WO2025115805A1 - Thermoelectric device and laminate - Google Patents

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

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

　Devices that can convert thermal energy into electrical energy or electrical energy into thermal energy are known. These devices have a thermoelectric conversion function, and for example, heat flow sensors are expected to be used in high-speed temperature control of home appliances and vehicles, in green building construction to detect thermal energy loss in walls, and in the medical field, such as deep temperature measurement and breath temperature monitoring. Among these, heat flow sensors that use the anomalous Nernst effect, which is one of the thermoelectric effects that occurs in magnetic materials, are easier to fabricate than conventional heat flow sensors, and are devices that can easily be made large-area and flexible. The anomalous Nernst effect is a phenomenon in which an electric field is generated in a direction perpendicular to a temperature gradient that occurs perpendicular to a magnetic material magnetized in one direction, and is expressed by the following equation (1).

　Ｅ_ＡＮＥは発生するネルンスト電界、Ｓ_ＡＮＥは磁性体が持つネルンスト電界能、∇Ｔは温度勾配、Ｍは磁化である。

E _ANE is the generated Nernst electric field, S _ANE is the Nernst electric field capability of the magnetic material, ∇T is the temperature gradient, and M is the magnetization.

Reported examples of applications of this anomalous Nernst effect include a thermoelectric generation device in which thin films made of single layers of magnetic material are connected in series, and a thermoelectric generation device in which thin films of magnetic material are stacked (see Patent Documents 1 and 2).

When a magnetic material generates magnetization M, a demagnetizing field H _D that works in a direction that cancels out the magnetization M is generated inside the magnetic material. Therefore, the magnetization M that is saturated by applying a uniform external magnetic field is influenced by the demagnetizing field H _D and becomes smaller as the external magnetic field approaches zero, so the resulting Nernst electric field E _ANE also becomes smaller near the zero magnetic field. In general, the magnitude of the demagnetizing field H _D is determined by the ratio of the width and height of the magnetic material, and it is known that when the magnetic material is a thin film, the smaller the film thickness dimension is due to shape magnetic anisotropy, the smaller the demagnetizing field H _D in the film plane direction becomes, and magnetization M is generated in the film plane direction of the magnetic material.

1 is a graph showing the relationship between the film thickness (nm) of a magnetic thin film and the magnetization M. The horizontal axis indicates the magnetic field H, and the vertical axis indicates the magnetization M. The graph shows the results (hysteresis curves) 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 confirmed that, as described above, the smaller the film thickness dimension, the smaller the effect of the demagnetizing field H _D becomes, and the larger the magnetization M becomes near zero magnetic field.

In addition, Figure 1 confirms that the larger the film thickness of the magnetic material, the smaller the slope of the hysteresis curve, and a larger external magnetic field is required until the magnetization M becomes saturated. In other words, 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 less stable it becomes.

From the above, the problem arises that the larger the film thickness of the magnetic material, the smaller the output voltage near zero magnetic field, as well as the lower the stability against an external magnetic field. In other words, when applying the anomalous Nernst effect to a device, a small film thickness of the magnetic thin film is preferable in order to improve the output voltage near zero magnetic field and the stability against an external magnetic field. However, when the film thickness of the magnetic thin film becomes small, the internal resistance of the device increases, which causes output noise. Thus, for example, in the single-layer magnetic 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.

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 this 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.

However, as mentioned above, Patent Document 2 does not mention the effects of improving the output voltage near zero magnetic field, which is the actual usage environment of the device, or the stability against external magnetic fields and reducing internal resistance. In addition, 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 crystal structure of the group consisting of cubic and hexagonal crystals. Furthermore, the crystal structure of the magnetic layer (alloy layer) requires the provision of a buffer layer containing AlN with a crystal structure on the substrate, making the manufacturing process complicated.

Patent No. 6079995 JP 2022-129848 A Patent No. 6611167

The object of the present invention is to provide a thermoelectric device and laminate that can suppress output degradation near zero magnetic field, provide stability against external magnetic fields, and reduce internal resistance that causes output noise.

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

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

Furthermore, the laminate according to the embodiment of the present invention is characterized by a structure in which magnetic thin film layers and non-magnetic thin film layers are alternately laminated in the power generating body.

Embodiments of the present invention can provide a thermoelectric device and laminate that can suppress output degradation near zero magnetic field, provide stability against external magnetic fields, and reduce internal resistance that causes output noise.

1 is a graph showing the relationship between the film thickness and magnetization of a magnetic thin film. 1 is a configuration diagram showing a thermoelectric device according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a power generating body in the thermoelectric device. 13 is a graph showing the evaluation results of the thermoelectric device. 13 is a graph showing evaluation results of a thermoelectric device.

A thermoelectric device according to an embodiment of the present invention will now be described with reference to Fig. 2 and Fig. 3. Fig. 2 is a configuration diagram showing a thermoelectric device, and Fig. 3 is a schematic cross-sectional view showing a power generating body.
In each drawing, the scale of each component is appropriately changed for the purpose of explanation so that each component can be recognized. Also, the same reference numerals are used for the same or corresponding parts, and duplicate explanations are omitted.

The thermoelectric device of this embodiment has a structure in which the power generating body is alternately laminated with 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 reduced internal resistance.

In FIG. 2, a thermoelectric device is shown, and a heat flow sensor 10 is shown as an example. The heat flow sensor 10 is, for example, a sensor that detects a voltage V that is 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.

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 crystal orientation such as Si or MgO is applicable. In addition, rigid substrates or thin flexible substrates made of low-oriented polycrystalline, non-oriented polycrystalline, amorphous, or non-crystalline materials such as ultra-thin non-crystalline glass substrates and resin substrates such as polyimide are suitable. Specifically, low-oriented polycrystalline refers to polycrystalline with a half-width of the X-ray diffraction peak of the crystal orientation greater than 1°.

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 below is more likely to be 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.

The power generator 12 (12a, 12b) is a laminated body having a laminated structure of magnetic thin film layers and non-magnetic thin film layers described below, and is structured so that multiple pieces are arranged parallel to each other on the substrate 11. The power generator 12 is a thin wire with a rectangular parallelepiped shape with a width of several μm to several hundred μm and a length of several mm to several hundred mm.

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 made of a metal that conducts electricity, for example, Au. 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 also to the other end of the power generator 12b.

The power generating body 12b is then connected to the electrical connector 13b. In other words, the multiple power generating bodies 12 arranged in the heat flow sensor 10 have a meander wiring structure in which they are connected in series by the electrical connectors 13. The meander wiring structure allows the heat flow sensor 10 to be made smaller.

With this configuration, magnetization M is generated in the short direction of the power generator 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, making it possible to measure the heat flow density passing through the heat flow sensor 10.

Next, the cross-sectional structure of the power generator 12 will be described with reference to Figure 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.

The magnetic thin film layer 22 can be formed directly on the substrate 11. As long as the magnetic material exhibits the anomalous Nernst effect, there is no restriction on whether the magnetic material is hard or soft, and for example, FeGa is used. It is preferable that at least a portion of at least one layer of the magnetic thin film layer 22 is low-oriented polycrystalline, non-oriented polycrystalline, or amorphous. The smaller the crystal orientation, the smaller the thermal conductivity, so the thermal conductivity in the direction perpendicular to the surface of the heat flow sensor 10 decreases, and the increase in the temperature gradient ∇T makes it possible to detect even smaller heat flows, improving sensitivity. Furthermore, low-oriented polycrystalline, non-oriented polycrystalline, and amorphous materials have higher deformation resistance than single crystals and highly oriented polycrystalline materials, so they can be expected to be applied to 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°. There is no restriction on the thickness dimension of the magnetic thin film layer 22 as long as each can be formed into a continuous film. A thin film with a thickness of preferably 10 nm to 300 nm, more preferably 10 nm to 100 nm, and particularly preferably 10 nm to 30 nm is preferred.

The non-magnetic thin film layer 23 is made of a non-magnetic metal, semiconductor, or insulator, and examples of such materials include Ta, Pt, Si, Ge, _SiO2 , and MgO. 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 the 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.

Furthermore, it is preferable that at least a portion of at least one layer of the non-magnetic thin film layer 23 is low-oriented polycrystalline, non-oriented polycrystalline, or amorphous. The smaller the crystal orientation, the smaller the thermal conductivity, and therefore the larger the temperature gradient ∇T in the direction perpendicular to the surface of the heat flow sensor 10, making it possible to detect smaller heat flows and improving sensitivity. Furthermore, compared to single crystals and highly oriented polycrystalline, low-oriented polycrystalline, non-oriented polycrystalline, and amorphous have higher deformation resistance, so they can be expected to be used in flexible sensors. Specifically, low-oriented polycrystalline refers to polycrystalline with a half-width of the X-ray diffraction peak of the crystal orientation greater than 1°. Similarly, there is no limit to the thickness of the non-magnetic thin film layer 23, as long as each layer can form a continuous film. 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.

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 non-magnetic thin film layers 23a, magnetic thin film layers 22b, and non-magnetic thin film layers 23b. The laminated structure preferably has at least three layers, and more preferably has five layers or more.

Since the magnetic thin film layer 22 and the non-magnetic thin film layer 23 are alternately laminated, for example, the non-magnetic thin film layer 23a is interposed between the magnetic thin film layer 22a and the magnetic thin film layer 22b, and the magnetic coupling is broken. By making it a laminated structure, the film thickness of the magnetic thin film layer 22 can be made small, and as described above, the smaller the film thickness, the smaller the effect of the demagnetizing field H _D in the film plane direction, and the larger the magnetization M near zero magnetic field. In other words, the output voltage in zero magnetic field can be maintained high, and the stability against external magnetic fields is also increased. In addition, if the laminated structure is three or more layers, it is possible to make the magnetic thin film layer 22 thin while maintaining the total thickness of the power generation body 12 thick, resulting in a heat flow sensor 10 with low internal resistance.

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

Here, as the evaluation sample used in the measurement, a sample was prepared in which a magnetic thin film layer 22 made of a 100 nm thick FeGa thin film and a non-magnetic thin film layer 23 made of 5 nm thick Ta were alternately formed 10 times each, to produce a layered structure power generator 12 with a total thickness of approximately 1000 nm. In addition, as a comparative sample, a sample was prepared in which the power generator 12 was made of a single layer FeGa with a total thickness of 1000 nm.

In Figure 4, the horizontal axis indicates the magnetic field H, and the vertical axis indicates the magnetization M. Figure 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 residual magnetization near zero magnetic field is improved in the power generator 12, which has a layered structure, and that stability against external magnetic fields is also improved.

Figures 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 1V to 7V to a ceramic heater placed above the surface of the sample. The horizontal axis shows the heat flow density, and the vertical axis shows the voltage.

The graph shows the change in the Nernst electric 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 is saturated. Here, FIG. 5(a) shows the results for a sample having a power generating body 12 made of a laminated structure according to the present 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 FeGa. For each sample, the Nernst electric field E has a linear relationship with the heat flow density, and the resulting slope is the output sensitivity. As a result, it can be confirmed that the output sensitivity at zero magnetic field obtained with the power generating body 12 made of a laminated structure is improved from 0.021 μV/W·m ⁻² to 0.032 μV/W·m ⁻² compared to the output sensitivity at zero magnetic field obtained with the power generating body 12 made of a single-layer FeGa.

As described above, according to this embodiment, it is possible to provide a thermoelectric device and laminate that can suppress output reduction near zero magnetic field, achieve stability against external magnetic fields, and reduce internal resistance that causes output noise. This improves the output of the thermoelectric device under actual usage conditions.

The heat flow sensor of this embodiment can also be applied to power generation devices that generate electricity using 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 it will be used in clothing and bags that generate electricity by utilizing the difference between body temperature and the outside temperature, and in spontaneous power generation recycling systems that use waste heat from computers.

The present invention is not limited to the configuration of the above-described embodiment, and various modifications are possible without departing from the gist 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 in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

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 (11)

A substrate having at least a surface layer that is insulating and is 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 an electrical connector disposed between the power generating bodies and electrically connecting the power generating bodies in series,
The power generating body has a structure in which magnetic thin film layers and non-magnetic thin film layers are alternately laminated, and each of the magnetic thin film layers is magnetized in an in-plane direction. When a temperature gradient occurs in a direction perpendicular to the magnetization direction of the power generating body, an output voltage is generated due to the anomalous Nernst effect. The thermoelectric device according to claim 1, characterized in that the thermoelectric device is a heat flow sensor or a power generation device. The thermoelectric device according to claim 1 or 2, characterized in that the half-width of the X-ray diffraction peak of the surface layer is greater than 1°. The thermoelectric device according to claim 1 or 2, characterized in that the layered structure of the power generating body has at least three layers. 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 low-oriented polycrystalline, non-oriented polycrystalline, or amorphous. The thermoelectric device according to claim 5, characterized in that the half-width of the X-ray diffraction peak of at least one of the magnetic thin film layers is greater than 1°. 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. The thermoelectric device according to claim 7, characterized in that the half-width of the X-ray diffraction peak of at least one of the non-magnetic thin film layers is greater than 1°. The thermoelectric device according to claim 1 or 2, characterized in that the non-magnetic thin film layer is a metal or a semiconductor. The thermoelectric device according to claim 1 or 2, characterized in that the power generating body and the electrical connector have a meandering wiring structure in which they are connected in series. The power generating body described in claim 1 is a laminate having a structure in which magnetic thin film layers and non-magnetic thin film layers are alternately laminated.

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