N-type mg-sb-bi-based thermoelectric material having metal electrode layer solid-state bonded thereto and manufacturing method therefor

Abstract

The present disclosure relates to an n-type Mg-Sb-Bi-based thermoelectric material having a metal electrode layer solid-state bonded thereto and a manufacturing method therefor. The technical gist of the present invention is to include: a n-type thermoelectric material layer containing magnesium (Mg), antimony (Sb), and bismuth (Bi); and a metal electrode layer disposed on the surface of the n-type thermoelectric material layer, wherein the metal electrode layer is formed by sequentially stacking a first metal layer including magnesium in the form of a foil and a second metal layer including metals other than magnesium of the first metal layer, and the n-type thermoelectric material layer and the metal electrode layer are solid-state bonded through hot pressing.

Description

N-type MG-SB-BI thermoelectric material with solid-state bonding of metal electrode layer and manufacturing method thereof

[0001] The present invention relates to an n-type Mg-Sb-Bi thermoelectric material having a solid-state bonded metal electrode layer and a method for manufacturing the same.

[0002] Thermoelectric cooling technology utilizing the Peltier effect is widely used in noiseless small cooling devices and precision temperature control devices, and recently, thermoelectric power generation technology utilizing the Seebeck effect is attracting attention as a promising means of recovering distributed waste heat.

[0003] Currently, thermoelectric cooling and thermoelectric power generation technologies are primarily utilized at low temperatures below 500 K, and bismuth telluride (Bi2Te3)-based thermoelectric materials are the most commonly used. Since its development in the 1950s, bismuth telluride has demonstrated outstanding thermoelectric properties at low temperatures and is the only commercially available material. However, Te, the main component of bismuth telluride, is rare and expensive, limiting its industrial application and mass production. Consequently, the need for novel low-temperature thermoelectric materials composed of common and inexpensive elements is increasing.

[0004] n-type Mg3Sb reported in 2016 2-x Bi x Thermoelectric materials have shown promise as a replacement for n-type bismuth telluride. These materials not only possess excellent thermoelectric properties, but their key components are common and inexpensive, making them highly industrially viable. Despite this strong interest, research on the metallization process essential for thermoelectric module development remains relatively insufficient.

[0005] In relation to this, Fig. 1 is a cross-sectional structural diagram of a typical low-temperature thermoelectric module. An ohmic junction layer is formed on the upper and lower parts of the p-type and n-type thermoelectric legs, and this is bonded to a direct bonded Cu (DBC) ceramic substrate with a solder layer, so that all pn leg pairs are connected in series. In this process, the formation of the ohmic junction layer and soldering are key. In the existing Bi2Te3 material, the ohmic junction layer and diffusion barrier layer are formed through Ni plating, and lead-free SAC305 solder is used for soldering.

[0006] As new thermoelectric materials are introduced, new materials and formation methods for the ohmic contact layer must be developed to match. These must exhibit superior electrical and physical properties, such as contact resistance and bonding strength, while process simplicity and suitability for mass production are also key considerations.

[0007] As an example of a conventional metallization process, n-type Mg3Sb is prepared using Fe, Ni, and SUS powders. 2-x Bi x There is a method for synthesizing a monolithic sintered body by sintering it with a thermoelectric material. However, this method has difficulty in uniformly forming the thickness and properties of the ohmic contact layer, and its industrial practicality is low. In addition, wet processes such as nickel electroless plating are not suitable for Mg3Sb. 2-x Bi x Thermoelectric materials are difficult to apply because they are chemically fragile.

[0008] Therefore, n-type Mg3Sb 2-x Bi x There is an urgent need to develop a dry process that can stably form an ohmic junction layer with high reproducibility, uniformity, and excellent conductivity for thermoelectric materials.

[0009] The present invention was invented to solve the above-mentioned problem, and the technical task of the present invention is to provide an n-type Mg-Sb-Bi thermoelectric material and a method for manufacturing the same in which a metal electrode layer is solid-state bonded so as to form an ohmic junction through solid-state bonding using magnesium foil.

[0010] In order to solve the above technical problem, the present invention provides an n-type Mg-Sb-Bi thermoelectric material in which the metal electrode layer is solid-state bonded, comprising: an n-type thermoelectric material layer including magnesium (Mg), antimony (Sb), and bismuth (Bi); and a metal electrode layer disposed on the surface of the n-type thermoelectric material layer; wherein the metal electrode layer is formed by sequentially stacking a first metal layer including magnesium in a foil form and a second metal layer including the remaining metal except for magnesium of the first metal layer, and wherein the n-type thermoelectric material layer and the metal electrode layer are solid-state bonded through heat pressing.

[0011] In the present invention, the second metal layer is characterized in that it is a metal foil made of one of copper, nickel, and a copper-nickel alloy.

[0012] In the present invention, the metal electrode layer is characterized in that it further includes a third metal layer formed by further arranging, on the surface of the second metal layer, a metal foil made of one of copper, nickel, and a copper-nickel alloy, excluding the metal foil selected from the second metal layer.

[0013] In the present invention, the solid-state bonding is characterized in that it is performed through heat compression at a maximum temperature of less than 477°C.

[0014] In the present invention, the n-type thermoelectric material layer is characterized by satisfying the following chemical formula 1.

[0015] [Chemical Formula 1]

[0016] Mg3Sb 2-x Bi x (However, in the above chemical formula 1, x is 0 < x < 2.)

[0017] In the present invention, the interfacial contact resistance between the solid-state bonded n-type thermoelectric material layer and the metal electrode layer is characterized by being at most 100 μΩ ㎠ or less.

[0018] Meanwhile, in order to solve the above technical problem, the present invention includes a first step of manufacturing an n-type thermoelectric material layer by mixing and sintering magnesium (Mg), antimony (Sb), and bismuth (Bi); and a second step of forming a metal electrode layer by sequentially laminating a first metal layer including magnesium in a foil form on the surface of the n-type thermoelectric material layer and a second metal layer including the remaining metal except for the magnesium of the first metal layer; and a method for manufacturing an n-type Mg-Sb-Bi thermoelectric material in which a metal electrode layer is solid-state bonded, characterized in that the second step is characterized in that the n-type thermoelectric material layer and the metal electrode layer are solid-state bonded by heat and compression.

[0019] In the present invention, the solid-state bonding is characterized in that it is performed through heat compression at a maximum temperature of less than 477°C.

[0020] In the present invention, the n-type thermoelectric material layer is characterized by satisfying the following chemical formula 1.

[0021] [Chemical Formula 1]

[0022] Mg3Sb 2-x Bi x (However, in the above chemical formula 1, x is 0 < x < 2.)

[0023] In the present invention, the interfacial contact resistance between the solid-state bonded n-type thermoelectric material layer and the metal electrode layer is characterized by being at most 100 μΩ ㎠ or less.

[0024] In the present invention, the second metal layer of the second step is characterized in that it is a metal foil made of one of copper, nickel, and a copper-nickel alloy.

[0025] In the present invention, the second step is characterized by further laminating a third metal layer made of a metal foil made of one of copper, nickel, and a copper-nickel alloy, excluding the metal foil selected from the second metal layer, on the surface of the second metal layer, and then performing solid-state bonding.

[0026] According to the present invention as a means for solving the above problem, since the n-type thermoelectric material layer and the metal electrode layer are directly solid-state bonded through a dry process, there is an advantage in that there is no risk of corrosion or deterioration of the thermoelectric material that may occur in the existing metal plating process.

[0027] In addition, the metal electrode layer can be simply formed using magnesium and a metal other than magnesium (e.g., copper, nickel, or a copper-nickel alloy) in the form of a foil rather than a powder. Accordingly, the interface between the n-type thermoelectric material layer, the first metal layer including the magnesium foil, the second metal layer including the remaining metal foils other than the magnesium foil, or in some cases, another third metal layer disposed on the second metal layer is flat, and the thickness of the double metal electrode layer or triple metal electrode layer can be maintained uniformly under any conditions, thereby ensuring the advantage of process reproducibility.

[0028] In particular, since a continuous and uniform ohmic junction layer is formed between the thermoelectric material layer and the metal electrode layer by the solid-state bonding through heat compression and the mutual diffusion of the metal electrode layer, the interfacial contact resistance between the n-type thermoelectric material layer and the metal electrode layer can be reduced to a maximum of 100 μΩ ㎠ or less. This low interfacial contact resistance can not only minimize electrical loss and improve the electrical conductivity of the thermoelectric material, thereby improving the overall performance of the thermoelectric module, but also prevent component changes or polarity switching occurring at the bonding interface between the thermoelectric material layer and the metal electrode layer, which ultimately has the advantage of ensuring the long-term stability and reliability of the thermoelectric material.

[0029] Figure 1 is a cross-sectional structural diagram of a typical low-temperature thermoelectric module.

[0030] Figure 2 is a process diagram showing a method for manufacturing a thermoelectric material according to the present invention.

[0031] Figure 3 is a phase equilibrium diagram of magnesium-copper according to the present invention.

[0032] Figure 4 is an SEM photograph of a thermoelectric material according to Example 1.

[0033] Figure 5 is an SEM photograph of a thermoelectric material according to Comparative Example 1.

[0034] Figure 6 shows the results of Potential-Seebeck Microprobe (PSM) analysis on a thermoelectric material according to Example 1.

[0035] Figure 7 is a distribution diagram of the measured Seebeck coefficient values ​​of Figure 6.

[0036] Figure 8 shows the results of Potential-Seebeck Microprobe (PSM) analysis on a thermoelectric material according to Comparative Example 1.

[0037] Figure 9 is a graph analyzing the contact resistance of a thermoelectric material according to Example 1.

[0038] Figure 10 is a graph analyzing the contact resistance of a thermoelectric material according to Comparative Example 1.

[0039] The present invention is susceptible to various modifications and embodiments. Specific embodiments are illustrated and described in detail in the drawings. However, this is not intended to limit the present invention to specific embodiments, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention. Throughout the description of each drawing, similar reference numerals have been used to designate similar components.

[0040] The terminology used herein is merely for the purpose of describing specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In the present invention, it should be understood that the terms "comprise" or "have" indicate the presence of a feature, number, step, reaction, component, or combination thereof described in the specification, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, reactions, components, or combinations thereof.

[0041] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and shall not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0042] Before explaining the present invention, n-type Mg3Sb 2-x Bi x In the metallization process of thermoelectric materials, Fe or Ni has been mainly used as an ohmic contact layer. For this purpose, Fe or Ni powder is sintered into Mg3Sb using powder sintering. 2-x Bi x The method of forming a monolithic sintered body by sintering with thermoelectric material powder was mainly used. However, Mg3Sb 2-x Bi x Due to the low chemical vulnerability of thermoelectric materials, it is difficult to apply the wet plating process, and the powder sintering method has difficulty in reproducing uniform thickness and properties, which reduces industrial practicality. Therefore, a reliable and simple dry process metallization process is required.

[0043] Accordingly, the present invention provides an n-type Mg-Sb-Bi thermoelectric material in which a metal electrode layer is solid-state bonded. The n-type Mg-Sb-Bi thermoelectric material of the present invention comprises an n-type thermoelectric material layer including magnesium (Mg), antimony (Sb), and bismuth (Bi), and a metal electrode layer disposed on the surface of the n-type thermoelectric material layer. At this time, the metal electrode layer is sequentially formed by stacking a first metal layer including foil-shaped magnesium and a second metal layer including the remaining metal except for the magnesium of the first metal layer, and in particular, the n-type thermoelectric material layer, the first metal layer, and the second metal layer are solid-state bonded through heat compression below 477 ℃, which is the phase equilibrium temperature of magnesium and copper, and are characterized in that the interface contact resistance between the n-type thermoelectric material layer and the metal electrode layer (specifically, the first metal layer) is reduced to a maximum of 100 μΩ ㎠ or less.

[0044] According to these characteristics, a metal electrode layer composed of a first metal layer including magnesium in a foil form and a second metal layer including the remaining metal except for the magnesium of the first metal layer, and an n-type thermoelectric material layer can form an ohmic junction that is structurally strong and has excellent electrical conductivity through interdiffusion through solid-state bonding at the interface.

[0045] It is preferable that the n-type thermoelectric material layer according to the present invention satisfies the following chemical formula 1.

[0046] [Chemical Formula 1]

[0047] Mg3Sb 2-x Bi x

[0048] However, in the above chemical formula 1, x is 0 < x < 2. Preferably, considering the molar ratio of Mg, Sb, and Bi, it may be 0.5 ≤ x ≤ 1.5.

[0049] Mg3Sb 2-x Bi xis a thermoelectric material that has recently begun to attract attention, and a method for forming a metal electrode layer suitable for Mg-Sb-Bi thermoelectric materials is needed. Mg3Sb 2-x Bi x Since it deteriorates when it comes into contact with water, acid or base, it is difficult to apply the nickel electroless plating technology that has been widely used in the past. Accordingly, the present invention simplifies the process by applying a dry process instead of a wet process, and Mg3Sb 2-x Bi x By fundamentally preventing deterioration of the n-type thermoelectric material layer and the metal electrode layer, stable solid-state bonding is possible.

[0050] The metal electrode layer is formed by sequentially laminating a first metal layer made of magnesium foil on the upper and lower surfaces of the n-type thermoelectric material layer, and a second metal layer made of a metal foil other than magnesium. For example, the second metal layer may be a metal foil made of one of copper, nickel, and a copper-nickel alloy. In this case, the metal electrode layer may be said to be formed of a double metal electrode layer.

[0051] Alternatively, the metal electrode layer may be composed of a triple metal electrode layer. This can be achieved by further laminating and arranging metal foils, excluding the metal foil selected from the second metal layer, on the surface of the second metal layer among metal foils made of one of copper, nickel, and a copper-nickel alloy, to additionally form a third metal layer. For example, when the second metal layer is nickel and the third metal layer is copper, the metal electrode layer can be a triple metal electrode layer having a Mg-Ni-Cu structure.

[0052] Mg3Sb 2-x Bi x The reason why Mg was chosen as the metal that is in direct contact with the upper and lower parts of the n-type thermoelectric material layer is that even if Mg is diffused, Mg3Sb is formed at the interface between the n-type thermoelectric material layer and the first metal layer. 2-x Bi x Because it does not cause Mg deficiency. Mg3Sb2-x Bi x Since the thermoelectric material layer itself contains magnesium, by using magnesium as the first metal layer, the chemical affinity between the n-type thermoelectric material layer and the first metal layer increases, enabling mutual bonding. That is, even if some of the magnesium in the first metal layer diffuses into the n-type thermoelectric material layer during the solid-state bonding process, the composition of the thermoelectric material does not change significantly, so that chemical imbalances or defects at the interface between the n-type thermoelectric material layer and the first metal layer can be minimized. This enables the formation of a continuous and uniform ohmic junction layer, which can contribute to smooth electron flow and lower contact resistance. In other words, in the case of magnesium, since it forms an ohmic contact without an energy barrier when in contact with an n-type semiconductor thermoelectric material, it allows electrons to move freely without resistance when passing through the interface, thereby reducing the contact resistance.

[0053] And as the second metal layer, one of the metal foils made of copper, nickel, and a copper-nickel alloy is selected to surround the first metal layer so that the subsequent soldering process can proceed in the same way as the process of bismuth telluride. If there is only the second metal layer including copper without the first metal layer including the magnesium foil, the copper is Mg3Sb 2-x Bi x It has low chemical affinity with thermoelectric materials, which causes defects at the interface, hindering the flow of electrons and increasing the interface contact resistance. In other words, copper is Mg3Sb 2-x Bi x Because it does not diffuse well into the thermoelectric material, bonding at the bonding interface becomes difficult, which reduces electrical conductivity and increases contact resistance.

[0054] The first metal layer is formed by disposing magnesium foil instead of magnesium powder, and the second metal layer is also formed by disposing metal foil instead of metal powder. In this way, by using magnesium and metals other than magnesium, which constitute the first and second metal layers, in the form of foil instead of powder, the interface between the n-type thermoelectric material layer, the first metal layer, and the second metal layer is flat, and the thickness of the metal electrode layer can be maintained uniformly under any conditions, thereby stably securing process reproducibility.

[0055] In particular, the n-type thermoelectric material layer, the first metal layer, and the second metal layer are solid-state bonded through heat compression at a temperature lower than 477°C, which is the phase equilibrium temperature of magnesium (the first metal layer) and copper (the second metal layer), thereby reducing the contact resistance between the n-type thermoelectric material layer and the metal electrode layer. This can be confirmed through Fig. 3, which shows the phase equilibrium diagram of magnesium-copper.

[0056] In the phase equilibrium diagram of Fig. 3, the x-axis represents the at% content of copper and magnesium, and the y-axis represents temperature. The phase equilibrium temperature is the temperature at which copper and magnesium react with each other in a solid state to form a new phase. Copper and magnesium form a new compound at a specific temperature through a diffusion reaction, and the temperature at this time is 477 ℃.

[0057] Below 477 ℃, copper and magnesium exist stably in a solid state and do not react with each other to form other phases. However, referring to part A of Fig. 3, when it reaches 477 ℃, magnesium and copper react with each other, and magnesium melts into a liquid state. Although magnesium has a melting point of approximately 650 ℃, it is converted into liquid magnesium when pressure is applied at 477 ℃. Magnesium that has been converted into a liquid state at 477 ℃ can easily escape due to pressure, which can cause an imbalance in the composition of the metal electrode layer and the n-type thermoelectric material layer, and deteriorate the bonding quality between the metal electrode layer and the n-type thermoelectric material layer, which can result in a decrease in electrical conductivity and an increase in contact resistance.

[0058] Accordingly, when solid-state bonding the first metal layer and the second metal layer to the n-type thermoelectric material layer, it is important to prevent the eutectic point of Mg and Cu from being reached at a temperature not exceeding 477°C, thereby preventing liquid phase formation and loss of the first metal layer made of Mg foil.

[0059] The above n-type Mg-Sb-Bi thermoelectric material can be described in detail through FIG. 2, which is a process diagram showing a method for manufacturing a thermoelectric material according to the present invention. As illustrated in FIG. 2, the n-type Mg-Sb-Bi thermoelectric material is manufactured through a first step (S10) of mixing and sintering magnesium, antimony, and bismuth to manufacture an n-type thermoelectric material layer, and a second step (S20) of sequentially stacking a first metal layer composed of magnesium foil on the upper and lower surfaces of the n-type thermoelectric material layer, and a second metal layer composed of the remaining metals except for the magnesium of the first metal layer, to form a metal electrode layer.

[0060] According to the above-described manufacturing method, first, the first step is a step of manufacturing an n-type thermoelectric material layer by mixing and sintering magnesium, antimony, and bismuth (S10).

[0061] As shown in Fig. 2, a bulk-shaped n-type thermoelectric material sintered body (110) is manufactured by mixing and sintering magnesium, antimony, and bismuth.

[0062] When mixing magnesium, antimony, and bismuth raw materials, the molar ratio of magnesium, antimony, and bismuth can be (3 + α) : (2 - x) : x. α means that magnesium is added in excess in advance in consideration of the loss due to volatilization during the manufacture of the n-type thermoelectric material layer, and preferably, it can be in the range of 0 < α ≤ 0.5. α can vary greatly depending on the detailed conditions during the manufacture of the n-type thermoelectric material layer. For example, the α value increases as the process continues at a high temperature for a long time. However, the range of the x value in the above molar ratio can be 0 < x < 2.

[0063] In the case of magnesium, it is preferable to maintain an inert atmosphere while blocking contact with the atmosphere, and to manufacture a bulk-shaped n-type thermoelectric material sintered body (110) through powderization and sintering through mechanical alloying, while omitting the melting process in which magnesium is lost, and because magnesium is easily oxidized.

[0064] The bulk shape may be a long cylindrical shape, and there is no limitation on the shape of the n-type thermoelectric material sintered body (110) as long as it can form the n-type thermoelectric material layer (100) in a coin shape.

[0065] Thereafter, the bulk-type n-type thermoelectric material sintered body (110) is cut at regular intervals in the length direction and processed into a coin-shaped n-type thermoelectric material layer (100). The coin-shaped body means a shape like a thin coin or button, and the cross-sectional shape may be circular. However, the coin-shaped n-type thermoelectric material layer (100) may be a circular plate shape corresponding to the shape of the n-type thermoelectric material sintered body (110), and may have an elliptical or polygonal cross-sectional shape depending on the shape of the n-type thermoelectric material sintered body (110).

[0066] By lightly sanding the upper and lower surfaces of the n-type thermoelectric material layer (100) obtained in this way with sandpaper to artificially induce surface roughness, the bonding surface with the first metal layer (210) including the magnesium foil is widened, thereby further increasing the solid-state bonding strength with the n-type thermoelectric material layer (100).

[0067] Next, the second step is a step of sequentially stacking and arranging a first metal layer (210) including magnesium foil on the upper and lower surfaces of an n-type thermoelectric material layer (100) and a second metal layer (220) including the remaining metal except for magnesium, and then forming a metal electrode layer (200) through solid-state bonding (S20).

[0068] Before explaining the second step, the metal in contact with the n-type thermoelectric material layer (100) containing magnesium, antimony and bismuth must have high electrical conductivity and strong bonding force with the n-type thermoelectric material layer (100). If the type of the n-type thermoelectric material layer (100) is changed, the metal components constituting the metal electrode layer must also be changed, and Mg3Sb based on magnesium antimonide 2-x Bi x Research on forming metal electrode layers for thermoelectric materials remains insufficient. Typically, thermoelectric materials and metal powders are placed together in a sintering mold and sintered. However, this method is only suitable for research purposes and has limited industrial applicability.

[0069] Accordingly, in the second step, a multilayer metal electrode layer (200) is formed, and by forming a two-layer or three-layer structure of a metal electrode layer using a metal foil rather than using metal powder, an ohmic junction layer of uniform thickness can be reproducibly formed. Mg, one of the main components of the n-type thermoelectric material layer (100), was selected as the ohmic junction layer to minimize chemical heterogeneity, and Mg3Sb 2-x Bi xPrevents Mg from being lost from the thermoelectric material through vaporization or outdiffusion.

[0070] That is, the metal that comes into contact with the upper and lower surfaces of the n-type thermoelectric material layer (100) is made of magnesium foil, and the remaining metals, for example, copper foil, are overlapped and placed on the surface of the magnesium foil to increase the temperature and heat and press at once to achieve direct solid-state bonding, which is a dry process rather than a wet process, thereby forming a double or triple structure metal electrode layer (200) on the upper and lower surfaces of the n-type thermoelectric material layer, respectively, so that the height of the thermoelectric leg and the thickness of the ohmic junction layer can be independently optimized.

[0071] Since magnesium foil and copper foil are used, the interface between the n-type thermoelectric material layer (100), the first metal layer (210) including magnesium foil, and the second metal layer (220) including copper foil can be maintained flat, making it possible to manufacture a thermoelectric material of uniform thickness.

[0072] Moreover, while the conventional nickel electroless plating process may damage the thermoelectric material during the process of immersing it in an acid or base solution, the present invention has the advantage of not damaging the thermoelectric material because it performs a solid-state bonding process, which is a dry process.

[0073] In the case of solid-state bonding, it is performed by heating and pressing at a pressure of 20 to 80 MPa for 5 to 20 minutes below the maximum 477 ℃, which is the phase equilibrium temperature of copper and magnesium. If the solid-state bonding time is less than 5 minutes, the contact time between the n-type thermoelectric material layer and the metal electrode layer is short, which is disadvantageous in the process. If it exceeds 20 minutes, the effect is not superior to the case of solid-state bonding for a shorter time, so there is no need to heat and press for more than 20 minutes, and there is the disadvantage of a long process time. If the pressure condition is less than 20 MPa, the bonding strength between the n-type thermoelectric material layer and the metal electrode layer is low, so the solid-state bonding time may have to be set to more than 20 minutes. If it exceeds 80 MPa, the pressure is excessively high, which may cause damage to the n-type thermoelectric material layer or the metal electrode layer, which is not desirable. However, a condition of 50 MPa at 450 ℃ for 10 minutes is desirable.

[0074] When the solid-state bonding process as described above is performed, a magnesium-copper compound may be generated at the interface between the first metal layer including the magnesium foil and the second metal layer including the copper foil, thereby forming a magnesium-copper compound interface layer. At a solid-state bonding temperature of less than 477°C (more specifically, 450°C), mutual diffusion between magnesium and copper occurs, thereby generating a solid-state magnesium-copper compound without forming a liquid phase, thereby forming a magnesium-copper compound interface layer, which helps improve the bonding strength between the n-type thermoelectric material layer (100) and the metal electrode layer (200), and thus may contribute to having a low interface contact resistance of less than or equal to 100 μΩ ㎠.

[0075] Hereinafter, embodiments of the present invention will be described in more detail. However, the following embodiments are provided merely to aid understanding of the present invention, and the scope of the present invention is not limited thereby.

[0076] <Example 1> Solid-state bonding conditions: 450 ℃, 10 minutes, 50 MPa

[0077] Prepare Mg (5-25 mm turnings, 99.95%, Sigma Aldrich), Sb (ca. 2 mm grains, 99.999%, Kojundo Chemical), Bi (1-12 mm pieces, 99.999%, Sigma Aldrich), weigh and mix in a molar ratio of magnesium: antimony: bismuth = (3 + α) : (2 - x) : x, and then perform mechanical alloying in a ball milling device (BM-450, Spex-Cole-Parmer) to obtain Mg3Sb 2-x Bi x Powder was synthesized. At this time, Mg was added in excess of the quantitative ratio to prepare for Mg loss during the sintering process, and was appropriately adjusted to the range of 0 < α ≤ 0.5, and x was set to 0.5.

[0078] The above Mg3Sb 2-x Bi x The powder was charged into a plasma-activated sintering device (Ed-PAS IV, Elenix) and sintered at 1073 K to synthesize a cylindrical n-type thermoelectric material sintered body with a diameter of 12.7 mm. In this way, an Ar atmosphere was maintained during the mechanical alloying and sintering processes to prevent oxidation of Mg as much as possible.

[0079] The synthesized cylindrical n-type thermoelectric material sintered body was cut into a coin shape of approximately 1.2 mm, and then Mg foil (99.9%, Alfa Aesar) and Cu foil (99.9%, Alfa Aesar), each 100 μm thick, were placed on the upper and lower sides of the coin to overlap each other, and the ohmic contact layer was solid-state bonded by applying a pressure of 50 MPa for 10 minutes while creating an Ar atmosphere in a hot press sintering device and changing the temperature to 450°C.

[0080] Subsequently, Mg3Sb was solid-state bonded with Mg foil and Cu foil. 2-x Bi x The coin was cut into 2 mm × 2 mm length and width using a wire saw to complete the thermoelectric leg.

[0081] <Comparative Example 1> Solid-state bonding conditions: 500 ℃, 10 minutes, 50 MPa

[0082] In Comparative Example 1, a thermoelectric material was manufactured using the same method as Example 1, but only the temperature condition during solid-state bonding was changed to 500°C.

[0083] <Comparative Example 2> Solid-state bonding conditions: 400 ℃, 10 minutes, 50 MPa

[0084] In Comparative Example 2, a thermoelectric material was manufactured using the same method as Example 1, but only the temperature condition during solid-state bonding was changed to 400°C.

[0085] <Test Example 1> SEM Photo Analysis

[0086] In this test example, Mg3Sb 2-x Bi x The structural integrity of the bond required for the fabrication of a thermoelectric module was evaluated by performing solid-state bonding using a Mg-Cu double metal electrode layer, a new metallization process for thermoelectric materials.

[0087] First, when the solid-state bonded samples of Example 1, Comparative Example 1, and Comparative Example 2 were cut into leg shapes of width × length = 2 mm × 2 mm using a wire saw for SEM photography, it was observed that the bonding force between the thermoelectric material and the metal in the sample of Comparative Example 2 solid-state bonded at 400°C was weak, causing most of the metal foil to fall off. Therefore, SEM photography was not possible and was therefore excluded.

[0088] Figure 4 is an SEM photograph of a thermoelectric material according to Example 1, Mg3Sb 2-x Bi xIt shows a structure in which a first metal layer made of magnesium foil is placed on the upper and lower parts of the thermoelectric material, and a second metal layer made of copper foil is overlapped on the surface of the first metal layer. Cu-Mg-n type Mg3Sb formed through solid-state bonding at 450 ℃ 2-x Bi x -The thermoelectric leg with the Mg-Cu structure has a very flat interface, a double metal electrode layer with a uniform thickness, and an ohmic contact with almost no defects is confirmed.

[0089] Fig. 5 is an SEM photograph of a thermoelectric material according to Comparative Example 1, which shows a case where the same material was used but the bonding conditions were not optimized. In Comparative Example 1, only a single electrode layer was observed, and EDS analysis confirmed that it was Cu. The reason why the Mg electrode layer is not observed in Fig. 5 can be seen from the Cu-Mg phase diagram of Fig. 3. Among the three eutectic points in Fig. 3, the lowest temperature was 477°C, and it was determined that when solid-state bonding was performed at 500°C, a liquid phase mixed with Mg and Cu was formed, which was then lost to the outside of the sample by a pressure of 50 MPa.

[0090] Also in Fig. 5, Mg3Sb 2-x Bi x Although no delamination was observed at the interface between the thermoelectric material and the Cu electrode layer, microscopic defects and uneven electrode layer thickness were observed. These defects indicate a deterioration in the bonding quality between the n-type thermoelectric material layer and the Cu electrode layer. Therefore, the solid-state bonding of the Mg-Cu bimetallic electrode layer not only provides a high-quality bonding structure, but also demonstrates stability and reproducibility, which are important for industrial applications.

[0091] <Experimental Example 2> Potential-Seebeck Microprobe Analysis

[0092] In this test example, Mg3Sb 2-x Bi xWe performed a solid-state bonding process using a Mg-Cu dual metal electrode layer on a thermoelectric material, and evaluated the thermoelectric performance of the thermoelectric module fabricated through this process. Potential-Seebeck Microprobe analysis was used to confirm the distribution of the Seebeck coefficient at the bonding interface, and the influence of the bonding process on maintaining the polarity of the thermoelectric material and preventing changes in its composition was verified.

[0093] Fig. 6 is the result of Potential-Seebeck Microprobe analysis on the thermoelectric material according to Example 1. Fig. 6 is a two-dimensional visualization of the distribution of Seebeck coefficient (S) for the thermoelectric leg according to Example 1 of Fig. 4 using Potential-Seebeck Microprobe, and Mg3Sb 2-x Bi x It shows that the n-type polarity is maintained uniformly throughout the thermoelectric material.

[0094] This means that the thermoelectric properties are stably maintained because the polarity conversion to p-type due to outdiffusion of Mg does not occur at the interface between the double metal electrode layer and the thermoelectric material layer through solid-state junction at 450 ℃, and no change in components due to Mg diffusion occurs.

[0095] Figure 7 is a distribution diagram of the Seebeck coefficient measurement values ​​of Figure 6. As shown in Figure 7, the Seebeck coefficient distribution also has a normal shape clearly divided into n-type thermoelectric material and metal, indicating that a normal solid-state junction between the thermoelectric material and the metal has been formed.

[0096] Figure 8 shows the results of Potential-Seebeck Microprobe analysis on the thermoelectric material according to Comparative Example 1. Figure 8 shows the results of two-dimensional mapping of the Seebeck coefficient using Potential-Seebeck Microprobe in the case of solid-state bonding at 500°C, and the analysis results show that Mg3Sb 2-x Bi x An uneven distribution of the Seebeck coefficient is observed between the thermoelectric material and the metal. In particular, the Seebeck coefficient value appears to change rapidly near the interface between the thermoelectric material and the metal, which is attributed to excessive outdiffusion of Mg during solid-state bonding at 500°C, resulting in the formation of Mg3Sb. 2-x Bi x It appeared that this was because the thermoelectric material was partially converted to p-type.

[0097] <Test Example 3> Contact resistance analysis

[0098] In this test example, the interfacial contact resistance between the thermoelectric material layer and the metal electrode layer of the thermoelectric material manufactured according to Example 1 and Comparative Example 1 was analyzed. The thermoelectric material, which is a type of semiconductor material, and the electrode, which is a metal material, are different materials and resistance is generated through contact. This was confirmed through Figs. 9 and 10.

[0099] In relation to this, Fig. 9 is a graph analyzing the contact resistance of the thermoelectric material according to Example 1. Fig. 9 is a graph showing the results of measuring the voltage and Seebeck coefficient by line scanning the PSM in the direction perpendicular to the bonding interface for the cross-section of the thermoelectric material bonded in Example 1. The interface between the magnesium-copper double metal electrode layer and the thermoelectric material layer, where the Seebeck coefficient is close to 0, is clearly distinguished, and the sudden voltage difference at the location of the two interfaces is due to the contact resistance of the electrode and the thermoelectric material. As shown in Fig. 9, the voltage difference at the bonding interface between the thermoelectric material and the Mg foil was measured to be almost the same as 0.0014 mV, and since a current of 1 mA was passed when performing the PSM measurement, the Mg foil-n-type Mg3Sb with a cross-sectional area of ​​0.0384 ㎠ formed by the solid-state bonding 2-x Bi x The contact resistance of the thermoelectric material interface was calculated using the following calculation formula (1).

[0100] 0.0014 mV / 1 mA × 0.0384 ㎠ = 53.8 μΩ ㎠ … … … … … … … … … … … (1)

[0101] Through the calculation formula (1), the contact resistance of Example 1 is 53.8 μΩ ㎠. Considering that the contact resistance of 210 μΩ ㎠ when nickel is integrally sintered to the existing n-type bismuth telluride is quite high, the contact resistance value of 53.8 μΩ ㎠ according to Example 1 satisfies the condition of 100 μΩ ㎠ or less, and thus a good value of contact resistance can be obtained, confirming that the electrical resistance characteristics are good and that the industrial practicality is high.

[0102] Fig. 10 is a graph analyzing the contact resistance of a thermoelectric material according to Comparative Example 1. Fig. 10 shows the results of measuring the voltage and Seebeck coefficient in the vertical direction along the interface between the thermoelectric material and the electrode layer using a Potential-Seebeck Microprobe.

[0103] In the graph of Fig. 10, the interface between the thermoelectric material and the electrode layer is unclear, and an uneven voltage change is observed at the junction. This is confirmed to be due to a change in the composition of the thermoelectric material and an increase in contact resistance caused by excessive outdiffusion of Mg. The voltage difference is larger than in Fig. 9, and thus the contact resistance is measured to be relatively high. Therefore, Comparative Example 1 means that the thermoelectric performance and electrical characteristics at the junction interface were deteriorated because the bonding process conditions were not optimized.

[0104] Comparative Example 1 has only a Cu electrode layer without a Mg electrode layer, Cu foil-n type Mg3Sb 2-x Bi x The contact resistance of the thermoelectric material interface was calculated using the following formula (2).

[0105] 0.0029 mV / 1 mA × 0.0489 ㎠ = 1,418 μΩ ㎠ … … … … … … … … … … (2)

[0106] Through the calculation formula (2), the contact resistance of Comparative Example 1, in which the Mg electrode layer was lost, was 1,418 μΩ ㎠, which was a high interfacial contact resistance value that far exceeded 100 μΩ ㎠, compared to the contact resistance of the thermoelectric material having the Mg electrode layer (first metal layer) and the Cu electrode layer (second metal layer) of Example 1, which was 53.8 μΩ ㎠. It was confirmed that this resulted in poor electrical resistance characteristics and low industrial practicality.

[0107] In summary, the present invention relates to a thermoelectric material in which an n-type thermoelectric material layer including magnesium (Mg), antimony (Sb), and bismuth (Bi), a first metal layer including magnesium in a foil form on the surface thereof, and a second metal layer including the remaining metal except for the magnesium of the first metal layer are sequentially laminated, and in some cases, a third metal layer is further laminated on the surface of the second metal layer, and a method for manufacturing the same, wherein the n-type thermoelectric material layer and the metal electrode layer are solid-state bonded through heating and pressing, and thus have the characteristic of lowering the interface contact resistance between the n-type thermoelectric material layer and the metal electrode layer.

[0108] According to these characteristics, the resistance occurring at the bonding interface between the n-type thermoelectric material layer and the metal electrode layer can be minimized, so that excellent electrical performance can be secured, and the stability of thermoelectric performance can be maintained by preventing component change or polarity switching due to outdiffusion of Mg during the bonding process.

[0109] Through this, the bonding quality is improved during the production of a thermoelectric module, and a contact resistance of less than 100 μΩ ㎠, which is lower than that of existing n-type bismuth telluride-based thermoelectric materials, can be realized, which is of great significance in terms of industrial practicality.

[0110] In addition, by setting the solid-state junction temperature to less than 477 ℃, deterioration and structural defects of the thermoelectric material can be minimized.

[0111] Therefore, the present invention is Mg3Sb 2-x Bi x By forming a metal electrode layer very simply through a solid-state bonding method using magnesium foil on a thermoelectric material layer, an ohmic junction with high electrical conductivity can be obtained, and a thermoelectric module with excellent thermoelectric performance and high reliability can be realized. Therefore, it is expected that the thermoelectric material will be able to secure competitiveness in commercial application and mass production by replacing the n-type Bi2Te3 thermoelectric material in the future.

[0112] The above description is merely an illustrative description of the technical idea of ​​the present invention, and those skilled in the art will appreciate that various modifications and variations can be made without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of ​​the present invention, but rather to illustrate it, and the scope of the technical idea of ​​the present invention is not limited by these embodiments. The scope of protection of the present invention should be interpreted by the claims, and all technical ideas within a scope equivalent thereto should be interpreted as being included in the scope of the rights of the present invention.

Claims

1. An n-type thermoelectric material layer containing magnesium (Mg), antimony (Sb), and bismuth (Bi); and A metal electrode layer disposed on the surface of the n-type thermoelectric material layer; The above metal electrode layer, A first metal layer including magnesium in the form of a foil and a second metal layer including the remaining metal except for the magnesium of the first metal layer are sequentially laminated and formed. An n-type Mg-Sb-Bi thermoelectric material in which the metal electrode layer is solid-state bonded, characterized in that the n-type thermoelectric material layer and the metal electrode layer are solid-state bonded through heat compression.

2. In paragraph 1, The second metal layer is, An n-type Mg-Sb-Bi thermoelectric material characterized by a solid-state bonding of a metal electrode layer, wherein the metal foil is made of one of copper, nickel, and a copper-nickel alloy.

3. In paragraph 2, The above metal electrode layer, An n-type Mg-Sb-Bi thermoelectric material having a solid-state bonded metal electrode layer, characterized in that it further comprises a third metal layer formed by further arranging, on the surface of the second metal layer, a metal foil made of one of copper, nickel, and a copper-nickel alloy, the remaining metal foils excluding the metal foil selected from the second metal layer.

4. In paragraph 1, The above solid state joint is, An n-type Mg-Sb-Bi thermoelectric material characterized in that the metal electrode layer is solid-state bonded through heat pressing at a maximum temperature of less than 477°C.

5. In paragraph 1, The above n-type thermoelectric material layer is, An n-type Mg-Sb-Bi thermoelectric material having a solid-state bonded metal electrode layer, characterized in that it satisfies the following chemical formula 1: [Chemical Formula 1] Mg3Sb 2-x Bi x (However, in the above chemical formula 1, x is 0 < x < 2.) 6. In paragraph 1, The interfacial contact resistance between the above-mentioned solid-state bonded n-type thermoelectric material layer and the above-mentioned metal electrode layer is An n-type Mg-Sb-Bi thermoelectric material having a solid-state bonded metal electrode layer, characterized in that the maximum is 100 μΩ ㎠ or less.

7. A first step of manufacturing an n-type thermoelectric material layer by mixing and sintering magnesium (Mg), antimony (Sb), and bismuth (Bi); and A second step of forming a metal electrode layer by sequentially stacking a first metal layer including magnesium in a foil form on the surface of the n-type thermoelectric material layer and a second metal layer including the remaining metal except for the magnesium of the first metal layer; The second step above is, A method for manufacturing an n-type Mg-Sb-Bi thermoelectric material with a metal electrode layer in a solid state, characterized in that the n-type thermoelectric material layer and the metal electrode layer are solid-state bonded through heat pressing.

8. In paragraph 7, The above solid state joint is, A method for manufacturing an n-type Mg-Sb-Bi thermoelectric material having a solid-state bonded metal electrode layer, characterized in that the method is performed through heat pressing at a maximum temperature of less than 477°C.

9. In paragraph 7, The above n-type thermoelectric material layer is, A method for manufacturing an n-type Mg-Sb-Bi thermoelectric material having a solid-state bonded metal electrode layer, characterized in that it satisfies the following chemical formula 1: [Chemical Formula 1] Mg3Sb 2-x Bi x (However, in the above chemical formula 1, x is 0 < x < 2.) 10. In paragraph 7, The interfacial contact resistance between the above-mentioned solid-state bonded n-type thermoelectric material layer and the above-mentioned metal electrode layer is A method for manufacturing an n-type Mg-Sb-Bi thermoelectric material having a solid-state bonded metal electrode layer, characterized in that the thickness is 100 μΩ ㎠ or less.

11. In paragraph 7, The second metal layer of the second step is, A method for manufacturing an n-type Mg-Sb-Bi thermoelectric material having a solid-state bonded metal electrode layer, characterized in that the metal foil is made of one of copper, nickel, and a copper-nickel alloy.

12. In paragraph 11, The second step above is, A method for manufacturing an n-type Mg-Sb-Bi thermoelectric material with a solid-state bonded metal electrode layer, characterized in that a third metal layer is further laminated on the surface of the second metal layer, and the third metal layer is made of a metal foil selected from among copper, nickel, and a copper-nickel alloy, and then solid-state bonded.

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