WO2002021608A1

WO2002021608A1 - Thermoelement

Info

Publication number: WO2002021608A1
Application number: PCT/JP2001/007362
Authority: WO
Inventors: Takao Abe
Original assignee: Shin-Etsu Handotai Co., Ltd.
Priority date: 2000-09-04
Filing date: 2001-08-28
Publication date: 2002-03-14
Also published as: JP2002076448A

Abstract

A thermoelement having a structure capable of increasing the durability of connection parts between the electrodes and wirings of thermoelectric materials against a heat cycle applied to a high temperature side when the thermoelement is used as a thermoelement for use on the ground and providing an excellent thermoelectric performance, comprising the connection parts having the electrodes and wirings of a plurality of thermoelectric materials electrically connected to each other and formed of a structure having the electrodes, wirings, and connection parts disposed at two positions, low temperature and high temperature sides, wherein at least the high temperature side connection parts of the connection parts are formed so that the wirings and electrodes are electrically connected to each other by contact without being integrated with each other.

Description

Description Thermoelectric element Technical field

The present invention relates to a connection structure between a thermoelectric material electrode and a wiring in a thermoelectric element, and particularly to a connection structure and a wiring suitably used for a thermoelectric element using a silicon-germanium (SiGe) -based thermoelectric material. The present invention relates to a thermoelectric element having a material. Background art

When a P-type semiconductor material and an n-type semiconductor material are joined at two locations and a temperature difference is applied between the two locations, a thermoelectric power is generated between the two locations due to the so-called Seebeck effect. I do.

Thermoelectric elements that apply this principle have no moving parts and have a simple structure.Therefore, there is a high possibility that a thermoelectric element with high reliability, a long service life, and easy maintenance can be used. . For this purpose, various thermoelectric element materials have been conventionally manufactured and developed.

Among them, SiGe is known as a chemically stable and typical thermoelectric element material, and many proposals have been made for improving its performance and manufacturing methods [JP-A-6-11-1]. No. 494553 (U.S. Pat.No. 4,711,971; European Patent No. 1,849,499); Japanese Unexamined Patent Publication No. H8-56020; Patent No. 2623 No.172 publication etc.].

As an example of a thermoelectric element (thermoelectric conversion module), the Voyager launched in 1981 was made of a thermoelectric material made by sintering Si and Ge powder by hot pressing. The formed thermoelectric element uses fission as a heat source Used for space applications. In addition, ground-based applications have been developed for thermal power generation, or as thermoelectric generators that use vehicle exhaust heat or combustion heat as a heat source.

FIG. 2 is a schematic explanatory view showing a general cross-sectional structure of such a conventional thermoelectric element (thermoelectric conversion module).

In FIG. 2, reference numeral 30 denotes a conventional thermoelectric element, in which a plurality of thermoelectric materials, that is, a p-type thermoelectric semiconductor 32 and an n-type thermoelectric semiconductor 34 are electrically connected via a high-temperature side wiring 36 and a low-temperature side wiring 38. High-temperature side connections 32a, 34a and high-temperature side electrodes 33a, 35a, and low-temperature side connections 32b, 34b and low-temperature side electrodes 33b, 35 has b. In addition, 40 is a high-temperature side substrate, 42 is a low-temperature side substrate, 44 is a bonding agent and a bonding agent for bonding the wirings 36, 38 and the connecting portions 32a, 34a and 32b, 34b. Numeral 6 denotes a heat insulating insulator such as silicate glass for welding between the p-type thermoelectric semiconductor 32 and the n-type thermoelectric semiconductor 34.

The thermoelectric material conventionally intensification of S i G e based material, tellurium materials and such _{_{B i 2 T e 3 P b}} T e, such as iron Kei Motokei material such as F e S i ₂ is used Diffusion bonding, brazing, soldering, or bonding using a bonding agent made of a specific alloy can be used as a method of connecting the electrodes and wiring of these thermoelectric materials (Japanese Patent Application Laid-Open No. H11-16881). 72) was commonly used.

However, when used as ground-based thermoelectric elements such as for thermal power generation, there is a high-temperature thermal cycle of about 500 to 100 ° C at the high-temperature side connection-between the thermoelectric material electrode and wiring. Thermal strain occurred, and durability was a problem. Particularly in the case of a thermoelectric material having a large coefficient of thermal expansion, a large stress is generated when the temperature rises and falls, so that the connection portion is easily broken. In the case of SiGe, despite its high thermoelectric performance, there was a problem in the durability of such a connection due to a large coefficient of thermal expansion, which hindered its practical use. Disclosure of the invention

The present invention has been made in view of such a problem, and the present invention has been made in consideration of a heat cycle applied to a high temperature side when used as a terrestrial thermoelectric element, in which a connection between an electrode of thermoelectric material and a wiring is provided. An object of the present invention is to provide a thermoelectric element having a structure capable of improving durability and having excellent thermoelectric performance.

In order to achieve the above object, a thermoelectric element of the present invention has a connection portion in which electrodes and wires of a plurality of thermoelectric materials are electrically connected, and the electrodes, the wires and the connection portions are connected to a low-temperature side. In a thermoelectric element having a structure divided into a high-temperature side and a high-temperature side, at least a high-temperature-side connection portion of the connection portions is electrically connected by contact without integrating the wiring and the electrode. It is characterized by the following.

As described above, if the electrodes of the thermoelectric material and the wiring are not integrated, and the contact is made to be in a uniform contact state, even if subjected to a thermal cycle, no destruction due to a difference in thermal expansion coefficient occurs. A stable conduction can be obtained.

At this time, it is preferable that at least the high-temperature side wiring be formed on a PBN (pyroboron nitride) plate. In this way, PBN has high rigidity even at high temperatures, so it is possible to avoid poor contact between electrodes and wiring. In addition, since it is a material that is transparent to heat rays, the connection part on the high-temperature side can be efficiently heated to high temperatures. can do.

In addition, it is preferable to use a PG (pyrographite) film as a wiring material at least on the high-temperature side. Since the PG film is a good electrical conductor at high temperatures, it does not cause a decrease in thermoelectric efficiency, and since it is an absorber for heat rays, the connection portion on the high temperature side can be heated to higher temperatures more efficiently. As a thermoelectric material constituting the thermoelectric element, it is preferable to use a silicon-germanium-based material capable of obtaining high thermoelectric performance. In order to obtain higher thermoelectric performance, the silicon-germanium-based material is preferably a polycrystal having a large particle size, and more preferably a single crystal. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic explanatory view showing a cross-sectional structure of one embodiment of the thermoelectric element of the present invention.

FIG. 2 is a schematic explanatory view showing an example of a cross-sectional structure of a conventional thermoelectric element. BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described with reference to the drawings, taking a SiGe crystal as an example, but it can be said that various modifications can be made to this embodiment without departing from the technical idea of the present invention. Not even.

FIG. 1 is a schematic explanatory view showing a cross-sectional structure of a thermoelectric element of the present invention. In FIG. 1, the same or similar members as those in FIG. 2 are denoted by the same reference numerals.

In FIG. 1, reference numeral 10 denotes a thermoelectric element according to the present invention, in which a plurality of thermoelectric materials, that is, P-type thermoelectric semiconductors 32 and n-type thermoelectric semiconductors 34 are electrically connected to the high-temperature side wiring 36 and the low-temperature side wiring 38. High-temperature side connections 32a, 34a and high-temperature side electrodes 33a, 35a, low-temperature side connection 32b, 34b and low-temperature side electrodes 33b, 35b The basic structure in which a high-temperature side substrate 40 is connected to the high-temperature side wiring 36 and a low-temperature side substrate 42 is connected to the low-temperature side wiring 38 is shown in FIG. There is no difference from the structure of the conventional thermoelectric element. In this structure, the P-type thermoelectric semiconductor 32 and the n-type thermoelectric semiconductor 34 alternate between the high-temperature side substrate 40 and the low-temperature side substrate 42 via the high-temperature side wiring 36 and the low-temperature side wiring 38. Placed in As the thermoelectric material in the present invention, that is, the p-type thermoelectric semiconductor 32 and the n-type thermoelectric semiconductor 34, SiGe crystals are suitably used. The S i G e crystals used are prepared by Chiyokurarusuki method, p-type or Formula was contained n-type dopant preparative _{_{S i t. X G e χ}} S i represented by (0 <X <1) It is a G e crystal. The Chiyokurarusuki method, approximately the size of the crystal grains over the entire X has a ⁵ X 1 0- 5 mm ³ or more, the number of performance finger high crystallinity as thermoelectric elements (polycrystalline or monocrystalline) is obtained (Japanese Patent Application No. 10-33 358 904). The obtained crystal is divided into, for example, a size of about 2 × 2 × 2 mm, and n-type SiGe crystal (n-type thermoelectric semiconductor) 32 and p-type SiGe crystal (p-type thermoelectric semiconductor) 34 Used as

In the structure of the conventional thermoelectric element 30 as shown in FIG. 2, the P-type and n-type thermoelectric semiconductors 32 and 34 are welded and fixed by a heat insulating insulator 54 such as silicate glass. ing.

However, taking into consideration that fixing the p-type and n-type thermoelectric semiconductors 32 and 34 as in the conventional structure of FIG. It has a structure in which the n-type thermoelectric semiconductors 32 and 34 are not fixed, for example, a structure in which a cavity 12 is provided. Reference numeral 14 denotes a hollow portion provided in the low-temperature substrate 42, and the temperature of the low-temperature substrate 42 can be adjusted by introducing a fluid, for example, air. In order to realize such a structure in which the p-type and n-type thermoelectric semiconductors 32, 34 unique to the present invention are not fixed, as shown in FIG. Forming protrusions 40a and 42a, respectively, to hold the p-type and n-type thermoelectric semiconductors 32 and 34 and the high-temperature and low-temperature wirings 36 and 38. What is necessary is just to comprise so that it may fit and hold via the part 40a and 42a. Thus, the thermoelectric material, that is, the electrode portions 33a, 35a and 33b, 35b at both ends of the p-type and n-type thermoelectric semiconductors 32, 34 are formed. Unlike the conventional structure shown in Fig. 2 in which the high-temperature side wiring and low-temperature side wiring 36, 38 are joined together with a bonding agent 44 as in the conventional structure shown in Fig. 2, they can be fixed without being integrated. it can.

In this way, the electrodes 33a, 33b and 35a, 35b of the thermoelectric materials 32, 34 and the wirings 36, 38 are not integrated with the wirings 36, 38, but the ohmic contact is obtained by contact. In this manner, even when subjected to a thermal cycle, the contact portion relaxes the thermal stress, so that the effect of the present invention that stable conduction can be obtained without causing destruction due to a difference in thermal expansion coefficient is obtained.

Also, in order to obtain a good ohmic contact by contact without being integrated, the thermoelectric material in contact with the high-temperature side wiring 36, that is, the surface of the p-type thermoelectric semiconductor 32 and the surface of the n-type thermoelectric semiconductor 34, It is preferable to form an alloy of a high melting point metal such as Ti, W, Mo and Ta, a laminated film, a silicide or the like as an electrode. Also, by using a low-resistivity thermoelectric material, that is, a p-type thermoelectric semiconductor 32 and an n-type thermoelectric semiconductor 34, the surface can be directly contacted with the wiring as an electrode without forming such a film. Although it is possible to take an ohmic contact, in that case, if a natural oxide film is formed on the surface of the thermoelectric material, that is, the p-type thermoelectric semiconductor 32 and the n-type thermoelectric semiconductor 34, a good ohmic contact is obtained. Therefore, it is desirable to remove the natural oxide film on the surface as much as possible by hydrofluoric acid treatment or the like.

As a material for forming the high-temperature side wiring 36, a PG film is preferable. PG (Pyrographite) is a pyrolytic graphiteite obtained by laminating multiple graphiteite layers by chemical vapor deposition, and it is a good electrical conductor at high temperatures and therefore reduces thermoelectric efficiency. Since it is a low heat absorber, it can efficiently transfer external heat. It is appropriate that the thickness of the PG film used is about 0.1 to 1 mm.If PG is also used for the wiring 38 on the low temperature side, the thickness on the high temperature side should be considered in consideration of heat conduction. It is preferable that the thickness be smaller.

As the high temperature side substrate 40, it is preferable to use a PBN plate. PBN (pyroboron nitride) is a pyrolytic boron nitride layer obtained by stacking multiple boron nitride layers by chemical vapor deposition, and is stable at high temperatures up to 180 ° C. Because it is an insulator and has high rigidity even at high temperatures, the high-temperature side wiring 36 and the thermoelectric material, that is, the electrodes 33a, 33b and p-type thermoelectric semiconductor 32 and n-type thermoelectric semiconductor 34 electrodes不良 In addition to avoiding poor contact with 35a and 35b, and because it is a material that is transparent to heat rays, high-temperature side wiring 36 and thermoelectric materials, that is, p-type thermoelectric semiconductors 32 and n-type The thermoelectric semiconductor 34 can be efficiently heated to a high temperature. The thickness of the PBN plate to be used is preferably from 0.1 to: Lmm. '

PG and PBN can be used as the material of the low-temperature side wiring 38 and the low-temperature side substrate 42 as in the case of the high-temperature side, but the high melting point metal such as Ti, W, Mo, and Ta described above is used. In addition to alloys, laminated films, and silicides, metals such as Cu, Al, Au, Ni, and Pt can also be used.

In addition, since the thermal strain at the low temperature side is smaller than that at the high temperature side, it can be integrated as in the past depending on the combination and temperature of the thermoelectric material, electrode material and wiring material. Industrial applicability

INDUSTRIAL APPLICABILITY As described above, according to the present invention, it is possible to improve the durability of a connection portion between an electrode and wiring of a thermoelectric material against a heat cycle applied to a high temperature side when used as a ground thermoelectric element. A thermoelectric element having a structure and excellent thermoelectric performance can be obtained, and the use of the thermoelectric element can be expanded.

Claims

The scope of the claims

1. A thermoelectric element having a connection part in which electrodes and wirings of a plurality of thermoelectric materials are electrically connected, and having a structure in which the electrodes, the wirings, and the connection parts are divided into a low-temperature side and a high-temperature side. 3. The thermoelectric element according to claim 1, wherein at least the high-temperature side connection portion of the connection portions is electrically connected by contact without integrating the wiring and the electrode.

2. The thermoelectric element according to claim 1, wherein at least the high-temperature side wiring is wired on a PBN (pyroboron nitride) plate.

3. The thermoelectric element according to claim 1, wherein at least the high-temperature-side wiring is a PG (pyrographite) film.

4. The thermoelectric element according to any one of claims 1 to 3, wherein the thermoelectric material is a silicon-germanium-based material.

5. The thermoelectric element according to claim 4, wherein the silicon-germanium-based material is single crystal or polycrystal.