JP2014239158A - Thermoelectric transducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a high performance thermoelectric transducer with an inexpensive material and a manufacturing method.SOLUTION: The thermoelectric transducer uses a nano-sheet composed of a transition metal chalcogenide material as an electromotive film deposited on a magnetic material layer. The transition metal chalcogenide film is a composite composed of transition metal such as W, Nb, Ta, Mo, Ti, and Hf and a chalcogen element such as S, Se, and Te, and has a layered structure having electrical conduction properties anisotropic in a two-dimensional plane direction (electric conductivity is especially high in a direction parallel to a film surface).

Description

  The present invention relates to an apparatus for generating electricity from a temperature gradient and a method for manufacturing the same.

  In recent years, an electronic technology called “spintronics” has attracted attention. Conventional electronics have used only “charge”, which is one property of electrons, while spintronics also actively uses “spin”, which is another property of electrons. In particular, “spin-current”, which is a flow of spin angular momentum of electrons, is an important concept. Since the energy dissipation of the spin current is small, there is a possibility that highly efficient information transfer can be realized by using the spin current. Therefore, generation, detection and control of spin current are important themes.

  For example, a phenomenon is known in which a spin current is generated when a current flows. This is called the “spin-hall effect”. It is also known as an opposite phenomenon that an electromotive force is generated when a spin current flows. This is called the “inverse spin-Hall effect”. By using the inverse spin Hall effect, the spin current can be detected. Both the spin Hall effect and the inverse spin Hall effect are significantly expressed in a substance (eg, Pt, Pd) having a large “spin orbit coupling”.

  Recent research has also revealed the existence of the “spin-Seebeck effect” in magnetic materials. The spin Seebeck effect is a phenomenon in which, when a temperature gradient is applied to a magnetic material, a spin current is induced in a direction parallel to the temperature gradient (see Patent Document 1). That is, heat is converted into a spin current by the spin Seebeck effect (thermal spin current conversion). In patent document 1, the spin Seebeck effect in the NiFe film | membrane which is a ferromagnetic metal is reported. Non-Patent Documents 1 and 2 report the spin Seebeck effect at the interface between a magnetic insulator such as yttrium iron garnet (YIG, Y3Fe5O12) and an electromotive film.

  The spin current induced by this temperature gradient can be converted into an electrical signal (current, voltage) using the above-described inverse spin Hall effect. That is, by using the spin Seebeck effect and the inverse spin Hall effect in combination, “thermoelectric conversion” that converts a temperature gradient into electricity becomes possible.

  On the other hand, Patent Document 2 and Non-Patent Document 1 disclose so-called “vertical” spin-flow thermoelectric conversion elements that apply a temperature gradient perpendicular to the surface of a magnetic layer (in the direction perpendicular to the surface). In this case, the spin current flowing out / inflowing into the electromotive film due to the spin Seebeck effect is also in the same plane normal direction, and the electromotive force due to the reverse spin Hall effect is a plane orthogonal to the magnetization direction of the magnetic material and the direction of the temperature gradient, respectively. Occurs inward.

  In the case of such a vertical spin Seebeck element, since the element can be configured with a simple two-layer structure composed of a metal film and a magnetic layer, in principle, a large area and a low manufacturing cost can be achieved. In fact, in Non-Patent Document 1, the magnetic layer is formed by a highly productive coating process.

  In these spin current thermoelectric conversion elements, the magnitude of the electromotive force obtained is “the magnitude of the spin current generated in the magnetic layer” and “the injection efficiency of the spin current at the interface between the magnetic layer and the electromotive film”. Further, it is determined by three factors: “efficiency converted into electromotive force by the reverse spin Hall effect in the electromotive film”.

  Among them, “improving the efficiency of converting spin current into electromotive force by the inverse spin Hall effect in the electromotive film” is an important issue in other spintronic devices, and so far, various methods have been studied. Has been done.

  As a parameter defining this efficiency, an index called a spin Hall angle corresponding to the mutual conversion efficiency between spin current and current is known. Previous reports of spin-flow thermoelectric conversion elements often used Pt having a large spin Hall angle among single metals.

  Other metals such as Au, Ag, and Cu do not reach the spin hole angle of Pt alone, but, for example, a small amount of Fe is introduced into Au as an impurity, or an impurity such as Bi is introduced into Cu. Thus, the possibility of obtaining a large spin Hall angle has been reported.

  Further, the electromotive film that exhibits such a spin Hall effect is not necessarily “metal”. For example, even a semiconductor material can be used as an electromotive film as long as it is a material containing a heavy element having electrical conductivity and a large spin-orbit interaction.

  In order to obtain high efficiency in the spin-flow thermoelectric conversion element, it is necessary to optimize the film thickness of the electromotive film in addition to the selection of an appropriate electromotive film material. By increasing the film thickness, the internal resistance of the electromotive film decreases, but conversely, if it is too thick, the spin current relaxes before reaching the interface with the magnetic material and does not contribute to thermoelectric power generation. The power extraction efficiency as a whole decreases. Therefore, in order to maximize the power extraction efficiency, it is desirable that the film thickness be about the spin relaxation length of the electromotive film material. In order to obtain a large output voltage, it is desirable that the film thickness be less than the spin relaxation length.

  The spin relaxation length of Pt is about 10-15 nm, and other noble metal materials are about several tens of nm. For this reason, a very thin metal thin film is generally used as an electromotive film for a normal spin current thermoelectric conversion element.

JP 2009-130070 A JP 2011-249746 A

Akihiro Kirihara, Ken-ichi Uchida, Yosuke Kajiwara, Masahiko Ishida, Yasunobu Nakamura, Takashi Manako, Eiji Saitoh & Shinichi Yorozu, "Spin-current-driven thermoelectric coating", Nature Materials 11 (2012), 686-689 Q. H. Wang, K .; Kalantar-Zadeh, A .; Kis, J .; N. Coleman and M.M. S. Strano, “Electronics and optoelectronics of two-dimensional transition metal dichogenides”, Nature Nanotechnology 7, 699-712.

  However, the inventors of the present application have developed the conventional electromotive film, that is, paying attention to the following problems in terms of efficiency and cost in the spin current-current conversion film.

  Regarding the efficiency, there is a problem that the conversion efficiency from the spin current in the perpendicular direction to the current in the in-plane direction is lowered because the electroconductive property of the electromotive film is insufficient. As described above, in order to optimize the conversion efficiency between the spin current and the current in the electromotive film, it is necessary to reduce the film thickness to several tens of nm or less. However, if the film thickness is too thin, the electrical conductivity may decrease. FIG. 9 shows a thermoelectric conversion element in which an electromotive film 103 made of a metal thin film is formed on a magnetic layer 102 formed on a substrate 104. For example, in the case of an element using a metal thin film of about 10 nm, as shown in FIG. 9, the in-plane electric conductivity is affected by scattering at the grain boundary 105 between the surface oxide layer 106 and the grains forming the metal thin film. Compared to the bulk, it is greatly reduced. For this reason, there is a problem that even if a temperature gradient is applied to develop the spin Seebeck effect, this cannot be sufficiently extracted as a current.

  There is also a cost issue. Conventionally used electromotive film materials are expensive noble metals such as Pt and Pd. Therefore, in order to apply to a wide range of applications, it is necessary to replace them with cheaper spin current-current conversion materials. In addition, almost all of the electromotive film materials reported so far have been produced by using a film forming method in a high vacuum. Since low-cost film formation such as a coating method can be applied to the magnetic layer, it is expected that the production process of the electromotive film is greatly improved.

  For example, when a metal thin film having a nano-order film thickness is manufactured by a low-cost process such as in a low vacuum, the in-plane conductivity deterioration becomes more remarkable depending on conditions, such as rough grain. Therefore, it has been very difficult to solve the above efficiency and cost problems at the same time.

  An object of the present invention is to solve the above problems and to realize a high-performance thermoelectric conversion element while suppressing the use of expensive noble metals.

  In one aspect of the present invention, a thermoelectric conversion element is formed on a magnetic layer and the magnetic layer, and is configured to generate an electromotive force in an in-plane direction by a reverse spin Hall effect, and includes a transition metal chalcogenide-based material. The electromotive film is formed, and two terminal portions are formed so as to be in contact with the electromotive film at two places where potentials due to the electromotive force are different.

  Since the transition metal chalcogenide forms an electromotive film having excellent electrical conductivity in the in-plane direction, a high-performance thermoelectric conversion element can be realized while suppressing the use of expensive noble metals.

The perspective view of the thermoelectric conversion element which is 1st Embodiment. The elements on larger scale of the thermoelectric conversion element which is 1st Embodiment. The figure explaining the spin current-current conversion in the thermoelectric conversion element which is 1st Embodiment. The figure explaining the spin hole angle. The perspective view of the thermoelectric conversion element which is 2nd Embodiment. The top view of the thermoelectric conversion element which is 2nd Embodiment. The figure which shows another structural example of 2nd Embodiment. Partial enlarged view of another configuration example of the second embodiment The perspective view of the thermoelectric conversion element which is 3rd Embodiment. The figure explaining the spin current-current conversion in the thermoelectric conversion element which is 3rd Embodiment. The perspective view of the thermoelectric conversion element which is 4th Embodiment. The figure which shows the subject of the conventional spin-flow thermoelectric conversion element.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
[First Embodiment]
(Element structure and operating principle)
FIG. 1A is a perspective view schematically showing a configuration of a thermoelectric conversion element 1 according to the present embodiment. FIG. 1B is an enlarged side view of a region P1 in FIG. 1A. The thermoelectric conversion element 1 includes a magnetic layer 2, an electromotive film 3, and a base 4 that supports them.

  The magnetic layer 2 is a magnetic material that exhibits a spin Seebeck effect. When the temperature difference ΔT is generated in the perpendicular direction (thickness direction, z-axis in the figure), the magnetic layer 2 generates (drives) a spin current Js from the temperature gradient ∇T (grad (T)) by the spin Seebeck effect. To do. The direction of the spin current Js is parallel or antiparallel to the direction of the temperature gradient ∇T. In the example shown in FIGS. 1A and 1B, a temperature gradient ∇T in the + z direction is applied, and a spin current Js along the + z direction or the −z direction is generated.

The material of the magnetic layer 2 may be a ferromagnetic metal or a magnetic insulator. Examples of the ferromagnetic metal include NiFe, CoFe, and CoFeB. Examples of magnetic insulators include yttrium iron garnet (YIG, Y ₃ Fe ₅ O ₁₂ ), YIG added with bismuth (Bi) (Bi: YIG, BiY ₂ Fe ₅ O ₁₂ ), and YIG added with lanthanum (La) ( _{la: YIG, LaY 2 Fe 5} O 12), yttrium gallium iron garnet _{(Ga: YIG, Y 3 Fe} 5-x Ga x O 12) , and the like. From the viewpoint of thermoelectric conversion efficiency, it is desirable that the magnetic layer 2 has a low thermal conductivity. Therefore, it is desirable to use a magnetic insulator in which no current flows (electrons do not carry heat).

  The electromotive film 3 plays a role of converting the spin current that flows in by the spin Seebeck effect of the magnetic layer 2 into an electromotive force by the inverse spin Hall effect. That is, the electromotive film 3 generates an electromotive force from the spin current Js by the inverse spin Hall effect. Here, the direction of the generated electromotive force (electric field E) is given by the outer product of the direction of the magnetization M of the magnetic layer 2 and the direction of the temperature gradient ∇T (E∝M × ∇T). In the present embodiment, the element is configured such that the direction of the electromotive force is the in-plane direction of the electromotive film 3 for efficient power generation. For example, as shown in FIGS. 1A and 1B, the direction of the magnetization M of the magnetic layer 2 is the + y direction, the direction of the temperature gradient ∇T is the −z direction, and the direction of the electromotive force is the + x direction. .

In this embodiment, a transition metal chalcogenide material is used as the electromotive film 3. The transition metal chalcogenide material is a compound composed of a transition metal element such as W, Nb, Ta, Mo, Ti, and Hf and a chalcogen element such as S, Se, and Te. The transition metal element M, when the chalcogen element and X, have a composition of normal MX _2. The electromotive film 3 formed using this material has strong interatomic bonds in the two-dimensional direction within the film surface, that is, in the x-axis direction and the y-axis direction in FIG. 1A. Therefore, as shown in FIG. 1B, the electromotive film 3 can be considered to have a layered structure including a plurality of thin layers overlapping in the perpendicular direction (z-axis direction). Such properties of transition metal chalcogenide materials are described in Non-Patent Document 2, for example. In the present embodiment, a transition metal chalcogenide material having a composition other than the transition metal dichalcogenide having the composition of MX ₂ can also be employed.

  Such an electromotive film has, for example, a layered structure in which unit layers formed by strong bonds such as covalent bonds are stacked by van der Waals force, which is a weak bond force. For this reason, the unit layer having a strong electronic bond exhibits anisotropic electric conductivity in the two-dimensional in-plane direction (particularly good electric conductivity in the direction parallel to the film surface).

The electromotive film 3 preferably contains a heavy element capable of expressing a large spin-orbit interaction in order to increase the mutual conversion efficiency between the spin current and the current. Specifically, it is desirable that the transition metal chalcogenide material MX _{2 includes} a transition metal M (Hf, Ta, W, etc.) having an element number of 72 or more, for example, WS ₂ , WSe ₂ , WTe ₂ , TaS ₂ , TaSe _2. TaTe ₂ or the like is desirable.

  The electromotive film 3 made of a transition metal chalcogenide has a layered structure, and even if it is a thin film of several nanometers to several tens of nanometers, it becomes a nanosheet having excellent electrical conductivity in the in-plane direction. Therefore, it is particularly suitable as an electromotive film for a spin current thermoelectric conversion element that requires a nano-order thin film conductor. In the present embodiment, in order to obtain a large electromotive force, an electromotive film having a film thickness of 30 nm or less and a layer number of 30 layers or less is used. More preferably, a film having a thickness of 15 nm or less and a number of layers of 15 or less is preferably used. By using such a material / structure, a good nano-electromotive thin film that achieves both efficient spin current-current conversion and high in-plane electrical conductivity can be realized.

  The substrate 4 is for stably supporting the thermoelectric conversion element, and substrates and films made of various materials can be used. The substrate 4 itself may be a heat source for applying a temperature gradient to the thermoelectric conversion element. Further, the substrate 4 may be omitted.

  The terminals 5a and 5b are formed so as to be in contact with the metal film 8 at two places where the potentials due to the electromotive force are different, and play a role of taking out the electromotive force generated by the electromotive film 3 to the outside. Since E∝M × ∇T, the electromotive force can be taken out if the two terminals 5a and 5b are provided at positions shifted at least in the direction perpendicular to the direction of the magnetization M in the film plane. The temperature gradient ∇T is considered to be generally oriented in the direction perpendicular to the surface (z-axis direction) in a typical usage method such as attaching the substrate 4 to a heat source. In that case, it is desirable that the terminal 5a and the terminal 5b are connected to positions separated from each other in the direction (x-axis direction) orthogonal to the direction of the magnetization M (y-axis direction) in the plane of the electromotive film 3.

  In FIG. 1A, the terminals 5a and 5b are electrically connected to both ends of the electromotive film 3, respectively. Therefore, it is possible to supply power to the load 10 by connecting the load 10 from these terminals as shown in FIG. 1A. From the viewpoint of impedance matching for supplying the maximum power, it is desirable that the internal resistance of the electromotive film 3 between the terminals 5a and 5b is approximately the same as the external resistance of the load 10 as a power supply destination.

  A cover layer 6 is provided on the electromotive film 3. Here, the material of the cover layer 6 is not particularly limited. For example, an organic resin material such as polyimide or polyester can be used. In addition, in providing the thermoelectric conversion function, the cover layer 6 is not essential.

(Effect of this embodiment)
As an advantage of using the electromotive film 3 made of the transition metal chalcogenide as described above, in addition to avoiding the use of an expensive noble metal such as Pt, the thermoelectric conversion performance is improved by a highly efficient spin current-current conversion effect. The effect of is mentioned.

  By using a transition metal chalcogenide for a part of the electromotive film 3 of the thermoelectric conversion element 1 and using a material such as Pt or the like that has been conventionally studied for the remaining part, the amount of the noble metal used is reduced, The effect of reducing the cost can be obtained.

  2A and 2B are conceptual diagrams of the spin current-current conversion effect. When the spin current 32 is injected into the electromotive film 3, the electrons responsible for the spin current 32 are perpendicular to the magnetization (electron spin) 31 direction and the spin current 32 direction due to the spin-orbit interaction in the electromotive film 3. It is bent in the in-plane direction and converted into a current 33. This is called an inverse spin Hall effect, and an index of efficiency converted (electrons are bent) at this time is a spin Hall angle θ. When a layered effect having a particularly high in-plane electrical conductivity is used as in this embodiment, electrons are easily bent in the in-plane direction, so that a large spin hole angle can be effectively obtained and high efficiency can be obtained. Spin current-current conversion becomes possible.

(Method for manufacturing thermoelectric conversion element)
Next, the manufacturing method of the thermoelectric conversion element 1 which concerns on this Embodiment is demonstrated.
First, as a method for forming the magnetic layer 2, any one of a sputtering method, an organometallic decomposition method (MOD method), a sol-gel method, an aerosol deposition method (AD method), a ferrite plating method, a liquid phase epitaxy method, etc. The method of forming into a film using is mentioned. In this case, the magnetic layer 2 is formed on a certain substrate.

  As a method of forming a transition metal chalcogenide film having a layered structure as the electromotive film 3, (1) a method of forming a film by cleaving a layered structure film from a bulk body or powder on a substrate, (2) The method is roughly classified into two, that is, a method in which a layered structure film is directly bottom-up grown on a substrate by chemical vapor deposition.

  As the method (1), it is desirable to use a liquid phase peeling method. In this method, a raw material powder of transition metal chalcogenide having a diameter of several μm is ultrasonically dispersed in an organic solvent such as isopropyl alcohol (IPA), N-methylpyrrolidone (NMP), N-vinylpyrrolidone (NVP), It exfoliates into a layered flake body by, for example, centrifuging. A raw material turbid liquid containing such a release body is spin-coated on the magnetic layer 2 to form a film.

  Further, an intercalation method in which layers are separated by inserting different materials such as Li into gaps in the layered structure can also be used. In this method, as a first step, a raw material powder of transition metal chalcogenide is reacted with a Grignard reagent such as n-butyllithium to generate a compound in which metal Li is inserted between layers. Next, by putting this intercalation compound into pure water, it is decomposed into layered flakes using the energy when Li and water react. Film formation is performed by spin-coating a raw material turbid liquid containing such a peeled body on, for example, the magnetic layer 2.

  After the formation of the electromotive film 3, two terminal portions (terminals 5a and 5b) are formed so as to come into contact with the electromotive film 3 at two places where potentials due to electromotive forces are different.

[Second Embodiment]
Next, the thermoelectric conversion element with a metal pad which is the 2nd Embodiment of this invention is demonstrated with reference to the perspective view shown in FIG. 3, and the top view of FIG.

  The electromotive film 3 in the thermoelectric conversion element 1 of the first embodiment shows high electrical conductivity in the two-dimensional in-plane direction, but the electromotive force is taken out from the terminals 5a and 5b in the direction perpendicular to the surface. A loss occurs in the amount of electric power that can be extracted due to the high contact resistance between the terminal and the electromotive film. In order to prevent this, in the thermoelectric conversion element 1a of the present embodiment, the metal pad 7a, the end of the electromotive film 3 in the direction of electromotive force generation (between the electromotive film 3 and the terminals 5a and 5b) 7b was newly added. In this embodiment, the current generated in the electromotive film 3 is taken out to the terminals 5a and 5b through the metal pads 7a and 7b.

  Here, as the metal pads 7a and 7b, a metal material having a high electrical conductivity is used in order to minimize a take-out loss due to resistance. For example, Au, Cu, Al, Ag or the like is used. The film thickness is desirably thicker than the electromotive film 3, and is preferably 50 nm or more.

  Further, the shape of the metal pads 7a and 7b is long in the direction perpendicular to the electromotive force generation direction as shown in FIG. 4 when the thermoelectric conversion element 1a is viewed from above for the purpose of minimizing the electromotive force extraction loss. It is desirable to have an elongated shape. In particular, assuming that the temperature gradient ∇T faces the direction perpendicular to the plane, the electromotive force faces the direction (x-axis direction) perpendicular to the magnetization M (y-axis direction) in the plane, so that the metal pads 7a and 7b have the magnetization M It is desirable to have a shape extending long in a direction parallel to the.

  Further, as shown in the perspective view of FIG. 5A and the side view of FIG. 5B in which the region P2 is enlarged, the metal pads 7a and 7b are formed so as to hang over the end portions of the electromotive film 3, and the like. Electrical contact may be made with the side surface of the electromembrane 3. Such a configuration can be formed as follows, for example. When the electromotive film 3 is formed on the magnetic layer 2, the electromotive film 3 is formed to have a slightly smaller dimension than the magnetic layer 2 at both ends in the direction in which the current Je flows (x-axis direction). To do. As a result, an L-shaped surface formed by the upper surface of the magnetic layer 2 and the side surface normal to the x-axis direction of the electromotive film 3 is formed in a region elongated in the y-axis direction at both ends in the x-axis direction. Exposed. Thereafter, metal pads 7 a and 7 b are formed so as to contact the L-shaped surface and the upper surface of the electromotive film 3. In such a configuration, the adhesion of the metal pads 7a and 7b to the electromotive film 3 is improved, and the current Je can be collected with high efficiency.

(Specific examples)
Next, specific examples based on the second embodiment will be described.
Here, a crystalline gadolinium gallium garnet (GGG) wafer having a size of 1 inch and a thickness of 0.7 mm is used as a base 4, and a spin current thermoelectric conversion element is manufactured thereon. Bismuth-substituted yttrium iron garnet (Bi: YIG, composition is BiY 2 Fe 5 O 12) is used for the magnetic layer 2, and tungsten sulfide (WS 2), which is one of transition metal chalcogenide materials, is used for the electromotive film 3.

  The Bi: YIG film is formed by an organometallic decomposition method (MOD method). As the solution, a MOD solution manufactured by Kojundo Chemical Laboratory Co., Ltd. is used. In this solution, a metal raw material having an appropriate molar ratio (Bi: Y: Fe = 1: 2: 5) is dissolved at a concentration of 5% in acetate in a carboxylated state. This solution is applied onto a GGG substrate by spin coating (rotation speed: 1000 rpm, rotation for 30 s), dried on a hot plate at 150 ° C. for 5 minutes, and then subjected to temporary annealing at 450 ° C. for 5 minutes, and finally in an electric furnace. The main annealing is performed for 14 hours at a high temperature of 700 ° C. and in an air atmosphere. Thereby, a crystalline Bi: YIG film having a film thickness of about 100 nm is formed on the GGG substrate.

  The tungsten sulfide film is formed using a liquid phase separation method. About 30 mg of tungsten sulfide powder WS2 having a particle size of about 3 μm manufactured by Kojundo Chemical Laboratory Co., Ltd. is dispersed in 20 ml of isopropyl alcohol (IPA) using an ultrasonic dispersion device. Thereafter, this liquid is further subjected to a centrifuge at 500 rpm for 1 hour. As a result of such centrifugation, the dispersion is neatly separated into a portion in which the powder is dispersed and a portion in which the layered flakes separated from the powder are dispersed. The raw material solution of the electromotive film 3 is produced by scooping out only the turbid liquid in which the layered flakes are dispersed. Thereafter, this raw material solution was spin-coated on a Bi: YIG film at a rotational speed of 2000 rpm and dried at a high temperature at 150 ° C. to obtain a tungsten sulfide thin film having a thickness of about 8 nm.

  Finally, metal pads 7a and 7b made of Ag having a thickness of 500 nm were formed at the ends by screen printing using Ag paste.

  As described above, the thermoelectric conversion element was manufactured by forming the magnetic layer 2, the electromotive film 3, and the metal pads 7a and 7b by using a non-vacuum process.

[Third Embodiment]
Next, a third embodiment of the present invention will be described based on the perspective view of FIG. In the thermoelectric conversion element 1c of the present embodiment, in order to increase the spin current injection efficiency from the magnetic layer 2 to the transition metal chalcogenide photovoltaic film 3 while being based on the element structure of the second embodiment, A metal film 8 is newly inserted.

  As described above, the transition metal chalcogenide photovoltaic film 3 has a high electrical conductivity in the in-plane direction due to the layered structure, and exhibits excellent spin current-current conversion characteristics. However, depending on the material, since the electron density is smaller than that of a general metal, the absolute amount of spin current thermally injected from the magnetic layer 2 becomes small, and a sufficient amount of power generation cannot be obtained. There was a case.

  Therefore, in the present embodiment, the metal film 8 is inserted between the magnetic layer 2 and the electromotive film 3 as shown in FIG. As a result, when spin Seebeck appears due to a temperature gradient, a spin current efficiently flows into the metal film 8 first, and when the spin current reaches the electromotive film 3, thermoelectric conversion is performed by effective spin current-current conversion. Is achieved (FIG. 7).

  There are no significant restrictions on the material of the metal film 8, and for example, Cu, Al, Ag, Au, Pt, or the like can be used. However, in order to transmit the spin current to the electromotive film 3, the thickness of the metal film 8 is preferably less than or equal to the spin relaxation length of the metal material, and more preferably 30 nm or less. Similarly to the first embodiment, the electromotive film 3 has a film thickness of 30 nm or less and a layer number of 30 layers or less. More preferably, a film having a thickness of 15 nm or less and a number of layers of 15 or less is preferably used.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described based on the perspective view of FIG. In the thermoelectric conversion element 1d of the present embodiment, a plurality of electromotive films 3 and metal films 8 of the third embodiment are provided, and a plurality of electromotive films 3 and metal films 8 are alternately stacked to be multilayered. .

  In other words, in the present embodiment, a plurality of electromotive films 3 and a plurality of metal films 8, 9, and 11 are alternately arranged on the magnetic layer 2. The electromotive film 3 and the metal film 8 of the third embodiment are considered to be one of the plurality of electromotive films 3 and one of the plurality of metal films 8, 9, and 11, respectively.

  Efficiency can be further improved by extracting current from the plurality of electromotive films 3. Further, by sandwiching the electromotive film 3 with a metal film, an additional effect of improving the adhesion between the electromotive film material and the metal film material can be obtained.

  As in the third embodiment, there are no significant restrictions on the materials of the metal films 8, 9, and 11, and for example, Cu, Al, Ag, Au, Pt, or the like can be used. However, the film thicknesses of the metal films 8, 9, and 11 are desirably less than or equal to the spin relaxation length of the metal material, and more desirably 30 nm or less. In order to optimize the power generation efficiency, it is desirable that the total thickness of the multilayer film composed of the electromotive film 3 and the metal films 8, 9, and 11 is 100 nm or less.

  Further, as in the first embodiment, each film thickness of the electromotive film 3 is 30 nm or less, and the number of layers is 30 layers or less. More preferably, a film having a thickness of 15 nm or less and a number of layers of 15 or less is preferably used.

  In the example of FIG. 8, the electromotive force generated by the electromotive film 3 is taken out from the uppermost metal film 8. Since the metal film 8 and the electromotive film 3 are extremely thin, it is considered that sufficient electric power can be taken out even with such a simple configuration. However, in order to further increase the current collection efficiency, a metal pad 7 having an L-shaped cross section as shown in FIGS. 5A and 5B can be provided. In this case, the metal pads 7 a and 7 b are in contact with the side surfaces of the plurality of electromotive films 3 and the metal film 8.

  As mentioned above, although several embodiment of this invention was described, it is also possible to combine those embodiment in the range which does not mutually contradict.

1. Thermoelectric conversion element 2. 2. Magnetic layer 3. Electromotive film 4. Bases 5a, 5b. Terminal 6. Cover layers 7a, 7b. Metal pad 8. Metal film 9. Metal film 10. External load11. Metal film 31. Electron spin 32. Spin current 33. Current

Claims (11)

A magnetic layer;
An electromotive film formed on the magnetic layer and formed of a transition metal chalcogenide-based material;
A thermoelectric conversion element comprising two terminal portions formed so as to be in contact with the electromotive film at two places where potentials due to the electromotive force are different. The electromotive film is a thermoelectric conversion element configured to generate an electromotive force in an in-plane direction by an inverse spin Hall effect. The thermoelectric conversion element according to claim 1, wherein the electromotive film has a larger electric conductivity in an in-plane direction than in a perpendicular direction. The thermoelectric conversion element according to claim 1, wherein the electromotive film has a thickness of 30 nm or less. The thermoelectric conversion element according to claim 1, wherein the electromotive film includes any one of W, Ta, and Hf that are transition metals. Furthermore, the thermoelectric conversion element in any one of Claims 1-5 provided with the metal pad which touches both the said electromotive film and the said terminal part. The thermoelectric conversion element according to claim 1, further comprising a metal film disposed between the magnetic layer and the electromotive film. The thermoelectric conversion element according to claim 7, wherein the metal film has a thickness of 30 nm or less. The electromotive film is one of a plurality of electromotive films disposed on the magnetic layer,
The metal film is one of a plurality of metal films disposed on the magnetic layer,
The thermoelectric conversion element according to claim 7 or 8, wherein the plurality of electromotive films and the plurality of metal films are alternately stacked. The thermoelectric conversion element according to claim 9, wherein the sum of the thickness of the plurality of electromotive films and the thickness of the plurality of metal films is 100 nm or less. Forming an electromotive film with a transition metal chalcogenide-based material on the magnetic layer;
Forming two terminal portions so as to come into contact with the electromotive film at two locations where potentials due to the electromotive film are different from each other.

Images