Thermoelectric conversion element, thermoelectric conversion module, and method of manufacturing thermoelectric conversion element

Abstract

The thermoelectric conversion element comprises: a first electrode; a photoelectric conversion material part that converts heat to electricity; an intermediate layer disposed on the thermoelectric conversion material part; an electroconductive bonding material that is disposed between the intermediate layer and the first electrode and that bonds the first electrode to the intermediate layer; and a second electrode that connects to the thermoelectric conversion material part. The intermediate layer comprises: a dopant-containing first layer disposed on the thermoelectric conversion material part; and a second layer that is disposed on the first layer and inhibits element diffusion. The interfacial resistivity of the intermediate layer is 0.0001 mΩcm2 to 0.5 mΩcm2.

Description

[Technical Field]

[0001] The present disclosure relates to a thermoelectric conversion element, a thermoelectric conversion module, and a method for manufacturing a thermoelectric conversion element.

[0002] This application claims priority to Japanese Application No. 2021-109138, filed on June 30, 2021, and incorporates by reference all of the contents of said Japanese application. [Background technology]

[0003] A thermoelectric device including a thermoelectric element containing Si (silicon) has been disclosed (for example, Patent Document 1). In the thermoelectric device disclosed in Patent Document 1, the thermoelectric element containing Si is connected to an electrode via a high-melting-point silicide. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-202274 Summary of the Invention

[0005] A thermoelectric conversion element according to the present disclosure includes a first electrode, a thermoelectric conversion material portion made of SiGe containing an amorphous phase and a crystalline phase and converting heat into electricity, an intermediate layer disposed on the thermoelectric conversion material portion, a conductive bonding material disposed between the intermediate layer and the first electrode and bonding the first electrode to the intermediate layer, and a second electrode disposed apart from the first electrode and connected to the thermoelectric conversion material portion. The intermediate layer is disposed on the thermoelectric conversion material portion and includes a first layer containing a dopant, and a second layer disposed on the first layer and suppressing element diffusion. The interfacial resistivity of the intermediate layer is 0.0001 mΩ cm. 2 More than 0.5mΩcm 2 The following is the result. [Brief explanation of the drawings]

[0006] [Figure 1]FIG. 1 is a schematic cross-sectional view showing the structure of a thermoelectric conversion element according to the first embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view showing an enlarged portion of the thermoelectric conversion element shown in FIG. [Figure 3] FIG. 3 is a schematic diagram showing the results of EDX near the first layer. [Figure 4] FIG. 4 is a schematic diagram showing a measuring device used to measure the interface resistivity. [Figure 5] FIG. 5 is a graph showing the interface resistivity when the intermediate layer does not include the first layer and when the intermediate layer includes the first layer. [Figure 6] FIG. 6 is a flowchart showing typical steps of a method for manufacturing a thermoelectric conversion element according to the first embodiment. [Figure 7] FIG. 7 is a schematic cross-sectional view showing a die and a punch used in the process of obtaining a sintered body. [Figure 8] FIG. 8 is a schematic cross-sectional view showing the obtained sintered body. [Figure 9] FIG. 9 is a diagram showing an example of the structure of a power generation module. DETAILED DESCRIPTION OF THE INVENTION

[0007] [Problem to be solved by this disclosure] A thermoelectric conversion element including a thermoelectric conversion material portion that converts heat into electricity is required to achieve high thermoelectric conversion efficiency. Therefore, one of the objects is to provide a thermoelectric conversion element that can achieve high thermoelectric conversion efficiency.

[0008] [Effects of this disclosure] The thermoelectric conversion element described above can achieve high thermoelectric conversion efficiency.

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described. A thermoelectric conversion element according to the present disclosure includes a first electrode, a thermoelectric conversion material portion composed of SiGe containing an amorphous phase and a crystalline phase and converting heat into electricity, an intermediate layer disposed on the thermoelectric conversion material portion, a conductive bonding material disposed between the intermediate layer and the first electrode and bonding the first electrode to the intermediate layer, and a second electrode disposed apart from the first electrode and connected to the thermoelectric conversion material portion. The intermediate layer includes a first layer disposed on the thermoelectric conversion material portion and containing a dopant, and a second layer disposed on the first layer and suppressing element diffusion. The interfacial resistivity of the intermediate layer is 0.0001 mΩ cm. 2 More than 0.5mΩcm 2 The following is the result.

[0010] In a thermoelectric conversion element, electricity generated in a thermoelectric conversion material section, which converts heat (temperature difference) into electricity, is output using electrically connected first and second electrodes. The inventors considered the effect of reactions at the bonding material between the electrodes and the thermoelectric conversion material section, which can impair thermoelectric conversion efficiency, when the thermoelectric conversion element is used at high temperatures, such as several hundred degrees. The diffusion of elements constituting the bonding material toward the thermoelectric conversion material section reduces the thermoelectric conversion efficiency of the thermoelectric conversion material section. Therefore, providing a layer to suppress the diffusion of the bonding material is an option. However, simply providing this diffusion-suppressing layer increases the contact resistance at the interface, preventing high thermoelectric conversion efficiency. The inventors conducted extensive research to minimize the effects of providing this diffusion-suppressing layer, leading to the creation of the present invention.

[0011] The thermoelectric conversion element of the present disclosure includes a thermoelectric conversion material portion made of SiGe (silicon germanium), and therefore can achieve high thermoelectric conversion efficiency even when used at high temperatures. The thermoelectric conversion element includes an intermediate layer including a first layer containing a dopant and a second layer that suppresses element diffusion. This reduces the electrical barrier between the first layer and the thermoelectric conversion material portion, thereby reducing contact resistance. Furthermore, the second layer prevents elements constituting the bonding material from diffusing toward the thermoelectric conversion material portion, which would reduce the thermoelectric conversion efficiency of the thermoelectric conversion material portion. Here, the interface resistivity of the intermediate layer is 0.0001 mΩ cm. 2 More than 0.5mΩcm 2 The following is an example. Therefore, the first layer disposed between the thermoelectric conversion material section and the second layer can reduce the electrical barrier between the thermoelectric conversion material section and the second layer. This reduces contact resistance. As a result, the thermoelectric conversion element of the present disclosure can achieve high thermoelectric conversion efficiency.

[0012] In the thermoelectric conversion element, the dopant may include at least one of P, Fe, Au, B, Ni, V, Ti, Sb, As, Ga, Mo, Y, Cu, and Zr. These elements are suitable as elements constituting the dopant contained in the first layer.

[0013] In the thermoelectric conversion element, the concentration of the dopant may be 3 at % or more and 20 at % or less, which makes it possible to more reliably reduce the resistance and achieve high thermoelectric conversion efficiency.

[0014] In the thermoelectric conversion element, the second layer may be made of at least one of iron silicide, nickel silicide, and titanium boride, which can more efficiently suppress the diffusion of elements constituting the bonding material.

[0015] In the thermoelectric conversion element, the thickness of the first layer may be 10 nm or more and 1 mm or less. If the thickness of the first layer is too thin, the second layer and the thermoelectric conversion material section may come into direct contact with each other if there are irregularities on the end surfaces of the second layer and the thermoelectric conversion material section, which may increase contact resistance. If the thickness of the first layer is too thick, a temperature difference may occur in the first layer, reducing the effective temperature difference applied to the thermoelectric conversion material section and reducing the amount of power generation. Therefore, by setting the thickness of the first layer to 10 nm or more and 1 mm or less, the risk of increasing contact resistance and reducing the amount of power generation can be reduced.

[0016] The thermoelectric conversion module of the present disclosure includes a plurality of the thermoelectric conversion elements described above. According to the thermoelectric conversion module of the present disclosure, by including a plurality of the thermoelectric conversion elements of the present disclosure that can achieve high thermoelectric conversion efficiency, it is possible to obtain a thermoelectric conversion module that can achieve high thermoelectric conversion efficiency.

[0017] The method for manufacturing a thermoelectric conversion element of the present disclosure includes the steps of: mixing Si powder, Ge powder, and a powder constituting a dopant for the semiconductor material SiGe to obtain a first mixture; mixing Si powder with a raw material powder constituting a layer that suppresses element diffusion to obtain a second mixture; placing the first mixture on the second mixture, and obtaining a sintered body by spark plasma sintering while applying a pressure of 20 MPa to 1 GPa to the first and second mixtures while maintaining a temperature of 400°C or higher; and joining electrodes to the sintered body.

[0018] According to the method for manufacturing a thermoelectric conversion element of the present disclosure, it is possible to efficiently manufacture a thermoelectric conversion element having the above-described configuration.

[0019] [Details of the embodiments of the present disclosure] Next, an embodiment of a thermoelectric conversion element according to the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference characters, and description thereof will not be repeated.

[0020] (Embodiment 1) A first embodiment of a thermoelectric conversion element according to the present disclosure will be described with reference to Fig. 1. Fig. 1 is a schematic cross-sectional view showing the structure of a thermoelectric conversion element according to the first embodiment. Fig. 2 is a schematic cross-sectional view showing an enlarged portion of the thermoelectric conversion element shown in Fig. 1. Note that, to facilitate understanding, the first electrode and the second electrode in Fig. 2 are illustrated in a simplified form.

[0021] 1 and 2, thermoelectric conversion element 11 is a so-called π-type thermoelectric conversion element. Thermoelectric conversion element 11 of the present disclosure is used at relatively high temperatures, for example, in a temperature range of several hundred degrees. Thermoelectric conversion element 11 includes p-type thermoelectric conversion material portion 12, which is a first thermoelectric conversion material portion; n-type thermoelectric conversion material portion 13, which is a second thermoelectric conversion material portion; intermediate layers 30a, 30b, 30c, and 30d; first electrode 14 disposed on the high-temperature side; second electrode 15 disposed on the low-temperature side; second electrode 16, which is also disposed on the low-temperature side; conductive bonding materials 21, 22, 23, and 24; and wiring 17. The intermediate layers 30a, 30b, 30c, and 30d are arranged on the thermoelectric conversion material portions 12 and 13 and include first layers 31a, 31b, 31c, and 31d containing dopants, and second layers 32a, 32b, 32c, and 32d are arranged on the first layers 31a, 31b, 31c, and 31d and suppress diffusion of elements.

[0022] The thermoelectric conversion material sections 12 and 13 are made of SiGe containing an amorphous phase and a crystalline phase. The thermoelectric conversion material sections 12 and 13 convert heat (temperature difference) into electricity. The thermoelectric conversion material section 12 is made of a thermoelectric conversion material whose component composition is adjusted to have a p-type conductivity, for example. The thermoelectric conversion material section 13 is made of a thermoelectric conversion material whose component composition is adjusted to have an n-type conductivity, for example.

[0023] The first layers 31a and 31b are disposed on the thermoelectric conversion material portion 12. Specifically, the first layer 31a is disposed on one end 26 of the thermoelectric conversion material portion 12. The interface between the first layer 31a and the thermoelectric conversion material portion 12 is indicated by a boundary 37a. The first layer 31b is disposed on the other end 28 of the thermoelectric conversion material portion 12. The first layers 31c and 31d are disposed on the thermoelectric conversion material portion 13. Specifically, the first layer 31c is disposed on one end 27 of the thermoelectric conversion material portion 13. The first layer 31d is disposed on the other end 29 of the thermoelectric conversion material portion 13. The first layers 31a, 31b, 31c, and 31d are each a material layer containing a dopant. The direction from the end 28 to the end 26 is indicated by an arrow Z.

[0024] The thickness D1 of the first layer 31a in the Z direction from one end face 33a to the other end face 34a of the first layer 31a is 10 nm (nanometers) or more and 1 mm (millimeters) or less. In this embodiment, the thickness D1 of the first layer 31a is 70 μm (micrometers). The first layer 31a contains P (phosphorus) as a dopant. The dopant contained in the first layer 31a is not limited to P. The first layer 31a may contain at least one of P, Fe (iron), Au (gold), B (boron), Ni (nickel), V (vanadium), Ti (titanium), Sb (antimony), As (arsenic), Ga (gallium), Mo (molybdenum), Y (yttrium), Cu (copper), and Zr (zirconium) as a dopant. The dopant contained in the first layer 31a is determined by the conductivity type of the thermoelectric conversion material portion 12, etc. The concentration of the dopant P is 3 at % or more and 20 at % or less. The configurations of the other first layers 31b, 31c, and 31d are the same as that of the first layer 31a, and therefore description thereof will be omitted.

[0025] The second layers 32a, 32b, 32c, and 32d are disposed on the first layers 31a, 31b, 31c, and 31d, respectively. The interface between the first layer 31a and the second layer 32a is indicated by a boundary 38a. The second layers 32a, 32b, 32c, and 32d are disposed in contact with the bonding materials 21, 22, 23, and 24. The second layers 32a, 32b, 32c, and 32d suppress element diffusion. Specifically, the second layers 32a, 32b, 32c, and 32d suppress the diffusion of elements constituting the bonding materials 21, 22, 23, and 24 toward the thermoelectric conversion material portions 12 and 13.

[0026] The thickness D2 of the second layer 32a in the Z direction from one end surface 35a to the other end surface 36a of the second layer 32a is 50 nm or more and 1 mm or less. In this embodiment, the thickness D2 of the second layer 32a is 700 μm. The second layer 32a is made of iron silicide (Fe—Si). The second layer 32a is not limited to iron silicide, and may be made of at least one of iron silicide, nickel silicide (Ni—Si), and titanium boride (TiB). The configuration of the second layer 32a is determined by the types of bonding materials 21, 22, 23, and 24, the elements contained in the bonding materials 21, 22, 23, and 24, and the like. The configurations of the other second layers 32b, 32c, and 32d are similar to that of the second layer 32a, and therefore will not be described here.

[0027] The conductive bonding materials 21, 22, 23, and 24 contain at least one of Ag (silver), Cu (copper), Ti (titanium), and Sn (tin) as a primary component. Specifically, the bonding materials 21, 22, 23, and 24 include, for example, an Ag-Cu bonding material containing Ag and Cu as primary components, an Ag-Cu-Ti bonding material containing Ag, Cu, and Ti as primary components, an Ag-Cu-Ti-Sn bonding material containing Ag, Cu, Ti, and Sn as primary components, and a bonding material composed of an inorganic binder containing Ag as a primary component. The conductive bonding materials 21, 22, 23, and 24 that bond the first electrode 14, the second electrode 15, and the intermediate layers 30a, 30b, 30c, and 30d have excellent conductivity because they contain at least one of Ag, Cu, Ti, and Sn as a primary component. Therefore, it is possible to reduce power loss when electricity converted from heat (temperature difference) by the thermoelectric conversion material parts 12 and 13, which are respectively joined by the joining materials 21, 22, 23, and 23 via intermediate layers 30a, 30b, 30c, and 30d, is transmitted to the first electrode 14 and the second electrode 15, 16.

[0028] The thermoelectric conversion material section 12 and the thermoelectric conversion material section 13 are arranged side by side with a gap between them. The first electrode 14 is arranged to extend from one end 26 of the thermoelectric conversion material section 12 to one end 27 of the thermoelectric conversion material section 13. The bonding material 21 bonds the first electrode 14 to the intermediate layer 30a. The first electrode 14 is bonded to the thermoelectric conversion material section 12 via the bonding material 21, via the intermediate layer 30a. The bonding material 22 bonds the first electrode 14 to the intermediate layer 30c. The first electrode 14 is bonded to the thermoelectric conversion material section 13 via the intermediate layer 30c, via the bonding material 22. The first electrode 14 is made of a conductive material, for example, a metal such as Mo (molybdenum).

[0029] The second electrode 15 is disposed separately from the first electrode 14 and the other second electrode 16. The bonding material 23 bonds the second electrode 15 to the intermediate layer 30b. The second electrode 15 is bonded to the thermoelectric conversion material portion 12 via the bonding material 23 and the intermediate layer 30b. The second electrode 15 is made of a conductive material, for example, a metal such as Mo.

[0030] The second electrode 16 is disposed apart from the first electrode 14. The bonding material 24 bonds the second electrode 16 to the intermediate layer 30d. The second electrode 16 is bonded to the thermoelectric conversion material portion 13 via the intermediate layer 30d by the bonding material 24. The second electrode 16 is made of a conductive material, for example, a metal such as Mo.

[0031] The wiring 17 is made of a conductor such as a metal, and electrically connects the second electrode 15 and the second electrode 16 to each other.

[0032] In the thermoelectric conversion element 11, when a temperature difference is created such that, for example, one end 26 of the thermoelectric conversion material section 12 and one end 27 of the thermoelectric conversion material section 13 are at a higher temperature and the other end 28 of the thermoelectric conversion material section 12 and the other end 29 of the thermoelectric conversion material section 13 are at a lower temperature, p-type carriers (holes) move from one end 26 to the other end 28 in the thermoelectric conversion material section 12. At the same time, n-type carriers (electrons) move from one end 27 to the other end 29 in the thermoelectric conversion material section 13. As a result, a current flows in the wiring 17 in the direction of arrow I. In this way, in the π-type thermoelectric conversion element 11, power generation is achieved by thermoelectric conversion utilizing the temperature difference. In other words, the thermoelectric conversion element 11 is a power generation element.

[0033] The thermoelectric conversion element 11 includes thermoelectric conversion material portions 12 and 13 made of SiGe (silicon germanium), thereby achieving high thermoelectric conversion efficiency even when used at high temperatures. The thermoelectric conversion element 11 includes intermediate layers 30a, 30b, 30c, and 30d, each including a first layer 31a, 31b, 31c, and 31d containing a dopant and a second layer 32a, 32b, 32c, and 32d that suppress element diffusion. This reduces the electrical barrier between the first layer 31a, 31b, 31c, and 31d and the thermoelectric conversion material portions 12 and 13, thereby reducing contact resistance. Furthermore, the second layers 32a, 32b, 32c, and 32d prevent elements constituting the bonding materials 21, 22, 23, and 24 from diffusing toward the thermoelectric conversion material portions 12 and 13, thereby preventing a decrease in the thermoelectric conversion efficiency of the thermoelectric conversion material portions 12 and 13. Here, the interface resistivity of the intermediate layers 30a, 30b, 30c, and 30d is 0.0001 mΩcm 2 More than 0.5mΩcm 2 The following is true. Therefore, the first layers 31a, 31b, 31c, and 31d disposed between the thermoelectric conversion material sections 12 and 13 and the second layers 32a, 32b, 32c, and 32d can reduce the electrical barrier between the thermoelectric conversion material sections 12 and 13 and the second layers 32a, 32b, 32c, and 32d. This reduces contact resistance. As a result, the thermoelectric conversion element 11 of the present disclosure can achieve high thermoelectric conversion efficiency.

[0034] According to this embodiment, the concentration of the dopant is 3 at % or more and 20 at % or less, which makes it possible to more reliably reduce the resistance and achieve high thermoelectric conversion efficiency.

[0035] According to this embodiment, the thickness D1 of the first layers 31a, 31b, 31c, and 31d is 10 nm or more and 1 mm or less. If the thicknesses of the first layers 31a, 31b, 31c, and 31d are too thin, the second layers 32a, 32b, 32c, and 32d may come into direct contact with the thermoelectric conversion material sections 12 and 13 if the end surfaces of the second layers 32a, 32b, 32c, and 32d and the thermoelectric conversion material sections 12 and 13 are uneven, which may increase contact resistance. If the thicknesses of the first layers 31a, 31b, 31c, and 31d are too thick, a temperature difference may occur in the first layers 31a, 31b, 31c, and 31d, reducing the effective temperature difference applied to the thermoelectric conversion material sections 12 and 13, which may result in a decrease in power generation. Therefore, by setting the thickness of the first layers 31a, 31b, 31c, and 31d to be 10 nm or more and 1 mm or less, it is possible to reduce the risk of an increase in contact resistance and a decrease in the amount of power generation.

[0036] FIG. 3 is a schematic diagram showing the results of EDX (Energy Dispersive X-ray spectrometry) near the first layer 31a. EDX was measured by taking a transmission electron microscope (TEM) image of a portion of the thermoelectric conversion element 11. The TEM image was taken using a JEM-2800 (manufactured by JEOL Ltd.) under measurement conditions of an acceleration voltage of 200 kV, a probe size of 0.5 nm, and a CL aperture of 3. The atom detection conditions by EDX were an EDX (manufactured by Thermo Fisher Scientific K.K.) under measurement conditions of a spot size of 0.5 nm, a CL aperture of 3, a mapping analysis mode, and a 20-minute analysis time. In FIG. 3, the black dots in image 39a indicate the distribution of iron atoms, the black dots in image 39b indicate the distribution of silicon atoms, the black dots in image 39c indicate the distribution of germanium atoms, and the black dots in image 39d indicate the distribution of phosphorus atoms. The left-right (lateral) width of each of the images 39a, 39b, 39c, and 39d is 500 μm.

[0037] 3, images 39a, 39b, and 39c show that iron atoms are abundant above boundary 38a, and germanium atoms are abundant below boundary 37a. Image 39b shows that silicon atoms are present throughout the entire structure. Image 39d shows that phosphorus atoms, which serve as a dopant, are abundant between boundary 37a and boundary 38a. This indicates that a first layer 31a containing a large amount of phosphorus as a dopant is formed between boundary 37a and boundary 38a. The thickness D1 of first layer 31a in this embodiment is 70 μm.

[0038] Here, a method for measuring interface resistivity will be described. Interface resistivity is measured using a four-terminal method. FIG. 4 is a schematic diagram showing a measurement device used for measuring interface resistivity. Referring to FIG. 4, measurement device 51 includes a voltmeter 52, a conductive probe 54, wires 55a and 55b, and a current source 60. A thermoelectric conversion material part 56, which is the object to be measured, is block-shaped, with a first electrode 57 attached to one end and a second electrode 58 attached to the other end. The first electrode 57, the thermoelectric conversion material part 56, and the second electrode 58 are attached so that their respective surfaces 59a, 59b, and 59c are connected. The conductive probe 54 and the first electrode 57 are connected by wire 55a. The voltmeter 52 is attached between the conductive probe 54 and the first electrode 57 and measures the voltage between the conductive probe 54 and the first electrode 57. The first electrode 57 and the second electrode 58 are connected by a wire 55b. In the four-terminal method, two terminals 53a and 53b through which a current flows from a current source 60 are connected to the first electrode 57 and the second electrode 58, respectively. Of the two terminals 53c and 53d through which a voltage is measured in the four-terminal method, one terminal 53c is connected to the first electrode 57, and the other terminal 53d is connected to the conductive probe 54.

[0039] During the measurement, while the first electrode 57 and the second electrode 58 are energized, the conductive probe 54, which is in contact with the surface 59a of the first electrode 57, is moved to the surface 59b of the thermoelectric conversion material portion 56 and the surface 59c of the second electrode 58, scanning in the direction of the arrow. By measuring the voltage with the voltmeter 52 while the conductive probe 54 is scanning, the resistance value from the second electrode 58 to the conductive probe 54 can be derived. This allows the relationship between the travel distance X and the resistance value R at that time to be determined. The cross-sectional resistivity can be obtained by differentiating the resistance value R with respect to the travel distance X and normalizing it with the cross-sectional area (multiplying it by the cross-sectional area). The interface resistivity is derived at each interface position according to the travel distance X.

[0040] 5 is a graph showing the interface resistivity when the intermediate layer does not include the first layer and when the intermediate layer includes the first layer. In FIG. 5, the vertical axis represents the interface resistivity (mΩcm 2 ) is shown. When the intermediate layer does not include the first layer, that is, when there is no first layer, the intermediate layer is manufactured by joining the second layer and the thermoelectric conversion material part by hot pressing. Referring to Figure 5, when there is no first layer, as shown by the bar graph on the left, the interface resistivity is 1.1 mΩ cm 2 and 0.5 mΩ cm 2 In contrast, when the first layer is included in the intermediate layer shown in the bar graph on the right, that is, when the first layer is present, the interface resistivity is 0.05 mΩ cm 2 and 0.0001 mΩ cm 2 More than 0.5mΩcm 2 The reason is as follows: That is, the intermediate layer included in the thermoelectric conversion element 11 includes the first layer, so that the interface resistivity can be significantly reduced.

[0041] The thermoelectric conversion element 11 according to the first embodiment can be manufactured by, for example, the following manufacturing method. FIG. 6 is a flowchart showing typical steps of the manufacturing method for the thermoelectric conversion element 11 according to the first embodiment. Referring to FIG. 6, in the manufacturing method for the thermoelectric conversion element 11 according to the first embodiment, a step (S10) of obtaining a first mixture is performed. In this step (S10), first, Si (silicon) powder, Ge (germanium) powder, and P (phosphorus) powder as a powder constituting a dopant for the semiconductor material SiGe are prepared. Then, predetermined amounts are weighed and milled in a ball mill to obtain a first mixture. Here, the P content is adjusted to be supersaturated with respect to SiGe. "Adjusting to be supersaturated" means that the P content is greater than the amount stoichiometrically incorporated into the crystal. Next, a step (S20) of obtaining a second mixture is performed. In this step (S20), Si powder and Fe (iron) powder are prepared as raw material powders constituting a layer that suppresses element diffusion. Then, a predetermined amount is weighed and milled in a ball mill to obtain a second mixture. Note that the steps (S20) and (S10) may be performed in the reverse order.

[0042] Next, a step (S30) of obtaining a sintered body is performed. In this step (S30), first, a hollow cylindrical die and two solid cylindrical punches are prepared. FIG. 7 is a schematic cross-sectional view showing the die and punches used in the step of obtaining a sintered body. Referring to FIG. 7, in the step of obtaining a sintered body, a hollow cylindrical die 45 having a through hole 46 and two solid cylindrical punches 47a and 47b are prepared. The diameter of the through hole 46 is selected to be, for example, 10 mm. The diameters of the punches 47a and 47b are also selected to be, for example, 10 mm. The punches 47a and 47b are each configured to be able to be placed in the through hole 46 of the die 45.

[0043] First, one punch 47b is placed in the through-hole 46, and the second mixture 42b is poured onto one surface 48b of the punch 47b. At this time, the second mixture 42b is poured to a thickness of, for example, about 0.5 mm. Next, the first mixture 41 is poured into the through-hole 46. At this time, the first mixture 41 is poured to a thickness of, for example, about 5.0 mm. Thereafter, the second mixture 42a is poured again. At this time, the second mixture 42a is poured to a thickness of, for example, about 0.5 mm. As a result, in the through-hole 46, the first mixture 41 is placed on the second mixture 42b, and the second mixture 42a is placed on the first mixture 41. That is, in the through-hole 46, the first mixture 41 is sandwiched between the second mixtures 42a and 42b.

[0044] Next, as shown in FIG. 7, the other punch 47a is placed on the second mixture 42a. At this time, one surface 48a of the punch 47a is placed in contact with the second mixture 42a. Thereafter, spark plasma sintering is performed. That is, while applying pressure in the direction indicated by arrow F1 with punch 47a and in the direction indicated by arrow F2 with punch 47b, the material is heated by pulse current using punches 47a and 47b. The pressure at this time is selected to be, for example, 400 MPa, and the heating temperature is selected to be, for example, 700°C. In this manner, the material is sintered to obtain a sintered body.

[0045] FIG. 8 is a schematic cross-sectional view showing the resulting sintered body. Referring to FIG. 8, a sintered body 49 is formed by spark plasma sintering. The sintered body 49 includes a thermoelectric conversion material portion 12 and intermediate layers 30a and 30b, each including a first layer 31a and 31b and a second layer 32a and 32b. When the materials are heated by spark plasma sintering, heat is concentrated at the interface between the first mixture 41 and the second mixtures 42a and 42b due to interfacial resistance, causing the dopant P to precipitate. Since the dopant P is supersaturated in solid solution, it is easy to precipitate at the interface. Furthermore, because SiGe has an amorphous phase, P is not incorporated into the SiGe crystals and is easily precipitated near the interface. This precipitation results in the formation of first layers 31a and 31b with the desired thickness. That is, the interfaces between the second layers 32a, 32b and the thermoelectric conversion material portion 12 are heated intensively, forming first layers 31a, 31b of precipitated P. In these first layers 31a, 31b, P is highly doped into the SiGe, lowering the electrical barrier between the Fe—Si layers of the second layers 32a, 32b and the SiGe of the thermoelectric conversion material portion 12, thereby reducing interface resistance. The reduced interface resistance also reduces electrical resistance, thereby mitigating the concentration of heat during spark plasma sintering. The amount of precipitation is then suppressed once resistance is reduced, thereby preventing an increase in resistance due to excessive precipitation. In this manner, a sintered body 49 is obtained.

[0046] Thereafter, step (S40) of bonding electrodes is performed. In step (S40), for example, Ag-Cu based bonding materials 21, 22, 23, and 24 are applied to the obtained sintered body 49, and first electrode 14 and second electrodes 15 and 16 made of Mo (molybdenum) are placed on the sintered body 49, and the sintered body 49 is heated to a temperature of 600°C. By firing bonding materials 21, 22, 23, and 24, first electrode 14 and second electrodes 15 and 16 are mechanically and electrically bonded to sintered body 49. In this manner, thermoelectric conversion element 11 according to the first embodiment is obtained.

[0047] According to such a method for manufacturing the thermoelectric conversion element 11, the thermoelectric conversion element 11 having the above-described configuration can be manufactured efficiently.

[0048] The manufacturing method of the thermoelectric conversion element 11 is not limited to the above, and for example, a large amount of P powder may be placed near the interface between the material constituting the thermoelectric conversion material portion and the material constituting the second layer, and then sintering may be carried out.

[0049] In the above-described embodiment, the electrode material may also be prepared as a powder and then sintered together to produce the electrode.

[0050] In the above embodiment, a π-type thermoelectric conversion element has been described as an example of a thermoelectric conversion element of the present disclosure, but the thermoelectric conversion element of the present disclosure is not limited to this. The thermoelectric conversion element of the present disclosure may also be a thermoelectric conversion element having another structure, such as an I-type (uni-leg) thermoelectric conversion element. Furthermore, in the above embodiment, at least one of the thermoelectric conversion material portions 12 and 13 may have the above configuration.

[0051] (Embodiment 2) A power generation module serving as a thermoelectric conversion module can be obtained by electrically connecting a plurality of the above-described π-type thermoelectric conversion elements 11. A power generation module 61, which is a thermoelectric conversion module of this embodiment, has a structure in which a plurality of π-type thermoelectric conversion elements 11 are connected in series. Note that, for ease of understanding, intermediate layers, i.e., the first layer and the second layer, are not shown in FIG. 9.

[0052] Fig. 9 is a diagram showing an example of the structure of a power generation module. Referring to Fig. 9, a power generation module 61 of the present embodiment includes a plurality of p-type thermoelectric conversion material sections 12, a plurality of n-type thermoelectric conversion material sections 13, a plurality of first electrodes 14, a plurality of second electrodes 15, 16, a first insulator substrate 19, a second insulator substrate 18, and bonding materials (not shown) that bond the thermoelectric conversion material sections 12, 13, the first electrodes 14, and the second electrodes 15, 16 to each other. The first insulator substrate 19 and the second insulator substrate 18 are made of ceramic such as alumina.

[0053] The p-type thermoelectric conversion material portions 12 and the n-type thermoelectric conversion material portions 13 are arranged alternately. The second electrodes 15 and 16 are bonded to the p-type thermoelectric conversion material portions 12 and the n-type thermoelectric conversion material portions 13, respectively, by a bonding material via an intermediate layer (not shown), similar to the thermoelectric conversion element 11. The first electrode 14 is bonded to the p-type thermoelectric conversion material portions 12 and the n-type thermoelectric conversion material portions 13 by a bonding material via an intermediate layer (not shown), similar to the thermoelectric conversion element 11. The p-type thermoelectric conversion material portions 12 are connected to the adjacent n-type thermoelectric conversion material portions 13 on one side by a common first electrode 14. Furthermore, the p-type thermoelectric conversion material portions 12 are connected to the adjacent n-type thermoelectric conversion material portions 13 on the other side by common second electrodes 15 and 16. In this way, all the p-type thermoelectric conversion material portions 12 and the n-type thermoelectric conversion material portions 13 are connected in series.

[0054] The second insulator substrate 18 is disposed on the main surface side of the plate-shaped second electrodes 15, 16 opposite to the side in contact with the p-type thermoelectric conversion material section 12 and the n-type thermoelectric conversion material section 13. One second insulator substrate 18 is disposed for each of the plurality (all) of second electrodes 15, 16. The first insulator substrate 19 is disposed on the side of the plate-shaped first electrode 14 opposite to the side in contact with the p-type thermoelectric conversion material section 12 and the n-type thermoelectric conversion material section 13. One first insulator substrate 19 is disposed for each of the plurality (all) of first electrodes 14.

[0055] Wiring 62, 63 is connected to first electrode 14 or second electrode 15, 16 joined to p-type thermoelectric conversion material section 12 or n-type thermoelectric conversion material section 13 located at both ends of p-type thermoelectric conversion material section 12 and n-type thermoelectric conversion material section 13 connected in series. When a temperature difference is created such that first insulator substrate 19 side is higher and second insulator substrate 18 side is lower, current flows in the direction of arrow I through p-type thermoelectric conversion material section 12 and n-type thermoelectric conversion material section 13 connected in series, as in the case of thermoelectric conversion element 11. In this way, power generation is achieved in power generation module 61 by thermoelectric conversion utilizing the temperature difference.

[0056] Such a power generation module 61 includes a plurality of thermoelectric conversion elements 11 according to the present disclosure, which can achieve high thermoelectric conversion efficiency, and thus can achieve high thermoelectric conversion efficiency.

[0057] It should be understood that the embodiments disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present disclosure is defined not by the above description but by the scope of the claims, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0058] 11 thermoelectric conversion element, 12, 13, 56 thermoelectric conversion material portion, 14, 57 first electrode, 15, 16, 58 second electrode, 17, 55a, 55b, 62, 63 wiring, 18 second insulator substrate, 19 first insulator substrate, 21, 22, 23, 24 bonding material, 26, 27, 28, 29 end, 30a, 30b, 30c, 30d intermediate layer, 31a, 31b, 31c, 31d first layer, 32a, 32b, 32c, 32d second layer, 33a, 34a, 35a, 36a end surface, 37a, 38a boundary, 39a, 39b, 39c, 39d image, 41 first mixture, 42a, 42b second mixture, 45 die, 46 Through hole, 47a, 47b punch, 48a, 48b surface, 49 sintered body, 51 measuring device, 52 voltmeter, 53a, 53b, 53c, 53d terminal, 54 conductive probe, 59a, 59b, 59c surface, 60 current source, 61 power generation module, D1, D2 thickness, F1, F2, I, Z arrow, R resistance value, X movement distance

Claims

1. a first electrode; a thermoelectric conversion material portion that is made of SiGe containing an amorphous phase and a crystalline phase and converts heat into electricity; an intermediate layer disposed on the thermoelectric conversion material portion; a conductive bonding material disposed between the intermediate layer and the first electrode, bonding the first electrode and the intermediate layer; a second electrode disposed apart from the first electrode and connected to the thermoelectric conversion material portion, The intermediate layer is a first layer disposed in contact with the thermoelectric conversion material portion and including a dopant; a second layer disposed on the first layer in contact with the bonding material, the second layer suppressing element diffusion; the conductivity type of the first layer is the same as the conductivity type of the thermoelectric conversion material portion; a concentration of a dopant in the first layer is higher than a concentration of a dopant contained in the thermoelectric conversion material portion; The interfacial resistivity of the intermediate layer is 0.0001 mΩcm ２ More than 0.5 mΩcm ２ The thermoelectric conversion element is as follows.

2. 2. The thermoelectric conversion element according to claim 1, wherein the dopant includes at least one of P, Fe, Au, B, Ni, V, Ti, Sb, As, Ga, Mo, Y, Cu, and Zr.

3. 3. The thermoelectric conversion element according to claim 1, wherein the concentration of the dopant is 3 at % or more and 20 at % or less.

4. 4. The thermoelectric conversion element according to claim 1, wherein the second layer is made of at least one of iron silicide, nickel silicide, and titanium boride.

5. 5. The thermoelectric conversion element according to claim 1, wherein the first layer has a thickness of 10 nm to 1 mm.

6. A thermoelectric conversion module comprising a plurality of thermoelectric conversion elements according to claim 1 .

7. a step of obtaining a first mixture by mixing Si powder, Ge powder, and a powder constituting a dopant for SiGe, which is a semiconductor material, so that the powder constituting the dopant is supersaturated with the SiGe; a step of mixing Si powder with a raw material powder constituting a layer that suppresses element diffusion to obtain a second mixture; a step of disposing the first mixture on the second mixture, and obtaining a sintered body by spark plasma sintering while applying a pressure of 20 MPa to 1 GPa to the first mixture and the second mixture while maintaining the temperature of the first mixture and the second mixture at 400°C or higher; and joining electrodes to the sintered body.

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