JP2001060727A - Method for manufacturing thermoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the orientation property of anisotropic thermoelectric materials in a thermoelectric element. SOLUTION: Conductive plastic materials such as Ag paste is added to anisotropic thermoelectric materials in a Bi-Te system or the like so that plastic thermoelectric materials can be obtained. Then, the plastic thermoelectric materials are repeatedly pressed so as to be extended 30 that crystal particles 30 can be oriented, and the anisotropic direction can be aligned to an X direction. Thus, the direction of the currents of the thermoelectric elements is aligned to the X direction so that the thermoelectric efficiency can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for manufacturing a thermoelectric element,
In particular, it relates to improving the orientation of an anisotropic thermoelectric material.

[0002]

2. Description of the Related Art Conventionally, a Peltier effect caused by flowing a current through a junction of a p-type semiconductor / metal / n-type semiconductor;
That is, thermoelectric elements utilizing heat absorption or heat generation at the joint surface have been developed, and application to local cooling of non-CFC refrigerators and electronic elements, or precise temperature control near room temperature is considered.

In order to form a thermoelectric element, it is necessary to form p-type and n-type thermoelectric materials into a desired shape, and press-mold the crystal grains of the thermoelectric material and then sinter them to obtain a polycrystalline thermoelectric material. An element was formed.

[0004]

As materials for thermoelectric elements, Bi-Te and the like are considered promising, but they are also known to have anisotropy at the same time.

FIG. 7 schematically shows a bonding structure of Bi ₂ Te ₃ crystal as an example. Bi and Te (1) are linked by a covalent bond and an ionic bond, and Bi and Te (2) are linked by a covalent bond. On the other hand, Te (1) and Te (1)
The space is relatively weakly joined by Van der Waals force, and the surface joined by this van der Waals force tends to be a cleavage surface.

FIG. 8 shows a cleaved Bi ₂ Te ₃ crystal fragment. In the figure, if the direction perpendicular to the cleavage plane is the c-axis, and the direction parallel to the cleavage plane and the direction perpendicular to the c-axis is the a-axis and b-axis, the crystal fragments easily grow in the a-axis direction and the b-axis direction. Since it is easily cleaved perpendicular to the axis, it is long in the ab axis direction. In addition, the figure of merit of the thermoelectric characteristics in the a-axis direction and the b-axis direction shows a value nearly twice as large as the figure of merit in the c-axis direction. Specifically, the figure of merit is Z (Z = α ² / ρ · λ)
Where α is the Seebeck coefficient, ρ is the specific resistance, λ is the thermal conductivity), and the figure of merit Zab in the a-axis or b-axis direction
And the ratio Zab / Zc between the figure of merit in the c-axis direction and Zc is about 2.
Sometimes it reaches 2.

As described above, when the thermoelectric material has anisotropy, it is important to improve the orientation by aligning the crystal orientation of each crystal in the thermoelectric material in order to obtain better thermoelectric characteristics.

Therefore, conventionally, sintering while pressing, that is, so-called hot pressing, has been performed to improve the crystal orientation. However, since the compression ratio in the press has a limit, the orientation of crystal grains is limited. However, there has been a problem that the thermoelectric properties cannot be sufficiently improved, and the thermoelectric properties inherent in the thermoelectric material cannot be efficiently revealed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has an object to improve the compression ratio more than the conventional hot press, thereby improving the orientation of crystal grains. An object of the present invention is to provide a manufacturing method that can make thermoelectric characteristics more obvious than before.

[0010]

In order to achieve the above object, a method of manufacturing a thermoelectric element according to the present invention comprises the steps of adding a conductive plastic material to an anisotropic thermoelectric material; Rolling the applied thermoelectric material.

Further, the rolling step is repeated a plurality of times.

In the rolling step, a plurality of the rolled anisotropic thermoelectric materials are stacked and further rolled.

[0013] The compression direction in the step of rolling is substantially perpendicular to the direction in which the anisotropic thermoelectric material is energized.

Further, the conductive plastic material is a viscous liquid or gel containing conductive particles.

Further, the conductive plastic material is an Ag paste.

However, the "anisotropic thermoelectric material" in the present invention
The term “having thermoelectric properties in particles” means that the particle shape is anisotropic.

As described above, in the present invention, the thermoelectric material is made plastic by adding the conductive plastic material. By making it plastic, the polycrystal can be more compressed than in the case of pressing without plasticity, and the crystal grains having anisotropy can be oriented in the same direction. The specific method of compressing the thermoelectric material provided with plasticity is rolling, and by applying a predetermined pressure from two opposing directions and extending thinly, the a and b axes of the crystal grains are perpendicular to the pressure application direction. Orientation. The material that imparts plasticity to the thermoelectric material needs to have conductivity so as not to impair the electrical characteristics of the thermoelectric element. By having conductivity higher than the grain boundary of the conventional polycrystalline body, the electrical characteristics of the thermoelectric element itself can be improved. Here, the conductivity is inherent to the material, that is, it always has conductivity in all steps including the rolling process, and the material itself does not show conductivity or shows little conductivity. Also, there is included a material that, when added to the thermoelectric material, chemically reacts with the thermoelectric material and changes its physical properties to make the conductivity obvious. Of course, a material which does not exhibit conductivity in the additional step, but exhibits conductivity due to a change in physical properties in a molding step including a subsequent rolling step may be used.

Preferably, the rolling step is repeated not only once but also a plurality of times. This increases the compression ratio,
The orientation of the crystal grains can be further improved. By compressing a plurality of rolled thermoelectric materials and further rolling them integrally, the compression ratio can be further increased. When a plurality of thermoelectric materials are rolled and stacked, the properties may be non-uniform at the overlapped boundary, but fusion between the plastic rolled bodies occurs and this effect is reduced, in addition to the compression direction, that is, When the direction in which the pressure is applied is substantially perpendicular to the direction in which the current is applied, the direction of the current is substantially parallel to the direction of the boundary, and the influence of the non-uniformity of the crystal at the boundary on the thermoelectric characteristics can be further suppressed. .

The conductive plastic material can be a viscous liquid or gel containing conductive particles. The viscosity of the viscous liquid or gel can impart plasticity to the thermoelectric material. Note that the gel refers to a gel obtained by solidifying a colloid solution in a jelly state, and can be formed into a conductive gel by using conductive particles as colloid particles. Further, an Ag paste can be used as the conductive plastic material. Ag paste is easily available, has excellent conductivity, and can impart plasticity to a thermoelectric material at low cost.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the overall configuration of a temperature control device using thermoelectric elements. A plurality of pairs of a p-type semiconductor element (thermoelectric element) 10 and an n-type semiconductor element (thermoelectric element) 12 are provided, one end of each pair is connected to each other by an electrode 14, and the other end of each pair is adjacent to an electrode 16. (A so-called π-type module). Therefore, the plurality of p-type semiconductor elements 10 and the n-type semiconductor elements 12 are electrically connected in series, and when a predetermined voltage is applied, a current flows as shown by a chain line in the figure.

Further, Al plates 18 and 19 are provided above the electrode 14 and below the electrode 16, and radiating fins 20 are further provided below the Al plate 19.

In such a configuration, when a current flows as indicated by a chain line in the figure, the p-type semiconductor element 10 and the Al plate 1
8 and the junction between the n-type semiconductor element 12 and the Al plate 18 generate heat absorption (or heat generation), and the Al plate 1
8 is cooled (or heated). For example, by mounting an electronic component on the Al plate 18, the electronic component can be cooled (or heated), and the cooling temperature (or the heating temperature) can be controlled by adjusting the amount of current. . Note that by reversing the direction of the current, it is possible to change from cooling to heating or from heating to cooling.

FIG. 2 is an enlarged view of a part (a part) in FIG. Ni plating 22 is formed below the p-type semiconductor element (thermoelectric element) 10,
The u electrode 16 is connected. Since the Al plate 19 needs to be insulated, the Al plate 19 is connected to the Cu electrode 16 via the alumite 26. Connection between p-type semiconductor element 10 and Al plate 18, and n-type semiconductor element 12 and Al plate 1
The same applies to the connection portions 8 and 19. Thermoelectric elements 10, 12
May have a prism shape of, for example, 3 mm × 3 mm × 5 mm.

As described above, it is necessary to mold the thermoelectric element into a desired shape. However, if the thermoelectric material is hot-pressed as in the prior art, the orientation of the crystal grain boundaries is not sufficient, and the thermoelectric properties and Further, the efficiency of the temperature control device in which the thermoelectric element is incorporated is reduced.

Therefore, in the present embodiment, instead of hot pressing, plasticity is given to the thermoelectric material by adding a conductive plastic material, and the plastic thermoelectric material is rolled to orient the crystal grains of the thermoelectric material. It is solidified by sintering and molded.

FIG. 3 schematically shows the state of rolling in the present embodiment. The thermoelectric material (A) which has become plastic by adding the conductive plastic material,
Rolling is performed by applying pressure from the direction. 8, the plate-like crystal grains 30 are the crystal grains shown in FIG. 8, and the longitudinal direction corresponds to the a and b axes in FIG. When rolled from the state of (A), the thermoelectric material is in a thinly stretched state as shown in (B), and is further thinned as shown in (C) by repeatedly rolling by applying pressure from the same direction. . In a plurality of rolling steps, the crystal grains 30 receive pressure and are oriented in a direction substantially perpendicular to the pressure application direction (the x direction in the figure), and by repeating the rolling step a further required number of times, almost all of the crystal grains are formed. The orientation can be aligned. Note that the smaller the particle size of the plastic material added to the thermoelectric material, the better.

FIG. 4 shows one method of rolling.
The thermoelectric material 32 to which plasticity has been imparted is sent to the rolling roller 34 at a constant feed speed, and the thermoelectric material 32 is rolled by rotating the rolling roller 34 at a predetermined speed, and is thinned (having a thickness equal to the gap between the rolling rollers 34). ) The extended thermoelectric material 36 is obtained. By using a plurality of rolling rollers 34 in which the gap between the rollers is appropriately adjusted, the thermoelectric material can be sequentially rolled. The number of times of rolling is the number of times necessary for causing no breakage of the thermoelectric material and sufficiently orienting the crystal grains, and can be appropriately set according to the content of the thermoelectric material or the plastic material.

The orientation can be improved by repeating rolling a single thermoelectric material a plurality of times. However, a plurality of thermoelectric materials compressed by a plurality of rollings are stacked, and the thermoelectric material is further stacked. By rolling, the compression ratio (or deformation ratio) can be further increased. FIG. 5 shows an example of such a case. A plurality of thermoelectric materials are prepared as shown in (A), and each is rolled as shown in (B). Then, a plurality of thermoelectric materials rolled as shown in (C) are stacked, and the stacked thermoelectric materials are further rolled as shown in (D). The number of thermoelectric elements stacked on each other may be three or more.

When the thermoelectric material rolled and oriented as described above is used as a thermoelectric element, as shown in FIG. 6, the orientation i (perpendicular to the compression direction and the x direction in FIG. 3) (Same direction) is parallel to the direction of current flow. Thereby, the figure of merit Z of the thermoelectric element can be increased, and the thermoelectric efficiency can be improved. Further, as shown in FIG. 5, when a plurality of thermoelectric materials are rolled while being overlapped, there is a possibility that the thermoelectric material becomes non-uniform at the overlapped boundary, but the boundary exists in parallel with the i direction in FIG. Does not affect the thermoelectric properties.

In the case of an anisotropic thermoelectric material in which thermoelectric properties are remarkably exhibited in a direction perpendicular to the orientation direction i, it is preferable that the electric current is supplied in a direction perpendicular to the orientation direction i. Needless to say.

Hereinafter, the manufacturing method will be described more specifically.
As the thermoelectric material, Bi-Te having anisotropy as described above is used.
For example, Bi _0.5 Sb _1.5 Te _{3 for} a p-type semiconductor device, Bi ₂ Te _2.7 Se ₀ ... For an n-type semiconductor device can be used _{. 3} + HgBr ₂ can be used. It is necessary that the plastic material has conductivity and does not lose its conductivity even after molding. Is also good. In addition, since it is a plastic material, it is preferably in the form of a paste, a viscous liquid or a gel, and for example, a room-temperature-curable Ag paste can be used. The addition amount of the plastic material can be, for example, 30 vol%. Ag paste is added to the thermoelectric material and sufficiently stirred.
The plate is 30 mm thick and 10 mm thick. Then, rolling is repeated about five times, and the sheet is compressed to a thickness of about 1 mm. Prepare ten flat thermoelectric materials obtained by rolling several times,
These are stacked and cut into a plane size of 30 mm × 30 mm. Then, the same rolling is performed on the 10 stacked
Repeat about once and compress again to a thickness of about 1 mm. Furthermore, 30 obtained plate-like thermoelectric materials are laminated, cut into a plane size of 30 mm × 30 mm, and rolled about 5 times to a thickness of 3 mm. The thermoelectric material rolled in this manner is cut into a plane size of 5 mm × 5 mm and a thickness of 3 mm.
The Ag paste is hardened at room temperature by leaving it for about an hour to harden the thermoelectric material.

In this embodiment, the thermoelectric material is solidified by using a room temperature curing paste to obtain a thermoelectric element. However, it goes without saying that the thermoelectric element may be solidified by molding into a predetermined shape and then sintering. .

The thermal conductivity of the plastic material should be as low as possible, preferably a material lower than the thermal conductivity of the thermoelectric material.

Further, the function of the plastic material is to impart the plasticity to the thermoelectric material so that the thermoelectric material can be rolled. Therefore, the plastic material disappears in, for example, the sintering process after the completion of the rolling process, and the final thermoelectric element is formed. It is also preferable to use a material that does not remain in the resin.

[0036]

As described above, according to the present invention,
The crystal orientation of the thermoelectric material having anisotropy can be improved, and the thermoelectric efficiency of the thermoelectric element can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a temperature control module using a thermoelectric element of an embodiment.

FIG. 2 is a partially enlarged configuration diagram of FIG. 1;

FIG. 3 is an explanatory view showing a rolling step of the embodiment.

FIG. 4 is an explanatory diagram illustrating a rolling method according to the embodiment.

FIG. 5 is an explanatory view showing another rolling step of the embodiment.

FIG. 6 is an explanatory diagram showing a relationship between an orientation and a current direction in the embodiment.

FIG. 7 is an explanatory diagram of a crystal structure of a Bi—Te-based thermoelectric material.

FIG. 8 is an explanatory diagram of crystal grains of a Bi—Te-based thermoelectric material.

[Explanation of symbols]

10 p-type semiconductor device, 12 n-type semiconductor device, 14,
16 electrodes, 18, 19 Al plate, 20 radiation fins,
30 crystal grains, 32 thermoelectric materials (before rolling), 34 rolling rollers, 36 thermoelectric materials (after rolling).

Claims (6)

[Claims] 1. A method for manufacturing a thermoelectric element, comprising: adding a conductive plastic material to an anisotropic thermoelectric material; and rolling the thermoelectric material plasticized by the conductive plastic material. A method for manufacturing a thermoelectric element, comprising: 2. The method according to claim 1, wherein the step of rolling is repeated a plurality of times. 3. The method according to claim 2, wherein, in the rolling step, a plurality of the anisotropic thermoelectric materials after rolling are stacked and further rolled. 4. The method according to claim 1, wherein a compression direction in the rolling is substantially perpendicular to a direction in which the anisotropic thermoelectric material is energized. Thermoelectric element manufacturing method. 5. The method according to claim 1, wherein the conductive plastic material is a viscous liquid or gel containing conductive particles. 6. The method according to claim 1, wherein the conductive plastic material is an Ag paste.