Thermoelectric module

A thermoelectric module includes a thermoelectric element and an electrode. The thermoelectric element has a rectangular end face. The electrode includes a first joint portion joined to a center portion of the end face; and a second joint portion joined to one end and a third joint portion joined to the other end. Each of the second joint portion and the third joint portion is disposed at a distance from each of four corners of the end face. A joint length in the second direction orthogonal to the first direction between the first joint portion and the end face is longer than each of a joint length in the second direction between the second joint portion and the end face, and a joint length in the second direction between the third joint portion and the end face.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thermoelectric module, and particularly to a thermoelectric module including a thermoelectric element and an electrode.

2. Description of the Background Art

Generally, a thermoelectric module is configured such that an electrode is joined to an end face of a thermoelectric element. Such a thermoelectric module is disclosed, for example, in Japanese Patent Laying-Open No. 2000-101152.

In the thermoelectric module disclosed in the above-mentioned patent document, however, since the electrode is joined to a part of the end face of the thermoelectric element, the area of the electrode joined to the end face of the thermoelectric element becomes relatively small. This poses a problem of decreasing the effect of heat transfer between an object and the thermoelectric element. In order to improve the effect of heat transfer between the object and the thermoelectric element, it is conceivable to join the electrode to the entire end face of the thermoelectric element.

This however also causes the following problem. Specifically, when a current is caused to flow through the thermoelectric module, one end face of the thermoelectric element is cooled while the other end face opposite to one end face is heated. In this case, since a temperature difference occurs in the thermoelectric element between one end face and the other end face, unbalanced deformation tends to occur in one end face and the other end face of the thermoelectric element in accordance with the thermal expansion coefficient thereof. However, since electrodes are joined to one end face and the other end face, respectively, of the thermoelectric element, deformation of the thermoelectric element is prevented by these electrodes. Consequently, thermal stress occurs in the thermoelectric element. Since this thermal stress is noticeably concentrated in four corners of the end face of the thermoelectric element, these four corners of the end face of the thermoelectric element may be destroyed by the thermal stress.

SUMMARY OF THE INVENTION

The present invention has been made in light of the above-described problems. An object of the present invention is to provide a thermoelectric module by which concentration of thermal stress in four corners of the end face of the thermoelectric element can be prevented, and the area of the electrode joined to the end face of the thermoelectric element can be enlarged.

The thermoelectric module according to the present invention includes a thermoelectric element and an electrode. The thermoelectric element has a rectangular end face. The electrode is joined to the end face to be electrically connected to the thermoelectric element. The electrode includes a first joint portion joined to a center portion of the end face in a first direction in which opposite sides of the end face face each other; and a second joint portion joined to one end of the end face across the center portion in the first direction and a third joint portion joined to the other end of the end face. Each of the second joint portion and the third joint portion is disposed at a distance from each of four corners of the end face. A joint length in a second direction orthogonal to the first direction between the first joint portion and the end face is longer than each of a joint length in the second direction between the second joint portion and the end face, and a joint length in the second direction between the third joint portion and the end face.

According to the thermoelectric module of the present invention, each of the second joint portion and the third joint portion is disposed at a distance from each of the four corners of the end face. Accordingly, the electrode is not joined to the four corners of the end face of the thermoelectric element. Thereby, concentration of the thermal stress in the four corners of the end face of the thermoelectric element can be prevented. Furthermore, the joint length in the second direction between the first joint portion and the end face is longer than each of the joint length in the second direction between the second joint portion and the end face, and the joint length in the second direction between the third joint portion and the end face. Accordingly, the area of the electrode joined to the end face of the thermoelectric element can be enlarged as compared with the case where the joint length between the first joint portion and the end face is equal to each of the joint length between the second joint portion and the end face, and the joint length between the third joint portion and the end face.

According to the above-described thermoelectric module, a length of a portion including the first joint portion of the electrode in the second direction is equal to or longer than a length of the end face of the thermoelectric element in the second direction. Accordingly, the joint length between the first joint portion and the end face is equal to the length of the end face of the thermoelectric element in the second direction. Therefore, the joint length between the first joint portion and the end face can be maximized, with the result that the area of the electrode connected to the end face of the thermoelectric element can be enlarged.

According to the above-described thermoelectric module, the electrode includes a plate-shaped portion and a protrusion protruding from the plate-shaped portion in a thickness direction of the plate-shaped portion. The protrusion is joined to the end face of the thermoelectric element. Accordingly, the thermal stress generated in the thermoelectric element can be released to the protrusion of the electrode. Furthermore, even if the thermal stress is concentrated in the protrusion, the durability of the thermoelectric module can be improved because the electrode is greater in mechanical strength than the thermoelectric element.

According to the above-described thermoelectric module, the plate-shaped portion and the protrusion of the electrode are integrally formed. Accordingly, since the mechanical strength of the electrode can be improved, the durability of the thermoelectric module can be further improved.

According to the above-described thermoelectric module, the thermoelectric module further includes a base film formed of polyimide and joined to the electrode. The electrode includes one face and the other face facing each other. One face is joined to the end face of the thermoelectric element, and the other face is joined to the base film. Accordingly, the thermal stress can be released to the base film formed of polyimide. Polyimide readily deforms, so that the thermal stress can be readily released. Therefore, the durability of the thermoelectric module can be improved.

According to the above-described thermoelectric module, the thermoelectric element has one side configured as a heat-absorption side and the other side configured as a heat-dissipation side. The electrode is disposed on the heat-absorption side of the thermoelectric element. In the thermoelectric module, the heat-absorption side generally serves to regulate the temperature of an object, and undergoes a relatively large temperature change as compared with the heat dissipation side. Consequently, the operating condition is stricter on the heat-absorption side than on the heat-dissipation side. Accordingly, it is required to prevent concentration of the thermal stress on the heat-absorption side. Since the electrode is disposed on the heat-absorption side of the thermoelectric element, concentration of the thermal stress can be prevented on the heat-absorption side. Therefore, the durability of the thermoelectric module can be effectively improved.

As described above, according to the present invention, concentration of the thermal stress in the four corners of the end face of the thermoelectric element can be prevented while the area of the electrode joined to the end face of the thermoelectric element can be enlarged.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be hereinafter described with reference to the accompanying drawings.

First Embodiment

The configuration of a thermoelectric module in the first embodiment of the present invention will be first hereinafter described.

Referring toFIG. 1, a thermoelectric module10according to the present embodiment mainly includes a plurality of thermoelectric elements1, a plurality of electrodes2, a pair of base films3, a first lead wire4a, a second lead wire4b, and solder5.

Thermoelectric module10is configured such that the plurality of thermoelectric elements1are jointed between the pair of base films3so as to be electrically connected in series in an alternate manner by a plurality of electrodes2. A pair of thermoelectric elements1are joined to each electrode2other than two electrodes2to which first lead wire4aand second lead wire4bare joined.

First lead wire4aand second lead wire4bare attached to two electrodes2, respectively, with solder5. Thereby, first lead wire4aand second lead wire4bare electrically connected to two electrodes2, respectively. It is to be noted that only one thermoelectric element1is mounted on each of these two electrodes2.

Referring toFIGS. 2 and 3, each of thermoelectric elements1has a rectangular parallelepiped shape. Each of thermoelectric elements1has a rectangular end face1a. End face1ahas a side1band a side1cfacing each other. Furthermore, end face1ahas a center portion11, and one end12and the other end13that are located across center portion11.

Each of electrodes2is joined to end face1a, thereby being electrically connected to thermoelectric element1. Electrode2is formed in a plate shape and has a cutout portion in each of its four corners. Electrode2also has a plurality of cutout portions in its center portion in the longitudinal direction. These cutout portions are arc-shaped. Furthermore, these cutout portions are formed so as to be located on the four corners of end face1aof thermoelectric element1in the state where these cutout portions are joined to end face1aof thermoelectric element1. Electrode2can be made of Cu (copper), for example. Furthermore, the surface of electrode2may be covered by Ni (nickel), Au (gold) or the like.

In the present embodiment, one electrode2has two first joint portions21to two third joint portions23. First joint portion21is joined to center portion11of end face1ain a first direction Al in which opposite sides1band1cof end face1aface each other. Second joint portion22and third joint portion23are joined to one end12and the other end13, respectively, of end face1aacross center portion11in first direction A1. Center portion11only has to be located between one end12and the other end13in first direction A1, but is not necessarily located in the center of end face la in first direction A1. Second joint portion22and third joint portion23are disposed so as to face each other across first joint portion21. Second joint portion22may be provided so as to extend along side1b. Third joint portion23may be provided so as to extend along side1c.

Each of second joint portion22and third joint portion23is located at a distance from each of four corners of end face1a. These four corners of end face1aare located so as to be exposed from electrode2. A joint length21ain a second direction A2 orthogonal to first direction A1 between first joint portion21and end face1ais longer than each of a joint length22ain the second direction between second joint portion22and end face1a, and a joint length23ain the second direction between third joint portion23and end face1a. Furthermore, a length20of a portion including first joint portion21of electrode2in second direction A2 is equal to or longer than the length of end face1aof thermoelectric element1in second direction A2.

Electrode2has one face2aand the other face2bfacing each other. One face2ais joined to end face1aof thermoelectric element1. The other face2bis joined to base film3. Base film3is formed of polyimide. Base film3is transparently formed. Base film3is joined to a plurality of electrodes2. A pair of base films3includes a heat-absorption side base film3aand a heat-dissipation side base film3b. Heat-absorption side base film3ais joined to heat-absorption side electrode2ewhile heat-dissipation side base film3bis joined to heat-dissipation side electrode2f.

Then, the first modification of thermoelectric module10in the present embodiment will be described with reference toFIG. 4. In the first modification of thermoelectric module10in the present embodiment, electrode2has a cutout portion that is linearly formed. Furthermore, a plurality of cutout portions formed in the center of electrode2are continuously provided. Also in this first modification, each of second joint portion22and third joint portion23is joined to end face1aat a distance, by the cutout portions, from the four corners of end face1a. Also, joint length21a(not shown) is longer than each of joint length22aand joint length23a.

Furthermore, the second modification of thermoelectric module10in the present embodiment will be hereinafter described with reference toFIG. 5. In the second modification of thermoelectric module10in the present embodiment, the outer circumferential surface of each end of electrode2is formed in an arc-like shape. The outer circumferential surface of electrode2is not located on the four corners of end face1aof thermoelectric element1. Accordingly, each of second joint portion22and third joint portion23is arranged at a distance from each of the four corners of end face1a. Furthermore, joint length21a(not shown) is longer than each of joint length22aand joint length23a.

Referring toFIG. 6, a description will be made regarding a plasma processing apparatus100on which thermoelectric module10of the present embodiment is mounted. Plasma processing apparatus100mainly includes a thermoelectric module10, a chamber101, an electrode102, a high-frequency oscillator103, an electrostatic chuck104, and a water cooling plate105. InFIG. 6, a silicon wafer110is adsorbed onto electrostatic chuck104.

Within chamber101, electrode102is disposed so as to face silicon wafer110. adsorbed onto electrostatic chuck104. Electrostatic chuck104is configured such that it can adsorb silicon wafer110. Thermoelectric module10and water cooling plate105are disposed below electrostatic chuck104. Water cooling plate105is configured to allow a coolant to circulate through a pipe unit105a. Heat-absorption side base film3aand heat-absorption side electrode2eof thermoelectric module10are arranged on the electrostatic chuck104side while heat-dissipation side base film3band heat-dissipation side electrode2fare arranged on the water cooling plate105side.

Thermoelectric element1has one side configured as a heat-absorption side and the other side configured as a heat-dissipation side. Thermoelectric element1is provided on one side with one end face1a1and on the other side with the other end face1a2. In other words, one end face1a1is disposed on the heat-absorption side while the other end face1a2is disposed on the heat-dissipation side. In the present embodiment, heat-absorption side electrode2eis joined to one end face1a1while heat-dissipation side electrode2fis joined to the other end face1a2. Electrode2only has to be disposed at least on the heat-absorption side of thermoelectric element1.

In plasma processing apparatus100, silicon wafer110is adsorbed onto electrostatic chuck104. After reactive gas for plasma generation is introduced into chamber101through an inlet101aof chamber101, high-frequency oscillator103applies a high-frequency wave to electrode102, thereby generating plasma. By this plasma, silicon wafer110is subjected to a process such as etching. Then, the reactive gas used for generating plasma is removed through an outlet101bby vacuum evacuation.

When silicon wafer110is subjected to a process such as etching by this plasma, the temperature of silicon wafer110needs to be controlled at a target temperature in order to improve the yield of silicon wafer110. In plasma processing apparatus100in the present embodiment, a current is caused to flow through thermoelectric module10, which causes a heat absorption phenomenon to occur in heat-absorption side electrode2eand a heat dissipation phenomenon to occur in heat-dissipation side electrode2f. Specifically, heat-absorption side electrode2eis cooled while heat-dissipation side electrode2fis heated. Accordingly, silicon wafer110is cooled by heat-absorption side base film3aand heat-absorption side electrode2ewith electrostatic chuck104interposed between silicon wafer110and each of heat-absorption side base film3aand heat-absorption side electrode2e. In this way, the temperature of silicon wafer110is controlled at a target temperature. On the other hand, thermoelectric element1is cooled by water cooling plate105with heat-dissipation side base film3band heat-dissipation side electrode2finterposed therebetween.

Then, referring toFIG. 7, a description will be made regarding a chemical circulator (a fluid temperature regulation apparatus)200on which thermoelectric module10of the present embodiment is mounted.

Chemical circulator200mainly includes a thermoelectric module10, a main body201and a water cooling plate202. Thermoelectric modules10are arranged so as to have main body201interposed therebetween, and water cooling plates202are arranged so as to have thermoelectric modules10interposed therebetween. Main body201is formed so as to allow the temperature-regulated fluid to circulate therethrough. Water cooling plate202is configured so as to allow water to circulate therethrough by a pipe unit (not shown).

A control unit210is electrically connected to thermoelectric module10of chemical circulator200. A temperature sensor211is connected to control unit210. Temperature sensor211is immersed in a chemical solution221(a temperature-regulated fluid) such that it can measure the temperature of chemical solution221stored in a processing bath220.

A pipe line203ais connected to processing tub220so as to allow circulation of chemical solution221. A pump230is connected to processing tub220for circulating chemical solution221through pipe line203a. A filter240is disposed between pump230and chemical circulator200through pipe line203a. Pipe line203ais connected to main body201of chemical circulator200.

Chemical solution221circulates through pipe line203awith pump230in the direction indicated by an arrow in the figure. In this case, the temperature of chemical solution221is controlled at a target temperature by chemical circulator200. In other words, in chemical circulator200of the present embodiment, a current is caused to flow through thermoelectric module10, thereby cooling the main body201side of thermoelectric module10while heating the water cooling plate202side thereof. In this way, the temperature of chemical solution221flowing through main body201is controlled at the target temperature. Also, thermoelectric element I is cooled by water cooling plate202.

Although the above description is about the case where base film3formed of polyimide is used, the present invention is not limited thereto, but electrode2may be joined to the substrate. In this case, the substrate may be made of Al2O3(aluminum oxide), AlN (aluminum nitride), SiC (silicon carbide), Si3N4(silicon nitride), and the like.

Then, the functions and effects of the present embodiment will be described.

According to thermoelectric module10in the present embodiment, each of second joint portion22and third joint portion23is disposed at a distance from each of the four corners of end face1a. Accordingly, electrode2is not joined to the four corners of end face1aof thermoelectric element1, with the result that concentration of thermal stress in the four corners of end face1aof thermoelectric element1can be prevented. Furthermore, joint length21ain second direction A2 between first joint portion21and end face1ais longer than each of joint length22ain second direction A2 between second joint portion22and end face1a, and joint length23ain second direction A2 between third joint portion23and end face1a. Accordingly, the area of electrode2joined to end face1aof thermoelectric element1can be enlarged, as compared with the case where joint length21abetween first joint portion21and end face1ais equal to each of joint length22abetween second joint portion22and end face1a, and joint length23abetween third joint portion23and end face1a.

According to thermoelectric module10of the present embodiment, length20of a portion including first joint portion21of electrode2in second direction A2 is equal to or longer than the length of end face1aof thermoelectric element1in second direction A2. Accordingly, joint length21abetween first joint portion21and end face1ais equal to the length of end face1aof thermoelectric element1in second direction A2. Therefore, joint length21abetween first joint portion21and end face1acan be maximized. Consequently, the area of electrode2connected to end face la of thermoelectric element1can be enlarged.

According to thermoelectric module10in the present embodiment, one face2aof electrode2is joined to end face1aof thermoelectric element1while the other face2bis joined to base film3formed of polyimide. Accordingly, the thermal stress can be released to base film3formed of polyimide. Since polyimide readily deforms, it is less likely to generate thermal stress on thermoelectric element1. Therefore, as in the case of the thermoelectric module using Al2O3(aluminum oxide), AlN (aluminum nitride), SiC (silicon carbide), Si3N4(silicon nitride), and the like for the material of a base material, the durability of thermoelectric module10can be improved without causing the substrate to generate thermal stress on thermoelectric element1.

According to thermoelectric module10in the present embodiment, thermoelectric element1has one side configured as a heat-absorption side and the other side configured as a heat-dissipation side, in which electrode2is disposed on the heat-absorption side of thermoelectric element1. Since electrode2is disposed on the heat-absorption side of thermoelectric element1, concentration of thermal stress can be prevented on the heat-absorption side. Accordingly, the durability of thermoelectric module10can be effectively improved.

Second Embodiment

The configuration of a thermoelectric module in the second embodiment of the present invention will be hereinafter described. It is to be noted that the elements having the same functions as those in the first embodiment of the present invention are designated by the same reference characters, and the description thereof will not be repeated unless particularly needed.

Referring toFIGS. 8 and 9, according to thermoelectric module10in the present embodiment, electrode2has a plate-shaped portion2cand a protrusion2d.Protrusion2dis circular in plan view. Protrusion2dis formed so as to protrude from plate-shaped portion2cin the thickness direction of plate-shaped portion2c.Specifically, electrode2is provided with a stepped portion such that there is a difference in height. Protrusion2dis joined to end face1aof thermoelectric element1. In other words, thermoelectric element1is joined to the upper surface portion of the stepped portion of electrode2. However, protrusion2dis not joined to each of the four corners of end face1aof thermoelectric element1.

Referring toFIGS. 9 and 10, the outer circumferential edge of circular protrusion2dis located so as to be aligned with the outer circumferential edge of rectangular end face1a. Accordingly, each of second joint portion22and third joint portion23is arranged at a distance from each of the four corners of end face1a.

Furthermore, first joint portion21has a length equal to the diameter of circular protrusion2d. Each of second joint portion22and third joint portion23is equal in length to each end of circular protrusion2din first direction A1 in which opposite sides1band1cof end face1aface each other. Accordingly, joint length21ais longer than each of joint length22aand joint length23a. Furthermore, length20of a portion including first joint portion21of electrode2in second direction A2 is equal to or longer than the length of end face1aof thermoelectric element1in second direction A2.

Then, referring toFIGS. 11 and 12, a modification of thermoelectric module10in the present embodiment will be hereinafter described. In the modification of thermoelectric module10in the present embodiment, protrusion2dis formed as a rhombus in plan view. Rhombus-shaped protrusion2dis located in such a position that it is rotated at approximately 45 degrees with respect to end face1ain plan view. Four vertices of rhombus-shaped protrusion2deach are located outside with respect to end face1a. Specifically, as seen in first direction A1, the length of the diagonal line of rhombus-shaped protrusion2dis longer than the length of end face1. Also, as seen in second direction A2, the length of the diagonal line of rhombus-shaped protrusion2dis longer than the length of end face1.

Accordingly, each of second joint portion22and third joint portion23is disposed at a distance from each of the four corners of end face1a. Furthermore, joint length21ais longer than each of joint length22aand joint length23a. Furthermore, length20of a portion including first joint portion21of electrode2in second direction A2is equal to or longer than the length of end face1aof thermoelectric element1in second direction A2.

Although the above description is about the case where protrusion2dhas a circular shape or a rhombus shape, protrusion2dcan have any shape as long as protrusion2dis not in contact with each of the four corners of end face1a, that is, protrusion2dis not joined to each of the four corners of end face1a.

According to thermoelectric module10in the present embodiment, as in the first embodiment, electrode2is not joined to the four corners of end face1aof thermoelectric element1, so that concentration of thermal stress in the four corners of end face1aof thermoelectric element1can be prevented. Furthermore, the area of electrode2joined to end face1aof thermoelectric element1can be enlarged, as compared with the case where joint length21abetween first joint portion21and end face1ais equal to each of joint length22abetween second joint portion22and end face1a, and joint length23abetween third joint portion23and end face1a.

Furthermore, according to thermoelectric module10in the present embodiment, protrusion2dof electrode2is joined to end face1aof thermoelectric element1. Accordingly, the thermal stress generated in thermoelectric element1can be released to protrusion2dof electrode2. Also, even if the thermal stress is concentrated in protrusion2d, the durability of thermoelectric module10can be improved because electrode2is greater in mechanical strength than thermoelectric element1.

According to thermoelectric module10in the present embodiment, plate-shaped portion2cand protrusion2dof electrode2are integrally formed. Consequently, the mechanical strength of electrode2can be improved, thereby allowing further improvement in durability of thermoelectric module10.

EXAMPLES

An example of the present invention will be hereinafter described.

In the present example, the durability test was first carried out using the thermoelectric module of the above-described first embodiment and a thermoelectric module of a comparative example. In the thermoelectric module of the comparative example, an electrode is joined to four corners of an end face of a thermoelectric element. The thermoelectric elements used in this example include a thermoelectric element having a height of 2.6 mm and a length and a width of 2.14 mm, and a thermoelectric element having a height of 2.6 mm and a length and a width of 1.73 mm.

In the durability test, the thermoelectric module was immersed in the fluorine-based inert fluid regulated at a temperature of 10° C. In this state, a current was caused to flow such that an electrode on one side (on the surface side) and an electrode on the other side (on the back surface side) alternately reached a relatively low temperature and a relatively high temperature, thereby repeating a cycle caused by temperature amplitude. The cycle time was 15 seconds, and a direct current of12A was applied for 7.5 seconds in each of the forward direction and the backward direction. The electrode temperatures on the heating side and the cooling side after a lapse of 7.5 seconds were 120° C. and 15° C., respectively. Thus, there was a temperature difference of 105° C. between the heat-dissipation side electrode and the heat-absorption side electrode.

Destruction of the thermoelectric module was evaluated based on the change (increase) rate of the inner electrical resistance of the thermoelectric module obtained when this cycle was repeated. Specifically, the change rate of the inner electrical resistance of the thermoelectric module was measured, and it was evaluated that destruction occurred when the change rate reached 2%. Consequently, the thermoelectric module of the first embodiment required 20% or more cycles than that in the case of the thermoelectric module of the comparative example until the change rate reached 2%. Accordingly, it was recognized that the thermoelectric module of the first embodiment was improved in durability by 20% or more as compared with the thermoelectric module of the comparative example.

Furthermore, the thermoelectric module of the above-described first embodiment and the thermoelectric module of the comparative example were subjected to thermal stress analysis. In the thermoelectric module of the comparative example, an electrode is joined to the four corners of the end face of the thermoelectric element. Consequently, the maximum stress generated in the four corners of the thermoelectric element of the thermoelectric module in the present embodiment showed a value of about 60 percent of the maximum stress generated in the four corners of the thermoelectric element of the thermoelectric module in the comparative example. In other words, it was recognized in the thermoelectric module of the present embodiment that the four corners of the thermoelectric element undergoes stress relaxation that is about 40% of stress relaxation in the thermoelectric module of the comparative example.