Vertical thermoelectric conversion element using lateral thermoelectric effect, and evaluation method of vertical thermoelectric conversion element

Abstract

The present invention is a vertical thermoelectric conversion element that uses a lateral thermoelectric effect and has a laminated structure in which a magnetic material and a thermoelectric material are in direct electrical contact with each other, and is configured as follows. The present invention is equipped with: a thermoelectric layer 10 comprising a thermoelectric material, the two ends of which are on the low temperature side and the high temperature side; a magnetic body layer 20 which is laminated onto the thermoelectric layer 10, has an external magnetic field and / or a magnetizing component in the film-thickness direction of the magnetic body layer 20, has conductivity, and generates an electric potential in the direction of the cross product of the temperature gradient direction of the magnetic body layer 20 and the magnetization direction and / or the external magnetic field direction; and an output terminal which takes out the electric potential generated in the cross product direction, and is provided at both end sections in the cross product direction of both end sections of the thermoelectric layer 10 and / or the magnetic body layer 20, which is the direction of the cross product of the temperature gradient direction of the thermoelectric layer 10 and the magnetization direction of the magnetic body layer 20 and / or the external magnetic field direction. Therein, the ratio of the thickness of the thermoelectric layer 10 to the total of the thickness of the thermoelectric layer 10 and the thickness of the magnetic body layer 20 is determined on the basis of a value for maximizing the lateral thermoelectric power (Sy tot).

Description

Vertical thermoelectric conversion element using transverse thermoelectric effect and evaluation method for vertical thermoelectric conversion element

[0001] The present invention relates to a vertical thermoelectric conversion element using the transverse thermoelectric effect, and a method for evaluating the vertical thermoelectric conversion element.

[0002] 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 achieving large areas, low durability and flexibility, and high cost.

[0003] On the other hand, in magnetic materials, there is a phenomenon in which an electric field is generated in the cross product direction of magnetization M and ∇T (∇T × M direction), which is known as the anomalous Nernst effect. Utilizing this transverse thermoelectric effect, in which an electric field is generated in a direction perpendicular to ∇T, makes it possible to function as a thermoelectric power generation module or heat flow sensor with an extremely simple in-plane connection type structure, and it is therefore expected that a new thermoelectric power generation laminate that solves the above-mentioned problems will be created (Patent Document 1, Non-Patent Document 1).

[0004] However, the thermoelectric power of the anomalous Nernst effect of magnetic materials reported to date at room temperature is less than 10 μV / K (Non-Patent Document 2), and materials with larger transverse thermoelectric power are being actively searched for. In this context, the inventors recently 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. They 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).

[0005] JP 2014-072256 A

[0006] W. Zhou, and Y. Sakuraba, Appl. Phys. Express 13, 043001 (2020)K. Uchida, W. Zhou, and Y. Sakuraba, Appl. Phys. Lett. 118, 140504 (2021)W. Zhou, K. Yamamoto, A. Miura et al., Nat. Mater. vol. 20, 463-467 (2021)K. Yamamoto, R. Iguchi, A. Miura et al., J. Appl. Phys. 129, 223908 (2021)

[0007] The thermoelectric power due to the anomalous Nernst effect is still small compared to the Seebeck effect of thermoelectric materials, and higher transverse thermoelectric power is required for practical applications. While vertical thermoelectric conversion elements composed of magnetic and thermoelectric materials can achieve high transverse thermoelectric power, they require a closed-circuit structure in which the magnetic and thermoelectric materials are electrically connected only on the high-temperature and low-temperature sides of ∇T and are electrically insulated elsewhere. The end conductors and insulating layers required for the closed circuit complicate the structure of the thermoelectric conversion element, hindering miniaturization and modularization. For example, in the vertical thermoelectric conversion element disclosed in Patent Document 2, the output terminals are connected only to both ends of the magnetic layer in the direction of potential generation, complicating the connection process. Furthermore, if the output terminals are connected to the thermoelectric layer stacked on the magnetic layer, the voltage generated by the thermoelectric power is actually lower than when connected only to the magnetic layer.

[0008] The present invention solves the problems of the conventional technology described above, and aims to provide a vertical thermoelectric conversion element using the lateral thermoelectric effect, which has a laminated structure in which the magnetic material and the thermoelectric material are in direct electrical contact without requiring end conductors and insulating layers. Another aim of the present invention is to provide an evaluation method for a vertical thermoelectric conversion element using the lateral thermoelectric effect, which is suitable for use in material search and optimization design of a vertical thermoelectric conversion element using the lateral thermoelectric effect.

[0009] [1] As shown in FIG. 1, 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 both a magnetization component and an external magnetic field in the film thickness direction of the magnetic layer 20, and having electrical conductivity, and having a magnetic field in the temperature gradient direction of the magnetic layer 20 and a magnetic field in the direction of the temperature gradient of the magnetic layer 20. and a magnetic layer 20 that generates a potential in the magnetization direction, the external magnetic field direction, or the cross product direction of the magnetization direction and the external magnetic field direction in the thermoelectric layer 10, and output terminals (26a, 26b) provided at both ends of the 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; ｚ ＴＥ ) and the thickness of the magnetic layer 20 (L ｚ Ｍ ) the thickness (L ｚ ＴＥ ) ratio (x) is the transverse thermoelectric power (S ｙ ｔｏｔ The lower limit is the x value that maximizes the above equation (2), and the upper limit is the value obtained by adding 0.2 to the x value that maximizes the above equation (2). If the lower limit is negative, the lower limit is set to zero, and if the upper limit is greater than 1, the upper limit is set to 1.

[0010] [2] In the vertical thermoelectric conversion element [1] of the present invention, preferably, the transverse thermoelectric power (S ｙ ｔｏｔ ) is preferably formulated as follows:

[0011] [3] In the vertical thermoelectric conversion element [1] of the present invention, preferably, 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, and the thickness (L ｚ ＴＥ ) and the thickness of the magnetic layer (L ｚ Ｍ ) to the total thickness (Lｚ ＴＥ ) is 0.98≦L ｚ ＴＥ / (L ｚ ＴＥ +L ｚ Ｍ In this case, the transverse thermoelectric power S ｙ ｔｏｔ is 6.8 (μV / K) or more, and the magnetic material is Fe ７０ Ga ３０ [4] In the vertical thermoelectric conversion element [3] of the present invention, the magnetic material of the magnetic layer is preferably Fe. ｘ Ga １－ｘ (0.5≦x≦0.9), the thermoelectric material of the thermoelectric layer is n-type Si, and the thickness (L ｚ ＴＥ ) and the thickness of the magnetic layer (L ｚ Ｍ ) to the total thickness (L ｚ ＴＥ ) is 0.99≦L ｚ ＴＥ / (L ｚ ＴＥ +L ｚ Ｍ In this case, the transverse thermoelectric power S ｙ ｔｏｔ is 10 (μV / K) or more, and the magnetic material is Fe ７０ Ga ３０ [5] In the vertical thermoelectric conversion element [4] of the present invention, the magnetic material of the magnetic layer is preferably Fe. ｘ Ga １－ｘ (0.5≦x≦0.9), the thermoelectric material of the thermoelectric layer is n-type Si, and the thickness (L ｚ ＴＥ ) and the thickness of the magnetic layer (L ｚ Ｍ ) to the total thickness (L ｚ ＴＥ ) is 0.994≦L ｚ ＴＥ / (L ｚ ＴＥ+L ｚ Ｍ In this case, the transverse thermoelectric power S ｙ ｔｏｔ is 12.5 (μV / K) or more, and the magnetic material is Fe ７０ Ga ３０ [6] In the vertical thermoelectric conversion element [1] of the present invention, preferably, the magnetic material of the magnetic layer is made of one kind of magnetic material selected from the following group (A) to (H): (A) One or more kinds of L selected from the group consisting of FePt, CoPt, FePd, CoPd, FeNi, MnAl, and MnGa. １０ Regular pattern alloy, (B)Co ２ MnGa and Co ２ (C) one or two Heusler alloys selected from the group consisting of MnAl; ３ Ga, Mn ２ FeGa, Mn ２ CoGa and Mn ２ One or more types of D0 selected from the group consisting of RuGa ２２ (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) SmCo ５ system magnet, Sm ２ Co １７ Nd-based magnets and ２ Fe １４ (F) one or more types of permanent magnet materials selected from the group consisting of B-based magnets; (G) one or two types of multilayer film materials selected from the group consisting of Co / Pt and Co / Pd laminates; (H) Mn ４ N, Fe ４ one or two perovskite nitride materials selected from the group consisting of (H)Mn ３ Ga, Mn ３ Ge, and Mn ３ Sn, one or more kinds of D0 １９[7] In the vertical thermoelectric conversion element [6] of the present invention, the FeGa is preferably an FeGa-type ordered alloy. ｘ Ga １－ｘ (0.5≦x≦0.9). [8] In the vertical thermoelectric conversion element [1] of the present invention, the thermoelectric material of the thermoelectric layer is preferably Bi. ２ Te ３ , PbTe, Si, Ge, FeSi alloy, CrSi alloy, MgSi alloy, CoSb ３ Alloy, Fe ２ VAl-based Heusler alloys and SrTiO ３ [9] In the vertical thermoelectric conversion element [8] of the present invention, preferably, the Bi ２ Te ３ , 0.1x10 for PbTe, Si, or Ge １９ ~3x10 １９ cm －３ Preferably, the vertical thermoelectric conversion element [1] of the present invention is doped with a p-type or n-type element so as to have a carrier concentration of . When the Si is p-type Si, the sign of the transverse thermoelectric power is opposite to that of n-type Si.

[10] In the vertical thermoelectric conversion element [1] of the present invention, preferably, 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.

[11] A thermoelectric power generation module or heat flow sensor using the vertical thermoelectric conversion element [1] to

[10] .

[0012]

[12] 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, The thickness of the thermoelectric layer (L ｚ ＴＥ ) and the thickness of the magnetic layer (L ｚ Ｍ ) to the total thickness of the thermoelectric layer (L ｚ ＴＥ ) ratio (x) is defined as the transverse thermoelectric power (S ｙ ｔｏｔ) is determined to maximize the value of the symbol. Here, each symbol is defined as follows:

[13] In the evaluation method for a vertical thermoelectric conversion element according to the present invention

[12] , it is preferable to further define the range of this ratio (x) as the range of the transverse thermoelectric power (S ｙ ｔｏｔ The lower limit is set to a value obtained by subtracting 0.2 from the value that maximizes the value of (1) above, and the upper limit is set to a value obtained by adding 0.2 to the value that maximizes the value of (2) above. When the lower limit is negative, the lower limit is set to zero, and when the upper limit is greater than 1, the upper limit is set to 1.

[14] In the evaluation method

[12] of the vertical thermoelectric conversion element of the present invention, it is preferable to set the value so as to maximize the power coefficient (PF) of the transverse thermoelectric power defined by the following formula: Here, the effective resistivity (ρ eff ) is defined as follows:

[15] In 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 the isothermal dimensionless figure of merit (zT), which represents the efficiency of the transverse thermoelectric effect and is defined by the following equation: Here, the effective thermal conductivity (k eff ) is defined as follows:

[0013] According to the vertical thermoelectric conversion element of the present invention, the output terminals may be connected not only to both ends of the magnetic layer in the potential generation direction but also to the thermoelectric layer laminated on the magnetic layer, which has the effect of facilitating the connection of the output terminals. Furthermore, even if the connection position of the output terminals extends to the thermoelectric layer laminated on the magnetic layer, the decrease in voltage generated by thermoelectric power remains within an acceptable range compared to when the output terminals are connected only to the magnetic layer. Furthermore, according to 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 multiple sandwich structures of magnetic layers and thermoelectric layers are laminated, the thickness (L ｚ ＴＥ) and the thickness of the magnetic layer (L ｚ Ｍ ) to the total thickness of the thermoelectric layer (L ｚ ＴＥ ) is preferably a ratio of the transverse thermoelectric power (S ｙ ｔｏｔ ) is set as the lower limit value by subtracting 0.2 from the value that maximizes the transverse thermoelectric power (S ｙ ｔｏｔ ) to maximize the thickness of the thermoelectric layer (L ｚ ＴＥ ) and the thickness of the magnetic layer (L ｚ Ｍ ) to the total thickness of the thermoelectric layer (L ｚ ＴＥ Furthermore, it is possible to obtain a shape of a vertical thermoelectric conversion element that maximizes the power factor and the isothermal dimensionless figure of merit (zT), which represents the efficiency of the transverse thermoelectric effect.

[0014] 1 is an explanatory diagram of a vertical thermoelectric conversion element according to an embodiment of the present invention, showing the transverse thermoelectric effect, material dimensions, and thermoelectric layer thickness ratio (x) in a two-layer structure of magnetic material and thermoelectric material; 2 is an explanatory diagram of a vertical thermoelectric conversion element according to an embodiment of the present invention, showing the two-layer structure of magnetic material and thermoelectric material; 3 is an explanatory diagram of a vertical thermoelectric conversion element according to an embodiment of the present invention, showing a cross-sectional view of a laminated structure in which magnetic material and thermoelectric material are multilayered; 4 is a structural diagram of a sample used in the embodiment; 5 is an explanatory diagram of the calculation results of the embodiment and the experimental results obtained from the sample of FIG. 3, where the horizontal axis is the thermoelectric layer thickness ratio (x) and the vertical axis is the transverse thermoelectric power S ｙ ｔｏｔ (μV / K). (A) is an enlarged view of the entire range of 0≦x≦1, and (B) is an enlarged view of the range of 0.97≦x≦1.00.

[0015] The present invention will be described below with reference to the drawings. 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 the two-layer structure of magnetic material and thermoelectric material. In the coordinate system in the drawing, the left-right direction is the x-axis, the oblique direction in the front-back direction is the y-axis, and the up-down direction is the z-axis. In this case, the transverse thermoelectric power (S ｙ ｔｏｔ) is expressed by the following formula (1).

[0016] In the vertical thermoelectric conversion element of the present invention, the thickness of the thermoelectric layer (L ｚ ＴＥ ) and the thickness of the magnetic layer (L ｚ Ｍ ) to the total thickness of the thermoelectric layer (L ｚ ＴＥ ) ratio (x) is defined as the transverse thermoelectric power (S ｙ ｔｏｔ Furthermore, it is advisable to determine the allowable range of the ratio (x) taking into consideration the manufacturing yield. For example, the thickness (L ｚ ＴＥ ) and the thickness of the magnetic layer (L ｚ Ｍ ) to the total thickness of the thermoelectric layer (L ｚ ＴＥ ) ratio (x) is the transverse thermoelectric power (S ｙ ｔｏｔ The lower limit is set to a value obtained by subtracting 0.2 from the value that maximizes the thickness (L ｚ ＴＥ ) and the thickness of the magnetic layer (L ｚ Ｍ ) to the total thickness of the thermoelectric layer (L ｚ ＴＥ ) ratio (x) is the transverse thermoelectric power (S ｙ ｔｏｔ ) may be used as the reference value, and the value obtained by subtracting 0.1 from the value that maximizes the transverse thermoelectric power (S ｙ ｔｏｔ The lower limit may be a value obtained by subtracting 0.05 from the value that maximizes the above-mentioned (2) and the upper limit may be a value obtained by adding 0.05 to the value that maximizes the above-mentioned (2).

[0017] The dimensions of the material are the length Lx in the x-axis direction, the width Ly in the y-axis direction, and the thickness Lz in the z-axis direction, which are expressed by the following equations (2) to (4). ｚ Ｍand the thickness L of the thermoelectric material TE ｚ ＴＥ are expressed by the following equations (5) and (6).

[0018] 1, 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, and ∇T indicates the direction of the temperature gradient from the low temperature side to the high temperature side. The magnetic flux density B is determined by the magnetization M, the external magnetic field H, and the magnetic permeability μ ０ Using the above, it is expressed by the following equation: B = μ ０ H+M (7)

[0019] 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. For example, electric heating, exhaust heat steam from a boiler, or high-temperature wastewater can be used to heat the high-temperature end 14. For example, air cooling or water cooling can be used to cool the low-temperature end 12, or a solid heat dissipation member can be attached. An example of a thermoelectric material having the Seebeck effect is Bi. ２ Te ３ , PbTe, Si, Ge, FeSi alloy, CrSi alloy, MgSi alloy, CoSb ３ Alloy, Fe ２ VAl-based Heusler alloys and SrTiO ３ To adjust the resistivity and thermoelectric figure of merit Z, Bi ２ Te ３ , PbTe, Si, Ge doped with p-type or n-type elements at a concentration of 0.1 × 10 １９ ~3x10 １９ cm －３ It is preferable to dope the silicon dioxide so that the carrier concentration becomes 100%.

[0020] The magnetic material layer M20 is a magnetic material layer M laminated on the thermoelectric material layer TE10. Magnetization and / or an external magnetic field are applied to the magnetic material layer M20 in the thickness direction. The magnetic material layer M20 is conductive and generates a potential in the cross product direction of the temperature gradient direction ∇T and the magnetization direction M of the magnetic material layer M20. The magnetic material layer M20 is preferably made of a conductive magnetic material having an anomalous Hall angle of 1% or more. While any magnetic material exhibits both the anomalous Nernst effect and the anomalous Hall effect, it is preferable to select a magnetic material exhibiting a large anomalous Hall effect (anomalous Hall angle) to obtain a large assist effect. Here, the anomalous Hall angle is a parameter that indicates the degree to which current is deflected 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 and the magnetization direction M of the magnetic material layer M is low, making it undesirable for a vertical thermoelectric conversion element. Furthermore, since spontaneous magnetization is required at room temperature or above for practical use, it is preferable for spontaneous magnetization to be maintained at temperatures above 100°C. 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 is the magnetization direction when only magnetization occurs and no external magnetic field is applied. The second is the external magnetic field direction when only an external magnetic field is applied and no magnetization occurs. The third 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.

[0021] Such a magnetic material having an anomalous Hall angle of 1% or more and spontaneous magnetization up to 100°C or more is L1 ０ Regular pattern alloy, Heusler alloy, D0 ２２ ordered alloys, binary disordered alloys, permanent magnet materials, multilayer magnetic materials, perovskite nitride materials, and D0 １９ There is one type of magnetic material selected from the group consisting of L1 ordered alloys. ０ Examples of the ordered alloys include FePt, CoPt, FePd, CoPd, FeNi, MnAl, and MnGa. Examples of the Heusler alloys include Co ２ MnGa and Co ２ Examples include MnAl. ２２ As the ordered alloy, for example, Mn ３Ga, Mn ２ FeGa, Mn ２ CoGa and Mn ２ 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 SmCo. ５ system magnet, Sm ２ Co １７ Nd-based magnets and ２ Fe １４ Examples of multilayer magnetic materials include Co / Pt and Co / Pd. Examples of perovskite nitride materials include Mn ４ N, Fe ４ There is N. D0 １９ As the ordered alloy, for example, Mn ３ Ga, Mn ３ Ge, and Mn ３ Examples thereof include Sn.

[0022] The output terminals 26a and 26b are provided at both ends of the cross product direction of the magnetic material layer M, 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 output terminals for extracting the potential generated in the cross product direction. In the vertical thermoelectric conversion element shown in FIG. 1 configured in this manner, when the temperature gradient ∇T is in the length x-axis direction and magnetization or an external magnetic field is applied in the thickness z-axis direction, a transverse thermal electric field E is generated in the width y-axis direction. ｙ ｔｏｔ occurs.

[0023] 2A is a cross-sectional view or a front view of a vertical thermoelectric conversion element in an xz plane 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 thickness of the magnetic material M is L. ｚ Ｍ and the thickness of the thermoelectric material TE is L ｚ ＴＥ is.

[0024] 2B is a cross-sectional view or a front view of a vertical thermoelectric conversion element in an xz plane 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. ｚ Ｍ，ｉ , (i=1, 2, ..., m), and the thickness of each layer of the thermoelectric material TE is L ｚ ＴＥ，ｊ , (j=1, 2, ..., n). In the case of a two-layer structure in which the magnetic material and the thermoelectric material are perfectly paired, m=n. However, in the case where some layers are made into a single-layer structure of magnetic material or thermoelectric material instead of a two-layer structure of magnetic material and thermoelectric material, taking into account the ratio (x) of the thermoelectric layer thicknesses, m≠n.

[0025] Figure 3 shows the structure of a sample used to demonstrate that the transverse thermoelectric power reaches its maximum value when the layer thickness ratio (x) is appropriate as shown in formula (1) in the laminated structure of the present invention in which the magnetic material and thermoelectric material are in direct electrical contact. A commercially available SOI (Si-on-insulator) substrate was purchased (manufactured by Ultrasil LLC, California, USA). A 20 μm-thick n-type Si layer on this SOI substrate was used as the thermoelectric material, and the n-type Si layer was covered with a 1 μm-thick SiO ２ The insulating layer acts to insulate the Si substrate underneath. ７０ Ga ３０ The (FeGa) alloy thin film is prepared by sputtering. The sputtering equipment is manufactured by Eiko Co., Ltd. and its model name is ES-350L. The thickness of the FeGa thin film (t ＦｅＧａ Several samples with different thicknesses (t) were prepared and measured to investigate the influence of the thermoelectric layer thickness ratio x of the laminated structure on the transverse thermoelectric power. ＦｅＧａ and the corresponding thermoelectric layer thickness ratio x are shown in Table 1.

[0026]

[0027] In addition, there is a 2 nm thick anti-oxidation layer of Au on the FeGa alloy thin film. FeGa is known as Galfenol, and is described 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, by Hiroya Sakuraba, and in "Thermoelectric Power Generation Using the Anomalous Nernst Effect" by Hiroya Sakuraba. ｘ Ga１－ｘ The characteristics when the composition ratio x is varied within the range of (0.5≦x≦0.9) are disclosed, and this description is incorporated herein by reference.

[0028] Reference samples were prepared separately to examine the characteristics of the FeGa alloy and n-type Si, and the values ​​of these samples and the above formula were used to calculate the tendency of the transverse thermoelectric power at room temperature in the laminated structure as a function of the thermoelectric layer thickness ratio x. The calculation results are shown in Figure 4. Figure 4 is an explanatory diagram of the calculation results of the example and the experimental results obtained from the sample in Figure 3, with the horizontal axis representing the thermoelectric layer thickness ratio (x) and the vertical axis representing the transverse thermoelectric power S ｙ ｔｏｔ (μV / K), where (A) is the entire range of 0≦x≦1, and (B) is an enlarged view of 0.97≦x≦1.00. Here, x=0 means that all materials are magnetic, and x=1 means that all materials are thermoelectric.

[0029] From Fig. 4(B), it can be seen that the transverse thermoelectric power reaches a maximum value near the thermoelectric layer thickness ratio x = 0.997. The experimental results tend to reach the same maximum value as the calculated results, and both reach a maximum value at the same thermoelectric layer thickness ratio x, demonstrating the effect of this embodiment. Furthermore, from Fig. 4(B), the experimental results show a transverse thermoelectric power greater than the calculated results, and this amplification of the transverse thermoelectric power is due to the thickness t of the FeGa thin film. ＦｅＧａ This suggests that the effect of the interface between the FeGa alloy and n-type Si amplifies the transverse thermoelectric power. ＦｅＧａ In the vertical thermoelectric conversion element of this example, a large transverse thermoelectric power of 15 μV / K was obtained in the sample with a thickness of 70 nm. ７０ Ga ３０ In a two-layer structure with a (FeGa) alloy thin film as the magnetic material and n-type Si as the thermoelectric material, a transverse thermoelectric power of 15 μV / K was obtained at the optimal thermoelectric layer thickness ratio x = 0.997 calculated using the above formula. This value is higher than the anomalous Nernst coefficient of the FeGa alloy alone and exceeds the thermoelectric power of the anomalous Nernst effect reported to date.

[0030] When extracting power from a vertical thermoelectric conversion element, a low internal impedance is preferable, and therefore a low resistivity thermoelectric layer is preferable. Furthermore, since output terminals are connected to both ends of the thermoelectric layer, the magnetic layer, or both 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, the work of attaching the output terminals to the vertical thermoelectric conversion element is easy.

[0031] In the above embodiment, 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, and the thickness of the thermoelectric layer (L ｚ ＴＥ ) and the thickness of the magnetic layer (L ｚ Ｍ ) to the total thickness of the thermoelectric layer (L ｚ ＴＥ ) is, for example, 0.98≦L ｚ ＴＥ / (L ｚ ＴＥ +L ｚ Ｍ )≦0.995, the present invention is not limited to this, and the thermoelectric material of the thermoelectric layer may be p-type Si. Furthermore, depending on the combination of the magnetic material of the magnetic layer and the thermoelectric material of the thermoelectric layer, the transverse thermoelectric power (S ｙ ｔｏｔ ) is maximized by the ratio (x) of 0.3≦L ｚ ＴＥ / (L ｚ ＴＥ +L ｚ Ｍ ) ≦0.7. In such cases, 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 made up of multiple layers and the thermoelectric layer is made up of multiple layers sandwiching the magnetic layer, the work of attaching the output terminals to the vertical thermoelectric conversion element will be easier.

[0032] Next, the evaluation method for vertical thermoelectric conversion elements will be explained in more detail. In the vertical thermoelectric conversion element of the present invention, 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, has been devised (Figs. 1 and 2). Terminals for extracting the power generated by the lateral thermoelectric power may be attached only to the magnetic material, only to the thermoelectric material, or to both. There is a temperature gradient in the in-plane direction of each layer. The in-plane dimensions of the vertical thermoelectric conversion element are the length L in the x-axis direction, ｘ , width L in the y-axis direction ｙ is expressed as in equation (10). Compared to this in-plane dimension, 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). At this time, the transverse thermoelectric power (S ｙ ｔｏｔ ) can be formulated as in the above equation (1). The symbols are the same as those mentioned above.

[0033] In-plane (x-y plane) effective resistivity (ρ eff ) can be formulated as follows: The power factor (PF) of the transverse thermoelectric power can be formulated using the above results as follows: In-plane (x-y plane) effective thermal conductivity (k eff ) can be formulated as follows:

[0034] The isothermal dimensionless figure of merit (zT), which represents the efficiency of the transverse thermoelectric effect, can be formulated as follows using the above results:

[0035] The evaluation method for a vertical thermoelectric conversion element of the present invention provides the following effects. (A) By using the formula (1) for evaluation, an optimal structure for a vertical thermoelectric conversion element that generates high transverse 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) By using a magnetic material with a large anomalous Hall effect and a thermoelectric material with a large Seebeck coefficient, higher transverse thermoelectric power can be obtained. (D) By using the formulas (1), (15) to (18), each characteristic (S ｙ ｔｏｔ , PF, zT) can be estimated.

[0036] The vertical thermoelectric conversion element of the present invention is suitable for use in a thermoelectric power generation module or a heat flow sensor. Here, a heat flow sensor refers to a sensor that can quantitatively measure heat flux transmitted as conductive heat as a voltage signal through thermoelectric phenomena or the like. Because it can quickly detect heat inflow and outflow 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.

[0037] The vertical thermoelectric conversion element of the present invention utilizes the high lateral thermoelectric power of the laminated structure of the magnetic material and the thermoelectric material, and while maintaining a simple in-plane connection structure, it can obtain a higher output voltage than that of a single thermoelectric material, which is expected to have effects such as improving the output of the thermoelectric power generation module and increasing the sensitivity to the heat flow sensor, making it suitable for use in thermoelectric power generation modules and heat flow sensors.The evaluation method of the vertical thermoelectric conversion element of the present invention is suitable for use in material search and optimization design of vertical thermoelectric conversion elements using the lateral thermoelectric effect.

[0038] 10 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 terminal L ｚ Ｍ Thickness of magnetic layer (z direction) L ｚ ＴＥ Thickness of thermoelectric layer (z direction) S ＡＮＥ Anomalous Nernst coefficient of magnetic material S Ｍ Seebeck coefficient of magnetic material SＴＥ Seebeck coefficient of thermoelectric material S ｙ ｔｏｔ Lateral thermopower ρ ＡＨＥ Anomalous Hall resistivity ρ of magnetic materials Ｍ Resistivity of magnetic material ρ ＴＥ Resistivity of thermoelectric materials

Claims

1. A thermoelectric layer made of a thermoelectric material exhibiting the Seebeck effect, wherein one end of the thermoelectric layer is the low-temperature side, and the other end opposite the low-temperature side is the high-temperature side. A magnetic layer laminated on the thermoelectric layer, the magnetic layer having a magnetization component, an external magnetic field, or a magnetization component and an external magnetic field in the thickness direction of the magnetic layer, and being conductive, and generating a potential in the temperature gradient direction of the magnetic layer, and in the cross product direction of the magnetization direction, the external magnetic field direction, or the magnetization direction and the external magnetic field direction, and Output terminals provided at both ends of the thermoelectric layer, the magnetic layer, or the thermoelectric layer and the magnetic layer, for extracting the potential generated in the cross product direction, such that the temperature gradient direction of the thermoelectric layer and the magnetization direction, external magnetic field direction, or cross product direction of the magnetization direction and the external magnetic field direction of the magnetic layer, Equipped with, The thickness (L) of the aforementioned thermoelectric layer ｚ ＴＥ ) and the thickness (L) of the magnetic layer ｚ Ｍ The thickness of the thermoelectric layer (L) relative to the sum of the ) ｚ ＴＥ The ratio of ) is the transverse thermoelectric power (S ｙ ｔｏｔ A vertical thermoelectric element in which the value that maximizes ) is used as the basis, with 0.2 subtracted from the lower limit and 0.2 added to the upper limit, and if the lower limit is negative, the lower limit is set to zero, and if the upper limit is greater than 1, the upper limit is set to 1.

2. The horizontal thermoelectric power (S ｙ ｔｏｔ ) is formulated by the following equation, the vertical thermoelectric conversion element according to claim 1. [Math 1]

3. The magnetic material of the aforementioned magnetic layer is Fe ｘ Ga １－ｘ (0.5 ≤ x ≤ 0.9), the thermoelectric material of the thermoelectric layer is n-type Si, and the thickness of the thermoelectric layer (L ｚ ＴＥ ) and the thickness (L) of the magnetic layer ｚ Ｍ The thickness of the thermoelectric layer (L) relative to the sum of the ) ｚ ＴＥ The ratio of ) is, 0.98≦L ｚ ＴＥ / (8) ｚ ＴＥ +7 ｚ Ｍ )≦0.9995 The vertical thermoelectric element according to claim 1.

4. The magnetic material of the aforementioned magnetic layer is Fe ｘ Ga １－ｘ (0.5 ≤ x ≤ 0.9), the thermoelectric material of the thermoelectric layer is n-type Si, and the thickness of the thermoelectric layer (L ｚ ＴＥ ) and the thickness (L) of the magnetic layer ｚ Ｍ The thickness of the thermoelectric layer (L) relative to the sum of the ) ｚ ＴＥ The ratio of ) is, 0.99≦L ｚ ＴＥ / (8) ｚ ＴＥ +7 ｚ Ｍ )≦0.999 The vertical thermoelectric element according to claim 3.

5. The magnetic material of the aforementioned magnetic layer is Fe ｘ Ga １－ｘ (0.5 ≤ x ≤ 0.9), the thermoelectric material of the thermoelectric layer is n-type Si, and the thickness of the thermoelectric layer (L ｚ ＴＥ ) and the thickness (L) of the magnetic layer ｚ Ｍ The thickness of the thermoelectric layer (L) relative to the sum of the ) ｚ ＴＥ The ratio of ) is, 0.994≦L ｚ ＴＥ / (8) ｚ ＴＥ +7 ｚ Ｍ )≦0.998 The vertical thermoelectric element according to claim 4.

6. The magnetic material of the magnetic layer is made of one type of magnetic material selected from the following groups (A) to (H), the vertical thermoelectric element according to claim 1: (A) One or more L1 selected from the group consisting of FePt, CoPt, FePd, CoPd, FeNi, MnAl, and MnGa ０ type-regular alloy, (B) Co ２ MnGa and Co ２ One or two types of Heusler alloys selected from the group consisting of MnAl, (C) Mn ３ Ga, Mn ２ FeGa, Mn ２ CoGa and Mn ２ One or more types of D0 selected from the group consisting of RuGa ２２ type-regular alloy, (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) SmCo ５ system magnet, Sm ２ Co １７ Magnet system, and Nd ２ Fe １４ One or more permanent magnet materials selected from the group consisting of B-type magnets, (F) One or two multilayer film materials selected from the group consisting of Co / Pt and Co / Pd layers, (G) Mn ４ N, Fe ４ One or two perovskite-type nitride materials selected from the group consisting of N, and (H) Mn ３ Ga, Mn ３ Ge and Mn ３ One or more types of D0 selected from the group consisting of Sn １９ It is a type-ordered alloy.

7. The aforementioned FeGa is Fe ｘ Ga １－ｘ (0.5 ≤ x ≤ 0.9) The vertical thermoelectric element according to claim 6.

8. The thermoelectric material of the aforementioned thermoelectric layer is Bi ２ Te ３ , PbTe, Si, Ge, FeSi alloy, CrSi alloy, MgSi alloy, CoSb ３ Alloy, Fe ２ VAL-based Heusler alloys, and SrTiO ３ It consists of one type of thermoelectric material selected from the group of thermoelectric materials, The vertical thermoelectric element according to claim 1.

9. The aforementioned Bi ２ Te ３ , for PbTe, Si, or Ge, 0.1 x 10 １９ ~3x10 １９ cm －３ The element is doped with p-type or n-type elements to achieve the carrier concentration. The vertical thermoelectric element according to claim 8.

10. The magnetic layer is a single layer or multiple layers. The thermoelectric layer consists of a single layer in electrical contact with the magnetic layer, or multiple layers sandwiching the magnetic layer. A vertical thermoelectric element according to any one of claims 1 to 9.

11. A thermoelectric power generation module or heat flow sensor using a vertical thermoelectric conversion element according to any one of claims 1 to 9.

12. A method for evaluating a vertical thermoelectric element according to any one of claims 1 to 9, [Math 2] Based on the resistivity, Seebeck coefficient of the thermoelectric material, and the resistivity, Seebeck coefficient, anomalous Hall resistivity, and anomalous Nernst coefficient of the magnetic material, the thickness of the thermoelectric layer (L ｚ ＴＥ ), and the ratio (x) of the thickness of the thermoelectric layer (L ｚ Ｍ ) to the total thickness of the magnetic layer (L ｚ ＴＥ ) are determined so as to maximize the transverse thermoelectric power (S ｙ ｔｏｔ ). An evaluation method for a vertical thermoelectric conversion element. Here, each sign is defined as follows: [Math 3]

13. Furthermore, the range of this ratio (x) is defined as the transverse thermoelectric power (S ｙ ｔｏｔ A method for evaluating a vertical thermoelectric element according to claim 12, wherein the lower limit is set to the value that maximizes ) minus 0.2, the upper limit is set to the value obtained by adding 0.2, 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 is greater than 1.

14. A method for evaluating a vertical thermoelectric element according to claim 12, wherein the output coefficient (PF) of the transverse thermoelectric power, defined by the following equation, is determined to maximize the output coefficient (PF). [Math 4] Here, the effective resistivity (ρ) in the in-plane (x-y plane) of the vertical thermoelectric conversion element is eff ) is defined by the following equation: [Math 5]

15. A method for evaluating a vertical thermoelectric element according to claim 14, wherein the isothermal dimensionless figure of merit (zT), which represents the efficiency of the transverse thermoelectric effect defined by the following equation, is determined to maximize the zT. [Math 6] Here, the effective thermal conductivity (k) in the in-plane (x-y plane) of the vertical thermoelectric conversion element is eff ) is defined by the following equation: [Number 7]

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