JPH06310766A - Thermionic material and production thereof - Google Patents

Abstract

PURPOSE:To enhance the performance of thermionic material by employing a microstructure finer than a specific level in the arranging direction of at least second material among a plurality of materials having thermionic characteristics. CONSTITUTION:An FeMnSi2 layer 13 of single layer thin film and a layer 14 principally comprising SiO2 are laminated alternately, while being shifted laterally, on an inclining glass substrate 9 formed by evaporation substances entering through the end part of a slit. Consequently, a structure where the normal 15 of each single layer thin film is not aligned with the normal 16 of the laminated thin film, i.e., a structure inclining against the surface of the substrate, is brought about. In this regard, at least one of the single layer thin films 13, 14 has thickness of 1000Angstrom or below. In the filming method where the film part is shifted sequentially, thickness of the single layer films 13, 14 can be controlled relatively accurately by regulating the filming time while ensuring the compositional steepness of the interface between the single layer films.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric material used as a basic constituent material for temperature measurement, heat pumps, generators and the like, and a method for producing the same.

[0002]

2. Description of the Related Art As a parameter representing the performance of a thermoelectric material, there is a performance index Z derived from the Zeebeck coefficient S, the electrical conductivity σ and the thermal conductivity λ (Z = S ² σ / λ). According to the classical theory of thermoelectric phenomena of semiconductors, there is an inverse correlation between the Zeebeck coefficient S and the logarithm of the conductivity σ.
It was difficult to obtain a material having a large value, that is, a material having a large Zeebeck coefficient S and a large electric conductivity σ. As a result, Z was 3 × 10 ⁻³ / K in the Bi—Te system as the thermoelectric material exhibiting the largest performance index in the past.

On the other hand, when a fine structure (non-homogeneous structure) having a size approximately equal to the mean free path of phonons or charge carriers quantized by thermal vibration exists in the thermoelectric material, transport phenomena such as thermoelectric phenomenon occur. It cannot be handled by the usual thermoelectric phenomenon theory,
It is possible to obtain materials with a high figure of merit. In line with such an idea, fine particles (up to 100
(nm) is dispersed in another matrix material, and conversely, a structure in which fine particles such as boron nitride are dispersed in a semiconductor can provide a thermoelectric material having a large Zebeck coefficient and conductivity. Has been done. Ion engineering techniques such as ion cluster beam (ICB) have been proposed as means for achieving such a fine structure. Further, as a method for obtaining a fine structure of 10 angstrom to 1 μm order with good controllability, there is a thin film laminating method used for superlattice fabrication.

[0004]

Since the conventional thin film laminating method can obtain only a laminated structure of a single-layer thin film parallel to the substrate surface, the direction of current or heat flow when used as a thermoelectric material is set to the substrate surface. It cannot be vertical. Further, in a fine structure in which fine particles are dispersed in another material, it is difficult to quantitatively control the fine structure, such as the size of fine particles and the distance between fine particles. Furthermore, a manufacturing method for forming an ideal thermoelectric material has not been found, such as the crystallinity of the particles changing during the generation of the particles or the dispersion process.

Therefore, an object of the present invention is to provide a thermoelectric material having a fine structure capable of realizing higher performance. Another object of the present invention is to provide a method for producing a thermoelectric material having a fine structure whose size can be controlled quantitatively. Further, the present invention provides a thermoelectric material composed of laminated thin films in which each single-layer thin film is inclined with respect to the substrate, and a method for producing the same.

[0006]

The thermoelectric material of the present invention has a periodicity of a plurality of types of materials including a first material having thermoelectric properties and a second material having thermoelectric properties different from those of the first materials. And having at least the second material having an individual size of 100 in the arrangement direction.
It has a fine structure of 0 angstrom or less. In addition, one of the manufacturing methods for obtaining the above thermoelectric material is to irradiate a thin film made of a single material having a thermoelectric effect with stripes of ions having a high kinetic energy to form a thin film having fine parts with different thermoelectric properties. It is a method of reforming into a striped pattern including.

Further, the thermoelectric material of the present invention has a plurality of single-layer thin films including a thin film of a first material having a thermoelectric property and a thin film of a second material having a thermoelectric property different from that of the first material. Each of the single-layer thin films is formed of a laminated thin film so that its normal line does not coincide with the normal line of the laminated thin film. Further, the method for producing a thermoelectric material comprising this laminated thin film is
This is a method of manufacturing by moving the formation site of each single-layer thin film so as to be parallel to and partially overlap with the substrate surface during thin film formation.

[0008]

The Zeebeck effect is a phenomenon in which an electromotive force is generated in proportion to the temperature difference when a temperature difference occurs between two points of the conductive material. Then, this electromotive force is due to the density of the charge carrier-concentration that occurs as a result of movement of the charge carrier in order to make the free energy of the charge carrier constant in the material, and the scattering phenomenon of the charge carrier. There is a term due to temperature dependence, or a heat flow from a high temperature portion to a low temperature portion, that is, generated by interaction of a phonon flow and a charge carrier. Among these factors, the factors resulting from the scattering phenomenon of charge carriers and the interaction with phonons are such that the size of the thermoelectric material to be constructed is about the same as their mean free path (several hundred to 1,000 angstroms). , And strongly depends on its size.

The present invention focuses on this point, and configures the size and quality of the fine structure by controlling the film thickness and the film forming portion so that the scattering phenomenon and interaction of charge carriers and the like become good. By doing so, high thermoelectric properties are obtained. The present invention relates to a material having a fine structure that enables high thermoelectric properties as described above and a manufacturing method thereof, and basically, except that the type of the thermoelectric material to be formed can be formed into a film. But not limited to
In addition to the Fe-Si-based materials shown in the following examples, Sb-
Well-known materials in this field, such as annealed Bi ₂ Te _3, can be widely used.

[0010]

EXAMPLES Examples of the present invention will be described in detail below. Example 1 First, Fe _0.985 Mn _0.015 Si ₂ was formed into a film having a thickness of 1 to ₂ μm by a sputtering method on a hard glass substrate having a thermal expansion coefficient substantially equal to that of the Fe—Si-based material. Using a sintered body of Fe _0.985 Mn _0.015 Si ₂ as a _target , the substrate temperature was 200 ° C., and sputtering was performed with Ar at 300 W for 30 minutes. As a result of X-ray diffraction of the obtained thin film, it was confirmed that the thin film was in an amorphous state.
Next, a striped mask pattern with a minimum width of 1 μm was formed by a normal semiconductor manufacturing process, and the striped portion was removed by chemical etching. Furthermore, change the target to Si,
Oxygen was mixed into Ar as a sputtering gas to carry out reactive sputtering to form a striped portion mainly composed of SiO ₂ .

FIG. 1 shows a schematic view of a cross section of the obtained thin film. _{Reference numeral} 1 is a layer of Fe _0.985 Mn _0.015 Si ₂ which is a thermoelectric material, and 2 is a layer whose main component is SiO ₂ having different thermoelectric properties, which are alternately arranged on the glass substrate 3. The width of the top of layer 2 is 1 μm. Next, the results of measurement of thermoelectric properties in the direction crossing the striped structure of this thin film are shown in FIG.
Is shown by the curve A. The thermoelectric material according to the present invention has slightly lower conductivity than the thin film of Fe _0.985 Mn _0.015 Si ₂ shown by curve B, but the Zeebeck coefficient is greatly increased. As shown in FIG. 1, the conductivity did not decrease so much that the distance between the striped layers 1 was 1 in the deep portion of the thin film.
It is thought that it was closer than μm. However, when the etching time was lengthened or the width of SiO ₂ was increased too much, the conductivity of the film was extremely lowered and the Zeebeck coefficient was also decreased.

[Embodiment 2] Fe _0.985 Mn _0.015 Si ₂ obtained by a sputtering method and β-phased in the same manner as in Embodiment 1
Stripe-shaped boron ions (B
³⁺ ) was injected. The B ³⁺ ion beam accelerated to 1 to ³ MeV was squeezed to a diameter of 3 μm or less and irradiated in stripes at intervals of 10 μm. The conductivity of the portion injected with boron was considerably reduced, but the thermoelectric property was such that the conductivity did not significantly decrease, and
Beck coefficient improved. From this example, it is considered that the thermoelectric characteristics can be further improved by optimizing the ion species to be injected and the acceleration energy. In addition,
The ion beam irradiation can be patterned by using a slit having an ion beam shielding property.

Although the above-mentioned embodiment has a fine structure in which a material having a high thermoelectromotive force and a material having a low electric conductivity are alternately arranged in series, other materials having different thermoelectric properties such as Zeebeck coefficient are used. It has been found that the thermoelectric properties can be improved by arranging in series in one direction with a periodicity and making the size of at least the material inferior in the thermoelectric properties in the arranging direction a fine structure. The mean free path of charge carriers and phonons that cause thermoelectric phenomena is several μm at the longest, although it depends on the temperature. As a material having higher thermoelectric properties, it is considered desirable to have a finer periodic structure in the direction of heat flow or current. Therefore, an example using a film forming method which is finer and has higher structure controllability than the method using etching or ion beam is shown below.

[Embodiment 3] FIG. 3 shows a schematic structure of a film forming apparatus. Two targets 5 and 6 are arranged in a chamber-4, and a support 8 is provided below the targets 5 so as to slide back and forth on a pedestal 7, and a substrate 9 on the support occupies both targets. It is configured so that it can travel back and forth. Reference numeral 10 denotes a shutter drive device provided on the support base 8, and this device moves the shutter 11 on the substrate 9 back and forth. The shutter 11 is made of stainless steel, and slit holes 12 having a width of 10 μm are opened at intervals of 50 μm. Fe _0.985 Mn _0.015 Si ₂ was used as the target 5 and Si was used as the target 6, so that Ar and Ar + O ₂ could be introduced as the sputtering gas.

Thus, the sputtering of the Fe _0.985 Mn _0.015 Si ₂ target with the Ar gas was performed in the A mode and Si.
Sputtering the target with Ar + O ₂ gas B
Mode, the film formation was repeated for 5 minutes alternately in A mode and B mode. Meanwhile, the shutter drive device 10
The stainless steel shutter 11 was moved by 2 μm relative to the substrate 9 in synchronization with each mode. Film formation was performed for 150 minutes in total until the film formation part through one slit completely overlaps the film formation part by the adjacent slit.

FIG. 4 schematically shows a cross-sectional view of a thin film formed by this method in a direction perpendicular to the substrate. Fe _0.985 Mn _0.015 S, which is a single-layer thin film, is formed on the slope formed by the wraparound of the vapor deposition material from the slit end.
The i ₂ layer 13 and the SiO ₂ -based layer 14 are laterally displaced while being alternately laminated on the glass substrate 9, so that the normal 15 of each single-layer thin film is the normal 16 of the laminated thin film. It has a structure that does not coincide with the above, that is, a structure that is inclined with respect to the substrate surface. The film thickness of each single layer thin film was 500 to 1000 angstroms. According to the film forming method in which the film forming parts are sequentially moved, 1) the film thickness of each single layer film can be controlled relatively accurately by adjusting the film forming time. 2) It has excellent characteristics such as ensuring compositional steepness at the interface between single layer films. The Seebeck coefficient and conductivity measured in the moving direction of the shutter are shown in FIG.
Expressed as Curve b represents the characteristics of a single layer film of Fe _0.985 Mn _0.015 Si ₂ . According to the present invention, it was confirmed that the Seebeck coefficient can be significantly improved, although the conductivity is almost unchanged.

[0017]

According to the present invention, the performance of the thermoelectric material can be improved and the usefulness of the thermoelectric material can be further enhanced.

[Brief description of drawings]

FIG. 1 is a schematic view showing a cross section of a thermoelectric material according to an embodiment of the present invention.

FIG. 2 is a diagram showing characteristics of a thermoelectric material according to an example of the present invention in comparison with a conventional example.

FIG. 3 is a cross-sectional view showing a schematic configuration of a thermoelectric material manufacturing apparatus used in one example of the present invention.

FIG. 4 is a cross-sectional view of a thermoelectric material formed into a film according to an embodiment of the present invention.

FIG. 5 is a diagram showing characteristics of a thermoelectric material formed according to an example of the present invention in comparison with a conventional example.

[Explanation of symbols]

 1 substrate 2 layer of first material having thermoelectric properties 3 layer of second material having different thermoelectric properties 5, 6 target 8 substrate support 9 substrate 10 shutter drive device 11 shutter 12 slit 13 first layer having thermoelectric properties Thin film of material 14 Thin film of second material with different thermoelectric properties 15 Normal line of single layer thin film 16 Normal line of laminated thin film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akiko Nakasuji 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A plurality of types of materials including a first material having thermoelectric characteristics and a second material having different thermoelectric characteristics from the first material are arranged sequentially in one direction with periodicity. And the size of at least the second material in the arrangement direction is 10 or more.
A thermoelectric material having a fine structure of 00 angstroms or less. 2. A thin film made of a single material having a thermoelectric effect is irradiated with ions having a high kinetic energy in a striped pattern to modify the thin film into a striped pattern containing fine portions having different thermoelectric properties. The method for producing a thermoelectric material according to claim 1. 3. A laminated thin film formed by accumulating a plurality of single-layer thin films including a thin film of a first material having thermoelectric properties and a thin film of a second material having different thermoelectric properties from the first material, and The thermoelectric material, wherein each of the single-layer thin films is formed so that its normal line does not coincide with the normal line of the laminated thin film. 4. A thermoelectric material comprising a laminated thin film obtained by accumulating a plurality of single-layer thin films including a thin film of a first material having thermoelectric properties and a thin film of a second material having different thermoelectric properties from the first material. A method of manufacturing, wherein when forming each of the single-layer thin films forming the laminated thin film, the thin-film forming portion is moved parallel to the substrate surface so that the respective single-layer thin films partially overlap. Item 4. A method for producing a thermoelectric material according to Item 3.