Thermoelectric device and laminate

Abstract

Provided are a thermoelectric device and a laminate capable of suppressing output reduction in the vicinity of a zero magnetic field, achieving stability against an external magnetic field, and reducing internal resistance that causes output noise.　The present invention comprises: a substrate 11 in which at least a surface layer is insulating, and which is either a low-orientation polycrystal, an unoriented polycrystal, or an amorphous substance; a plurality of power generation bodies 12 that are arranged so as to be parallel to each other along the surface of the substrate 11; and an electrical connection body 13 that is disposed between the power generation bodies 12 and electrically connects the power generation bodies 12 in series, the power generation bodies 12 comprising a structure in which a magnetic body thin film layer 22 and a non-magnetic body thin film layer 23 are alternately laminated, each magnetic body thin film layer 22 being magnetized in the in-plane direction, and an output voltage being generated by the abnormal Nernst effect when a temperature gradient occurs in a direction perpendicular to the direction of magnetization of the power generation bodies 12.

Description

Thermoelectric device and laminate

[0001] The present invention relates to thermoelectric devices such as heat flow sensors and power generation devices, and laminates, which utilize the anomalous Nernst effect.

[0002] Devices capable of converting thermal energy into electrical energy or electrical energy into thermal energy are known. These devices possess thermoelectric conversion functions, and are expected to be used in applications such as heat flow sensors for high-speed temperature control in home appliances and automobiles, for detecting thermal energy loss in walls in green building construction, and for deep body temperature measurement and exhaled air temperature monitoring in the medical field. Among these, heat flow sensors utilizing the anomalous Nernst effect, a thermoelectric effect manifested in magnetic materials, are easier to fabricate than conventional heat flow sensors and can be easily made large-area and flexible. The anomalous Nernst effect is a phenomenon in which an electric field is generated perpendicular to a temperature gradient in a magnetic material magnetized in one direction, and is expressed by the following equation (1):

[0003] E ＡＮＥ is the generated Nernst field, S ＡＮＥ is the Nernst field potential of the magnetic material, ∇T is the temperature gradient, and M is the magnetization.

[0004] As examples of applications of this anomalous Nernst effect, a thermoelectric power generation device in which thin films formed of single layers of magnetic material are connected in series, and a thermoelectric power generation device in which thin films of magnetic material are stacked have been reported (see Patent Documents 1 and 2).

[0005] When a magnetic material generates magnetization M, a demagnetizing field H acts in a direction that cancels out the magnetization M. Ｄ Therefore, the magnetization M, which is saturated by applying a uniform external magnetic field, decreases as the external magnetic field approaches zero, resulting in a demagnetizing field H Ｄ Therefore, the resulting Nernst field E ＡＮＥ also becomes small near zero magnetic field. Generally, the demagnetizing field H ＤThe size of is determined by the ratio of the width to the height of the magnetic material. When the magnetic material is a thin film, the smaller the film thickness dimension is due to shape magnetic anisotropy, the larger the demagnetizing field H Ｄ It is known that the magnetization M occurs in the in-plane direction of the magnetic material.

[0006] FIG. 1 is a graph showing the relationship between the film thickness (nm) of a magnetic thin film and the magnetization M. The horizontal axis represents the magnetic field H, and the vertical axis represents the magnetization M. The graph shows the results (hysteresis curve) of measuring the change in magnetization M with respect to the external magnetic field H by changing the film thickness of the magnetic thin film. The magnetic material used here is a thin film of FeGa, and the film thicknesses are 100 nm, 300 nm, and 1000 nm. From this result, it can be seen that the smaller the film thickness, the greater the demagnetization field H, as mentioned above. Ｄ It can be seen that the influence of is small and the magnetization M is large near zero magnetic field.

[0007] 1, it can be seen that the larger the film thickness of the magnetic material, the smaller the slope of the hysteresis curve, and that a larger external magnetic field is required until the magnetization M is saturated. In other words, it can be seen that the larger the film thickness of the magnetic material, the more easily the magnetization M fluctuates in response to minute changes in the external magnetic field, and the lower the stability.

[0008] From the above, as the film thickness of the magnetic material increases, not only does the output voltage near zero magnetic field decrease, but also the stability against external magnetic fields decreases. In other words, when applying the anomalous Nernst effect to a device, a small film thickness of the magnetic material is preferable to improve the output voltage near zero magnetic field and the stability against external magnetic fields. However, as the film thickness of the magnetic material decreases, the internal resistance of the device increases, which causes output noise. Thus, for example, in the single-layer magnetic material thin film described in Patent Document 1, there is a trade-off between the stability of the output voltage near zero magnetic field and the output noise.

[0009] On the other hand, as an example of a multilayer structure, there is a device having a structure in which magnetic thin films are stacked, as described in Patent Document 2. The purpose of the stacked structure is to improve the heat treatment and heat resistance of the magnetic thin film, and it is described that the stacked structure reduces crystal defects in the magnetic layer (alloy layer), thereby improving the thermoelectric conversion efficiency and the sensitivity of the magnetic sensor.

[0010] However, as mentioned above, Patent Document 2 does not mention the effects of improving output voltage near zero magnetic field, which is the actual device usage environment, stability against external magnetic fields, and reducing internal resistance. Furthermore, the magnetic material used is specified as an oriented polycrystalline hard magnetic material (Co-Mn-Ga), and the material sandwiched between the layers is similarly specified as an AlN-based material with a cubic and hexagonal crystal structure. Furthermore, the crystalline structure of the magnetic layer (alloy layer) requires the provision of a buffer layer containing AlN with a crystalline structure on the substrate, which makes the manufacturing process complicated.

[0011] Japanese Patent No. 6079995 Japanese Patent Application Laid-Open No. 2022-129848 Japanese Patent No. 6611167

[0012] An object of embodiments of the present invention is to provide a thermoelectric device and a laminate that can suppress a decrease in output near zero magnetic field, achieve stability against an external magnetic field, and reduce internal resistance that causes output noise.

[0013] A thermoelectric device according to an embodiment of the present invention comprises a substrate having an insulating surface layer and being either low-oriented polycrystalline, non-oriented polycrystalline, or amorphous; a plurality of power generating bodies arranged parallel to each other along the surface of the substrate; and electrical connectors arranged between the power generating bodies and electrically connecting the power generating bodies in series, wherein the power generating bodies have a structure in which magnetic thin film layers and non-magnetic thin film layers are alternately stacked, and the magnetic thin film layers are each magnetized in an in-plane direction, and when a temperature gradient occurs in a direction perpendicular to the direction of magnetization of the power generating bodies, an output voltage is generated by the anomalous Nernst effect.

[0014] Thermoelectric devices include heat flow sensors that use the anomalous Nernst effect to sense heat flow and power generation devices that generate electricity.

[0015] The laminate according to the embodiment of the present invention is characterized in that the power generating body has a structure in which magnetic thin film layers and non-magnetic thin film layers are alternately laminated.

[0016] According to the embodiments of the present invention, it is possible to provide a thermoelectric device and a laminate that can suppress a decrease in output near zero magnetic field, achieve stability against an external magnetic field, and reduce internal resistance that causes output noise.

[0017] 1 is a graph showing the relationship between the film thickness dimension and magnetization of a magnetic thin film. FIG. 2 is a configuration diagram showing a thermoelectric device according to an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view showing a power generating body in the thermoelectric device. FIG. 4 is a graph showing the evaluation results of the thermoelectric device. FIG. 5 is a graph showing the evaluation results of the thermoelectric device.

[0018] A thermoelectric device according to an embodiment of the present invention will now be described with reference to Figs. 2 and 3. Fig. 2 is a structural diagram showing a thermoelectric device, and Fig. 3 is a schematic cross-sectional view showing a power generating body. Note that in each figure, the scale of each component has been appropriately changed for the purpose of explanation so that each component can be recognized. Furthermore, the same or corresponding parts are given the same reference numerals, and duplicate explanations will be omitted.

[0019] The thermoelectric device of this embodiment has a structure in which the power generating body is made of alternating magnetic thin film layers and non-magnetic thin film layers to exhibit the anomalous Nernst effect, thereby achieving improved output voltage near zero magnetic field, stability against external magnetic fields, and small internal resistance.

[0020] 2 shows a thermoelectric device, and an example of the heat flow sensor 10 is shown. The heat flow sensor 10 is, for example, a sensor that detects a voltage V generated based on a temperature gradient ∇T. The heat flow sensor 10 has a substrate 11, a power generating body 12, and an electrical connection body 13.

[0021] The substrate 11 is covered with an insulating layer whose surface is either low-oriented polycrystalline, non-oriented polycrystalline, or amorphous. For example, a substrate having a low-oriented polycrystalline, non-oriented polycrystalline, amorphous, or non-crystalline surface layer formed by fused silica or CVD on a surface layer of a material with crystalline orientation such as Si or MgO is applicable. Also suitable are rigid substrates or thin flexible substrates made of low-oriented polycrystalline, non-oriented polycrystalline, amorphous, or non-crystalline materials, such as ultrathin non-crystalline glass substrates and resin substrates such as polyimide. Specifically, low-oriented polycrystalline refers to polycrystalline with a half-width of the X-ray diffraction peak of the crystal orientation greater than 1°.

[0022] By using a substrate 11 in which at least the surface is covered with an insulating layer that does not have a crystalline orientation, the laminated film of the power generator 12 (described later) can be easily formed without a crystalline orientation. This reduces the thermal conductivity of the power generator 12 and increases the temperature gradient ∇T when heat flows through it, improving the sensitivity of the sensor.

[0023] The power generators 12 (12a, 12b) are laminates having a laminated structure of magnetic thin film layers and non-magnetic thin film layers, which will be described later, and are configured such that a plurality of them are arranged parallel to each other on the substrate 11. The power generators 12 are thin wires having a rectangular parallelepiped shape with a width of several μm to several hundred μm and a length of several mm to several hundred mm.

[0024] The electrical connectors 13 (13a, 13b) electrically connect each of the multiple arranged power generators 12, and are not particularly limited as long as they are a metal that conducts electricity, and may be made of, for example, Au, etc. The electrical connectors 13 are shaped like thin wires, and the electrical connector 13a is disposed between the power generators 12, i.e., the power generators 12a and 12b, and is connected to one end of the power generator 12a and the other end of the power generator 12b.

[0025] The power generating element 12b is then connected to the electrical connector 13b. In other words, the heat flow sensor 10 has a meander wiring structure in which the multiple power generating elements 12 arranged in series are connected by the electrical connectors 13. The meander wiring structure allows the heat flow sensor 10 to be made smaller.

[0026] With this configuration, magnetization M is generated in the short direction of the power generating body 12, and the Nernst electric field E is obtained when a temperature gradient ∇T occurs in the direction perpendicular to the surface of the heat flow sensor 10, thereby making it possible to measure the heat flow density passing through the heat flow sensor 10.

[0027] Next, the cross-sectional structure of the power generator 12 will be described with reference to Fig. 3. The power generator 12 is a laminate in which magnetic thin film layers and non-magnetic thin film layers are alternately stacked. The power generator 12 has a substrate 11, a magnetic thin film layer 22, and a non-magnetic thin film layer 23.

[0028] The magnetic thin-film layer 22 can be formed directly on the substrate 11. It can be made of any magnetic material, hard or soft, that exhibits the anomalous Nernst effect, such as FeGa. Preferably, at least a portion of at least one of the magnetic thin-film layers 22 is low-oriented polycrystalline, non-oriented polycrystalline, or amorphous. The smaller the crystal orientation, the lower the thermal conductivity. This reduces the thermal conductivity perpendicular to the heat flow sensor 10, increasing the temperature gradient ∇T, enabling the detection of smaller heat flows and improving sensitivity. Furthermore, low-oriented polycrystalline, non-oriented polycrystalline, and amorphous materials have higher deformation resistance than single crystals and highly oriented polycrystalline materials, making them suitable for flexible sensors. Low-oriented polycrystalline specifically refers to polycrystalline materials with a half-width of the X-ray diffraction peak of the crystal orientation greater than 1°. There are no thickness restrictions on the magnetic thin-film layers 22, as long as they can be formed into continuous films. The thickness of the thin film is preferably 10 nm to 300 nm, more preferably 10 nm to 100 nm, and particularly preferably 10 nm to 30 nm.

[0029] The non-magnetic thin film layer 23 is made of a non-magnetic metal, semiconductor, or insulator, such as Ta, Pt, Si, Ge, or SiO ２ and MgO can be used. Furthermore, when a metal or semiconductor is used for the non-magnetic thin-film layer 23, it is known that a voltage is also generated in the non-magnetic thin-film layer 23 due to the spin Seebeck effect, as described in non-patent document (R. Ramos et al., Physical Review B 92, 220407(R)(2015)). This is combined with the anomalous Nernst effect generated in the magnetic thin-film layer 22, and an amplification of the output voltage is expected.

[0030] Furthermore, it is preferable that at least a portion of at least one of the non-magnetic thin-film layers 23 be low-oriented polycrystalline, non-oriented polycrystalline, or amorphous. The smaller the crystal orientation, the smaller the thermal conductivity, resulting in a larger temperature gradient ∇T in the direction perpendicular to the surface of the heat flow sensor 10, enabling the detection of smaller heat flows and improving sensitivity. Furthermore, compared to single crystals and highly oriented polycrystalline, low-oriented polycrystalline, non-oriented polycrystalline, and amorphous materials have higher deformation resistance, making them suitable for flexible sensors. Specifically, low-oriented polycrystalline refers to polycrystalline materials with a half-width of the X-ray diffraction peak of the crystal orientation greater than 1°. Similarly, there are no thickness limitations for the non-magnetic thin-film layers 23, as long as they can be formed into continuous films. A thin film with a thickness of 3 nm to 10 nm is preferable, and a thickness of 3 nm to 5 nm is even more preferable.

[0031] The power generator 12 has a structure in which a magnetic thin film layer 22a is formed on the substrate 11, and then magnetic thin film layers 22 and non-magnetic thin film layers 23 are alternately laminated, such as a non-magnetic thin film layer 23a, a magnetic thin film layer 22b, and a non-magnetic thin film layer 23b. The laminated structure preferably has at least three layers, and more preferably five layers or more.

[0032] Since the magnetic thin film layers 22 and the non-magnetic thin film layers 23 are alternately laminated, for example, the non-magnetic thin film layer 23a is interposed between the magnetic thin film layers 22a and 22b, and the magnetic coupling is broken. By using a laminated structure, the thickness of the magnetic thin film layer 22 can be reduced, and as mentioned above, the smaller the thickness, the smaller the demagnetizing field H Ｄ The influence of the magnetic field is small, and the magnetization M is large near zero magnetic field. In other words, the output voltage in zero magnetic field can be maintained high, and stability against external magnetic fields is also high. In addition, if the laminated structure has three or more layers, it is possible to make the magnetic thin film layer 22 thin while maintaining the total thickness of the power generating body 12 thick, resulting in a heat flow sensor 10 with low internal resistance.

[0033] Next, the evaluation results of the thermoelectric device according to the above embodiment, that is, the heat flow sensor 10, will be described with reference to FIG. 4 and FIGS. 5(a) and 5(b).

[0034] The evaluation sample used for the measurements was fabricated by alternately forming 10 magnetic thin-film layers 22 made of FeGa thin films each having a thickness of 100 nm and 10 non-magnetic thin-film layers 23 made of Ta each having a thickness of 5 nm, thereby forming a power generating body 12 having a laminated structure with a total thickness of approximately 1000 nm. A comparative sample was also fabricated by fabricating a power generating body 12 made of a single FeGa layer having a total thickness of 1000 nm.

[0035] In Fig. 4, the horizontal axis represents the magnetic field H, and the vertical axis represents the magnetization M. Fig. 4 shows the change in magnetization when an external magnetic field is applied to each sample in the short direction of the power generator 12. This confirms that the power generator 12, which has a layered structure, has improved remanence near zero magnetic field and is also more stable against external magnetic fields.

[0036] 5(a) and (b) show the results for each sample when a uniform temperature gradient was applied in the direction perpendicular to the surface by applying a voltage of 1 V to 7 V to a ceramic heater placed above the surface of the sample. The horizontal axis represents the heat flow density, and the vertical axis represents the voltage.

[0037] The graph shows the change in the Nernst field E with respect to the heat flow density generated by applying a voltage to the ceramic heater, and plots the results at zero magnetic field and at 300 mT, where the magnetization saturates. Here, FIG. 5( a) shows the results for a sample having a power generating body 12 with a laminated structure according to this embodiment, and FIG. 5( b) shows the results for a sample having a power generating body 12 of a comparative example made of a single layer of FeGa. For each sample, the Nernst field E has a linear relationship with the heat flow density, and the resulting slope represents the output sensitivity. As a result, the output sensitivity at zero magnetic field obtained with the power generating body 12 with a laminated structure is 0.021 μV / W·m compared to the output sensitivity at zero magnetic field obtained with the power generating body 12 made of a single layer of FeGa. －２ to 0.032 μV / W m －２ It can be seen that there has been an improvement.

[0038] As described above, according to this embodiment, it is possible to provide a thermoelectric device and a laminate that can suppress a decrease in output power near zero magnetic field, that can achieve stability against external magnetic fields, and that can reduce internal resistance that causes output noise, thereby improving the output power of the thermoelectric device under actual use conditions.

[0039] The heat flow sensor of this embodiment can also be applied to power generation devices that generate electricity by utilizing the anomalous Nernst effect. Power generation devices can be used for a variety of purposes by utilizing temperature differences. For example, it is expected that power generation devices will be used in clothing and bags that generate electricity by utilizing the difference between body temperature and the ambient temperature, and in spontaneous power generation recycling systems that use waste heat from personal computers.

[0040] The present invention is not limited to the configuration of the above-described embodiment, and various modifications are possible within the scope of the invention. Furthermore, the above-described embodiment is presented as an example and is not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims.

[0041] 10: Heat flow sensor 11: Substrate 12: Power generating body 13: Electrical connection body 22: Magnetic thin film layer 23: Non-magnetic thin film layer

Claims

1. A substrate having at least an insulating surface layer and being either low-oriented polycrystalline, non-oriented polycrystalline, or amorphous, Multiple power generators are arranged parallel to each other along the surface of the substrate, The system comprises an electrical connector positioned between the power generators and electrically connecting the power generators in series, The power generation body has a structure in which magnetic thin film layers and non-magnetic thin film layers are alternately stacked, and the magnetic thin film layers are each magnetized in the in-plane direction, and an output voltage is generated by an abnormal Nernst effect when a temperature gradient occurs perpendicular to the direction of magnetization of the power generation body.

2. The thermoelectric device according to claim 1, characterized in that the power generation body is formed directly on the substrate.

3. The thermoelectric device according to claim 1 or 2, characterized in that the thermoelectric device is a heat flow sensor or a power generation device.

4. The thermoelectric device according to claim 1 or 2, characterized in that the full width at half maximum of the X-ray diffraction peak of the crystal orientation of the surface layer is greater than 1°.

5. The thermoelectric device according to claim 1 or 2, characterized in that the stacked structure of the power generation element consists of at least three layers.

6. The thermoelectric device according to claim 1 or 2, characterized in that at least a portion of at least one of the magnetic thin film layers is amorphous.

7. The thermoelectric device according to claim 1 or 2, characterized in that at least a portion of at least one layer of the magnetic thin film layer is low-oriented polycrystalline or non-oriented polycrystalline, and the full width at half maximum of the X-ray diffraction peaks of the crystal orientation is greater than 1°.

8. The thermoelectric device according to claim 1 or 2, characterized in that at least a portion of at least one of the non-magnetic thin film layers is low-oriented polycrystalline, non-oriented polycrystalline, or amorphous.

9. The thermoelectric device according to claim 8, characterized in that the full width at half maximum of the X-ray diffraction peaks of at least one crystal orientation of the non-magnetic thin film layer is greater than 1°.

10. The thermoelectric device according to claim 1 or 2, characterized in that the non-magnetic thin film layer is a metal or a semiconductor.

11. The thermoelectric device according to claim 1 or 2, characterized in that the power generation body and the electrical connector have a meander wiring structure connected in series.

12. A laminate used in the power generation element of the thermoelectric device described in claim 1, characterized in that it has a structure in which the magnetic thin film layer and the non-magnetic thin film layer are alternately laminated.