expected to enable more efficient thermal control and faster, more sensitive heat detection than a thermometer.
  • a thermoelectric power generation module refers to a power generation device that directly converts thermal energy (temperature difference) into electrical energy.
  • the vertical thermoelectric conversion element of the present invention utilizes the high lateral thermoelectric power provided by the laminated structure of the magnetic material and thermoelectric material, and while maintaining a simple in-plane connection type structure, a higher output voltage can be obtained compared to that of a thermoelectric material alone.Since this is expected to have effects such as improving the output of thermoelectric power generation modules and increasing the sensitivity to heat flow sensors, it is suitable for use in thermoelectric power generation modules and heat flow sensors.
  • the evaluation method for a vertical thermoelectric conversion element of the present invention is suitable for use in material search and optimization design of a vertical thermoelectric conversion element using the lateral thermoelectric effect.
  • thermoelectric layer (thermoelectric material layer) TE 12 Low temperature side (end) 14 High temperature side (end) 20 Magnetic layer (magnetic material layer) M 26a, 26b Output terminals L z M Thickness of magnetic layer (z direction) L z Thickness of the TE thermoelectric layer (z direction) S ANE Anomalous Nernst coefficient of magnetic material S M Seebeck coefficient of magnetic material S TE Seebeck coefficient of thermoelectric material S y tot Transverse thermoelectric power ⁇ AHE Anomalous Hall resistivity of magnetic material ⁇ M Resistivity of magnetic material ⁇ TE Resistance of thermoelectric material rate

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YAMAMOTO KAORU ET AL.: "Phenomenological analysis of transverse thermoelectric generation and cooling performance in magnetic/thermoelectric hybrid systems", JOURNAL OF APPLIED PHYSICS, vol. 129, 10 June 2021 (2021-06-10), pages 1 - 7, XP012257516, DOI: 10.1063/5.005 5475 *
ZHOU WEINAN ET AL.: "Seebeck-driven transverse thermoelectric generation in magnetic hybrid bulk materials", APPLIED PHYSICS LETTERS, vol. 122, 8 February 2023 (2023-02-08), pages 1 - 6, XP012272216, DOI: 10.1063/5.0126870 *
ZHOU WEINAN ET AL.: "Seebeck-driven transverse thermoelectric generation in on-chip devices", JOURNAL OF PHYSICS D: APPLIED PHYSICS, vol. 55, no. 33, 7 June 2022 (2022-06-07), pages 1 - 7, XP020424476, DOI: 10.1088/1361-6463/ac717a *

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