Patent Application
20140102500
The present application claims priority from Japanese Patent Application JP 2012-226858 filed on Oct. 12, 2012, the content of which is hereby incorporated by reference into this application.
The present invention relates to a thermoelectric device assembly with higher connection reliability between a thermoelectric device and an electrode, a thermoelectric module, and its manufacturing method.
A thermoelectric module that converts thermal energy to electric energy by the Seeback effect features the absence of a drive unit and the provision of a definite structure with no maintenance requirement. Such thermoelectric modules have been used only for products such as satellite power supplies because of its low conversion efficiency; meanwhile, such thermoelectric modules have received attention as a technique of collecting waste heat as thermal energy to realize an environmentally friendly society. The application of the technique to incinerators, industrial furnaces, and vehicle related products has been examined. Against this backdrop, thermoelectric modules with higher durability and higher conversion efficiency have been demanded at lower cost.
In a thermoelectric module, heat can be converted to electricity according to a temperature difference in a thermoelectric device. Thus, a stress is generated at a joint between the thermoelectric device and an electrode by a difference in coefficient of thermal expansion between the thermoelectric device and the electrode in an operating environment. This may cause a break at the joint or in the thermoelectric device. The stress generated thus increases with an ambient temperature or a difference in coefficient of thermal expansion between the thermoelectric device and a bonding material or the electrode.
It is known that thermoelectric devices have different temperature ranges with high conversion efficiency depending upon device materials. Moreover, a thermoelectric device may contain only one of a P-type material and an N-type material. Thus, in many cases, a combination of different device materials of P-type and N-type may constitute a thermoelectric module. Since coefficients of thermal expansion vary with device materials, a stress may concentrate at a connection between a device and an electrode because of a heat load during bonding and a temperature change during an operation. A stress at the connection may crack the device and the joint, considerably reducing the connection reliability.
The present invention provides a thermoelectric device assembly, a thermoelectric module, and its manufacturing method which can obtain high reliability and efficiently transmit a peripheral temperature to a thermoelectric device even at a high temperature or in an environment where a thermal stress is generated by a thermal cycle.
In order to solve the problem, the present invention is a thermoelectric device assembly including a P-type thermoelectric device and an N-type thermoelectric device that are electrically connected in series via an electrode member, wherein the electrode member has a portion connected to the P-type thermoelectric device according to the coefficient of thermal expansion of the P-type thermoelectric device and a portion connected to the N-type thermoelectric device according to the coefficient of thermal expansion of the N-type thermoelectric device, and the connected portion of the electrode to the P-type thermoelectric device and the connected portion of the electrode to the N-type thermoelectric device are made of different materials.
The present invention is a thermoelectric module including multiple P-type thermoelectric devices and multiple N-type thermoelectric devices that are alternately disposed so as to be electrically connected in series, wherein each of the electrode members has a portion connected to each of the P-type thermoelectric devices according to the coefficient of thermal expansion of the P-type thermoelectric devices and a portion connected to each of the N-type thermoelectric devices according to the coefficient of thermal expansion of the N-type thermoelectric devices, and the connected portion of each of the electrode members to each of the P-type thermoelectric devices and the connected portion of each of the electrode members to each of the N-type thermoelectric device are made of different materials.
In order to solve the problem, a method of manufacturing a thermoelectric module according to the present invention includes the steps of: disposing multiple electrode members, each being made of at least two materials with a first area composed of a first material joined to one of P-type thermoelectric devices according to the coefficient of thermal expansion of the P-type thermoelectric devices and a second material joined to one of N-type thermoelectric devices according to the coefficient of thermal expansion of the N-type thermoelectric devices; alternately disposing the P-type thermoelectric devices and the N-type thermoelectric devices with high temperature surfaces flush with each other and low temperature surfaces flush with each other; and electrically connecting each of the P-type thermoelectric devices and each of the N-type thermoelectric devices in series by joining each of the alternately disposed P-type thermoelectric devices to each of the electrode members in the first area of each of the electrode members and joining each of the N-type thermoelectric devices to each of the electrode members in the second area of each of the electrode members.
According to embodiments of the present invention, for the P-type thermoelectric device and the N-type thermoelectric device having different coefficients of thermal expansion, electrodes are made of materials having coefficients of thermal expansion close to those of the thermoelectric devices. This can suppress a thermal stress generated between the thermoelectric device and the electrode, achieving high connection reliability even in an actual use environment. The thermoelectric devices can be joined in a process similar to a conventional process without the need for additional bonding process.
These features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.
Embodiments of the present invention will be described in detail based on the following figures, wherein:
According to embodiments of the present invention, for a P-type thermoelectric device and an N-type thermoelectric device with different coefficients of thermal expansion in a thermoelectric module, electrodes are made of materials having coefficients of thermal expansion close to those of the device materials of the thermoelectric devices, and the devices are connected to the respective electrode members via bonding materials.
Embodiments of the present invention will be described below with reference to the accompanying drawings.
In the following embodiment, the P-type thermoelectric device 11 is made of silicon and germanium powder containing impurities of 1% or less with P-type semiconductor properties, for example, boron, aluminum, and gallium while the N-type thermoelectric device 12 is made of silicon and germanium powder containing impurities of 10% or less with N-type semiconductor properties, for example, aluminum. The thermoelectric devices are formed by sintering the powder by pulse discharge, hot pressing, and other methods. Specifically, in the present embodiment, the P-type thermoelectric device 11 is a silicon-germanium device while the N-type thermoelectric device 12 is a silicon-magnesium device. Furthermore, the P-type electrode 21 is made of molybdenum (a coefficient of thermal expansion of 5.8×10−6K−1) while the N-type electrode 22 is made of nickel (a coefficient of thermal expansion of 15.2×10−6K−1).
The P-type electrode 21 and the N-type electrode 22 may be joined to each other by any methods as long as remelting does not occur under a use environment. For example, the electrodes may be joined with a base material directly melted by electron beam welding, arc welding, spot welding, TIG welding, and other methods. Alternatively, the electrodes may be joined by solid-phase bonding such as a rolling process with a clad metal or may be joined with a bonding material such as a brazing filler metal.
As shown in
A temperature difference between the top surface and the undersurface of the thermoelectric device assembly makes an electric current pass through the thermoelectric device assembly 1. The electric current flows from the high temperature side to the low temperature side in the P-type thermoelectric device 11 (from the top to the bottom in
In this configuration, the P-type thermoelectric device 11 that is a silicon-germanium device has a coefficient of thermal expansion of 4.5×10−6K−1 while the N-type thermoelectric device 12 that is a silicon-magnesium device has a coefficient of thermal expansion of 15.5×10−6K−1. It is found that an amount of expansion/contraction varies between the P-type thermoelectric device 11 and the N-type thermoelectric device 12 during heating in a joining process or a temperature change in an actual use environment. In the case where the thermoelectric device is joined to the electrode, a stress and distortion are generated near the joint by a difference in coefficient of thermal expansion between an electrode member and the thermoelectric device. Thus, the joint may be broken or peeled, or a crack may occur on the P-type thermoelectric device 11 or the N-type thermoelectric device 12.
In the structure of the present embodiment, however, a difference in coefficient of thermal expansion is 1.3×10−6K−1 between the P-type thermoelectric device 11 composed of silicon-germanium (a coefficient of thermal expansion of 4.5×10−6K−1) and the P-type electrode 21 composed of molybdenum (a coefficient of thermal expansion of 5.8×10−6K−1). Such a small difference in coefficient of thermal expansion can reduce a stress or distortion near the joints of the P-type thermoelectric device 11. Similarly, a difference in coefficient of thermal expansion is 0.3×10−6K−1 between the N-type thermoelectric device 12 composed of silicon-magnesium (a coefficient of thermal expansion of 15.5×10−6K−1) and the N-type electrode 22 composed of nickel (a coefficient of thermal expansion of 15.2×10−6K−1). This can reduce a stress and distortion near the joints of the N-type thermoelectric device 12, forming the joints with high connection reliability.
Furthermore, in the present embodiment, a stress buffer layer does not need to be formed beforehand on the thermoelectric device. This can simplify the manufacturing process of the thermoelectric devices while reducing the total number of configurations in the thickness direction, leading to smaller variations in height.
Moreover, the joining pattern of the present embodiment reduces the absolute values of a stress and distortion on the joint as compared with a configuration disclosed in Japanese Patent Laid-Open No. 9-293906 in which, as described in
The bonding material 30 is desirably aluminum, nickel, tin, copper, zinc, germanium, magnesium, gold, silver, indium, lead, bismuth, tellurium, or an alloy mainly composed of one of the metals. In the assembling process, the bonding material 30 is aluminum or aluminum alloy foil containing materials such as silicon and germanium in aluminum, or the bonding material 30 is aluminum or foil of powder containing materials such as silicon and germanium in aluminum. The support jig 40 may be made of materials such as ceramics and metals that are not melted in a joining process. The support jig 40 is desirably made of a material not reacting with the bonding material 30, or a surface of the support jig 40 desirably has an unreactive layer that suppresses a reaction. The flow of assembling the thermoelectric device assembly 1 will be described below with reference to the method of assembling the thermoelectric module in
First, as shown in
Subsequently, as shown in
In this case, a pressure of at least 0.12 kPa is applied to prevent inclination of the P-type thermoelectric device 11 and the N-type thermoelectric device 12 during joining, and discharge a maximum amount of the bonding material 30 melted from the interface between the P-type thermoelectric device 11 and the N-type thermoelectric device 12. The upper limit of the pressure is not particularly limited but is set lower than the crushing strength of the device so as to prevent a break on the device. Specifically, the upper limit may be set at about 1000 MPa or less. In the present embodiment, a pressure of several MPa is sufficiently effective.
A joining atmosphere may be a non-oxidizing atmosphere. Specifically, the atmosphere may be a vacuum atmosphere, a nitrogen atmosphere, a nitrogen-hydrogen mixing atmosphere, and so on.
In the present embodiment, an example of the bonding material 30 is metal foil. The bonding material 30 may be aluminum powder or aluminum alloy powder containing aluminum primarily composed of silicon and germanium. In this case, a single powder may be used, a layer composed of various powders may be stacked, or mixed powder thereof may be used. In the use of these powders, a molded body formed by compacting only powder may be located only at a point of joining the P-type thermoelectric device 11 and the N-type thermoelectric device 12, powder may be applied only at a point of joining the thermoelectric device beforehand, or paste powder of resin or the like may be applied to a point of joining the thermoelectric device. The application of powder beforehand can omit the step of attaching foil, further simplifying the manufacturing process.
As shown in
In the thermoelectric module according to the present embodiment, the P-type thermoelectric devices 11 and the N-type thermoelectric devices 12 may be connected via the electrode assemblies 20 so as to be electrically connected in series. The configuration illustrated in
The present embodiment reduces a difference in coefficient of thermal expansion between the P-type thermoelectric device 11 and the P-type electrode 21 and a difference in coefficient of thermal expansion between the N-type thermoelectric device 12 and the N-type electrode 22. This suppresses a thermal stress generated between the thermoelectric device and the electrode at a high temperature and a thermal stress generated between the thermoelectric device and the electrode at a temperature fluctuating between a room temperature and a high temperature, achieving high reliability in an actual use environment. In this case, it is preferable to set a difference in coefficient of thermal expansion between the P-type thermoelectric device 11 and the P-type electrode 21 and a difference in coefficient of thermal expansion between the N-type thermoelectric device 12 and the N-type electrode 22 at an absolute value of 6×10−6K−1 or less. An absolute value of 3×10−6K−1 or less is more preferable, and an absolute value of 1.5×10−6K−1 or less is still more preferable.
Referring to
As shown in
The P-type thermoelectric device 11 and the N-type thermoelectric device 12 are made of materials having thermoelectric conversion characteristics, for example, silicon-germanium, iron-silicon, bismuth-tellurium, magnesium-silicon, lead-tellurium, cobalt-antimony, bismuth-antimony, a Heusler alloy, and a half Heusler alloy. The P-type electrode 221 and the N-type electrode 221 are desirably made of nickel, molybdenum, titanium, iron, copper, manganese, tungsten, or an alloy mainly composed of one of the metals. The bonding material 30 is desirably aluminum, nickel, tin, copper, zinc, germanium, magnesium, gold, silver, indium, lead, bismuth, tellurium, or an alloy mainly composed of one of the metals.
In the following embodiment, the P-type thermoelectric device 11 is made of silicon and germanium powder containing impurities of 1% or less with P-type semiconductor properties, for example, boron, aluminum, and gallium while the N-type thermoelectric device 12 is made of silicon and germanium powder containing impurities of 10% or less with N-type semiconductor properties, for example, aluminum. The thermoelectric devices are formed by sintering the powder by pulse discharge, hot pressing, and other methods. Specifically, in the present embodiment, the P-type thermoelectric device 11 is a silicon-germanium device while the N-type thermoelectric device 12 is a silicon-magnesium device. Furthermore, the P-type electrode 211 is made of molybdenum (a coefficient of thermal expansion of 5.8×10−6K−1) while the N-type electrode 221 is made of nickel (a coefficient of thermal expansion of 15.2×10−6K1).
The P-type electrode 211 and the N-type electrode 221 may be joined to each other by any methods as long as remelting does not occur under a use environment. For example, the electrodes may be joined with a base material directly melted by electron beam welding, arc welding, spot welding, TIG welding, and other methods. Alternatively, the electrodes may be joined by solid-phase bonding such as a rolling process with a clad metal or may be joined with a bonding material such as a brazing filler metal.
As shown in
A temperature difference between the top surface and the undersurface passes a current through the thermoelectric device assembly 1. The current flows from the high temperature side to the low temperature side in the P-type thermoelectric device 11 (from the top to the bottom in
In this configuration, the P-type thermoelectric device that is a silicon-magnesium device has a coefficient of thermal expansion of 4.5×10−6K−1 while the N-type thermoelectric device 12 that is a silicon-magnesium device has a coefficient of thermal expansion of 15.5×10−6K−1. It is found that an amount of expansion/contraction varies between the P-type thermoelectric device 11 and the N-type thermoelectric device 12 during heating in a joining process or a temperature change in an actual use environment. In the case where the thermoelectric device is joined to the electrode, a stress and distortion are generated near the joint by a difference in coefficient of thermal expansion between an electrode member and the thermoelectric device. Thus, the joint may be broken or peeled, or a crack may occur on the P-type thermoelectric device 11 or the N-type thermoelectric device 12.
In the structure of the present embodiment, however, a difference in coefficient of thermal expansion is 1.3×10−6K−1 between the P-type thermoelectric device 11 composed of silicon-germanium (a coefficient of thermal expansion of 4.5×10−6K−1) and the P-type electrode 211 composed of molybdenum (a coefficient of thermal expansion of 5.8×10−6K−1). Such a small difference in coefficient of thermal expansion can reduce a stress or distortion near the joints of the P-type thermoelectric device 11.
Similarly, a difference in coefficient of thermal expansion is 0.3×10−6K−1 between the N-type thermoelectric device 12 composed of silicon-magnesium (a coefficient of thermal expansion of 15.5×10−6K−1) and the N-type electrode 221 composed of nickel (a coefficient of thermal expansion of 15.2×10−6K−1). This can reduce a stress and distortion near the joints of the N-type thermoelectric device 12, forming the joints with high connection reliability.
Furthermore, in the present embodiment, a stress buffer layer does not need to be formed beforehand on the thermoelectric device. This can simplify the manufacturing process of the thermoelectric devices while reducing the total number of configurations in the thickness direction, leading to smaller variations in height.
Moreover, the joining pattern of the present invention reduces the absolute values of a stress and distortion on the joint as compared with an electrode made of a single material in
In
The P-type thermoelectric device 11 and the N-type thermoelectric device 12 are made of materials having thermoelectric conversion characteristics, for example, silicon-germanium, iron-silicon, bismuth-tellurium, magnesium-silicon, lead-tellurium, cobalt-antimony, bismuth-antimony, a Heusler alloy, and a half Heusler alloy. The P-type electrode 212 and the N-type electrode 222 are desirably made of nickel, molybdenum, titanium, iron, copper, manganese, tungsten, or an alloy mainly composed of one of the metals. The support electrode 24 is preferably made of a material having a coefficient of thermal expansion between the coefficients of thermal expansion of the P-type electrode 212 and the N-type electrode 222. The bonding material 30 is desirably aluminum, nickel, tin, copper, zinc, germanium, magnesium, gold, silver, indium, lead, bismuth, tellurium, or an alloy mainly composed of one of the metals.
In the following embodiment, the P-type thermoelectric device 11 is made of silicon and germanium powder containing impurities of 1% or less with P-type semiconductor properties, for example, boron, aluminum, and gallium while the N-type thermoelectric device 12 is made of silicon and germanium powder containing impurities of 10% or less with N-type semiconductor properties, for example, aluminum. The thermoelectric devices are formed by sintering the powder by pulse discharge, hot pressing, and other methods. Specifically, in the present embodiment, the P-type thermoelectric device 11 is a silicon-germanium device while the N-type thermoelectric device 12 is a silicon-magnesium device. Furthermore, the P-type electrode 212 is made of molybdenum (a coefficient of thermal expansion of 5.8×10−6K−1) while the N-type electrode 222 is made of nickel (a coefficient of thermal expansion of 15.2×10−6K−1). The support electrode 24 is made of titanium (a coefficient of thermal expansion of 8.9×10−6K−1).
The P-type electrode 212 may be joined to the support electrode 24 while the N-type electrode 222 may be joined to the support electrode 24 by any methods as long as remelting does not occur under a use environment. For example, the electrodes may be joined with a base material directly melted by electron beam welding, arc welding, spot welding, TIG welding, and other methods. Alternatively, the electrodes may be joined by solid-phase bonding such as a rolling process with a clad metal or may be joined with a bonding material such as a brazing filler metal.
As shown in
A temperature difference between the top surface and the undersurface passes a current through the thermoelectric device assembly 1. The current flows from the high temperature side to the low temperature side in the P-type thermoelectric device 11 (from the top to the bottom in
In this configuration, the P-type thermoelectric device that is a silicon-magnesium device has a coefficient of thermal expansion of 4.5×10−6K−1 while the N-type thermoelectric device 12 that is a silicon-magnesium device has a coefficient of thermal expansion of 15.5×10−6K−1. It is found that an amount of expansion/contraction varies between the P-type thermoelectric device 11 and the N-type thermoelectric device 12 during heating in a joining process or a temperature change in an actual use environment. In the case where the thermoelectric device is joined to the electrode, a stress and distortion are generated near the joint by a difference in coefficient of thermal expansion between an electrode member and the thermoelectric device. Thus, the joint may be broken or peeled, or a crack may occur on the P-type thermoelectric device 11 or the N-type thermoelectric device 12.
In the structure of the present embodiment, however, a difference in coefficient of thermal expansion is 1.3×10−6K−1 between the P-type thermoelectric device 11 composed of silicon-germanium (a coefficient of thermal expansion of 4.5×10−6K−1) and the P-type electrode 211 composed of molybdenum (a coefficient of thermal expansion of 5.8×10−6K−1). Such a small difference in coefficient of thermal expansion can reduce a stress or distortion near the joints of the P-type thermoelectric device 11. Similarly, a difference in coefficient of thermal expansion is 0.3×10−6K−1 between the N-type thermoelectric device 12 composed of silicon-magnesium (a coefficient of thermal expansion of 15.5×10−6K−1) and the N-type electrode 222 composed of nickel (a coefficient of thermal expansion of 15.2×10−6K−1). This can reduce a stress and distortion near the joints of the N-type thermoelectric device 12, forming the joints with high connection reliability.
The support electrode 24 is made of titanium having a coefficient of thermal expansion (coefficient of thermal expansion of 8.9×10−6K−1) between those of molybdenum and nickel, thereby reducing a difference in expansion/contraction in the electrode assembly 20. Since the P-type electrode 212 and the N-type electrode 222 are independent from each other, the shape and size can be changed according to a device size.
Moreover, the joining pattern of the present invention reduces the absolute values of a stress and distortion on the joint as compared with an electrode made of a single material in
In the present embodiment, two layers are stacked in the electrode assembly 202. The electrode assembly 202 may have a laminated structure of at least two layers.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-226858 | Oct 2012 | JP | national |
